Special Guest: David Grinspoon is an astrobiologist, award-winning science communicator (“Dr. FunkySpoon”), and prize-winning author. He has a new book EARTH IN HUMAN HANDS. He is a Senior Scientist at the Planetary Science Institute and Adjunct Professor of Astrophysical and Planetary Science at the University of Colorado. His research focuses on climate evolution on Earth-like planets and potential conditions for life elsewhere in the universe. He is involved with several interplanetary spacecraft missions for NASA, the European Space Agency and the Japanese Space Agency. You can follow him on Twitter at @DrFunkySpoon, and visit his website FunkyScience.net.
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The appearing and disappearing feature observed in Titan's Lakes was dubbed "Magic Island". Image: NASA/JPL-Caltech/ASI/Cornell
Saturn’s largest Moon, Titan, is the only other world in our Solar System that has stable liquid on its surface. That alone, and the fact that the liquid is composed of methane, ethane, and nitrogen, makes it an object of fascination. The bright spot features that Cassini observed in the methane seas that dot the polar regions only deepen the fascination.
A new paper published in Nature Astronomy digs deeper into a phenomenon in Titan’s seas that has been puzzling scientists. In 2013, Cassini noticed a feature that wasn’t there on previous fly-bys of the same region. In subsequent images, the feature had disappeared again. What could it be?
One explanation is that the feature could be a disappearing island, rising and falling in the liquid. This idea took hold, but was only an initial guess. Adding to the mystery was the doubling in size of these potential islands. Others speculated that they could be waves, the first waves observed anywhere other than on Earth. Binding all of these together was the idea that the appearance and disappearance could be caused by seasonal changes on the moon.
Titan’s dense, hydrocarbon rich atmosphere remains a focal point of scientific research. Credit: NASA
Now, scientists at NASA’s Jet Propulsion Laboratory (JPL) think they know what’s behind these so-called ‘disappearing islands,’ and it seems like they are related to seasonal changes.
The study was led by Michael Malaska of JPL. The researchers simulated the frigid conditions on Titan, where the temperature is -179.2 Celsius. At that temperature, some interesting things happen to the nitrogen in Titan’s atmosphere.
On Titan, it rains. But the rain is composed of extremely cold methane. As that methane falls to the surface, it absorbs significant amounts of nitrogen from the atmosphere. The rain hits Titan’s surface and collects in the lakes on the moon’s polar regions.
The researchers manipulated the conditions in their experiments to mirror the changes that occur on Titan. They changed the temperature, the pressure, and the methane/ethane composition. As they did so, they found that nitrogen bubbled out of solution.
“Our experiments showed that when methane-rich liquids mix with ethane-rich ones — for example from a heavy rain, or when runoff from a methane river mixes into an ethane-rich lake — the nitrogen is less able to stay in solution,” said Michael Malaska of JPL. This release of nitrogen is called exsolution. It can occur when the seasons change on Titan, and the seas of methane and ethane experience a slight warming.
“Thanks to this work on nitrogen’s solubility, we’re now confident that bubbles could indeed form in the seas, and in fact may be more abundant than we’d expected,” said Jason Hofgartner of JPL, a co-author of the study who also works on Cassini’s radar team. These nitrogen bubbles would be very reflective, which explains why Cassini was able to see them.
The first-ever images of the surface of a new moon or planet are always exciting. The Huygens probe was launched from Cassini to the surface of Titan, but was not able investigate the lakes and seas on the surface. Image Credit: ESA/NASA/JPL/University of Arizona
The seas on Titan may be what’s called a prebiotic environment, where chemical conditions are hospitable to the appearance of life. Some think that the seas may already be home to life, though there’s no evidence of this, and Cassini wasn’t equipped to investigate that premise. Some experiments have shown that an atmosphere like Titan’s could generate complex molecules, and even the building blocks of life.
NASA and others have talked about different ways to explore Titan, including balloons, a drone, splashdown landers, and even a submarine. The submarine idea even received a NASA grant in 2015, to develop the idea further.
So, mystery solved, probably. Titan’s bright spots are neither islands nor waves, but bubbles.
Cassini’s mission will end soon, and it’ll be quite some time before Titan can be investigated further. The question of whether Titan’s seas are hospitable to the formation of life, or whether there may already be life there, will have to wait. What role the nitrogen bubbles play in Titan’s life question will also have to wait.
As you probably know, NASA recently announced plans to send a mission to Jupiter’s moon Europa. If all goes well, the Europa Clipper will blast off for the world in the 2020s, and orbit the icy moon to discover all its secrets.
And that’s great and all, I like Europa just fine. But you know where I’d really like us to go next? Titan.
Titan, as you probably know, is the largest moon orbiting Saturn. In fact, it’s the second largest moon in the Solar System after Jupiter’s Ganymede. It measures 5,190 kilometers across, almost half the diameter of the Earth. This place is big.
It orbits Saturn every 15 hours and 22 days, and like many large moons in the Solar System, it’s tidally locked to its planet, always showing Saturn one side.
Titan image taken by Cassini on Oct. 7, 2013 (Credit: NASA/JPL-Caltech/Space Science Institute)
Before NASA’s Voyager spacecraft arrived in 1980, astronomers actually thought that Titan was the biggest moon in the Solar System. But Voyager showed that it actually has a thick atmosphere, that extends well into space, making the true size of the moon hard to judge.
This atmosphere is one of the most interesting features of Titan. In fact, it’s the only moon in the entire Solar System with a significant atmosphere. If you could stand on the surface, you would experience about 1.45 times the atmospheric pressure on Earth. In other words, you wouldn’t need a pressure suit to wander around the surface of Titan.
You would, however, need a coat. Titan is incredibly cold, with an average temperature of almost -180 Celsius. For you Fahrenheit people that’s -292 F. The coldest ground temperature ever measured on Earth is almost -90 C, so way way colder.
You would also need some way to breathe, since Titan’s atmosphere is almost entirely nitrogen, with trace amounts of methane and hydrogen. It’s thick and poisonous, but not murderous, like Venus.
Titan has only been explored a couple of times, and we’ve actually only landed on it once.
The first spacecraft to visit Titan was NASA’s Pioneer 11, which flew past Saturn and its moons in 1979. This flyby was followed by NASA’s Voyager 1 in 1980 and then Voyager 2 in 1981. Voyager 1 was given a special trajectory that would take it as close as possible to Titan to give us a close up view of the world.
Saturn’s moon Titan lies under a thick blanket of orange haze in this Voyager 1 picture. Credit: NASA
Voyager was able to measure its atmosphere, and helped scientists calculate Titan’s size and mass. It also got a hint of darker regions which would later turn out to be oceans of liquid hydrocarbons.
The true age of Titan exploration began with NASA’s Cassini spacecraft, which arrived at Saturn on July 4, 2004. Cassini made its first flyby of Titan on October 26, 2004, getting to within 1,200 kilometers or 750 miles of the planet. But this was just the beginning. By the end of its mission later this year, Cassini will have made 125 flybys of Titan, mapping the world in incredible detail.
Cassini saw that Titan actually has a very complicated hydrological system, but instead of liquid water, it has weather of hydrocarbons. The skies are dotted with methane clouds, which can rain and fill oceans of nearly pure methane.
And we know all about this because of Cassini’s Huygen’s lander, which detached from the spacecraft and landed on the surface of Titan on January 14, 2005. Here’s an amazing timelapse that shows the view from Huygens as it passed down through the atmosphere of Titan, and landed on its surface.
Huygens landed on a flat plain, surrounded by “rocks”, frozen globules of water ice. This was lucky, but the probe was also built to float if it happened to land on liquid instead.
It lasted for about 90 minutes on the surface of Titan, sending data back to Earth before it went dark, wrapping up the most distant landing humanity has ever accomplished in the Solar System.
Although we know quite a bit about Titan, there are still so many mysteries. The first big one is the cycle of liquid. Across Titan there are these vast oceans of liquid methane, which evaporate to create methane clouds. These rain, creating mists and even rivers.
This false-color mosaic of Saturn’s largest moon Titan, obtained by Cassini’s visual and infrared mapping spectrometer, shows what scientists interpret as an icy volcano. Credit: NASA/JPL/University of Arizona
Is it volcanic? There are regions of Titan that definitely look like there have been volcanoes recently. Maybe they’re cryovolcanoes, where the tidal interactions with Saturn cause water to well up from beneath crust and erupt onto the surface.
