Posted on by Matt Williams

Scientists Find Evidence of Extreme Methane Storms On Titan

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. Image Credit: NASA/JPL-Caltech/Space Science Institute
According to a study from UCLA, Titan experiences severe methane rainstorms, leading to a the alluvial fans found found in both hemispheres. Credit: NASA/JPL-Caltech/Space Science Institute

Saturn’s largest moon, Titan, is a mysterious place; and the more we learn about it, the more surprises it seems to have in store. Aside from being the only body beyond Earth that has a dense, nitrogen-rich atmosphere, it also has methane lakes on its surface and methane clouds in its atmosphere. This hydrological-cycle, where methane is converted from a liquid to a gas and back again, is very similar to the water cycle here on Earth.

Thanks to the NASA/ESA Cassini-Huygens mission, which concluded on September 15th when the craft crashed into Saturn’s atmosphere, we have learned a great deal about this moon in recent years. The latest find, which was made by a team of UCLA planetary scientists and geologists, has to do with Titan’s methane rain storms. Despite being a rare occurrence, these rainstorms can apparently become rather extreme.

The study which details their findings, titled “Regional Patterns of Extreme Precipitation on Titan Consistent with Observed Alluvial Fan Distribution“, recently appeared in the scientific journal Nature Geoscience. Led by Saun P. Faulk, a graduate student at UCLA’s Department of Earth, Planetary, and Space Sciences, the team conducted simulations of Titan’s rainfall to determine how extreme weather events have shaped the moon’s surface.

Image of Titan’s atmosphere, snapped by the Cassini spacecraft. Credit: NASA/JPL/Space Science Institute

What they found was that the extreme methane rainstorms may imprint the moon’s icy surface in much the same way that extreme rainstorms shape Earth’s rocky surface. On Earth, intense rainstorms play an important role in geological evolution. When rainfall is heavy enough, storms can trigger large flows of water that transport sediment into low lands, where it forms cone-shaped features known as alluvial fans.

During it’s mission, the Cassini orbiter found evidence of similar features on Titan using its radar instrument, which suggested that Titan’s surface could be affected by intense rainfall. While these fans are a new discovery, scientists have been studying the surface of Titan ever since Cassini first reached the Saturn system in 2006. In that time, they have noted several interesting features.

These included the vast sand dunes that dominate Titan’s lower latitudes and the methane lakes and seas that dominate it’s higher latitudes – particularly around the  northern polar region. The seas – Kraken Mare, Ligeia Mare, and Punga Mare – measure hundreds of km across and up to several hundred meters deep, and are fed by branching, river-like channels. There are also many smaller, shallower lakes that have rounded edges and steep walls, and are generally found in flat areas.

In this case, the UCLA scientists found that the alluvial fans are predominantly located between 50 and 80 degrees latitude. This puts them close to the center of the northern and southern hemispheres, though slightly closer to the poles than the equator. To test how Titan’s own rainstorms could cause these features, the UCLA team relied on computer simulations of Titan’s hydrological cycle.

False-color mosaic of Titan’s northern lakes, made from infrared data collected by NASA’s Cassini spacecraft. Credit: NASA

What they found was that while rain mostly accumulates near the poles – where Titan’s major lakes and seas are located – the most intense rainstorms occur near 60 degrees latitude. This corresponds to the region where alluvial fans are most heavily concentrated, and indicates that when Titan does experience rainfall, it is quite extreme – like a seasonal monsoon-like downpour.

As Jonathan Mitchell – a UCLA associate professor of planetary science and a senior author of the study – indicated, this is not dissimilar to some extreme weather events that were recently experienced here on Earth. “The most intense methane storms in our climate model dump at least a foot of rain a day, which comes close to what we saw in Houston from Hurricane Harvey this summer,” he said.

The team also found that on Titan, methane rainstorms are rather rare, occurring less than once per Titan year – which works out to 29 and a half Earth years. But according to Mitchell, who is also the principal investigator of UCLA’s Titan climate modeling research group, this is more often than they were expecting. “I would have thought these would be once-a-millennium events, if even that,” he said. “So this is quite a surprise.”

In the past, climate models of Titan have suggested that liquid methane generally concentrates closer to the poles. But no previous study has investigated how precipitation might cause sediment transport and erosion, or shown how this would account for various features observed on the surface. As a result, this study also suggests that regional variations in surface features could be caused by regional variations in precipitation.

On top of that, this study is an indication that Earth and Titan have even more in common than previously thought. On Earth, contrasts in temperature are what lead to intense seasonal weather events. In North America, tornadoes occur during the early to late Spring, while blizzards occur during the winter. Meanwhile, temperature variations in the Atlantic ocean are what lead to hurricanes forming between the summer and fall.

Similarly, it appears that on Titan, serious variations in temperature and moisture are what triggers extreme weather. When cooler, wetter air from the higher latitudes interacts with warmer, drier air from the lower latitudes, intense rainstorms result. These findings are also significant when it comes to other bodies in our Solar System that  have alluvial fans on them – such as Mars.

