As soon as the Cassini-Huygens mission arrived the Saturn system in 2004, it began to send back a number of startling discoveries. One of the biggest was the discovery of plume activity around the southern polar region of Saturn’s moon Enceladus’, which appears to be the result of geothermal activity and an ocean in the moon’s interior. This naturally gave rise to a debate about whether or not this interior ocean could support life.
Since then, multiple studies have been conducted to get a better idea of just how likely it is that life exists inside Enceladus. The latest comes from the University of Washington’s Department of Earth and Space Sciences (ESS), which shows that concentrations of carbon dioxide, hydrogen and methane in Enceladus’ interior ocean (as well as its pH levels) are more conducive to life than previously thought.
The Cassini mission to Saturn ended a year and a half ago, but scientific results are still coming from all of the data it collected. When Cassini moved in closer to Saturn in its final months, it took a very detailed look at the gas giant’s rings, travelling between them and the planet itself. That detailed inspection raised quite a few questions about all the interactions shaping those rings.
A new paper published in Science presents some of the results from Cassini’s close-up look at the rings.
The Cassini mission to Saturn and its moons wrapped up in 2017, when the spacecraft was sent plunging into the gas giant to meet its end. But there’s still a lot of data from the mission to keep scientists busy. A team of scientists working with Cassini data have made a surprising discovery: Titan’s methane-filled lakes are much deeper, and weirder, than expected.
Can you imagine the Solar System without Saturn’s rings? Can you envision Earth at the time the dinosaurs roamed the planet? According to a new paper, the two may have coincided.
Data from the Cassini mission shows that Saturn’s rings may be only 10 to 100 million years old. They may not have been there during the reign of the dinosaurs, and may in fact be a fairly modern development in our Solar System.
Saturn’s moon Titan is a very strange place. It’s surrounded by a dense, opaque atmosphere, the only moon in the solar system with an atmosphere to speak of. It has lakes of liquid methane on its surface, maybe some cryovolcanoes, and some scientists speculate that it could support a form of life. Very weird life.
But we still don’t know a lot about it, because we haven’t really seen much of the surface. Until now.
Thanks to the Cassini mission, we have learned some truly amazing things about Saturn and its largest moon, Titan. This includes information on its dense atmosphere, its geological features, its methane lakes, methane cycle, and organic chemistry. And even though Cassini recently ended its mission by crashing into Saturn’s atmosphere, scientists are still pouring over all of the data it obtained during its 13 years in the Saturn system.
And now, using Cassini data, two teams led by researchers from Cornell University have released two new studies that reveal even more interesting things about Titan. In one, the team created a complete topographic map of Titan using Cassini’s entire data set. In the second, the team revealed that Titan’s seas have a common elevation, much like how we have a “sea level” here on Earth.
In the first paper, the authors described how topographic data from multiple sources was combined to create a global map of Titan. Since only about 9% of Titan was observed with high-resolution topography (and 25-30% in lower resolution) the remainder of the moon was mapped with an interpolation algorithm. Combined with a global minimization process, this reduced errors that would arise from such things as spacecraft location.
The map revealed new features on Titan, as well as a global view of the highs and lows of the moon’s topography. For instance, the maps showed several new mountains which reach a maximum elevation of 700 meters (about 3000 ft). Using the map, scientists were also able to confirm that two locations in the equatorial regions are depressions that could be the result of ancient seas that have since dried up or cryovolcanic flows.
The map also suggests that Titan may be more oblate than previously thought, which could mean that the crust varies in thickness. The data set is available online, and the map which the team created from it is already proving its worth to the scientific community. As Professor Corlies explained in a Cornell press release:
“The main point of the work was to create a map for use by the scientific community… We’re measuring the elevation of a liquid surface on another body 10 astronomical units away from the sun to an accuracy of roughly 40 centimeters. Because we have such amazing accuracy we were able to see that between these two seas the elevation varied smoothly about 11 meters, relative to the center of mass of Titan, consistent with the expected change in the gravitational potential. We are measuring Titan’s geoid. This is the shape that the surface would take under the influence of gravity and rotation alone, which is the same shape that dominates Earth’s oceans.”
Looking ahead, this map will play an important role when it comes tr scientists seeking to model Titan’s climate, study its shape and gravity, and its surface morphology. In addition, it will be especially helpful for those looking to test interior models of Titan, which is fundamental to determining if the moon could harbor life. Much like Europa and Enceladus, it is believed that Titan has a liquid water ocean and hydrothermal vents at its core-mantle boundary.
