Titan and Dione seen on December 10, 2011 by the Cassini spacecraft. (NASA/JPL/SSI/J. Major)
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It’s been said many times that the most Earthlike world in our solar system is not a planet at all, but rather Saturn’s moon Titan. At first it may not seem obvious why; being only a bit larger than the planet Mercury and coated in a thick opaque atmosphere containing methane and hydrocarbons, Titan sure doesn’t look like our home planet. But once it’s realized that this is the only moon known to even have a substantial atmosphere, and that atmosphere creates a hydrologic cycle on its surface that mimics Earth’s – complete with weather, rain, and gully-carving streams that feed liquid methane into enormous lakes – the similarities become more evident. Which, of course, is precisely why Titan continues to hold such fascination for scientists.
Now, researchers have identified yet another similarity between Saturn’s hazy moon and our own planet: Titan’s energy budget is in equilibrium, making it much more like Earth than the gas giant it orbits.
A team of researchers led by Liming Li of the Department of Earth and Atmospheric Sciences at the University of Houston in Texas has completed the first-ever investigation of the energy balance of Titan, using data acquired by telescopes and the Cassini spacecraft from 2004 to 2010.
Energy balance (or “budget”) refers to the radiation a planet or moon receives from the Sun versus what it puts out. Saturn, Jupiter and Neptune emit more energy than they receive, which indicates an internal energy source. Earth radiates about the same amount as it receives, so it is said to be in equilibrium… similar to what is now shown to be the case for Titan.
Blue hazes hover high above thicker orange clouds over Titan's south pole (NASA/JPL/SSI)
The energy absorption and reflection rates of a planet’s – or moon’s! – atmosphere are important clues to the state of its climate and weather. Different balances of energy or changes in those balances can indicate climate change – global cooling or global warming, for instance.
Of course, this doesn’t mean Titan is a balmy world. At nearly 300 degrees below zero (F) it has an environment that even the most extreme Earth-based life would find inhospitable. Although Titan’s atmosphere is ten times thicker than Earth’s its composition is very different, permitting easy passage of infrared radiation (a.k.a. “heat”) and thus exhibits an “anti-greenhouse” effect, unlike Earth or, on the opposite end of the scale, Venus.
Still, some stable process is in place on Saturn’s moon that allows for distribution of solar energy across its surface, within its atmosphere and back out into space. With results due in from Cassini from a flyby on Jan. 2, perhaps there will soon be even more clues as to what that may be.
The team’s report was published in the AGU’s Geophysical Research Letters on December 15, 2011. Li, L., et al. (2011), The global energy balance of Titan, Geophys. Res. Lett., 38, L23201, doi:10.1029/2011GL050053.
An artist's conception of AVIATR, an airplane mission to Saturn's largest moon Titan. Credit: Mike Malaska 2011
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It has been said that the atmosphere on Titan is so dense that a person could strap a pair of wings on their back and soar through its skies.
It’s a pretty fascinating thought. And Titan – Saturn’s largest moon – is a pretty fascinating place. After all, it’s the only other body in our solar system (besides Earth, of course) that has that type of atmosphere and evidence of liquid on its surface.
“As far as its scientific interest, Titan is the most interesting target in the Solar System,” Dr. Jason W. Barnes of the University of Idaho told Universe Today.
That’s why Barnes and a team of 30 scientists and engineers created an unmanned mission concept to explore Titan called AVIATR (Aerial Vehicle for In-situ and Airborne Titan Reconnaissance). The plan, which primarily consists of a 120 kg plane soaring through the natural satellite’s atmosphere, was published online late last month.
The goal of the plane concept – which according to Barnes can serve as a standalone mission or as part of a larger Titan-focused exploration program – is to study the moon’s geography (its mountains, dunes, lakes and seas), as well as its atmosphere (the wind, haze, clouds and rain. Did you know that Titan is the only other place is our solar system where it rains?)
AVIATR is composed of three vehicles: one for space travel, one for entry and descent into Titan, and a plane to fly through the atmosphere. AVIATR, estimated to cost $715 million, would not prevent other missions from occurring on Titan, Barnes said. Instead, it would supplement the science being done by other projects.
“The science that AVIATR could do complements the science that can be accomplished from both orbiting and landed platforms,” the article stated.
Unfortunately, it seems like the plane concept won’t be happening anytime soon.
That’s because Titan didn’t make the National Research Council’s “Decadal Survey” – a prioritization of future planetary missions. (Read more about the survey in this Universe Today post.)
“Titan was deferred to another decade,” Barnes said.
But, he hopes to continue to build support for AVIATR so that it can get onto the next decadal survey in 2020. “We certainly had a lot of interest from people. We are breaking the paradigm that a balloon was the right way to go to Titan,” Barnes said.