In the end, understanding the relationship between precipitation and planetary surfaces could lead to new insights about the impact climate change has on Earth and the other planets. Such knowledge would also go a long way towards helping us mitigate the effects it is having here on Earth, where the changes are only unnatural, but also sudden and very hazardous.

And who knows? Someday, it could even help us to alter the environments on other planets and bodies, thus making them more suitable for long-term human settlement (aka. terraforming)!

Further Reading: UCLA, Nature

Posted on by Nancy Atkinson

Loss of Signal: Cassini Spacecraft Plunges Into Saturn

Artist concept of Cassini's last moments at Saturn. Credit: NASA/JPL.

Until the very end, Cassini displayed just how robust and enduring this spacecraft has been throughout its entire 20 years in space and its 13-year mission at Saturn. As Cassini plummeted through the ringed-planet’s atmosphere, its thrusters fought the good fight to keep the antenna pointed at Earth for as long as possible, sending as much of the last drops of science data as it could.

Cassini endured about 40 seconds longer than expected before loss of signal was called at 11:55:46 UTC

“I hope you’re all deeply proud of this accomplishment,” said Cassini Project Manager Earl Maize in JPL’s Mission Control Center after Cassini’s signal was lost. “This has been an incredible mission, and incredible spacecraft and an incredible team. I’m going to call this the end of mission. Project Manager off the net.”

Of course, the actual demise of Cassini took place about an hour and 23 minutes before, as it took that long for the signal to travel the 1.5 billion km distance from Saturn to Earth.

“This is a bittersweet moment for all of us,” said JPL Director Mike Watkins, “but I think it is more sweet than bitter because Cassini has been such an incredible mission. This is a great time to celebrate the hard work and dedication of those who have worked on this mission.”

Watkins added that almost everything we know about Saturn comes from the Cassini mission. “It made discoveries so compelling that we have to back,” he said. “We will go back and fly through the geysers of Encleadus and we’ll go back to explore Titan… These are incredibly compelling targets.”

Cassini program manager at JPL, Earl Maize, left, and spacecraft operations team manager for the Cassini mission at Saturn, Julie Webster, right, embrace after the Cassini spacecraft plunged into Saturn, Friday, Sept. 15, 2017 at NASA’s Jet Propulsion Laboratory in Pasadena, California. Photo Credit: (NASA/Joel Kowsky)

Cassini launched on Oct. 15, 1997, and arrived at Saturn’s in 2004. It studied Saturn’s rings and sent back postcards almost every day of its journeys around the Saturn system, pictures of complex moons, the intriguing rings and the giant gas planet.

It revealed the moon Enceladus as one of the most geothermally active places in our solar system, showing it to be one of the prime targets in the search for life beyond Earth.

Saturn’s active, ocean-bearing moon Enceladus sinks behind the giant planet in a farewell portrait from NASA’s Cassini spacecraft.
Credits: NASA/JPL-Caltech/Space Science Institute

Also, piggybacking along was the Huygens probe to study Saturn’s largest moon, Titan. This landing in 2005 was the first spacecraft to land in the outer solar system.

During its final plunge, Cassini’s instruments captured data on Saturn’s atmosphere, sending a strong signal throughout. As planned, data from eight of Cassini’s science instruments will be providing new insights about Saturn, including hints about the planet’s formation and evolution, and processes occurring in its atmosphere.

This death plunge ensures Saturn’s moons will remain pristine for future exploration.

Over 260 scientists from 17 countries and hundreds of engineers worked with Cassini throughout the entire mission. During Cassini’s final days, mission team members from all around the world gathered at JPL to celebrate the achievements of this historic mission.

Here is the last picture taken by Cassini’s cameras, showing the place where Cassini likely met its demise:

This monochrome view is the last image taken by the imaging cameras on NASA’s Cassini spacecraft. It looks toward the planet’s night side, lit by reflected light from the rings, and shows the location at which the spacecraft would enter the planet’s atmosphere hours later. Credit: NASA/JPL-Caltech/Space Science Institute

If you can’t get enough of Cassini, there will be more information coming about this final data, and of course, you can go look at all the images it has sent back here. Also, NASA has provided an ebook for download that includes information and images from the mission.

Posted on by Nancy Atkinson

Cassini: The Mission That Will Live Forever

Artist rendition of the Cassini spacecraft over Saturn. Credit: NASA/JPL-Caltech/SSI/Kevin M. Gill.

“With Cassini, we had a rare opportunity and we seized it,” said Linda Spilker, Cassini Mission Scientist.

And on Friday, September 15, we say goodbye to this incredible spacecraft.

Since 2004, Cassini has been orbiting Saturn, exploring the magnificent gas giant planet while weaving through an incredibly diverse assortment of 60-plus icy moons, and skimming along the edges of the complex but iconic icy rings.