The second study, which also employed the new topographical map, was based on Cassini radar data that was obtained up to just a few months before the spacecraft burned up in Saturn’s atmosphere. Using this data, Assistant Professor Hayes and his team determined that Titan’s seas follow a constant elevation relative to Titan’s gravitational pull. Basically, they found that Titan has a sea level, much like Earth. As Hayes explained:
“We’re measuring the elevation of a liquid surface on another body 10 astronomical units away from the sun to an accuracy of roughly 40 centimeters. Because we have such amazing accuracy we were able to see that between these two seas the elevation varied smoothly about 11 meters, relative to the center of mass of Titan, consistent with the expected change in the gravitational potential. We are measuring Titan’s geoid. This is the shape that the surface would take under the influence of gravity and rotation alone, which is the same shape that dominates Earth’s oceans.”
This common elevation is important because liquid bodies on Titan appear to be connected by something resembling an aquifer system. Much like how water flows underground through porous rock and gravel on Earth, hydrocarbons do the same thing under Titan’s icy surface. This ensures that there is transference between large bodies of water, and that they share a common sea level.
“We don’t see any empty lakes that are below the local filled lakes because, if they did go below that level, they would be filled themselves,” said Hayes. “This suggests that there’s flow in the subsurface and that they are communicating with each other. It’s also telling us that there is liquid hydrocarbon stored on the subsurface of Titan.”
Meanwhile, smaller lakes on Titan appear at elevations several hundred meters above Titan’s sea level. This is not dissimilar to what happens on Earth, where large lakes are often found at higher elevations. These are known as “Alpine Lakes”, and some well-known examples include Lake Titicaca in the Andes, Lakes Geneva in the Alps, and Paradise Lake in the Rockies.
Last, but not least, the study also revealed the vast majority of Titan’s lakes are found within sharp-edged depressions that are surrounded by high ridges, some of which are hundreds of meters high. Here too, there is a resemblance to features on Earth – such as the Florida Everglades – where underlying material dissolves and causes the surface to collapse, forming holes in the ground.
The shape of these lakes indicate that they may be expanding at a constant rate, a process known as uniform scarp retreat. In fact, the largest lake in the south – Ontario Lacus – resembles a series of smaller empty lakes that have coalesced to form a single feature. This process is apparently due to seasonal change, where autumn in the southern hemisphere leads to more evaporation.
While the Cassini mission is no longer exploring the Saturn system, the data it accumulated during its multi-year mission is still bearing fruit. Between these latest studies, and the many more that will follow, scientists are likely to reveal a great deal more about this mysterious moon and the forces that shape it!
When the Cassini mission arrived in the Saturn system in 2004, it discovered something rather unexpected in Enceladus’ southern hemisphere. From hundreds of fissures located in the polar region, plumes of water and organic molecules were spotted periodically spewing forth. This was the first indication that Saturn’s moon may have an interior ocean caused by hydrothermal activity near the core-mantle boundary.
According to a new study based on Cassini data, which it obtained before diving into Saturn’s atmosphere on September 15th, this activity may have been going on for some time. In fact, the study team concluded that if the moon’s core is porous enough, it could have generated enough heat to maintain an interior ocean for billions of years. This study is the most encouraging indication yet that the interior of Enceladus could support life.
Prior to the Cassini mission’s many flybys of Enceladus, scientists believed this moon’s surface was composed of solid ice. It was only after noticing the plume activity that they came to realize that it had water jets that extended all the way down to a warm-water ocean in its interior. From the data obtained by Cassini, scientists were even able to make educated guesses of where this internal ocean lay.
All told, Enceladus is a relatively small moon, measuring some 500 km (311 mi) in diameter. Based on gravity measurements performed by Cassini, its interior ocean is believed to lie beneath an icy outer surface at depths of 20 to 25 km (12.4 to 15.5 mi). However, this surface ice thins to about 1 to 5 km (0.6 to 3.1 mi) over the southern polar region, where the jets of water and icy particles jet through fissures.
Based on the way Enceladus orbits Saturn with a certain wobble (aka. libration), scientists have been able to make estimates of the ocean’s depth, which they place at 26 to 31 km (16 to 19 mi). All of this surrounds a core which is believed to be composed of silicate minerals and metal, but which is also porous. Despite all these findings, the source of the interior heat has remained something of an open question.