Is there life there? This is perhaps the most intriguing possibility of all. The methane rich system has the precursor chemicals that life on Earth probably used to get started billions of years ago. There’s probably heated regions beneath the surface and liquid water which could sustain life. But there could also be life as we don’t understand it, using methane and ammonia as a solvent instead of water.
To get a better answer to these questions, we’ve got to return to Titan. We’ve got to land, rove around, sail the oceans and swim beneath their waves.
Now you know all about this history of the exploration of Titan. It’s time to look at serious ideas for returning to Titan and exploring it again, especially its oceans.
Planetary scientists have been excited about the exploration of Titan for a while now, and a few preliminary proposals have been suggested, to study the moon from the air, the land, and the seas.
The spacecraft, balloon, and lander of the Titan Saturn System Mission. Credit: NASA Jet Propulsion Laboratory
First up, there’s the Titan Saturn System Mission, a mission proposed in 2009, for a late 2020s arrival at Titan. This spacecraft would consist of a lander and a balloon that would float about in the atmosphere, and study the world from above. Over the course of its mission, the balloon would circumnavigate Titan once from an altitude of 10km, taking incredibly high resolution images. The lander would touch down in one of Titan’s oceans and float about on top of the liquid methane, sampling its chemicals.
As we stand right now, this mission is in the preliminary stages, and may never launch.
The Aerial Vehicle for In-situ and Airborne Titan Reconnaissance (AVIATR) concept for an aerial explorer for Titan. Credit: Mike Malaska
In 2012, Dr. Jason Barnes and his team from the University of Idaho proposed sending a robotic aircraft to Titan, which would fly around in the atmosphere photographing its surface. Titan is actually one of the best places in the entire Solar System to fly an airplane. It has a thicker atmosphere and lower gravity, and unlike the balloon concept, an airplane is free to go wherever it needs powered by a radioactive thermal generator.
Although the mission would only cost about $750 million or so, NASA hasn’t pushed it beyond the conceptual stage yet.
On the left is TALISE (Titan Lake In-situ Sampling Propelled Explorer), the ESA proposal. This would have it’s own propulsion, in the form of paddlewheels. Credit: bisbos.com
An even cooler plan would put a boat down in one of Titan’s oceans. In 2012, a team of Spanish engineers presented their idea for how a Titan boat would work, using propellers to put-put about across Titan’s seas. They called their mission the Titan Lake In-Situ Sampling Propelled Explorer, or TALISE.
Propellers are fine, but it turns out you could even have a sailboat on Titan. The methane seas have much less density and viscosity than water, which means that you’d only experience about 26% the friction of Earth. Cassini measured windspeeds of about 3.3 m/s across Titan, which half the average windspeed of Earth. But this would be plenty of wind to power a sail when you consider Titan’s thicker atmosphere.
And here’s my favorite idea. A submarine. This 6-meter vessel would float on Titan’s Kraken Mare sea, studying the chemistry of the oceans, measuring currents and tides, and mapping out the sea floor.
It would be capable of diving down beneath the waves for periods, studying interesting regions up close, and then returning to the surface to communicate its findings back to Earth. This mission is in the conceptual stage right now, but it was recently chosen by NASA’s Innovative Advanced Concepts Group for further study. If all goes well, the submarine would travel to Titan by 2038 when there’s a good planetary alignment.
Okay? Are you convinced? Let’s go back to Titan. Let’s explore it from the air, crawl around on the surface and dive beneath its waves. It’s one of the most interesting places in the entire Solar System, and we’ve only scratched the surface.
If I’ve done my job right, you’re as excited about a mission to Titan as I am. Let’s go back, let’s sail and submarine around that place. Let me know your thoughts in the comments.
The Aerial Vehicle for In-situ and Airborne Titan Reconnaissance (AVIATR) concept for an aerial explorer for Titan. Credit: Mike Malaska
Last week, from Monday Feb. 27th to Wednesday March 1st, NASA hosted the “Planetary Science Vision 2050 Workshop” at their headquarters in Washington, DC. During the course of the many presentations, speeches and addresses that made up the workshop, NASA and its affiliates shared their many proposals for the future of Solar System exploration.
A very popular theme during the workshop was the exploration of Titan. In addition to being the only other body in the Solar System with a nitrogen-rich atmosphere and visible liquid on its surface, it also has an environment rich in organic chemistry. For this reason, a team led by Michael Pauken (from NASA’s Jet Propulsion Laboratory) held a presentation detailing the many ways it can be explored using aerial vehicles.
The presentation, which was titled “Science at a Variety of Scientific Regions at Titan using Aerial Platforms“, was also chaired by members of the aerospace industry – such as AeroVironment and Global Aerospace from Monrovia, California, and Thin Red Line Aerospace from Chilliwack, BC. Together, they reviewed the various aerial platform concepts that have been proposed for Titan since 2004.
Artist depiction of the ESA’s Huygens lander setting down on Titan, which took place on January 14th. Credit: ESA
While the concept of exploring Titan with aerial drones and balloons dates back to the 1970s and 80s, 2004 was especially important since it was at this time that the Huygens lander conducted the first exploration of the moon’s surface. Since that time, many interesting and feasible proposals for aerial platforms have been made. As Dr. Pauken told Universe Today via email:
“The Cassini-Huygens mission revealed a lot about Titan we didn’t know before and that has also raised a lot more questions. It helped us determine that imaging the surface is possible below 40-km altitude so it’s exciting to know we could take aerial photos of Titan and send them back home.”
These concepts can be divided into two categories, which are Lighter-Than-Air (LTA) craft and Heavier-Than-Air (HTA) craft. And as Pauken explained, these are both well-suited when it comes to exploring a moon like Titan, which has an atmosphere that is actually denser than Earth’s – 146.7 kPa at the surface compared to 101 kPa at sea level on Earth – but only 0.14 times the gravity (similar to the Moon).
“The density of Titan’s atmosphere is higher than Earth’s so it is excellent for flying lighter-than-air vehicles like a balloon,” he said. “Titan’s low gravity is a benefit for heavier-than-air vehicles like helicopters or airplanes since they will ‘weigh’ less than they would on Earth.”
Titan’s atmosphere makes Saturn’s largest moon look like a fuzzy orange ball in this natural-color view from the Cassini spacecraft. Cassini captured this image in 2012. Credit: NASA/JPL-Caltech/Space Science Institute
“The Lighter-than-air LTA concepts are buoyant and don’t need any energy to stay aloft, so more energy can be directed towards science instruments and communications. The Heavier-than-air concepts have to consume power to stay in the air which takes away from science and telecom. But HTA can be directed to targets more quickly and accurately the LTA vehicles which mostly drift with the winds.”
TSSM Montgolfiere Balloon:
Plans for using a Montgolfiere balloon to explore Titan go back to 2008, when NASA and the ESA jointly developed the Titan Saturn System Mission (TSSM) concept. A Flagship Mission concept, the TSSM would consist of three elements including a NASA orbiter and two ESA-designed in-situ elements – a lander to explore Titan’s lakes and a Montgolfiere balloon to explore its atmosphere.
The orbiter would rely on a Radioisotopic Power System (RPS) and Solar Electric Propulsion (SEP) to reach the Saturn system. And on its way to Titan, it would be responsible for examining Saturn’s magnetosphere, flying through the plumes of Enceladus to analyze it for biological markers, and taking images of Enceladus’ “Tiger Stripes” in the southern polar region.
Artist’s concept of a Mongolfiere balloon and a deployable lander at Titan. Credit: NASA
Once the orbiter had achieved orbital insertion with Saturn, it would release the Montgolfiere during its first Titan flyby. Attitude control for the balloon would be provided by heating the ambient gas with RPS waste heat. The prime mission would last a total of about 4 years, comprised of a two-year Saturn tour, a 2-month Titan aero-sampling phase, and a 20-month Titan orbiting phase.
Of the benefits to this concept, the most obvious is the fact that a Montgolfiere vehicle powered by RPS could operate within Titan’s atmosphere for many years and would be able to change altitude with only minimal energy use. At the time, the TSSM concept was in competition with mission proposals for the moons of Europa and Ganymede.