Cassini’s findings have revolutionized our understanding of the entire Saturn system, providing intriguing insights on Saturn itself as well as revealing secrets held by moons such as Enceladus, which should be a big iceball but instead is one of the most geothermally active places in our solar system. And thanks to the Huygens lander, we now know Saturn’s largest moon, Titan is eerily Earthlike, but yet totally alien.

“The lasting story of Cassini will likely be its longevity and the monumental amount of scientific discovery,” Cassini Project Manager Earl Maize told me last year. “It was absolutely the right spacecraft in the right place at the right time to capture a huge array of phenomena at Saturn.”

But after 20 years in space, the Cassini spacecraft is running out of fuel, and so Cassini will conduct a sacred act known as ‘planetary protection.’ This self-sacrifice will ensure any potentially habitable moons of Saturn won’t be contaminated sometime in the future if the drifting, unpowered spacecraft were to accidentally crash land there. Microbes from Earth might still be adhering to Cassini, and its RTG power source still generates warmth. It could melt through the icy crust of one of Saturn’s moons, possibly, and reach a subsurface ocean.

Diagram of Cassini’s final week, showing some of the milestones as the spacecraft heads for its plunge into Saturn. Credit: NASA/JPL-Caltech

For a mission this big, this long and this unprecedented, it will end in spectacular fashion. Called the Grand Finale — which actually began last spring — Cassini has made 22 close passes through the small gap between Saturn’s cloud tops and the innermost ring. This series of orbits has sent the spacecraft on an inevitable path towards destruction.

And tomorrow, on its final orbit, Cassini will plunge into Saturn’s atmosphere at tens of thousands of kilometers per hour. Like the science-churning machine it has been throughout its mission, Cassini will continue to conduct science observations until the very end, sending back long-sought after data about Saturn’s atmosphere. But eventually, the spacecraft will be utterly destroyed by the gas planet’s heat and pressure. It will burn up like a meteor, and become part of the planet itself.

There’s no real way to sum up this amazing mission in one article, and so I’ll leave some links and information below for you to peruse.

But I’ll also leave you with this: Instead of feeling like the mission is over, I prefer to think of Cassini as living forever, because of all the data it provided that has yet to be studied. Linda Spilker told me this last year:

“In one way,” Spilker said, “the mission will end. But we have collected this treasure trove of data, so we have decades of additional work ahead of us. With this firehose of data coming back basically every day, we have only been able to skim the cream off the top of the best images and data. But imagine how many new discoveries we haven’t made yet! The search for a more complete understanding of the Saturn system continues, and we leave that legacy to those who come after, as we dream of future missions to continue the exploration we began.”

But if you want to say goodbye to Cassini, scientist Sarah Hörst might have suggested the best way to do it:

You can watch the live video coverage of Cassini’s end of mission on Friday starting at 7 a.m. EDT. on NASA TV

NASA has a great “Grand Finale” feature on its website, which is well worth the visit.

NASA also has all sorts of “Grand Finale” images, graphics and videos available here.

Follow the @CassiniSaturn twitter account for the latest info.

Imaging wizard Kevin Gill has put together a “Visions of Cassini” video with a great compilation of images from the mission. Here’s a shorter two minute version:

Or a longer, two and a half hour version!

These are one of the highest-resolution color images of any part of Saturn’s rings, taken on taken on July 6, 2017, with the Cassini spacecraft narrow-angle camera. This image shows a portion of the inner-central part of the planet’s B Ring. Credit: NASA/JPL-Caltech/Space Science Institute

Posted on by Matt Williams

Cassini Conducts a Final Flyby of Titan Before Crashing into Saturn

Illustration of the Cassini probe in orbit of Saturn. The probe will descend into Saturn's atmosphere on Sept. 15th, 2017. Credit: NASA/JPL-Caltech

When the Cassini spacecraft arrived around Saturn on July 1st, 2004, it became the fourth space probe to visit the system. But unlike the Pioneer 11 and Voyager 1 and 2 probes, the Cassini mission was the first to establish orbit around the planet for the sake of conducting long-term research. Since that time, the spacecraft and its accompanying probe – the Huygens lander – have revealed a startling amount about this system.

On Friday, September 15th, the Cassini mission will official end as the spacecraft descends into Saturn’s atmosphere. In part of this final maneuver, Cassini recently conducted one last distant flyby of Titan. This flyby is being referred to informally as “the goodbye kiss” by mission engineers, since it is providing the gravitational push necessary to send the spacecraft into Saturn’s upper atmosphere, where it will burn up.

In the course of this flyby, the spacecraft made its closest approach to Titan on Tuesday, September 12th, at 12:04 p.m. PDT (3:04 p.m. EDT), passing within 119,049 kilometers (73,974 mi) of the moon’s surface. The maneuver was designed to slow the probe down and lower the altitude of its orbit around the planet, which will cause it to descend into Saturn’s atmosphere in a few day’s time.