This mechanism would have to be active when the moon formed billions of years ago and is still active today (as evidenced by the current plume activity). As Dr. Choblet explained in an ESA press statement:
“Where Enceladus gets the sustained power to remain active has always been a bit of mystery, but we’ve now considered in greater detail how the structure and composition of the moon’s rocky core could play a key role in generating the necessary energy.”
For years, scientists have speculated that tidal forces caused by Saturn’s gravitational influence are responsible for Enceladus’ internal heating. The way Saturn pushes and pulls the moon as it follows an elliptical path around the planet is also believed to be what causes Enceladus’ icy shell to deform, causing the fissures around the southern polar region. These same mechanisms are believed to be what is responsible for Europa’s interior warm-water ocean.
However, the energy produced by tidal friction in the ice is too weak to counterbalance the heat loss seen from the ocean. At the rate Enceladus’ ocean is losing energy to space, the entire moon would freeze solid within 30 million years. Similarly, the natural decay of radioactive elements within the core (which has been suggested for other moons as well) is also about 100 times too weak to explain Enceladus interior and plume activity.
To address this, Dr. Choblet and his team conducted simulations of Enceladus’ core to determine what kind of conditions could allow for tidal heating over billions of years. As they state in their study:
“In absence of direct constraints on the mechanical properties of Enceladus’ core, we consider a wide range of parameters to characterize the rate of tidal friction and the efficiency of water transport by porous flow. The unconsolidated core of Enceladus can be viewed as a highly granular/fragmented material, in which tidal deformation is likely to be associated with intergranular friction during fragment rearrangements.”
What they found was that in order for the Cassini observations to be borne out, Enceladus’ core would need to be made of unconsolidated, easily deformable, porous rock. This core could be easily permeated by liquid water, which would seep into the core and gradually heated through tidal friction between sliding rock fragments. Once this water was sufficiently heated, it would rise upwards because of temperature differences with its surroundings.
This process ultimately transfers heat to the interior ocean in narrow plumes which rise to the meet Enceladus’ icy shell. Once there, it causes the surface ice to melt and forming fissures through which jets reach into space, spewing water, ice particles and hydrated minerals that replenish Saturn’s E-Ring. All of this is consistent with the observations made by Cassini, and is sustainable from a geophysical point of view.
In other words, this study is able to show that action in Enceladus’ core could produce the necessary heating to maintain a global ocean and produce plume activity. Since this action is a result of the core’s structure and tidal interaction with Saturn, it is perfectly logical that it has been taking place for billions of years. So beyond providing the first coherent explanation for Enceladus’ plume activity, this study is also a strong indication of habitability.
As scientists have come to understand, life takes a long time to get going. On Earth, it is estimated that the first microorganisms arose after 500 million years, and hydrothermal vents are believed to have played a key role in that process. It took another 2.5 billion years for the first multi-cellular life to evolve, and land-based plants and animals have only been around for the past 500 million years.
Knowing that moons like Enceladus – which has the necessary chemistry to support for life – has also had the necessary energy for billions of years is therefore very encouraging. One can only imagine what we will find once future missions begin inspecting its plumes more closely!
Ever since the Cassini mission entered the Saturn system and began studying its moons, Enceladus has become a major source of interest. Once the probe detected plumes of water and organic molecules erupting from the moon’s southern polar region, scientists began to speculate that Enceladus may possess a warm-water ocean in its interior – much like Jupiter’s moon Europa and other bodies in our Solar System.
In the future, NASA hopes to send another mission to this system to further explore these plumes and the interior of Enceladus. This mission will likely include a new instrument that was recently announced by NASA, known as the Submillimeter Enceladus Life Fundamentals Instrument (SELFI). This instrument, which was proposed by a team from the NASA Goddard Space Flight Center, recently received support for further development.
Prior to the Cassini mission, scientists thought that the surface of Enceladus was frozen solid. However, Cassini data revealed a slight wobble in the moon’s orbit that suggested the presence of an interior ocean. Much like Europa, this is caused by tidal forces that cause flexing in the core, which generates enough heat to hold liquid water in the interior. Around the southern pole, this results in the ice cracking open and forming fissures.