In February of 2009, both the TSSM and the the Europa Jupiter System Mission (EJSM) concept were chosen to move forward with development, but the EJSM was given first priority. This mission was renamed the Europa Clipper, and is slated for launch in 2020 (and arriving at Europa by 2026).
Titan Helium Balloon:
Subsequent research on Montgolfiere balloons revealed that years of service and minimal energy expenditure could also be achieved in a much more compact balloon design. By combining an enveloped-design with helium, such a platform could operate in the skies of Titan for four times as long as balloons here on Earth, thanks to a much slower rate of diffusion.
Artist’s concept of the Mechanical Compression Altitude Control (MCAC) balloon, which is comprised of a number of segments that are compressed by shortening a tether that runs down the axis of the balloon. Credit: Thin Red Line Aerospace.
Altitude control would also be possible with very modest amounts of energy, which could be provided either through pump or mechanical compression. Thus, with an RPS providing power, the platform could be expected to last longer that comparable balloon designs. This envelope-helium balloon could also be paired with a glider to create a lighter-than-air vehicle capable of lateral motion as well.
Examples of the this include the Titan Winged Aerobot (TWA, shown below), which was investigated as part of NASA’s Phase One 2016 Small-Business Innovation Research (SBIR) program. Developed by the Global Aerospace Corporation, in collaboration with Northrop Grumman, the TWA is a hybrid entry vehicle, balloon, and maneuverable glider with 3-D directional control that could satisfy many science objectives.
Like the Mongtolfiere concept, it would rely on minimal power provided by a single RPS. Its unique buoyancy system would also allow it to descend and ascend without the need for propulsion systems or control surfaces. One drawback is the fact that it cannot land on the moon’s surface to conduct research and then take off again. However, the design does allow for low-altitude flight, which would allow for the delivery of probes to the surface.
Other concepts that have been developed in recent years include heavier-than-air aircraft, which center around the development of fixed-wing vehicles and rotorcraft.
Concept for a Titan Winged Aerobot, a hybrid balloon glider that does not require significant power either to stay aloft or to achieve lateral motion. Credit: Global Aerospace Corp/Northrup Grumman
Fixed Wing Vehicles:
Concepts for fixed-wing aircraft have also been proposed in the past for a mission to Titan. A notable example of this is the Aerial Vehicle for In-situ and Airborne Titan Reconnaissance (AVIATR), an unmanned aerial vehicle (UAV) that was proposed by Jason Barnes and Lawrence Lemke in 2011 (of the University of Idaho and Central Michigan University, respectively).
Relying on an RPS that would use the waste heat of decaying Plutonium 238 to power a small rear-mounted turbine, this low-power craft would take advantage of Titan’s dense atmosphere and low gravity to conduct sustained flight. A novel “climb-then-glide” strategy, where the engine would shut down during glide periods, would also allow for power to be stored for optimal use during telecommunication sessions.
This addresses a major drawback of fixed-wing vehicles, which is the need to subdivide power between the needs of maintaining flight and conducting scientific research. However, the AVIATR is limited in one respect, in that it cannot descend to the surface to conduct science experiments or collect samples.
Rotorcraft:
Last, but not least, is the concept for a rotorcraft. In this case, the aerial platform would be a quadcopter, which would be well-suited to Titan’s atmosphere, would allow for easy ascent and descent, and for studies to be conducted on the surface. It would also take advantage of developments made in commercial UAVs and drones in recent years.
Artist’s concept of the Titan Aerial Daughtercraft (TAD) flying above one of Titan’s methane lake. Credit: NASA
This mission concept would consist of two components. On the one hand, there’s the rotorcraft – known as a Titan Aerial Daughtercraft (TAD) – which would rely on a rechargeable battery system to power itself while conducting short-duration flights (about an hour at a time). The second component is the “Mothercraft”, which would take the form of a lander or balloon, which the TAD would return to between flights to recharge from an onboard RPS.
Currently, NASA’s Jet Propulsion Laboratory is developing a similar concept, known as the Mars Helicopter “Scout”, for use on Mars – which is expected to be launched aboard the Mars 2020 mission. In this case, the design calls for two coaxial counter-rotating rotors, which would provide the best thrust-to-weight ratio in Mars’ thin atmosphere.
Another rotorcraft concept is being pursued by Elizabeth Turtle and colleagues from John Hopkins APL and the University of Idaho (including James Barnes). With support from NASA and members of Goddard Space Flight Center, Pennsylvania State University, and Honeybee Robotics, they have proposed a concept known as the “Dragonfly“.
Their aerial vehicle would rely on four-rotors to take advantage of Titan’s thick atmosphere and low gravity. Its design would also allow it to easily obtain samples and determine the composition of the surface in multiple geological settings. These findings will be presented at the upcoming 48th Lunar and Planetary Science Conference – which will be taking place from March 20th to 24th in The Woodlands, Texas.
Artist’s concept of the Titan Aerial Daughter quadcopter and its “Mothercraft” balloon. Credit: NASA/STMD
While the exploration of Titan is likely to take a back seat to the exploration of Europa in the coming decades, it is anticipated that a mission will be mounted before the mid-point of this century. Not only are the scientific goals very much the same in both cases – a chance to explore a unique environment and search for life beyond Earth – but the benefits will be comparable as well.
With every potentially life-bearing body we explore, we stand to learn more about how life began in our Solar System. And even if we do not find any life in the process, we stand to learn a great deal about the history and formation of the Solar System. On top of that, we will be one step closer to understanding humanity’s place in the Universe.
Ask me my favorite object in the Solar System, especially to see through a telescope, and my answer is always the same: Saturn.
Saturn is this crazy, ringed world, different than any other place we’ve ever seen. And in a small telescope, you can really see the ball of the planet, you can see its rings. It’s one thing to see a world like this from afar, a tiny jumping image in a telescope. To really appreciate and understand a place like Saturn, you’ve got to visit.
And thanks to NASA’s Cassini spacecraft, that’s just what we’ve been doing for the last 13 years. Take a good close look at this amazing ringed planet and its moons, and studying it from every angle.
Cassini orbiting Saturn. Credit: NASA
Throughout this article, I’m going to regale you with the amazing discoveries made by Cassini at Saturn. What it taught us, and what new mysteries it uncovered.
NASA’s Cassini spacecraft was launched from Earth on October 15, 1997. Instead of taking the direct route, it made multiple flybys of Venus, a flyby of Earth and a flyby of Jupiter. Each one of these close encounters boosted Cassini’s velocity, allowing it to make the journey with less escape velocity from Earth.
It arrived at Saturn on July 1st, 2004 and began its science operations shortly after that. The primary mission lasted 4 years, and then NASA extended its mission two more times. The first ending in 2010, and the second due to end in 2017. But more on that later.
Before Cassini, we only had flybys of Saturn. NASA’s Pioneer 11, and Voyagers 1 and 2 both zipped past the planet and its moons, snapping pictures as they went.
But Cassini was here to stay. To orbit around and around the planet, taking photos, measuring magnetic fields, and studying chemicals.
For Saturn itself, Cassini was able to make regular observations of the planet as it passed through entire seasons. This allowed it to watch how the weather and atmospheric patterns changed over time. The spacecraft watched lightning storms dance through the cloudtops at night.
This series of images from NASA’s Cassini spacecraft shows the development of the largest storm seen on the planet since 1990. These true-color and composite near-true-color views chronicle the storm from its start in late 2010 through mid-2011, showing how the distinct head of the storm quickly grew large but eventually became engulfed by the storm’s tail. Credit: NASA/JPL-Caltech/Space Science Institute
Two highlights. In 2010, Cassini watched a huge storm erupt in the planet’s northern hemisphere. This storm dug deep into Saturn’s lower atmosphere, dredging up ice from a layer 160 kilometers below and mixing it onto the surface. This was the first time that astronomers were able to directly study this water ice on Saturn, which is normally in a layer hidden from view.