Artist’s conception of Cassini winging by Saturn’s moon Titan (right) with the planet in the background. Credit: NASA/JPL-Caltech

The flyby also served as an opportunity to collect some final pictures and data on Saturn’s largest moon, which has been a major focal point for much of the Cassini-Huygens mission. These will all be transmitted back to Earth at 18:19 PDT (21:19 EDT) when the spacecraft makes contact, and navigators will use this opportunity to confirm that Cassini is on course for its final dive.

All told, the spacecraft made hundreds of passes over Titan during its 13-year mission. These included a total of 127 precisely targeted encounters at close and far range (like this latest flyby). As Cassini Project Manager Earl Maize, from NASA’s Jet Propulsion Laboratory, said in a NASA press statement:

“Cassini has been in a long-term relationship with Titan, with a new rendezvous nearly every month for more than a decade. This final encounter is something of a bittersweet goodbye, but as it has done throughout the mission, Titan’s gravity is once again sending Cassini where we need it to go.”

In the course of making its many flybys, the Cassini spacecraft revealed a great deal about the composition of Titan’s atmosphere, its methane cycle (similar to Earth’s hydrological cycle) and the kinds of weather it experiences in its polar regions. The probe also provided high-resolution radar images of Titan’s surface, which included topography and images of its northern methane lakes.

Artist depiction of Huygens lander touching down on the surface of Saturn’s largest moon Titan. Credit: ESA

Cassini’s first flyby of Titan took place on July 2nd, 2004 – a day after the spacecraft’s orbital insertion – where it approached to within 339,000 km (211,000 mi) of the moon’s surface. On December 25th, 2004, Cassini released the Huygens lander into the planet’s atmosphere. The probe touched down on January 14th, 2005, taking hundreds of pictures of the moon’s surface in the process.

In November of 2016, the spacecraft began the Grand Finale phase of its mission, where it would make 22 orbits between Saturn and its rings. This phase began with a flyby of Titan that took it to the gateway of Saturn’s’ F-ring, the outermost and perhaps most active ring around Saturn. This was followed by a final close flyby of Titan on April 22nd, 2017, taking it to within 979 km (608 mi) of the moon’s surface.

Throughout its mission, Cassini also revealed some significant things about Saturn’s atmosphere, its hexagonal storms, its ring system, and its extensive system of moons. It even revealed previously-undiscovered moons, such as Methone, Pallene and Polydeuces. Last, but certainly not least, it conducted studies of Saturn’s moon Enceladus that revealed evidence of a interior ocean and plume activity around its southern polar region.

These discoveries are part of the reason why the probe will end its mission by plunging into Saturn’s atmosphere, about two days and 16 hours from now. This will cause the probe to burn up, thus preventing contamination of moons like Titan and Enceladus, where microbial life could possibly exist. Finding evidence of this life will be the main focus of future missions to the Saturn system, which are likely to launch in the next decade.

So long and best wishes, Cassini! You taught so much in the past decade and we hope to follow up on it very soon. We’ll all miss you when you go!

Further Reading: NASA

Posted on by Matt Williams

Cassini Finds that Titan is Building the Chemicals that Might Have Led to Life on Earth

Image of Titan's atmosphere, snapped by the Cassini spacecraft. Credit: NASA/JPL/Space Science Institute

Titan, Saturn’s largest moon, has been a source of mystery ever since scientists began studying it over a century ago. These mysteries have only deepened with the arrival of the Cassini-Huygens mission in the system back in 2004. In addition to finding evidence of a methane cycle, prebiotic conditions and organic chemistry, the Cassini-Huygens mission has also discovered that Titan may have the ingredient that help give rise to life.

Such is the argument made in a recent study by an international team of scientists. After examining data obtained by the Cassini space probe, they identified a negatively charged species of molecule in Titan’s atmosphere. Known as “carbon chain anions”, these molecules are thought to be building blocks for more complex molecules, which could played a key role in the emergence of life of Earth.

The study, titled “Carbon Chain Anions and the Growth of Complex Organic Molecules in Titan’s Ionosphere“, recently appeared in The Astrophysical Journal Letters. The team included researchers from University College in London, the University of Grenoble, Uppsalla University, UCL/Birkbeck, the University of Colorado, the Swedish Institute of Space Physics, the Southwest Research Institute (SwRI), and NASA’s Goddard Space Flight Center.

Diagram of the internal structure of Titan according to the fully differentiated dense-ocean model. Credit: Wikipedia Commons/Kelvinsong

As they indicate in their study, these molecules were detected by the Cassini Plasma Spectrometer (CAPS) as the probe flew through Titan’s upper atmosphere at an distance of 950 – 1300 km (590  – 808 mi) from the surface. They also show how the presence of these molecules was rather unexpected, and represent a considerable challenge to current theories about how Titan’s atmosphere works.