So, why send an unmanned plane to study Titan’s atmosphere?
“Titan is the best place to fly an airplane in the whole solar system. We can go when and where we want,” Barnes said, adding that when compared to Earth, there’s four times more air and seven times less gravity on Titan. “A balloon is stuck in the wind.”
According to the article:
“A balloon entrained in primarily zonal winds near the equator would have no mechanism by which to travel to the polar regions to observe lakes and shoreline processes. Even if it were possible to get there, it is not clear that it would be desirable to send a balloon to the poles where Titan’s most violent meteorological activity takes place. AVIATR is both able to fly to the poles and is sufficiently robust to survive there.”
Mission poster for AVIATR. Credit: Mike Malaska
There’s also this issue: A shortage of plutonium-238.
“The radioactive decay of plutonium-238 provides the heat that powers RTGs, which can power spacecraft where there is insufficient sunlight for solar panels to operate. NASA is presently investing in a new type of RTG, called the ASRG,” the article stated. “A traditional hot-air balloon will not work on Titan with an ASRG owing to its lower heat production. In contrast, the AVIATR mission is specifically enabled by the use of ASRGs. The power density (in Watts per kilogram) and longevity of the ASRG allow an electrically-powered aircraft to fly on Titan.”
A plane could also find potential landing spots for future exploration. And, “since we are flying, we fly west the whole time so we can stay on the day side of Titan,” Barnes said.
That daylight would also help AVIATR collect photographic data during its travels and, according to Barnes, when it’s time to downlink that information, the plane would conserve energy by gliding through the air.
“And in doing so, we can also sample of bunch of altitude ranges,” Barnes said. “We are sampling the whole time.”
The plan seems interesting enough, but it’ll be quite a while before any data from the prospective mission would be coming back to Earth. If the plan is accepted (the earliest being 2020), the project would still have to be built, then once completed it would take 7 1/2 years to reach Titan. Once there, the mission would take about a nominal Earth year to study.
“I now realize that it’s a career-long project,” Barnes said to Universe Today. “The plan at this point is to keep this in the forefront of people’s minds and take whatever new ideas that people suggest and try to improve its prospect for selection.
To view the complete proposal, published in Experimental Astronomy, go here.
Dawn Orbiting Vesta. NASA's Dawn spacecraft achieved orbit at the giant asteroid Vesta in July 2011. The depiction of Vesta is based on images obtained by Dawn's framing cameras. Dawn is an international collaboration of the US, Germany and Italy. Credit: NASA/JPL-Caltech
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A year ago, 2011 was proclaimed as the “Year of the Solar System” by NASA’s Planetary Science division. And what a year of excitement it was indeed for the planetary science community, amateur astronomers and the general public alike !
NASA successfully delivered astounding results on all fronts – On the Story of How We Came to Be.
“2011 was definitely the best year ever for NASA Planetary Science!” said Jim Green in an exclusive interview with Universe Today. Green is the Director of Planetary Science for the Science Mission Directorate at NASA HQ. “The Search for Life is a significant priority for NASA.”
This past year was without doubt simply breathtaking in scope in terms of new missions, new discoveries and extraordinary technical achievements. The comprehensive list of celestial targets investigated in 2011 spanned virtually every type of object in our solar system – from the innermost planet to the outermost reaches nearly touching interplanetary space.
There was even a stunningly evocative picture showing “All of Humanity” – especially appropriate now in this Holiday season ! You and all of Humanity are here !
-- Earth & Moon Portrait by Juno from 6 Million miles away --
First Photo transmitted from Jupiter Bound Juno shows Earth (on the left) and the Moon (on the right). Taken on Aug. 26, 2011 when spacecraft was about 6 million miles (9.66 million kilometers) away from Earth. Credit: NASA/JPL-Caltech
Three brand new missions were launched and ongoing missions orbited a planet and an asteroid and flew past a comet.
“NASA has never had the pace of so many planetary launches in such a short time,” said Green.
And three missions here were awarded ‘Best of 2011’ for innovation !
Mars Science Laboratory (MSL), Dawn and MESSENGER named “Best of What’s New” in 2011 by Popular Science magazine. 3 NASA Planetary Science missions received the innovation award for 2011 from Popular Science magazine. Artist concept shows mosaic of MESSENGER, Mars Science Laboratory and Dawn missions. Credit: NASA/JPL-Caltech
Here’s the Top NASA Planetary Science Stories of 2011 – ‘The Year of the Solar System’ – in chronological order
1. Stardust-NExT Fly By of Comet Tempel 1
Starting from the first moments of 2011 at the dawn of Jan. 1, hopes were already running high for planetary scientists and engineers busily engaged in setting up a romantic celestial date in space between a volatile icy comet and an aging, thrusting probe on Valentine’s Day.