Natural color images taken by NASA’s Cassini wide-angle camera, showing the changing appearance of Saturn’s north polar region between 2012 and 2016.. Credit: NASA/JPL-Caltech/Space Science Institute/Hampton University
The second highlight, of course, is the massive hexagonal storm churning away in Saturn’s northern pole. This storm was originally seen by Voyager, but Cassini brought its infrared and visible wavelength instruments to bear.
Why a hexagon? That’s still a little unclear, but it seems like when you rotate fluids of different speeds, you get multi-sided structures like this.
Cassini showed how the hexagonal storm has changed in color as Saturn moved through its seasons.
This is one of my favorite images sent back by Cassini. It’s the polar vortex at the heart of the hexagon. Just look at those swirling clouds.
The polar vortex, in all its glory. Credit: NASA/JPL-Caltech/Space Science Institute
Now, images of Saturn itself are great and all, but there was so much else for Cassini to discover in the region.
Cassini studied Saturn’s rings in great detail, confirming that they’re made up of ice particles, ranging in size as small a piece of dust to as large as a mountain. But the rings themselves are actually quite thin. Just 10 meters thick in some places. Not 10 kilometers, not 10 million kilometers, 10 meters, 30 feet.
The spacecraft helped scientists uncover the source of Saturn’s E-ring, which is made up of fresh icy particles blasting out of its moon Enceladus. More on that in a second too.
Vertical structures, among the tallest seen in Saturn’s main rings, rise abruptly from the edge of Saturn’s B ring to cast long shadows on the ring in this image taken by NASA’s Cassini spacecraft two weeks before the planet’s August 2009 equinox. Credit: NASA/JPL/Space Science Institute
Here’s another one of my favorite images of the mission. You’re looking at strange structures in Saturn’s B-ring. Towering pillars of ring material that rise 3.5 kilometers above the surrounding area and cast long shadows. What is going on here?
They’re waves, generated in the rings and enhanced by nearby moons. They move and change over time in ways we’ve never been able to study anywhere else in the Solar System.
Daphnis, one of Saturn’s ring-embedded moons, is featured in this view, kicking up waves as it orbits within the Keeler gap. Credit: NASA/JPL-Caltech/Space Science Institute
Cassini has showed us that Saturn’s rings are a much more dynamic place than we ever thought. Some moons are creating rings, other moons are absorbing or distorting them. The rings generate bizarre spoke patterns larger than Earth that come and go because of electrostatic charges.
Speaking of moons, I’m getting to the best part. What did Cassini find at Saturn’s moons?
Let’s start with Titan, Saturn’s largest moon. Before Cassini, we only had a few low resolution images of this fascinating world. We knew Titan had a dense atmosphere, filled with nitrogen, but little else.
Cassini was carrying a special payload to assist with its exploration of Titan: the Huygens lander. This tiny probe detached from Cassini just before its arrival at Saturn, and parachuted through the cloudtops on January 14, 2005, analyzing all the way. Huygens returned images of its descent through the atmosphere, and even images of the freezing surface of Titan.
Huygen’s view of Titan. Credit: ESA/NASA/JPL/University of Arizona
But Cassini’s own observations of Titan took the story even further. Instead of a cold, dead world, Cassini showed that it has active weather, as well as lakes, oceans and rivers of hydrocarbons. It has shifting dunes of pulverized rock hard water ice.
If there’s one place that needs exploring even further, it’s Titan. We should return with sailboats, submarines and rovers to better explore this amazing place.
A view of Mimas from the Cassini spacecraft. Credit: NASA/JPL/Space Science Institute
We learned, without a shadow of a doubt, that Mimas absolutely looks like the Death Star. No question. But instead of a megalaser, this moon has a crater a third of its own size.
Saturn’s moon Iapetus. Image credit: NASA/JPL/SSI
Cassini helped scientists understand why Saturn’s moon Iapetus has one light side and one dark side. The moon is tidally locked to Saturn, its dark side always leading the moon in orbit. It’s collecting debris from another Saturnian moon, Phoebe, like bugs hitting the windshield of a car.
Perhaps the most exciting discovery that Cassini made during its mission is the strange behavior of Saturn’s moon Enceladus. The spacecraft discovered that there are jets of water ice blasting out of the moon’s southern pole. An ocean of liquid water, heated up by tidal interactions with Saturn, is spewing out into space.
And as you know, wherever we find water on Earth, we find life. We thought that water in the icy outer Solar System would be hard to reach, but here it is, right at the surface, venting into space, and waiting for us to come back and investigate it further.
Icy water vapor geysers erupting from fissures on Enceladus. Credit: NASA/JPL
On September 15, 2017, the Cassini mission will end. How do we know it’s going to happen on this exact date? Because NASA is going to crash the spacecraft into Saturn, killing it dead.
That seems a little harsh, doesn’t it, especially for a spacecraft which has delivered so many amazing images to us over nearly two decades of space exploration? And as we’ve seen from NASA’s Opportunity rover, still going, 13 years longer than anticipated. Or the Voyagers, out in the depths of the void, helping us explore the boundary between the Solar System and interstellar space. These things are built to last.
The problem is that the Saturnian system contains some of the best environments for life in the Solar System. Saturn’s moon Enceladus, for example, has geysers of water blasting out into space.
Cassini spacecraft is covered in Earth-based bacteria and other microscopic organisms that hitched a ride to Saturn, and would be glad to take a nice hot Enceladian bath. All they need is liquid water and a few organic chemicals to get going, and Enceladus seems to have both.
NASA feels that it’s safer to end Cassini now, when they can still control it, than to wait until they lose communication or run out of propellant in the future. The chances that Cassini will actually crash into an icy moon and infect it with our Earth life are remote, but why take the risk?
For the last few months, Cassini has been taking a series of orbits to prepare itself for its final mission. Starting in April, it’ll actually cross inside the orbit of the rings, getting closer and closer to Saturn. And on September 15th, it’ll briefly become a meteor, flashing through the upper atmosphere of Saturn, gone forever.
This graphic illustrates the Cassini spacecraft’s trajectory, or flight path, during the final two phases of its mission. The view is toward Saturn as seen from Earth. The 20 ring-grazing orbits are shown in gray; the 22 grand finale orbits are shown in blue. The final partial orbit is colored orange. Image credit: NASA/JPL-Caltech/Space Science Institute
Even in its final moments, Cassini is going to be sciencing as hard as it can. We’ll learn more about the density of consistency of the rings close to the planet. We’ll learn more about the planet’s upper atmosphere, storms and clouds with the closest possible photographs you can take.
And then it’ll all be over. The perfect finale to one of the most successful space missions in human history. A mission that revealed as many new mysteries about Saturn as it helped us answer. A mission that showed us not only a distant alien world, but our own planet in perspective in this vast Solar System. I can’t wait to go back.
How have the photos from Cassini impacted your love of astronomy? Let me know your thoughts in the comments.
ASA's Cassini spacecraft looks toward the night side of Saturn's largest moon and sees sunlight scattering through the periphery of Titan's atmosphere and forming a ring of color.
Credit: NASA/JPL-Caltech/Space Science Institute
Last week – from Monday, February 27th to Wednesday, March 1st – NASA hosted the “Planetary Science Vision 2050 Workshop” at their headquarters in Washington, DC. In the course of the many presentations, speeches and panel discussions, NASA’s shared its many plans for the future of space exploration with the international community.
Among the more ambitious of these was a proposal to explore Titan using an aerial explorer and a lander. Building upon the success of the ESA’s Cassini-Huygen mission, this plan would involve a balloon that would explore Titan’s surface from low altitude, along with a Mars Pathfinder-style mission that would explore the surface.
Ultimately, the goal a mission to Titan would be to explore the rich organic chemical environment the moon has, which presents a unique opportunity for planetary researchers. For some time, scientists have understood that Titan’s surface and atmosphere have an abundance of organic compounds and all the prebiotic chemistry necessary for life to function.
Artist depiction of Huygens landing on Titan. Credit: ESA
“Titan’s of particular interest because the abundant and complex organic chemistry can teach us about chemical interactions that could have occurred here on Earth (and elsewhere?) leading to the development of life. Furthermore, not only does Titan have an interior liquid-water ocean, but there will also have been opportunities for organic material to have mixed with liquid water at Titan’s surface, for example impact craters and possibly cryovolcanic eruptions. The combination of organic material with liquid water, of course, increases astrobiological potential.”