For some time, scientists have understood that within Titan’s ionosphere, nitrogen, carbon and hydrogen are subjected to sunlight and energetic particles from Saturn’s magnetosphere. This exposure drives a process where these elements are transformed into more complex prebiotic compounds, which then drift down towards the lower atmosphere and form a thick haze of organic aerosols that are thought to eventually reach the surface.

This has been the subject of much interest, since the process through which simple molecules form complex organic ones has remained something of a mystery to scientists. This could be coming to an end thanks to the detection of carbon chain anions, though their discovery was altogether unexpected. Since these molecules are highly reactive, they are not expected to last long in Titan’s atmosphere before combining with other materials.

However, the data showed that the carbon chains became depleted closer to the moon, while precursors to larger aerosol molecules underwent rapid growth. This suggests that there is a close relationship between the two, with the chains ‘seeding’ the larger molecules. Already, scientists have held that these molecules were an important part of the process that allowed for life to form on Earth, billions of years ago.

A halo of light surrounds Saturn’s moon Titan in this backlit picture, showing its atmosphere. Credit: NASA/JPL/Space Science Institute

However, their discovery on Titan could be an indication of how life begins to emerge throughout the Universe. As Dr. Ravi Desai, University College London and the lead author of the study, explained in an ESA press release:

“We have made the first unambiguous identification of carbon chain anions in a planet-like atmosphere, which we believe are a vital stepping-stone in the production line of growing bigger, and more complex organic molecules, such as the moon’s large haze particles. This is a known process in the interstellar medium, but now we’ve seen it in a completely different environment, meaning it could represent a universal process for producing complex organic molecules.”

Because of its dense nitrogen and methane atmosphere and the presence of some of the most complex chemistry in the Solar System, Titan is thought by many to be similar to Earth’s early atmosphere. Billions of years ago, before the emergence of microorganisms that allowed for subsequent build-up of oxygen, it is likely that Earth had a thick atmosphere composed of nitrogen, carbon dioxide and inert gases.

Therefore, Titan is often viewed as a sort planetary laboratory, where the chemical reactions that may have led to life on Earth could be studied. However, the prospect of finding a universal pathway towards the ingredients for life has implications that go far beyond Earth. In fact, astronomers could start looking for these same molecules on exoplanets, in an attempt to determine which could give rise to life.

This illustration shows Cassini above Saturn’s northern hemisphere prior to one of its 22 Grand Finale dives. Credit: NASA/JPL-Caltech

Closer to home, the findings could also be significant in the search for life in our own Solar System. “The question is, could it also be happening within other nitrogen-methane atmospheres like at Pluto or Triton, or at exoplanets with similar properties?” asked Desia. And Nicolas Altobelli, the Project Scientist for the Cassini-Huygens mission, added:

“These inspiring results from Cassini show the importance of tracing the journey from small to large chemical species in order to understand how complex organic molecules are produced in an early Earth-like atmosphere. While we haven’t detected life itself, finding complex organics not just at Titan, but also in comets and throughout the interstellar medium, we are certainly coming close to finding its precursors.“

Cassini’s “Grande Finale“, the culmination of its 13-year mission around Saturn and its system of moons, is set to end on September 15th, 2017. In fact, as of the penning of this article, the mission will end in about 1 month, 18 days, 16 hours, and 10 minutes. After making its final pass between Saturn’s rings, the probe will be de-orbited into Saturn’s atmosphere to prevent contamination of the system’s moons.

However, future missions like the James Webb Space Telescope, the ESA’s PLATO mission and ground-based telescopes like ALMA are expected to make some significant exoplanet finds in the coming years. Knowing specifically what kinds of molecules are intrinsic in converting common elements into organic molecules will certainly help narrow down the search for habitable (or even inhabited) planets!

Further Reading: ESA, The Astrophysical Journal Letters

Posted on by Nancy Atkinson

A Survivor’s Tale: Cassini Lives Through First Ring Dive

Artist's concept of Cassini diving between Saturn and its innermost ring. Credit: NASA/JPL-Caltech

One down, twenty-one to go! The Cassini spacecraft survived the first dive through the narrow gap between Saturn and its rings, and is now back communicating with Earth.

“No spacecraft has ever been this close to Saturn before. We could only rely on predictions, based on our experience with Saturn’s other rings, of what we thought this gap between the rings and Saturn would be like,” said Cassini Project Manager Earl Maize of NASA’s Jet Propulsion Laboratory in Pasadena, California. “I am delighted to report that Cassini shot through the gap just as we planned and has come out the other side in excellent shape.”

It was a long day for Cassini scientists and engineers at the Jet Propulsion Laboratory while the spacecraft was out of contact for 20 hours during this first dive, signaling the beginning of the end for the mission.

Cassini, running out of fuel, is heading toward its ultimate death by crashing into Saturn on September 15, 2017. But during the next few months, Cassini will make twenty-one more passes through the gap, and in doing so, further our understanding of how giant planets, and planetary systems everywhere, form and evolve.