The Cassini mission also discovered plumes emanating from about 100 different fissures which continuously spew icy particles, water vapor, carbon dioxide, methane, and other gases into space. To study these more closely, NASA has been developing some ambitious instruments that will rely on millimeter-wave or radio frequency (RF) waves to determine their composition and learn more about Enceladus’ interior ocean.
According to SELFI Principal Investigator Gordon Chin, SELFI represents a significant improving over existing submillimeter-wavelenght devices. Once deployed, it will measure traces of chemicals in the plumes of water and icy parties that periodically emanated from Enceladus’ southern fissures, also known as “Tiger Stripes“. In addition to revealing the chemical composition of the ocean, this instrument will also indicate it’s potential for supporting life.
On Earth, hydrothermal vents are home to thriving ecosystems, and are even suspected to be the place where life first emerged on Earth. Hence why scientists are so eager to study hydrothermal activity on moons like Enceladus, since these could represent the most likely place to find extra-terrestrial life in our Solar System. As Chin indicated in a NASA press statement:
“Submillimeter wavelengths, which are in the range of very high-frequency radio, give us a way to measure the quantity of many different kinds of molecules in a cold gas. We can scan through all the plumes to see what’s coming out from Enceladus. Water vapor and other molecules can reveal some of the ocean’s chemistry and guide a spacecraft onto the best path to fly through the plumes to make other measurements directly.”
Molecules like water, carbon dioxide and other elements broadcast specific radio frequencies, which submillimeter spectrometers are sensitive to. The spectral lines are very discrete, and the intensity at which they broadcast can be used to quantify their existence. In other words, instruments like SELFI will not only be able to determine the chemical composition of Enceladus’ interior ocean, but also the abundance of those chemicals.
For decades, spectrometers have been used in space sciences to measure the chemical compositions of planets, stars, comets and other targets. Most recently, scientists have been attempting to obtain spectra from distant planets in order to determine the chemical compositions of their atmospheres. This is crucial when it comes to finding potentially-habitable exoplanets, since water vapor, nitrogen and oxygen gas are all required for life as we know it.
Performing scans in the submillimeter band is a relatively new process, though, since submillimeter-sensitive instruments are complex and difficult to build. But with help of NASA research-and-development funding, Chin and his colleagues are increasing the instrument’s sensitivity using an amplifier that will boost the signal to around 557 GHz. This will allow SELFI to detect even minute traces of water and gases coming from the surface of Enceladus.
Other improvements include a more energy-efficient and flexible radio frequency data-processing system, as well as a sophisticated digital spectrometer for the RF signal. This latter improvement will employ high-speed programmable circuitry to convert RF data into digital signals that can be analyzed to measure gas quantities, temperatures, and velocities from Enceladus’ plumes.
These enhancements will allow SELFI to simultaneously detect and analyze 13 different types of molecules, which include various isotopes of water, methanol, ammonia, ozone, hydrogen peroxide, sulfur dioxide, and sodium chloride (aka. salt). Beyond Enceladus, Chin believes the team can sufficiently improve the instrument for proposed future missions. “SELFI is really new,”he said. “This is one of the most ambitious submillimeter instruments ever built.”
For instance, in recent years, scientists have spotted plume activity coming from the surface of Europa. Here too, this activity is believed to be the result of geothermal activity, which sends warm water plumes from the moon’s interior ocean to the surface. Already, NASA hopes to examine these plumes and those on Enceladus using the James Webb Space Telescope, which will be deploying in 2019.
Another possibility would be to equip the proposed Europa Clipper – which is set to launch between 2022 and 2025 – with an instrument like SELFI. The instrument package for this probe already calls for a spectrometer, but an improved submillimeter-wave and RF device could allow for a more detailed look at Europa’s plumes. This data could in turn resolve the decades-old debate as to whether or not Europa’s interior is capable of supporting life.
In the coming decades, one of the greatest priorities of space exploration is to investigate the Solar System’s “Ocean Worlds” for signs of life. To see this through, NASA and other space agencies are busy developing the necessary tools to sniff out all the chemical and biological indicators. Within a decade, with any luck, we might just find that life on Earth is not the exception, but part of a larger norm.
Chances are, at one time or another, we’ve all used Google Maps to find the shortest route from point A to point B. But if you are like some people, you’ve used this mapping tool to have a look at geographical features or places you hope to visit someday. In an age where digital technology is allowing for telecommuting and even telepresence, it’s nice to take virtual tours of the places we may never get to see in person.