For this reason, the exploration of Titan has been a scientific goal for decades. The only question is how best to go about exploring Titan’s unique environment. During previous Decadal Surveys – such as the Campaign Strategy Working Group (CSWG) on Prebiotic Chemistry in the Outer Solar System, of which Lorenz was a contributor – has suggested that a mobile aerial vehicle (such as an airship or a balloon) would well-suited to the task.
However, such vehicles would be unable to study Titan’s methane lakes, which are one of the most exciting draws of the moon as far as research into prebiotic chemistry goes. What’s more, an aerial vehicle would not be able to conduct in-situ chemical analysis of the surface, much like what the Mars Exploration Rovers (Spirit, Opportunity and Curiosity) have been doing on Mars – and with immense results!
The ESA’s TALISE (Titan Lake In-situ Sampling Propelled Explorer) on the left, and NASA’s Titan Mare Explorer (TiME) on the right. Credit: bisbos.com
At the same time, Lorenz and his colleagues examined concepts for the exploration of Titan’s hydrocarbon seas – like the proposed Titan Mare Explorer (TiME) capsule. As one of several finalists of NASA’s 2010 Discovery competition, this concept called for the deployment of nautical robot to Titan in the coming decades, where it would study its methane lakes to learn more about the methane cycle and search for signs of organic life.
While such a proposal would be cost-effective and presents some very exciting opportunities for research, it also has some limitations. For instance, during the 2020s-2030s, Titan’s northern hemisphere will be experiencing its winter season; at which point the thickness of its atmosphere will make direct-to-Earth communications and Earth views impossible. On top of that, a nautical vehicle would preclude the exploration of Titan’s land surfaces.
These offer some of the most likely prospects for studying Titan’s advanced chemical evolution, including Titan’s dune sands. As a windswept region, this area likely has material deposited from all over Titan and may also contain aqueously altered materials. Much as the Mars Pathfinder landing site was selected so it could collect samples from a wide area, such as location would be an ideal site for a lander.
As such, Lorenz and his colleagues advocated the type of mission that was articulated in the 2007 Flagship Study, which called for a Montgolfière balloon for regional exploration and a Pathfinder-like lander. This would provide the opportunity to conduct surface imaging at resolutions that are impossible from orbit (due to the thick atmosphere) as well as investigating the surface chemistry and interior structure of the moon.
Artist’s conception of a possible structure for underground liquid reservoirs on Saturn moon’s Titan. Credit: ESA/ATG medialab
So while the balloon would gather high-resolution geographical data of the moon, the lander could conduct seismological surveys that would characterize the thickness of the ice above Titan’s internal water ocean. However, a lander mission would be limited in terms of range, and the surface of Titan presents problems for mobility. This would make multiple landers, or a relocatable lander, the most desired option.
“Potential targets include areas where we can measure solid surface materials, the composition of which is still not well known, Titan’s dune sands, for example,” said Turtle. “Detailed in situ analysis is required to determine their composition. The lakes and seas are also intriguing; however, in the nearer term (missions arriving in the 2030s) most of those will be in winter darkness. So, exploring them would likely have to wait until the 2040s.”
This mission concept would also take advantage of several technological advances that have been made in recent years. As Lorenz explained in the course of the presentation:
“Heavier-than-air mobility at Titan is in fact highly efficient, moreover, improvements in autonomous aircraft in the two decades since the CSWG make such exploration a realistic prospect. Multiple in-situ landers delivered by an aerial vehicle like an airplane or a lander with aerial mobility to access multiple sites, would provide the most desirable scientific capability, highly relevant to the themes of origins, workings, and life.”
Updated maps of Titan, based on the Cassini imaging science subsystem. Credit: NASA/JPL/Space Science Institute
However, addressing some additional challenges not raised at the 2050 Vision Workshop, they will be presenting a slight twist on their idea. Instead of a balloon and multiple landers, they will present a mission concept involving a “Dragonfly” qaudcopter. This four-rotor vehicle would be able to take advantage of Titan’s thick atmosphere and low gravity to obtain samples and determine the surface composition in multiple geological settings.
This concept also incorporates a lot of recent advances in technology, which include modern control electronics and advances in commerical unmanned aerial vehicle (UAV) designs. On top of that, a quadcopter would do away with chemically-powered retrorockets and could power-up between flights, giving it a potentially much longer lifespan.
These and other concepts for exploring Saturn’s moon Titan are sure to gain traction in the coming years. Given the many mysteries locked away on this world – with includes abundant water ice, prebiotic chemistry, a methane cycle, and a subsurface ocean that is likely to be a prebiotic environment – it is certainly a popular target for scientific research.
The fascinating surface of Jupiter’s icy moon Europa looms large in this newly-reprocessed color view, made from images taken by NASA's Galileo spacecraft in the late 1990s. This is the color view of Europa from Galileo that shows the largest portion of the moon's surface at the highest resolution. Credits: NASA/JPL-Caltech/SETI Institute
Earlier this week, NASA hosted the “Planetary Science Vision 2050 Workshop” at their headquarters in Washington, DC. Running from Monday to Wednesday – February 27th to March 1st – the purpose of this workshop was to present NASA’s plans for the future of space exploration to the international community. In the course of the many presentations, speeches and panel discussions, many interesting proposals were shared.
Among them were two presentations that outlined NASA’s plan for the exploration of Jupiter’s moon Europa and other icy moons. In the coming decades, NASA hopes to send probes to these moons to investigate the oceans that lie beneath theirs surfaces, which many believe could be home to extra-terrestrial life. With missions to the “ocean worlds” of the Solar System, we may finally come to discover life beyond Earth.
Artist’s rendering of a potential future mission to land a robotic probe on the surface of Jupiter’s moon Europa. Credits: NASA/JPL-Caltech
This report was drafted by NASA’s Planetary Science Division (PSD) in response to a congressional directive to begin a pre-Phase A study to assess the scientific value and engineering design of a Europa lander mission. These studies, which are known as Science Definition Team (SDT) reports, are routinely conducted long before missions are mounted in order to gain an understanding of the types of challenges it will face, and what the payoffs will be.
In addition to being the co-chair of the Science Definition Team, Hand also served as head of the project science team, which included members from the JPL and the California Institute of Technology (Caltech). The report he and his colleagues prepared was finalized and issued to NASA on February 7th, 2017, and outlined several objectives for scientific study.
As was indicated during the course of the presentation, these objectives were threefold. The first would involve searching for biosignatures and signs of life through analyses of Europa’s surface and near-subsurface material. The second would be to conduct in-situ analyses to characterize the composition of non-ice near-subsurface material, and determine the proximity of liquid water and recently-erupted material near the lander’s location.
The third and final goal would be to characterize the surface and subsurface properties and what dynamic processes are responsible for shaping them, in support for future exploration missions. As Hand explained, these objectives are closely intertwined:
“Were biosignatures to be found in the surface material, direct access to, and exploration of, Europa’s ocean and liquid water environments would be a high priority goal for the astrobiological investigation of our Solar System. Europa’s ocean would harbor the potential for the study of an extant ecosystem, likely representing a second, independent origin of life in our own solar system. Subsequent exploration would require robotic vehicles and instrumentation capable of accessing the habitable liquid water regions in Europa to enable the study of the ecosystem and organisms.”
Artist’s impression of a hypothetical ocean cryobot (a robot capable of penetrating water ice) in Europa. Credit: NASA
In other words, if the lander mission detected signs of life within Europa’s ice sheet, and from material churned up from beneath by resurfacing events, then future missions – most likely involving robotic submarines – would definitely be mounted. The report also states that any finds that are indicative of life would mean that planetary protections would be a major requirement for any future mission, to avoid the possibility of contamination.
But of course, Hand also admitted that there is a chance the lander will find no signs of life. If so, Hand indicated that future missions would be tasked with gaining “a better understanding of the fundamental geological and geophysical process on Europa, and how they modulate exchange of material with Europa’s ocean.” On the other hand, he claimed that even a null-result (i.e. no signs of life anywhere) would still be a major scientific find.
Ever since the Voyager probes first detected possible signs of an interior ocean on Europa, scientists have dreamed of the day when a mission might be possible to explore the interior of this mysterious moon. To be able to determine that life does not exist there could no less significant that finding life, in that both would help us learn more about life in our Solar System.