A raw image of Saturn’s polar vortex, taken on April 26, 2017 by the Cassini spacecraft during the first close pass between Saturn and its rings. Credit: NASA/JPL-Caltech.

Project Scientist Linda Spilker said Cassini will be able to make close up measurements of Saturn and its rings to finally help us understand the mass and internal structure of Saturn. And the images should be absolutely stunning.

Contact was lost as the ring-plane crossing started at 2 a.m. PDT (5 a.m. EDT) on April 26. NASA’s Deep Space Network Goldstone Complex in California’s Mojave Desert acquired Cassini’s signal at 11:56 p.m. PDT on April 26, 2017 (2:56 a.m. EDT on April 27) and data began flowing at 12:01 a.m. PDT (3:01 a.m. EDT) on April 27.

Cassini was programmed to collect science data while close to the planet. As a protective measure, the spacecraft used its large, dish-shaped high-gain antenna (13 feet or 4 meters across) as a deflector shield, orienting it in the direction of oncoming ring particles. This orientation put the spacecraft out of contact with Earth.

“In the grandest tradition of exploration, NASA’s Cassini spacecraft has once again blazed a trail, showing us new wonders and demonstrating where our curiosity can take us if we dare,” said Jim Green, director of the Planetary Science Division at NASA Headquarters.

The gap between the rings and the top of Saturn’s atmosphere is about 1,500 miles (2,000 kilometers) wide, and Cassini came within about 1,000 miles (1,600 kilometers) of Saturn’s cloud tops.

The best models for the region suggested that if there were ring particles in the area where Cassini crossed the ring plane, they would be tiny, on the scale of smoke particles. However, the spacecraft was traveling at speeds of about 77,000 mph (124,000 kph) relative to the planet, so small particles hitting a sensitive area could potentially have disabled the spacecraft.

The spacecraft is being destroyed after a successful 13 year mission at Saturn, as NASA needs to follow the protocol of planetary protection, and not allow a spacecraft with possible microbes from Earth to crash into a potentially habitable moon such as Enceladus or Titan.

Cassini’s next dive through the gap is scheduled for May 2.

You can see the Cassini raw images page here, but look for more processed images to be available soon.

Jason Major put together this animation of some of the first images from Cassini’s close pass:

Source: JPL

Posted on by Matt Williams

Adieu Titan: So Long & Thanks For All The Hydrocarbons

Artist's conception of Cassini winging by Saturn's moon Titan (right) with the planet in the background. Credit: NASA/JPL-Caltech

The Cassini spacecraft has done some amazing things since it arrived in the Saturn system in 2004. In addition to providing valuable information on the gas giant and its system of rings, it has also provided us with extensive data and photographs of Saturn’s many moons. Nowhere has this been more apparent than with Saturn’s largest moon, the hydrocarbon-rich satellite known as Titan.

And with just a few hours left before Cassini makes its final plunge between Saturn and its innermost ring (something that no other spacecraft has ever done), we should all take this opportunity to say goodbye to Titan. In the past few years, it has dazzled us with its methane lakes, dense atmosphere, and potential for hosting life. And it shall be sorely missed!

Cassini’s last encounter with Titan – where it passed within 979 km (608 mi) of the moon’s surface – took place on April 21st, at 11:08 p.m. PDT (April 22nd, 2:08 a.m. EDT). The probe also used this opportunity to take some radar images of the moon’s northern polar region. While this area has been photographed before, this was the first time that radar images were acquired.

Unprocessed image of Saturn’s moon Titan, captured by NASA’s Cassini spacecraft during its final close flyby on April 21st, 2017. Credit: NASA/JPL-Caltech/Space Science Institute

Over the course of the next week, Cassini’s radar team hopes to pour over theses images, which provide a detailed look at the methane seas and lakes in the northern polar region. It is hoped that this data will allow scientists to shed more light on the depths and compositions of some of the small lakes in the area, as well as provide more information on the evolving surface feature known as “magic island“.

With this last pass complete (its 127th in total), Cassini is now beginning the final phase of its mission – known as the Grand Finale. This will consist of the spacecraft making a final set of 22 orbits around the ringed planet between April 26th and September 15th. The maneuver will allow Cassini to go where no other probe has gone before and get the closest look ever at Saturn’s outer rings.

The final pass over Titan was part of this maneuver, using the moon’s gravity to bend and reshape the probe’s orbit so that it would be able to pass through Saturn’s ring system – instead of passing just beyond the main rings. As Earl Maize, Cassini project manager at JPL, said in a NASA press release:

“With this flyby we’re committed to the Grand Finale. The spacecraft is now on a ballistic path, so that even if we were to forgo future small course adjustments using thrusters, we would still enter Saturn’s atmosphere on Sept. 15 no matter what.”