The comet chasing Stardust-Next spacecraft successfully zoomed past Comet Tempel 1 on Feb. 14 at 10.9 km/sec (24,000 MPH) after flying over 6 Billion kilometers (3.5 Billion mi).
6 Views of Comet Tempel 1 and Deep Impact crater during Stardust-NExT flyby on Feb. 14, 2011
Arrows show location of man-made crater created in 2005 by NASA’s prior Deep Impact comet mission and newly imaged as Stardust-NExT zoomed past comet in 2011. The images progress in time during closest approach to comet beginning at upper left and moving clockwise to lower left. Credit: NASA/JPL-Caltech/University of Maryland. Post process and annotations by Marco Di Lorenzo & Kenneth Kremer
The craft approached within 178 km (111mi) and snapped 72 astonishingly detailed high resolution science images over barely 8 minutes. It also fulfilled the teams highest hopes by photographing the human-made crater created on Tempel 1 in 2005 by a cosmic collision with a penetrator hurled by NASA’s Deep Impact spacecraft. The probe previously flew by Comet Wild 2 in 2004 and returned cometary coma particles to Earth in 2006
Tempel 1 is the first comet to be visited by two spaceships from Earth and provided the first-ever opportunity to compare observations on two successive passages around the Sun.
Don Brownlee, the original Principal Investigator, summarized the results for Universe Today; “A great bonus of the mission was the ability to flyby two comets and take images and measurements. The wonderfully successful flyby of Comet Tempel 1 was a great cap to the 12 year mission and provided a great deal of new information to study the diversity among comets.”
“The new images of Tempel showed features that form a link between seemingly disparate surface features of the 4 comets imaged by spacecraft. Combining data on the same comet from the Deep Impact and Stardust missions has provided important new insights in to how comet surfaces evolve over time and how they release gas and dust into space”.
2. MESSENGER at Mercury
On March 18, the Mercury Surface, Space Environment, Geochemistry, and Ranging, or MESSENGER, spacecraft became the first spacecraft inserted into orbit around Mercury, the innermost planet.
So far MESSENGER has completed 1 solar day – 176 Earth days- circling above Mercury. The probe has collected a treasure trove of new data from the seven instruments onboard yielding a scientific bonanza; these include global imagery of most of the surface, measurements of the planet’s surface chemical composition, topographic evidence for significant amounts of water ice, magnetic field and interactions with the solar wind.
“MESSENGER discovered that Mercury has an enormous core, larger than Earth’s. We are trying to understand why that is and why Mercury’s density is similar to Earth’s,” Jim Green explained to Universe Today.
The First Solar Day
After its first Mercury solar day (176 Earth days) in orbit, MESSENGER has nearly completed two of its main global imaging campaigns: a monochrome map at 250 m/pixel and an eight-color, 1-km/pixel color map. Small gaps will be filled in during the next solar day. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
“The primary mission lasts 2 solar days, equivalent to 4 Mercury years.”
“NASA has granted a 1 year mission extension, for a total of 8 Mercury years. This will allow the team to understand the environment at Mercury during Solar Maximum for the first time. All prior spacecraft observations were closer to solar minimum,” said Green.
MESSENGER was launched in 2004 and the goal is to produce the first global scientific observations of Mercury and piece together the puzzle of how Mercury fits in with the origin and evolution of our solar system.
NASA’s Mariner 10 was the only previous robotic probe to explore Mercury, during three flyby’s back in the mid-1970’s early in the space age.
3. Dawn Asteroid Orbiter
The Dawn spacecraft achieved orbit around the giant asteroid Vesta in July 2011 after a four year interplanetary cruise and began transmitting the history making first ever close-up observations of the mysteriously diverse and alien world that is nothing short of a ‘Space Spectacular’.
“We do not have a good analog to Vesta anywhere else in the Solar System,” Chris Russell said to Universe Today. Russell, from UCLA, is the scientific Principal Investigator for Dawn.
Before Dawn, Vesta was just another fuzzy blob in the most powerful telescopes. Dawn has completely unveiled Vesta as a remarkably dichotomous, heavily battered and pockmarked world that’s littered with thousands of craters, mountains and landslides and ringed by mystifying grooves and troughs. It will unlock details about the elemental abundances, chemical composition and interior structure of this marvelously intriguing body.
Cataclysmic collisions eons ago excavated Vesta so it lacks a south pole. Dawn discovered that what unexpectedly remains is an enormous mountain some 16 miles (25 kilometers) high, twice the height of Mt. Everest.