The Science Definition Team’s report will also be the subject of a townhall meeting at the 2017 Lunar and Planetary Science Conference (LPSC) – which will be taking place from March 20th to 24th in The Woodlands, Texas. The second event will be on April 23rd at the Astrobiology Science Conference (AbSciCon) held in Mesa, Arizona. Click here to read the full report.
Saturn’s moon Enceladus is another popular destination for proposed missions since it is believed to potentially host extra-terrestrial life. Credit: NASA/JPL/Space Science Institute
The second presentation, titled “Roadmaps to Ocean Worlds” took place later on Monday, Feb. 27th. This presentation was put on by members of the the Roadmaps to Ocean Worlds (ROW) team, which is chaired by Dr. Amandra Hendrix – a senior scientist at the Planetary Science Institute in Tuscon, Arizona – and Dr. Terry Hurford, a research assistant from NASA’s Science and Exploration Directorate (SED).
As a specialist in UV spectroscopy of planetary surfaces, Dr. Hendrix has collaborated with many NASA missions to explore icy bodies in the Solar System – including the Galileo and Cassini probes and the Lunar Reconnaissance Orbiter (LRO). Dr. Hurford, meanwhile, specializes in the geology and geophysics of icy satellites, as well as the effects orbital dynamics and tidal stresses have on their interior structures.
Founded in 2016 by NASA’s Outer Planets Assessment Group (OPAG), ROW was tasked with laying the groundwork for a mission that will explore “ocean worlds” in the search for life elsewhere in the Solar System. During the course of the presentation, Hendrix and Hurford laid out the findings from the ROW report, which was completed in January of 2017.
As they state in this report, “we define an ‘ocean world’ as a body with a current liquid ocean (not necessarily global). All bodies in our solar system that plausibly can have or are known to have an ocean will be considered as part of this document. The Earth is a well-studied ocean world that can be used as a reference (“ground truth”) and point of comparison.”
Dwarf planet Ceres is shown in this false-color renderings, which highlight differences in surface materials. The image is centered on Ceres brightest spots at Occator crater. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
By this definition, bodies like Europa, Ganymede,Callisto, and Enceladus would all be viable targets for exploration. These worlds are all known to have subsurface oceans, and there has been compelling evidence in the past few decades that point towards the presence of organic molecules and prebiotic chemistry there as well. Triton, Pluto,Ceres and Dione are all mentioned as candidate ocean worlds based on what we know of them.
Titan also received special mention in the course of the presentation. In addition to having an interior ocean, it has even been ventured that extremophile methanogenic lifeforms could exist on its surface:
“Although Titan possesses a large subsurface ocean, it also has an abundant supply of a wide range of organic species and surface liquids, which are readily accessible and could harbor more exotic forms of life. Furthermore, Titan may have transient surface liquid water such as impact melt pools and fresh cryovolcanic flows in contact with both solid and liquid surface organics. These environments present unique and important locations for investigating prebiotic chemistry, and potentially, the first steps towards life.”
Ultimately, the ROW’s pursuit of life on “ocean worlds” consists of four main goals. These include identifying ocean worlds in the solar system, which would mean determining which of the worlds and candidate worlds would be well-suited to study. The second is to characterize the nature of these oceans, which would include determining the properties of the ice shell and liquid ocean, and what drives fluid motion in them.
Artist’s conception of the Titan Aerial Daughtercraft on Saturn’s moon Titan. Credit: NASA
The third sub-goal involves determining if these oceans have the necessary energy and prebiotic chemistry to support life. And the fourth and final goal would be to determine how life might exist in them – i.e. whether it takes the form of extremophile bacteria and tiny organisms, or more complex creatures. Hendrix and Hurford also covered the kind of technological advances that will be needed for such missions to happen.
Naturally, any such mission would require the development of power sources and energy storage systems that would be suitable for cryogenic environments. Autonomous systems for pinpoint landing and technologies for aerial or landed mobility would also be needed. Planetary protection technologies would be necessary to prevent contamination, and electronic/mechanical systems that can survive in an ocean world environment too,
While these presentations are merely proposals of what could happen in the coming decades, they are still exciting to hear about. If nothing else, they show how NASA and other space agencies are actively collaborating with scientific institutions around the world to push the boundaries of knowledge and exploration. And in the coming decades, they hope to make some substantial leaps.
If all goes well, and exploration missions to Europa and other icy moons are allowed to go forward, the benefits could be immeasurable. In addition to the possibility of finding life beyond Earth, we will come to learn a great deal about our Solar System, and no doubt learn something more about humanity’s place in the cosmos.
Credit and copyright: ESA/DLR/FU Berlin (G. Neukum)
Ah, the good old days. ESA’s Mars Express imaged Reull Vallis, a river-like structure believed to have formed when running water flowed in the distant Martian past, cuts a steep-sided channel on its way towards the floor of the Hellas basin. A thicker atmosphere that included methane and hydrogen in addition to carbon dioxide may have allowed liquid water to flow on Mars at different times in the past according to a new study. Credit and copyright: ESA/DLR/FU Berlin (G. Neukum)
Water. It’s always about the water when it comes to sizing up a planet’s potential to support life. Mars may possess some liquid water in the form of occasional salty flows down crater walls, but most appears to be locked up in polar ice or hidden deep underground. Set a cup of the stuff out on a sunny Martian day today and depending on conditions, it could quickly freeze or simply bubble away to vapor in the planet’s ultra-thin atmosphere.
These rounded pebbles got their shapes after polished in a long-ago river in Gale Crater. They were discovered by Curiosity rover at the Hottah site. Credit: NASA/JPL-Caltech
Evidence of abundant liquid water in former flooded plains and sinuous river beds can be found nearly everywhere on Mars. NASA’s Curiosity rover has found mineral deposits that only form in liquid water and pebbles rounded by an ancient stream that once burbled across the floor of Gale Crater. And therein lies the paradox. Water appears to have gushed willy-nilly across the Red Planet 3 to 4 billion years ago, so what’s up today?
Blame Mars’ wimpy atmosphere. Thicker, juicier air and the increase in atmospheric pressure that comes with it would keep the water in that cup stable. A thicker atmosphere would also seal in the heat, helping to keep the planet warm enough for liquid water to pool and flow.
Different ideas have been proposed to explain the putative thinning of the air including the loss of the planet’s magnetic field, which serves as a defense against the solar wind.
This figure shows a cross-section of the planet Mars revealing an inner, high density core buried deep within the interior. Magnetic field lines are drawn in blue, showing the global scale magnetic field associated with a dynamic core. Mars must have had such a field long ago, but today it’s not evident. Perhaps the energy source that powered the early dynamo shut down. Credit: NASA/JPL/GSFC
Convection currents within its molten nickel-iron core likely generated Mars’ original magnetic defenses. But sometime early in the planet’s history the currents stopped either because the core cooled or was disrupted by asteroid impacts. Without a churning core, the magnetic field withered, allowing the solar wind to strip away the atmosphere, molecule by molecule.
Solar wind eats away the Martian atmosphere
Measurements from NASA’s current MAVEN mission indicate that the solar wind strips away gas at a rate of about 100 grams (equivalent to roughly 1/4 pound) every second. “Like the theft of a few coins from a cash register every day, the loss becomes significant over time,” said Bruce Jakosky, MAVEN principal investigator.
This graph shows the percent amount of the five most abundant gases in the atmosphere of Mars, as measured by the Sample Analysis at Mars (SAM) instrument suite on the Curiosity rover in October 2012. The season was early spring in Mars’ southern hemisphere. Credit: NASA/JPL-Caltech, SAM/GSFC
Researchers from the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) suggest a different, less cut-and-dried scenario. Based on their studies, early Mars may have been warmed now and again by a powerful greenhouse effect. In a paper published in Geophysical Research Letters, researchers found that interactions between methane, carbon dioxide and hydrogen in the early Martian atmosphere may have created warm periods when the planet could support liquid water on its surface.
The team first considered the effects of CO2, an obvious choice since it comprises 95% of Mars’ present day atmosphere and famously traps heat. But when you take into account that the Sun shone 30% fainter 4 billion years ago compared to today, CO2 alone couldn’t cut it.