Some key numbers for Cassini’s Grand Finale and final plunge into Saturn. Credit: NASA/JPL-Caltech

Cassini’s final pass with Titan allowed it to acquire a boost in velocity, increasing its speed by 860.5 meters per second (3098 km/h; 1,925 mph). It then reached its farthest point in its orbit around Saturn (apoapse) on April 22nd, :46 p.m. PDT (11:46 p.m. EDT). This effectively began the Grand Finale orbits, with the first dive coming on April 26th, at 02:00 a.m. PDT (05:00 a.m. EDT).

This orbit will provide Cassini with its best look to date at Saturn’s north pole, which it will be studying with both its  Visible and Infrared Mapping Spectrometer (VIMS) and Composite Infrared Spectrometer (CIRS). These studies will lead to the creation of the sharpest movies to date in the near-infrared band, which will also allow the science team to study the motions of the hexagon pattern around Saturn’s north pole in more detail.

Between now and September, when the mission will end, the probe will provide information that is expected to improve our understanding of how giant planets form and evolve. Things will finally wrap on  September 15th, 2017, when the probe will plunge into Saturn’s atmosphere. But even then, the probe will be sending back information until its very last seconds of operation.

Safe journeys Cassini! And so long Titan! We hope to be exploring you again someday soon, preferably with something that can float or fly around inside your dense atmosphere, or perhaps investigate your methane seas in serious depth!

In the meantime, be sure to check out this narrated, 360-degree animated video from NASA. As you can see, it simulates what a ride on the Cassini spacecraft might look like as it makes its Grand Finale:

Further Reading: NASA, Cassini – The Grand Finale

Posted on by Bob King

Earth Beams From Between Saturn’s Rings in New Cassini Image

Credit: NASA/JPL-Caltech
NASA’s Cassini spacecraft captured the view on April 13, 2017 at 12:41 a.m. CDT. The probe was 870 million miles (1.4 billion km) away from Earth when the image was taken. The part of Earth facing toward Cassini at the time was the southern Atlantic Ocean. Look closely to the left of Earth; that pinprick of light is the Moon. Credit: NASA/JPL Caltech

Look at us. Packed into a gleaming dot. The entire planet nothing more than a point of light between the icy rings of Saturn. The rings visible here are the A ring (top), followed by the Keeler and Encke gaps, and finally the F ring at bottom. During this observation, Cassini was looking toward the backlit rings with the sun blocked by the disk of Saturn.

Cassini first photographed Earth from Saturn in July 2013. Credit: NASA/JPL-Caltech

Seen from Saturn, Earth and the other inner solar system planets always appear close to the sun much like Venus and Mercury do from Earth. All orbit interior to Saturn; even at maximum elongation, they never get far from the Sun. Early this month, as viewed from Saturn, Earth was near maximum elongation east of the sun, thus an “evening star,” making it an ideal time to take a picture.

In this cropped view of the April 13 image, you can better see the Moon, located a short distance to the left of the Earth. Credit: NASA/JPL-Caltech

Opportunities to capture Earth from Saturn have been rare in the 13 years Cassini has spent orbiting the ringed planet. The only other photo I’m aware of was snapped on July 19, 2013. Each is a precious document with a clear message: we are all tiny, please let’s be kind to one another.

This graphic shows Cassini’s flight path during the final two phases of its mission. The 20 Ring-Grazing Orbits are in gray (completed) and the 22 Grand Finale Orbits are in blue. The final partial orbit is colored orange. The first of the Grand Finale orbits begins on April 22 at 10:46 p.m. CDT. Credit: NASA/JPL-Caltech/Space Science Institute

We’ll soon miss the steady stream of artistic images of Saturn, its rings and moons by the Cassini team. The probe will make its final close flyby of the planet’s largest moon, fog-enshrouded Titan, at 1:08 a.m. April 22, at a distance of just 608 miles (979 km). That night at 10:46 p.m. CDT, Cassini will enter the first of its Grand Finale orbits, a series of 22 weekly dives between the planet and the rings. The first ring plane crossing is slated for midnight CDT April 25-26.


Cassini at Saturn and the Grand Finale

The coming week will be a busy one for Cassini. On each orbit, the probe will draw closer and closer to the butterscotch ball of Saturn until it finally tears across the cloud tops and burns up as a spectacular fireball on September 15. Scientists would rather see the craft burn up in Saturn’s atmosphere instead crash into a moon and possibly contaminate it.

Cassini will become a brilliant fireball streaking over Saturn’s cloud tops on the last day of its operation on September 15. Credit: NASA/JPL-Caltech

After nearly 20 years in space, seven of them spent traveling to the ringed planet, Cassini feels like family. It won’t be easy to say goodbye, but thanks to the probe, Saturn’s family album is bursting with remarkable images that will forever remind us the tenacity of this amazing machine and the vision and work of those who kept it operating for so many years.

Posted on by Evan Gough

The Bubbly Streams Of Titan

The appearing and disappearing feature observed in Titan's Lakes was dubbed "Magic Island". Image: NASA/JPL-Caltech/ASI/Cornell
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
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 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.