But now, Google Maps is using its technology to enable the virtual exploration of something far grander: the Solar System! Thanks to images provided by the Cassini orbiter of the planets and moons it studied during its 20 year mission, Google is now allowing users to explore places like Venus, Mercury, Mars, Europa, Ganymede, Titan, and other far-off destinations that are impossible for us to visit right now.
Similar to how Google Earth uses satellite imagery to create 3D representations of our planet, this new Google Maps tool relies on the more than 500,000 images taken by Cassini as it made its way across the Solar System. This probe recently concluded its 20 year mission, 13 of which were spent orbiting Saturn and studying its system of moons, by crashing into the atmosphere of Saturn.
After launching from Earth on October 15th, 1997, Cassini conducted a flyby of Venus in order to pick up a gravity-assist. It then flew by Earth, obtaining a second gravity-assist, while making its way towards the Asteroid Belt. Before reaching the Saturn System, where it would begin studying the gas giant and its moons, Cassini also conducted a flyby of Jupiter – snapping pictures of its moons, rings, and Great Red Spot.
When it reached Saturn in July of 2004, Cassini went to work studying the planet and its larger moons – particularly Titan and Enceladus. During the next 13 years and 76 days, the probe would provide breathtaking images and sensor data on Saturn’s rings, atmosphere and polar storms and reveal things about Titan’s surface that were never before seen (such as its methane lakes, hydrological cycle, and surface features).
It’s flybys of Enceladus also revealed some startling things about this icy moon. Aside from detecting a tenuous atmosphere of ionized water vapor and Enceladus’ mysterious “Tiger Stripes“, the probe also detected jets of water and organic molecules erupting from the moon’s southern polar region. These jets, it was later determined, were indicative of a warm water ocean deep in the moon’s interior, and possibly even life!
Interestingly enough, the original Cassini mission was only planned to last for four years once it reached Saturn – from June 2004 to May 2008. But by the end of this run, the mission was extended with the Cassini Equinox Mission, which was intended to run until September of 2010. It was extended a second time with the Cassini Solstice Mission, which lasted until September 15th, 2017, when the probe was crashed into Saturn’s atmosphere.
Thanks to all the images taken by this long-lived mission, Google Maps is now able to offer exploratory tours of 16 celestial bodies in the Solar System – 12 of which are new to the site. These include Earth, the Moon, Mercury, Venus, Mars, Pluto, Ceres, Io, Europa, Ganymede, Mimas, Enceladus, Dione, Rhea, Titan, Iapetus and (available as of July 2017) the International Space Station.
This latest development also builds on several extensions Google has released over the years. These include Google Moon, which was released on July 20th, 2005, to coincide with the 36th anniversary of the Apollo 11 Moon Landing. Then there was Google Sky (introduced in 2007), which used photographs taken by the Hubble Space Telescope to create a virtual map of the visible universe.
In an age of high-speed internet and telecommunications, using the internet to virtually explore the many planets and bodies of the Solar System just makes sense. Especially when you consider that even the most ambitious plans to conduct tourism to Mars or the Moon (looking at you, Elon Musk and Richard Branson!) are not likely to bear fruit for many years, and cost an arm and a leg to boot!
In the future, similar technology could lead to all kinds of virtual exploration. This concept, which is often referred to as “telexploration”, would involve robotic missions traveling to other planets and even star systems. The information they gather would then be sent back to Earth to create virtual experiences, which would allow scientists and space-exploration enthusiasts to feel like they were seeing it firsthand.
In truth, this mapping tool is just the latest gift to be bestowed by the late Cassini mission. NASA scientists expect to be sifting through the volumes of data collected by the orbiter for years to come. Thanks to improvements made in software applications and the realms of virtual and augmented reality, this data (and that of present and future missions) is likely to be put to good use, enabling breathtaking and educational tours of our Universe!
Titan is tough moon to study, thanks to its incredibly thick and hazy atmosphere. But when astronomers have ben able to sneak a peak beneath its methane clouds, they have spotted some very intriguing features. And some of these, interestingly enough, are reminiscent of geographical features here on Earth. For instance, Titan is the only other body in the Solar System that is known to have a cycle where liquid is exchanged between the surface and the atmosphere.