“You can do climate calculations where you add CO2 and build up to hundreds of times the present day atmospheric pressure on Mars, and you still never get to temperatures that are even close to the melting point,” said Robin Wordsworth, assistant professor of environmental science and engineering at SEAS, and first author of the paper.
NASA’s Cassini spacecraft looks toward the night side of Saturn’s largest moon and sees sunlight scattering through the periphery of Titan’s atmosphere and forming a ring of color. The breakdown of methane at Titan into hydrogen and oxygen may also have occurred on Mars. The addition of hydrogen in the company of methane and carbon dioxide would have created a powerful greenhouse gas mixture, significantly warming the planet. Credit: NASA/JPL-Caltech/Space Science Institute
Carbon dioxide isn’t the only gas capable of preventing heat from escaping into space. Methane or CH4 will do the job, too. Billions of years ago, when the planet was more geologically active, volcanoes could have tapped into deep sources of methane and released bursts of the gas into the Martian atmosphere. Similar to what happens on Saturn’s moon Titan, solar ultraviolet light would snap the molecule in two, liberating hydrogen gas in the process.
When Wordsworth and his team looked at what happens when methane, hydrogen and carbon dioxide collide and then interact with sunlight, they discovered that the combination strongly absorbed heat.
Carl Sagan,American astronomer and astronomy popularizer, first speculated that hydrogen warming could have been important on early Mars back in 1977, but this is the first time scientists have been able to calculate its greenhouse effect accurately. It is also the first time that methane has been shown to be an effective greenhouse gas on early Mars.
This awesome image of the Tharsis region of Mars taken by Mars Express shows several prominent shield volcanoes including the massive Olympus Mons (at left). Volcanoes, when they were active, could have released significant amounts of methane into Mars’ atmosphere. Click for a larger version. Credit: ESA
When you take methane into consideration, Mars may have had episodes of warmth based on geological activity associated with earthquakes and volcanoes. There have been at least three volcanic epochs during the planet’s history — 3.5 billion years ago (evidenced by lunar mare-like plains), 3 billion years ago (smaller shield volcanoes) and 1 to 2 billion years ago, when giant shield volcanoes such as Olympus Monswere active. So we have three potential methane bursts that could rejigger the atmosphere to allow for a mellower Mars.
The sheer size of Olympus Mons practically shouts massive eruptions over a long period of time. During the in-between times, hydrogen, a lightweight gas, would have continued to escape into space until replenished by the next geological upheaval.
“This research shows that the warming effects of both methane and hydrogen have been underestimated by a significant amount,” said Wordsworth. “We discovered that methane and hydrogen, and their interaction with carbon dioxide, were much better at warming early Mars than had previously been believed.”
I’m tickled that Carl Sagan walked this road 40 years ago. He always held out hope for life on Mars. Several months before he died in 1996, he recorded this:
” … maybe we’re on Mars because of the magnificent science that can be done there — the gates of the wonder world are opening in our time. Maybe we’re on Mars because we have to be, because there’s a deep nomadic impulse built into us by the evolutionary process, we come after all, from hunter gatherers, and for 99.9% of our tenure on Earth we’ve been wanderers. And, the next place to wander to, is Mars. But whatever the reason you’re on Mars is, I’m glad you’re there. And I wish I was with you.”
The view of Titan from the descending Huygens spacecraft on January 14, 2005. Credit: ESA/NASA/JPL/University of Arizona.
On December 25, 2004, the piggybacking Huygens probe was released from the ‘mothership’ Cassini spacecraft and it arrived at Titan on January 14, 2005. The probe began transmitting data to Cassini four minutes into its descent through Titan’s murky atmosphere, snapping photos and taking data all the while. Then it touched down, the first time a probe had landed on an extraterrestrial world in the outer Solar System.
JPL has released a re-mix of the data and images gathered by Huygens 12 years ago in a beautiful new video. This is the last opportunity to celebrate the success of Huygens before Cassini ends its mission in September of 2017.
Watch as the incredible view of Titan’s surface comes into view, with mountains, a system of river channels and a possible lakebed.
After a two-and-a-half-hour descent, the metallic, saucer-shaped spacecraft came to rest with a thud on a dark floodplain covered in cobbles of water ice, in temperatures hundreds of degrees below freezing.
Huygens had to quickly collect and transmit all the images and data it could because shortly after landing, Cassini would drop below the local horizon, “cutting off its link to the home world and silencing its voice forever.”
How much of this video is actual images and data vs computer graphics?
Of course, the clips at the beginning and end of the video are obviously animations of the probe and orbiter. However, the slow descending 1st-person point-of-view video is made using actual images from Huygens. But Huygens did not take a continuous movie sequence, so a lot of work was done by the team that operated Huygens’ optical imager, the Descent Imager/Spectral Radiometer (DISR), to enhance, colorize, and re-project the images into a variety of formats.
The view of the cobblestones and the parachute shadow near the end of the video is also created from real landing data, but was made in a different way from the rest of the descent video, because Huygens’ cameras did not actually image the parachute shadow. However, the upward looking infrared spectrometer took a measurement of the sky every couple of seconds, recording a darkening and then brightening to the unobstructed sky. The DISR team calculated from this the accurate speed and direction of the parachute, and of its shadow to create a very realistic video based on the data.
If you’re a data geek, there are some great videos of Huygens’ data by the University of Arizona Lunar and Planetary Laboratory team, such as this one:
The movie shows the operation of the DISR camera during the descent onto Titan. The almost 4-hour long operation
of DISR is shown in less than five minutes in 40 times actual sped up to landing and 100 times actual speed thereafter.
Erich Karkoschka from the UA team explained what all the sounds in the video are. “All parts of DISR worked together as programmed, creating a harmony,” he said. Here’s the full explanation:
Sound was added to mark various events. The left speaker follows the motion of Huygens. The pitch of the tone indicates the rotational speed. Vibrato indicates vibration of the parachute. Little clicks indicate the clocking of the rotation counter. Noise corresponds to heating of the heat shield, to parachute deployments, to the heat shield release, to the jettison of the DISR cover, and to touch down.
The sound in the right speaker follows DISR data. The pitch of the continuous tone goes with the signal strength. The 13 different chime tones indicate activity of the 13 components of DISR. The counters at the top and bottom of the list get the high and low notes, respectively.
You can see more info and videos created from Huygens’ data here.
A collage of Saturn (bottom left) and some of its moons: Titan, Enceladus, Dione, Rhea and Helene. Credit: NASA/JPL/Space Science Institute
Welcome back to our series on Settling the Solar System! Today, we take a look at the largest of Saturn’s Moons – Titan, Rhea, Iapetus, Dione, Tethys, Enceladus, and Mimas.
From the 17th century onward, astronomers made some profound discoveries around the planet Saturn, which they believed was the most distant planet of the Solar System at the time. Christiaan Huygens and Giovanni Domenico Cassini were the first, spotting the largest moons of Saturn – Titan, Tethys, Dione, Rhea and Iapetus. More discoveries followed; and today, what we recognized as the Saturn system includes 62 confirmed satellites.
What we know of this system has grown considerably in recent decades, thanks to missions like Voyager and Cassini. And with this knowledge has come multiple proposals that claim how Saturn’s moons should someday be colonized. In addition to boasting the only body other than Earth to have a dense, nitrogen-rich atmosphere, there are also abundant resources in this system that could be harnessed.
Much like the idea of colonizing the Moon, Mars, the moons of Jupiter, and other bodies in the Solar System, the idea of establishing colonies on Saturn’s moons has been explored extensively in science fiction. At the same time, scientific proposals have been made that emphasize how colonies would benefit humanity, allowing us to mount missions deeper into space and ushering in an age of abundance!
A montage of images from Cassini of various moons and the rings around Saturn. Credit: NASA/JPL-Caltech/Space Science Institute
Examples in Fiction:
The colonization of Saturn has been a recurring theme in science fiction over the decades. For example, in Arthur C. Clarke’s 1976 novel Imperial Earth, Titan is home to a human colony of 250,000 people. The colony plays a vital role in commerce, where hydrogen is taken from the atmosphere of Saturn and used as fuel for interplanetary travel.