Dawn is now about midway through its 1 year mission at Vesta which ends in July 2012 with a departure for Ceres, the largest asteroid. So far the framing cameras have snapped more than 10,000 never-before-seen images.
“What can be more exciting than to explore an alien world that until recently was virtually unknown!. ” Dr. Marc Rayman said to Universe Today. Rayman is Dawn’s Chief Engineer from NASA’s Jet Propulsion Lab (JPL) in Pasadena, Calif.
“Dawn is NASA at its best: ambitious, exciting, innovative, and productive.”
4. Juno Jupiter Orbiter
The solar powered Juno spacecraft was launched on Aug. 5 at Cape Canaveral Air Force Station in Florida, to embark on a five year, 2.8 billion kilometer (1.7 Billion mi) trek to Jupiter, our solar system’s largest planet. It was the first of three NASA planetary science liftoffs scheduled in 2011.
Juno Jupiter Orbiter soars skyward to Jupiter on Aug. 5, 2011 from Cape Canaveral Air Force Station, Florida. Credit: Ken Kremer
Juno’s goal is to map to the depths of the planets interior and elucidate the ingredients of Jupiter’s genesis hidden deep inside. These measurements will help answer how Jupiter’s birth and evolution applies to the formation of the other eight planets.
The 4 ton spacecraft will arrive at the gas giant in July 2016 and fire its braking rockets to go into a polar orbit and circle the planet 33 times over about one year.
The suite of nine instruments will scan the gas giant to find out more about the planets origins, interior structure and atmosphere, measure the amount of water and ammonia, observe the aurora, map the intense magnetic field and search for the existence of a solid planetary core.
“Jupiter is the Rosetta Stone of our solar system,” said Scott Bolton, Juno’s principal investigator from the Southwest Research Institute in San Antonio. “It is by far the oldest planet, contains more material than all the other planets, asteroids and comets combined and carries deep inside it the story of not only the solar system but of us. Juno is going there as our emissary — to interpret what Jupiter has to say.”
5. Opportunity reaches Endeavour Crater on Mars
The long lived Opportunity rover finally arrived at the rim of the vast 14 mile (22 kilometer) wide Endeavour Crater in mid-August 2011 following an epic three year trek across treacherous dune fields – a feat once thought unimaginable. All told, Opportunity has driven more than 34 km ( 21 mi) since landing on the Red Planet way back in 2004 for a mere 90 sol mission.
Endeavour Crater Panorama from Opportunity Mars Rover in August 2011
Opportunity arrived at the rim of Endeavour on Sol 2681, August 9, 2011 after a three year trek. The robot photographed segments of the huge craters eroded rim in this panoramic vista. Endeavour Crater is 14 miles (22 kilometers) in diameter. Mosaic Credit: NASA/JPL/Cornell/Marco Di Lorenzo/Kenneth Kremer
In November, the rover discovered the most scientifically compelling evidence yet for the flow of liquid water on ancient Mars in the form of a water related mineral vein at a spot dubbed “Homestake” along an eroded ridge of Endeavour’s rim.
Read my story about the Homestake discovery here, along with our panoramic mosaic showing the location – created by Ken Kremer and Marco Di Lorenzo and published by Astronomy Picture of the Day (APOD) on 12 Dec. 2011.
Watch for my upcoming story detailing Opportunity’s accomplishments in 2011.
6. GRAIL Moon Mappers
The Gravity Recovery and Interior Laboratory, or GRAIL mission is comprised of twin spacecraft tasked to map the moon’s gravity and study the structure of the lunar interior from crust to core.
Twin GRAIL Probes GO for Lunar Orbit Insertion on New Year’s Eve and New Year’s Day
GRAIL spacecraft will map the moon's gravity field and interior composition. Credit: NASA/JPL-Caltech
The dynamic duo lifted off from Cape Canaveral on September 10, 2011 atop the last Delta II rocket that will likely soar to space from Florida. After a three month voyage of more than 2.5 million miles (4 million kilometers) since blastoff, the two mirror image GRAIL spacecraft dubbed Grail-A and GRAIL-B are sailing on a trajectory placing them on a course over the Moon’s south pole on New Year’s weekend.
Each spacecraft will fire the braking rockets for about 40 minutes for insertion into Lunar Orbit about 25 hours apart on New Year’s Eve and New Year’s Day.
Engineers will then gradually lower the satellites to a near-polar near-circular orbital altitude of about 34 miles (55 kilometers).
The spacecraft will fly in tandem and the 82 day science phase will begin in March 2012.
“GRAIL is a Journey to the Center of the Moon”, says Maria Zuber, GRAIL principal investigator from the Massachusetts Institute of Technology (MIT). “GRAIL will rewrite the book on the formation of the moon and the beginning of us.”