For example, previous images provided by NASA’s Cassini mission showed indications of steep-sided canyons in the northern polar region that appeared to be filled with liquid hydrocarbons, similar to river valleys here on Earth. And thanks to new data obtained through radar altimetry, these canyons have been shown to be hundreds of meters deep, and have confirmed rivers of liquid methane flowing through them.
This evidence was presented in a new study titled “Liquid-filled canyons on Titan” – which was published in August of 2016 in the journal Geophysical Research Letters. Using data obtained by the Cassini radar altimeter in May 2013, they observed channels in the feature known as Vid Flumina, a drainage network connected to Titan’s second largest hydrocarbon sea in the north, Ligeia Mare.
Analysis of this information showed that the channels in this region are steep-sided and measure about 800 m (half a mile) wide and between 244 and 579 meters deep (800 – 1900 feet). The radar echoes also showed strong surface reflections that indicated that these channels are currently filled with liquid. The elevation of this liquid was also consistent with that of Ligeia Mare (within a maring of 0.7 m), which averages about 50 m (164 ft) deep.
This is consistent with the belief that these river channels in area drain into the Ligeia Mare, which is especially interesting since it parallels how deep-canyon river systems empty into lakes here on Earth. And it is yet another example of how the methane-based hydrological cycle on Titan drives the formation and evolution of the moon’s features, and in ways that are strikingly similar to the water cycle here on Earth.
Alex Hayes – an assistant professor of astronomy at Cornell, the Director of the Spacecraft Planetary Imaging Facility (SPIF) and one of the authors on the paper – has conducted seversal studies of Titan’s surface and atmosphere based on radar data provided by Cassini. As he was quoted as saying in a recent article by the Cornell Chronicler:
“Earth is warm and rocky, with rivers of water, while Titan is cold and icy, with rivers of methane. And yet it’s remarkable that we find such similar features on both worlds. The canyons found in Titan’s north are even more surprising, as we have no idea how they formed. Their narrow width and depth imply rapid erosion, as sea levels rise and fall in the nearby sea. This brings up a host of questions, such as where did all the eroded material go?”
A good question indeed, since it raises some interesting possibilities. Essentially, the features observed by Cassini are just part of Titan’s northern polar region, which is covered by large standing bodies of liquid methane – the largest of these being Kraken Mare, Ligeia Mare and Punga Mare. In this respect, the region is similar to glacially eroded fjords on Earth.
However, conditions on Titan do not allow for the presence of glaciers, which rules out the likelihood that retreating sheets of ice could have carved these canyons. So this naturally begs the question, what geological forces created this region? The team concluded that there were only two likely possibilities – which included changes in the elevation of the rivers, or tectonic activity in the area.
Ultimately, they favored a model where the variation in surface elevation of liquid drove the formation of the canyons – though they acknowledge that both tectonic forces and sea level variations played a role. As Valerio Poggiali, an associate member of the Cassini RADAR Science Team at the Sapienza University of Rome and the lead author of the paper, told Universe Today via email:
“What the canyons on Titan really mean is that in the past sea level was lower and so erosion and canyon formation could take place. Subsequently sea level has risen and backfilled the canyons. This presumably takes place over multiple cycles, eroding when sea level is lower, depositing some when it is higher until we get the canyons we see today. So, what it means is that sea level has likely changed in the geological past and the canyons are recording that change for us.”
In this respect, there are many more Earth examples to choose from, all of which are mentioned in the study:
“Examples include Lake Powell, a reservoir on the Colorado River that was created by the Glen Canyon Dam; the Georges River in New South Wales, Australia; and the Nile River gorge, which formed as the Mediterranean Sea dried up during the late Miocene. Rising liquid levels in the geologically recent past led to the flooding of these valleys, with morphologies similar to those observed at Vid Flumina.”
Understanding the processes that led to these formations is crucial to understanding the current state of Titan’s geomorphology. And this study is significant in that it is the first to conclude that the rivers in the Vid Flumina region were deep canyons. In the future, the research team hopes to examine other channels on Titan that were observed by Cassini to test their theories.
Once again, our exploration of the Solar System has shown us just how weird and wonderful it truly is. In addition to all its celestial bodies having their own particular quirks, they still have a lot in common with Earth. By the time the Cassini mission is complete (Sept. 15th, 2017), it will have surveyed 67% the surface of Titan with its RADAR imaging instrument. Who knows what other “Earth-like” features it will notice before then?