In Piers Anthony’s Bio of a Space Tyrant series (1983-2001), Saturn’s moons have been colonized by various nations in a post-diaspora era. In this story, Titan has been colonized by the Japanese, whereas Saturn has been colonized by the Russians, Chinese, and other former Asian nations.
In the novel Titan (1997) by Stephen Baxter, the plot centers on a NASA mission to Titan which must struggle to survive after crash landing on the surface. In the first few chapters of Stanislaw Lem’s Fiasco(1986), a character ends up frozen on the surface of Titan, where they are stuck for several hundred years.
In Kim Stanley Robinson’s Mars Trilogy (1996), nitrogen from Titan is used in the terraforming of Mars. In his novel 2312 (2012), humanity has colonized several of Saturn’s moons, which includes Titan and Iapetus. Several references are made to the “Enceladian biota” in the story as well, which are microscopic alien organisms that some humans ingest because of their assumed medicinal value.
The moons of Saturn, from left to right: Mimas, Enceladus, Tethys, Dione, Rhea; Titan in the background; Iapetus (top) and irregularly shaped Hyperion (bottom). Credit: NASA/JPL/Space Science Institute
As part of his Grand Tour Series, Ben Bova’s novels Saturn (2003) and Titan (2006) address the colonization of the Cronian system. In these stories, Titan is being explored by an artificially intelligent rover which mysteriously begins malfunctioning, while a mobile human Space Colony explores the Rings and other moons.
Proposed Methods:
In his book Entering Space: Creating a Spacefaring Civilization (1999), Robert Zubrin advocated colonizing the outer Solar System, a plan which included mining the atmospheres of the outer planets and establishing colonies on their moons. In addition to Uranus and Neptune, Saturn was designated as one of the largest sources of deuterium and helium-3, which could drive the pending fusion economy.
He further identified Saturn as being the most important and most valuable of the three, because of its relative proximity, low radiation, and excellent system of moons. Zubrin claimed that Titan is a prime candidate for colonization because it is the only moon in the Solar System to have a dense atmosphere and is rich in carbon-bearing compounds.
On March 9th, 2006, NASA’s Cassini space probe found possible evidence of liquid water on Enceladus, which was confirmed by NASA in 2014. According to data derived from the probe, this water emerges from jets around Enceladus’ southern pole, and is no more than tens of meters below the surface in certain locations. This would would make collecting water considerably easier than on a moon like Europa, where the ice sheet is several km thick.
Data obtained by Cassini also pointed towards the presence of volatile and organic molecules. And Enceladus also has a higher density than many of Saturn’s moons, which indicates that it has a larger average silicate core. All of these resources would prove very useful for the sake of constructing a colony and providing basic operations.
In October of 2012, Elon Musk unveiled his concept for an Mars Colonial Transporter (MCT), which was central to his long-term goal of colonizing Mars. At the time, Musk stated that the first unmanned flight of the Mars transport spacecraft would take place in 2022, followed by the first manned MCT mission departing in 2024.
In September 2016, during the 2016 International Astronautical Congress, Musk revealed further details of his plan, which included the design for an Interplanetary Transport System (ITS) and estimated costs. This system, which was originally intended to transport settlers to Mars, had evolved in its role to transport human beings to more distant locations in the Solar System – which could include the Jovian and Cronian moons.
Artist’s rendering of possible hydrothermal activity that may be taking place on and under the seafloor of Enceladus. Credit: NASA/JPL
Potential Benefits:
Compared to other locations in the Solar System – like the Jovian system – Saturn’s largest moons are exposed to considerably less radiation. For instance, Jupiter’s moons of Io, Ganymede and Europa are all subject to intense radiation from Jupiter’s magnetic field – ranging from 3600 to 8 rems day. This amount of exposure would be fatal (or at least very hazardous) to human beings, requiring that significant countermeasures be in place.
In contrast, Saturn’s radiation belts are significantly weaker than Jupiter’s – with an equatorial field strength of 0.2 gauss (20 microtesla) compared to Jupiter’s 4.28 gauss (428 microtesla). This field extends from about 139,000 km from Saturn’s center out to a distance of about 362,000 km – compared to Jupiter’s, which extends to a distance of about 3 million km.
Of Saturn’s largest moons, Mimas and Enceladus fall within this belt, while Dione, Rhea, Titan, and Iapetus all have orbits that place them from just outside of Saturn’s radiation belts to well beyond it. Titan, for example, orbits Saturn at an average distance (semi-major axis) of 1,221,870 km, putting it safely beyond the reach of the gas giant’s energetic particles. And its thick atmosphere may be enough to shield residents from cosmic rays.
In addition, frozen volatiles and methane harvested from Saturn’s moons could be used for the sake of terraforming other locations in the Solar System. In the case of Mars, nitrogen, ammonia and methane have been suggested as a means of thickening the atmosphere and triggering a greenhouse effect to warm the planet. This would cause water ice and frozen CO² at the poles to sublimate – creating a self-sustaining process of ecological change.
Colonies on Saturn’s moons could also serve as bases for harvesting deuterium and helium-3 from Saturn’s atmosphere. The abundant sources of water ice on these moons could also be used to make rocket fuel, thus serving as stopover and refueling points. In this way, a colonizing the Saturn system could fuel Earth’s economy, and the facilitate exploration deeper into the outer Solar System.
Challenges:
Naturally, there are numerous challenges to colonizing Saturn’s moons. These include the distance involved, the necessary resources and infrastructure, and the natural hazards colonies on these moons would have to deal with. For starters, while Saturn may be abundant in resources and closer to Earth than either Uranus or Neptune, it is still very far.
On average, Saturn is approximately 1,429 billion km away from Earth; or ~8.5 AU, the equivalent of eight and a half times the average distance between the Earth and the Sun. To put that in perspective, it took the Voyager 1 probe roughly thirty-eight months to reach the Saturn system from Earth. For crewed spacecraft, carrying colonists and all the equipment needed to colonize the surface, it would take considerably longer to get there.
These ships, in order to avoid being overly large and expensive, would need to rely on cryogenics or hibernation-related technology in order to save room on storage and accommodations. While this sort of technology is being investigated for crewed missions to Mars, it is still very much in the research and development phase.
Artist’s concept of a Bimodal Nuclear Thermal Rocket in Low Earth Orbit. Credit: NASA
Any vessels involved in the colonization efforts, or used to ship resources to and from the Cronian system, would also need to have advanced propulsion systems to ensure that they could make the trips in a realistic amount of time. Given the distances involved, this would likely require rockets that used nuclear-thermal propulsion, or something even more advanced (like anti-matter rockets).
And while the former is technically feasible, no such propulsion systems have been built just yet. Anything more advanced would require many more years of research and development, and a major commitment in resources. All of this, in turn, raises the crucial issue of infrastructure.
Basically, any fleet operating between Earth and Saturn would require a network of bases between here and there to keep them supplied and fueled. So really, any plans to colonize Saturn’s moons would have to wait upon the creation of permanent bases on the Moon, Mars, the Asteroid Belt, and most likely the Jovian moons. This process would be punitively expensive by current standards and (again) would require a fleet of ships with advanced drive systems.
And while radiation is not a major threat in the Cronian system (unlike around Jupiter), the moons have been subject to a great deal of impacts over the course of their history. As a result, any settlements built on the surface would likely need additional protection in orbit, like a string of defensive satellites that could redirect comets and asteroids before they reached orbit.
The huge storm churning through the atmosphere in Saturn’s northern hemisphere overtakes itself as it encircles the planet in this true-color view from NASA’s Cassini spacecraft. Image credit: NASA/JPL-Caltech/SSI
Given its abundant resources, and the opportunities it would present for exploring deeper into the Solar System (and maybe even beyond), Saturn and its system of moons is nothing short of a major prize. On top of that, the prospect of colonizing there is a lot more appealing than other locations that come with greater hazards (i.e. Jupiter’s moons).
However, such an effort would be daunting and would require a massive multi-generational commitment. And any such effort would most likely have to wait upon the construction of colonies and/or bases in locations closer to Earth first – such as on the Moon, Mars, the Asteroid Belt, and around Jupiter. But we can certainly hold out hope for the long run, can’t we?