“By globally mapping the moon’s gravity field to high precision scientists can deduce information about the interior structure, density and composition of the lunar interior. We’ll evaluate whether there even is a solid or liquid core or a mixture and advance the understanding of the thermal evolution of the moon and the solar system,” explained co-investigator Sami Asmar to Universe Today. Asmar is from NASA’s Jet Propulsion Laboratory (JPL)
7. Curiosity Mars Rover
The Curiosity Mars Science Lab (MSL) rover soared skywards on Nov. 26, the last of 2011’s three planetary science missions. Curiosity is the newest, largest and most technologically sophisticated robotic surveyor that NASA has ever assembled.
“MSL packs the most bang for the buck yet sent to Mars.” John Grotzinger, the Mars Science Laboratory Project Scientist of the California Institute of Technology, told Universe Today.
The three meter long robot is the first astrobiology mission since the Viking landers in the 1970’s and specifically tasked to hunt for the ‘Ingredients of Life’ on Mars – the most Earth-like planet in our Solar System.
Video caption: Action packed animation depicts sequences of Curiosity departing Earth, the nail biting terror of the never before used entry, descent and landing on the Martian surface and then looking for signs of life at Gale Crater during her minimum two year expedition across hitherto unseen and unexplored Martian landscapes, mountains and craters. Credit: NASA
Curiosity will gather and analyze samples of Martian dirt in pursuit of the tell-tale signatures of life in the form of organic molecules – the carbon based building blocks of life as we know it.
NASA is targeting Curiosity to a pinpoint touch down inside the 154 km (96 mile) wide Gale Crater on Aug. 6, 2012. The crater exhibits exposures of phyllosilicates and other minerals that may have preserved evidence of ancient or extant Martian life and is dominated by a towering 3 mile (5 km) high mountain.
“10 science instruments are all aimed at a mountain whose stratigraphic layering records the major breakpoints in the history of Mars’ environments over likely hundreds of millions of years, including those that may have been habitable for life,” Grotzinger told me.
Titan Upfront
The colorful globe of Saturn's largest moon, Titan, passes in front of the planet and its rings in this true color snapshot from NASA's Cassini spacecraft. Credit: NASA/JPL-Caltech/Space Science InstituteCuriosity Mars Science Laboratory Rover and Ken Kremer - inside the Cleanroom at the Kennedy Space Center. Last View of Curiosity just prior to folding and encapsulation for launch. Credit: Ken Kremer
This past year Ken was incredibly fortunate to witness the ongoing efforts of many of these magnificent endeavors.
The moons Titan and Dione are photographed with rings and Saturn in the background. Credit: NASA/JPL-Caltech/Space Science Institute
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“Hey! Look what our Santa at Saturn has sent our way!” said Carolyn Porco, the Cassini imaging team lead, in a post on Twitter. This wonderful collection of just-released colorful images from the Saturn system are a holiday gift from the Cassini and CICLOPS (Cassini Imaging Central Laboratory for Operations)team.
Above, Saturn’s third-largest moon, Dione, can be seen through the haze of the planet’s largest moon, Titan, in this view of the two posing before the planet and its rings from NASA’s Cassini spacecraft.
More treats below!
Saturn's moon Tethys, with its stark white icy surface, peeps out from behind the larger, hazy, colorful Titan in this view of the two moons obtained by NASA's Cassini spacecraft. Saturn's rings lie between the two. Credit: NASA/JPL-Caltech/Space Science InstituteThese views from NASA's Cassini spacecraft look toward the south polar region of Saturn's largest moon, Titan, and show a depression within the moon's orange and blue haze layers near the south pole. Credit: NASA/JPL-Caltech/Space Science InstituteThe colorful globe of Saturn's largest moon, Titan, passes in front of the planet and its rings in this true color snapshot from NASA's Cassini spacecraft. Credit: NASA/JPL-Caltech/Space Science InstituteSaturn's largest moon, Titan, appears deceptively small paired here with Dione, Saturn's third-largest moon, in this view from NASA's Cassini spacecraft. Credit: NASA/JPL-Caltech/Space Science Institute
To see more details and larger versions of these images, visit the CICLOPS website. (And thanks, Carolyn and team for the beautiful gifts!)
Titan's thick atmosphere shines in backlight sunlight
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Made from one of the most recent Cassini images, this is a color-composite showing a backlit Titan with its dense, multi-layered atmosphere scattering sunlight in different colors. Titan’s atmosphere is made up of methane and complex hydrocarbons and is ten times as thick as Earth’s. It is the only moon in our solar system known to have a substantial atmosphere.