Posted on by Evan Gough

NASA Bombshell: Key Ingredient For Life Discovered On Enceladus

Scientists recently determined that a certain strain of Earth bacteria could thrive under conditions found on Enceladus. Credit: NASA/JPL/Space Science Institute


NASA has announced the discovery of hydrogen in the plumes on Enceladus. This is huge news, and Cassini scientists have looked forward to this day. What it means is that there is a potential source of energy for microbes in the oceans of Enceladus, and that energy from the Sun is not required to support life.

We’ve known about the plumes on Enceladus for a while now, and Cassini has even flown through those plumes to determine their content. But hydrogen was never discovered until now. What it means is that there is a geochemical source for hydrogen in Enceladus’ ocean, coming from the interaction between warm water and rocks.

“This is the closest we’ve come, so far, to identifying a place with some of the ingredients needed for a habitable environment.” – Thomas Zurbuchen, NASA.

This is a capstone finding, according to NASA. As far as we know, life needs three things to exist: water, energy, and the right chemicals. We know it has the necessary chemicals, we know it has water, and we now know it has a source of energy.

On Earth, hydrothermal vents deep in the ocean floor provide the energy for a web of life reliant on those vents. Bacteria live there, forming the base of a food chain that can include tube worms, shrimp, and other life forms. This discovery points to the possibility that similar communities might exist in the sub-surface ocean of Enceladus.

“This is the closest we’ve come, so far, to identifying a place with some of the ingredients needed for a habitable environment,” said Thomas Zurbuchen, associate administrator for NASA’s Science Mission Directorate at Headquarters in Washington.

Microbes in Enceladus’ ocean could use the hydrogen in a process called methanogenesis. They obtain energy by combining hydrogen with dissolved carbon dioxide in the water. This process produces a methane by-product. Methanogenesis is a bedrock process at the root of life here on Earth.

“Confirmation that the chemical energy for life exists within the ocean of a small moon of Saturn is an important milestone in our search for habitable worlds beyond Earth,” said Linda Spilker, Cassini project scientist at NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California.

Hubble Confirms Plumes On Europa

NASA has also announced that the Hubble Space Telescope has confirmed the presence of plumes on another of our Solar System’s icy moons, Europa.

These plumes were first seen by the Hubble in 2014, but were never seen again. Since repeatability is key in science, those findings were put on the back burner. But in 2016, NASA announced today, Hubble spotted them again, in the same place. This is the same spot that the Galileo probe noticed a thermal hot spot.

We don’t know if Europa has hydrogen in its oceans, but it’s easy to see where this is going. NASA’s excitement is palpable.

What’s Next?

NASA’s Europa Clipper mission will visit Europa and determine the thickness of its ice layer, as well as the depth and salinity of its ocean. It will also analyze the atmosphere and the composition of the plumes. Europa Clipper will fill in a lot of gaps in our understanding.

Europa Clipper will be launched around 2022, but a mission to Enceladus will have to wait a little longer. One mission under consideration in NASA’s Discovery program is ELF, Enceladus Life Finder. ELF would fly through Enceladus’ plumes 8 or 10 times, taking more detailed samples of their content.

This enhanced-color Cassini view of southern latitudes on Enceladus features the bluish “tiger stripe” fractures that rip across the south polar region. These tiger stripes form over hydrothermal vents in the ocean, the source of Enceladus’ plumes. Credits: NASA/JPL-Caltech/Space Science Institute

The discovery of hydrogen in the plumes of Enceladus is huge news any way you look at it. But that discovery begs the question: Are we doing it all wrong? Are we looking for life in the wrong places?

The search for life elsewhere in the Universe, so far, has mostly revolved around exoplanets. And then refining that search to identify exoplanets that are in the habitable zones of their stars. We’re searching for other Earths, basically.

But maybe we should be changing our focus. Maybe it’s the ice worlds, including icy exomoons, that are the most likely targets for our search. This new evidence from NASA’s Cassini mission, and from the Hubble Space Telescope, suggests that in our Solar System at least, they are the best place to search.

One Final Ingredient Needed?

There’s a fourth ingredient needed for life. Once there is water, energy, and the necessary chemicals, life needs time to get going. How much time, we’re not exactly certain. But this is where Enceladus and Europa are different.

Europa is about 4 billion years old, or so we think. That’s only half a billion years younger than Earth, and we think life started on Earth about 3.5 billion years ago. This hints that, if conditions on Europa are favorable, life has had a long time to get going. Of course, that doesn’t mean it has.

On the other hand, Enceladus is probably much younger. A study of the orbits of Saturn’s moons suggests that Enceladus may only be 100 million years old. If that’s true, it’s not very much time for life to get going.

The hydrogen discovery is huge news. There are still a lot of questions, of course, and lots to be debated. But confirming a source of energy on Enceladus builds the case for the same type of hydrothermal vent life that we see on Earth.

Now all we need is a mission to Enceladus.