Titan’s high-level hydrocarbon haze is nicely visible as a pale blue band encircling the moon.
Color image of Titan and sister moon Dione, seen by Cassini on Dec. 10. (NASA/JPL/SSI and J. Major)
At 3,200 (5,150 km) miles wide, Titan is one of the largest moons in the solar system – even larger than Mercury. Its thick atmosphere keeps a frigid and gloomy surface permanently hidden beneath opaque clouds of methane and hydrocarbons.
This image was made from three raw images acquired by Cassini on December 13. The raw images were in the red, green and blue visible light channels, and so the composited image you see here approximates true color.
This particular flyby of Titan (designated T-79) gave Cassini’s instruments a chance to examine Titan in many different wavelengths, as well as map its surface and measure its atmospheric temperature. Cassini passed by the giant moon at a distance of about 2,228 miles (3,586 kilometers) traveling 13,000 mph (5.8 km/sec). Read more on the flyby page here.
Credit: NASA / JPL / Space Science Institute. Edited by Jason Major.
See more color-composite images of Titan and other moons of Saturn on my Flickr set here.
The cracked ice surface of Europa. Credit: NASA/JPL
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Until fairly recently, the search for life elsewhere in the solar system has focused primarily on Mars, as it is the most Earth-like of all the other planets in the solar system. The possibility of finding any kind of life farther out in the outer solar system was considered very unlikely at best; too cold, too little sunlight, no solid surfaces on the gas giants and no atmospheres to speak of on any of the moons apart from Titan.
But now, some of the places that were previously considered the least likely to hold life have turned out to be perhaps some of the most likely to provide habitable environments. Moons that were thought be cold and frozen for eons are now known to be geologically active, in surprising ways. One of them is the most volcanically active place known in the solar system. At least two others appear to have oceans of liquid water beneath their surfaces. That’s right, oceans. And geysers. On the surface, they are ice worlds, but below, they are water worlds. Then there’s the one with rain, rivers, lakes and seas, but made of liquid methane instead of water. Billions of kilometres farther out from the Sun than the Earth. Who would have thought? Let’s look at those last three in a bit more detail…
Ever since the film 2001: A Space Odyssey first came out, Europa has been the subject of fascination. A small, icy moon orbiting Jupiter, its depiction in that movie, as an inhabited world beneath its ice crust was like a sort of foreshadowing, before the Voyager and Galileo spacecraft gave us our first real close-up looks of this intriguing place. Its surface shell of ice is covered with long cracks and fissures, giving it an appearance much like ice floes at the poles on Earth. More surprising though, was the discovery that, also like on Earth, this ice cover most likely is floating on top of a deep layer of liquid water below. In Europa’s case though, the water layer appears to cover the entire moon, a global subsurface ocean. How is this possible? If there is liquid water, there must be heat (or high concentrations of salts or ammonia), and if you have water and heat, could there be something living in those waters? Gravitational tugging from Jupiter indeed appears to provide enough heat to keep the water liquid instead of frozen. The environment is now thought to be similar to ocean bottoms on Earth. No sunlight, but if there are volcanic vents generating heat and minerals, as on Earth, such a spot could be ideal for at least simple forms of life. On Earth, places like these deep in the oceans are brimming with organisms which don’t require sunlight to survive.
Water vapour geysers on Enceladus. Credit: NASA/JPL
Then there’s Enceladus. Another very small icy moon, orbiting Saturn. Geological activity was considered very unlikely on such a tiny world, only a few hundred kilometres in diameter. But then Cassini saw the geysers, plumes of material erupting from the south polar region through large, warmer cracks nicknamed “tiger stripes.” Cassini has now flown directly through the geysers, analyzing their composition, which is mostly water vapour, ice particles, salts and organics. The latest analysis based on the Cassini data indicates that they almost certainly originate from a sea or ocean of liquid water below the surface. Warm, salty water loaded with organics; could Enceladus be another possible niche for extraterrestrial life? As with Europa, only further missions will be able to answer these questions, but the possibilities are exciting.
Radar image of one of many methane lakes on Titan. Credit: NASA/JPL
Titan is even more fascinating in some ways, the largest moon of Saturn. It is perpetually shrouded in a thick smoggy atmosphere of nitrogen and methane, so the surface has never been visible until now, when Cassini, and its small lander probe Huygens, first looked below the smog and clouds. Titan is like an eerily alien version of Earth, with rain, rivers, lakes and seas, but being far too cold for liquid water (not much heat here), its “water cycle” is composed of liquid methane/ethane. Appearance-wise, the surface and geology look amazingly Earth-like, but the conditions are uniquely Titan. For that reason, it has long been considered that the chances of any kind of life existing here are remote at best. In the last few years however, some scientists are starting to consider the possibility of life forming in just such environments, using liquids other than water, even in such cold conditions. Could life occur in a liquid methane lake or sea? How would it differ from water-based life? Last year, a discovery was made which might be interpreted as evidence of methane-based life on Titan – a seeming disappearance of hydrogen from the atmosphere near the surface and a lack of acetylene on the surface. Previous theoretical studies had suggested that those two things, if ever found, could be evidence for methane-based lifeforms consuming the hydrogen and acetylene. All of this is still highly speculative, and while a chemical explanation is probably more likely according to the scientists involved, a biological one cannot be ruled out yet. Future proposed missions for Titan include a floating probe to land in one of the lakes and a balloon to soar over the landscape, pursuing such mysteries as never before. How cool is that?
Oh, and the moon that is the most volcanically active place in the solar system? Io, although with the only known forms of liquid there being extremely hot lavas on that sulfuric hothouse, the chances of life are still thought to be unbelievably slim. But that’s ok when you start to find out that worlds with oceans and lakes, etc. may be much more common than previously imagined…
Global mosaic of VIMS infrared images acquired during the nominal and equinox Cassini mission. Differences in composition translate into subtle differences of colours in this mosaic, revealing the diversity of terrains on Titan, such as the brownish equatorial dune fields or the bright elevated terrains. (Colour coding : Red=5 um, Green=2.0 um, Blue=1.27 um). Credits JPL/NASA/Univ. of Arizona/CNRS/LPGNantes
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At the University of Nantes, a group of international scientists have been piecing together one of the most amazing jigsaw puzzles of all times… a color image of Saturn’s moon, Titan. For six years the Cassini mission has been busy gathering images and the resulting compilation was presented on October 4 by Stephane Le Mouelic at the 2011 EPSC-DPS Joint Meeting in Nantes, France. While it might not win the Cannes Film Festival, it’s certainly near and dear to an astronomer’s heart…
During the first seventy fly-bys of the famous Saturnian satellite, the Visual and Infrared Mapping Spectrometer (VIMS) gathered imaging records. But sewing together such a large quilt of information wasn’t an easy task. Not only does each image have to be adjusted for differences in lighting conditions, but a pixel-by-pixel match up has to occur to take atmospheric distortions into account. Titan’s methane rain and nitrogen atmosphere isn’t conducive to easy imaging and only a narrow band of infrared wavelengths allow us to take a closer look at the hidden, frozen surface. However, the results have been spectacular and little by little some very “terrestrial” features have come to light.
“As Cassini is orbiting Saturn and not Titan, we can observe Titan only once a month on average. The surface of Titan is therefore revealed year after year, as pieces of the puzzle are progressively put together.” says Le Mouelic. “Deriving a final map with no seams is challenging due to the effects of the atmosphere – clouds, mist etc. – and due to the changing geometries of observation between each flyby.”
Since 2004, Cassini has made 78 fly-bys of the exotic frozen world and another 48 are planned over the next five years. However, VIMS has had very few chances to image Titan with a high spatial resolution. While this still leaves many areas in the proverbial dark, all this can change in the future.
“We have created the maps using low resolution images as a background with the high resolution data on top. In the few opportunities where we have VIMS imagery from the closest approach, we can show details as low as 500 metres per pixel. An example of this is from the 47th flyby, which allowed the observation of the site where the Huygens descent module landed. This observation is a key one as it might help us to bridge the gap between the ground truth provided by Huygens, and ongoing global mapping from orbit, which will continue up to 2017.”
And what does the future hold? Along with updated spatial coverage, the team plans on documenting Titan’s changing seasons from both an atmospheric and surface viewpoint. Changes that are just now beginning to occur.
“Lakes in Titan’s northern hemisphere were first discovered by the RADAR instrument in 2006, appearing as completely smooth areas. However, we had to wait up to June 2010 to obtain the first infrared images of the northern lakes, emerging progressively from the northern winter darkness,” says Le Mouelic. “The infrared observations provide the additional opportunity to investigate the composition of the liquids within the lakes area. Liquid ethane has already been identified by this means.”
Fill ‘er up… We’ll be watching!
Original Story Source: Europlanet News Release. For an even more impressive look, check out the Animation of Titan Mosaic.
A Dictionary of the Space Age covers most aspects of space flight but is somewhat lacking in detail. Image Credit: John Hopkins University & Alan Walters/awaltersphoto.com
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Writing a dictionary is not the same as writing a novel. While it might seem difficult to mess up a dictionary, even one with terminology that is as complicated as that used within the space industry – getting it right can be challenging. For those that follow space flight having such a dictionary can be invaluable. While A Dictionary of the Space Age does meet the basic requirements easily it fails somewhat in terms of its comprehensiveness.
When normal folks, even space enthusiasts watch launches and other space-related events (EVAs, dockings, landings and such) there are so many acronyms and jargon thrown about – that it is extremely hard to follow. With A Dictionary of the Space Age on hand, one can simply thumb through and find out exactly what is being said, making it both easier to follow along and making the endeavor being witnessed far more inclusive. That is as long if you are only looking for the most general of terms. The book is far from complete – but given the complex nature of the topic – this might not have been possible.
Crewed, unmanned, military space efforts and satellites – all have key terms addressed within the pages of this book.
The book is published by The Johns Hopkins University Press and was compiled and written by aerospace expert Paul Dickson. One can purchase the book on the secondary market (Amazon.com) for around $12 (new for around $25). The dictionary also has a Kindle edition which is available for $37.76. Dickson’s previous works on space flight is Sputnik: The Shock of the Century.
Weighing in at 288 pages, the book briefly covers the primary terms used within the space community. In short, if you are interested in learning more about space flight – or wish to do so – this is a good book for you.
This image from the Cassini spacecraft, shows a huge arrow-shaped storm measuring 1,500km in length. Image Credit: NASA/JPL/SSI
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Titan is making news again, this time with Cassini images from 2010 showing a storm nearly as big as Texas. Jonathan Mitchell from UCLA and his research team have published their findings which help answer the question:
What could cause such large storms to develop on a freezing cold world?
For starters, the huge arrow isn’t a cosmic detour sign reminding us to “Attempt No Landings” on Jupiter’s moon Europa.
In the study by Mitchell and his team, a model of Titan’s global weather was created to understand how atmospheric waves affect weather patterns on Titan. During their research, the team discovered a “stenciling” effect that creates distinct cloud shapes, such as the arrow-shaped cloud shown in the Cassini image above.
“These atmospheric waves are somewhat like the natural, resonant vibration of a wine glass,” Mitchell said. “Individual clouds might ‘ring the bell,’ so to speak, and once the ringing starts, the clouds have to respond to that vibration.”
Titan is the only other body in the solar system (aside from Earth) known to have an active “liquid cycle”. Much like Titan’s warmer cousin Earth, the small moon has an atmosphere primarily composed of Nitrogen. Interestingly enough Titan’s atmosphere is roughly the same mass as Earth’s and has about 1.5 times the surface pressure. At the extremely low temperatures on Titan, hydrocarbons such as methane appear in liquid form, rather than the gaseous form found on Earth.
With an active liquid both on the surface and in the atmosphere of Titan, clouds form and create rain. In the case of Titan, the rain on the plain is mainly methane. Water on Titan is rock-hard, due to temperatures hovering around -200 c.
Studies of Titan show evidence of liquid runoff, rivers and lakes, further emphasizing Titan’s parallels to Earth. Researchers believe better understanding of Titan may offer clues to understanding Earth’s early atmosphere. In another parallel to earth, the weather patterns on Titan created by the atmospheric waves can create intense rainstorms, sometimes with more than 20 times Titan’s average seasonal rainfall. These intense storms may cause erosion patterns that help form the rivers seen on Titan’s surface. Mitchell described Titan’s climate as “all-tropics”, basically comparing the weather to what is usually found near Earth’s equator. Could these storms be Titan’s equivalent of monsoon season?
Mitchell stated “Titan is like Earth’s strange sibling — the only other rocky body in the solar system that currently experiences rain”. Mitchell also added, “In future work, we plan to extend our analysis to other Titan observations and make predictions of what clouds might be observed during the upcoming season”.
The research was published Aug. 14 in the online edition of the journal Nature Geoscience .
Three of Titan's major surface features-dunes, craters and the enigmatic Xanadu-appear in this radar image from NASA's Cassini spacecraft. Image credit: NASA/JPL-Caltech
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The name “Xanadu” just sounds exotic and enticing, and given that this region on Titan is right next to Shangri-la, how can we not be intrigued by the latest radar image of this region taken by the Cassini spacecraft? While Titan itself is shrouded in mystery with its thick, hazy atmosphere, via radar, Cassini can peer through and has found three major surface features: dunes, craters and the enigmatic Xanadu, a bright continent-sized feature centered near the moon’s equator. At upper right is the crater Ksa, first seen by Cassini in 2006. The dark lines running among Xanadu and Ksa are linear dunes, similar to sand dunes on Earth in Egypt and Namibia. In addition to the dunes, look closely at Xanadu to see hills, rivers and valleys which scientists believe are carved in ice rather than solid ground, by liquid methane or ethane.
This image was taken by Cassini’s Titan Radar Mapper on June 21, 2011.
