Cassini Data Suggests Enceladus Has a Subsurface Ocean

enceladusocean

Image Credit: NASA/JPL-Caltech

The treasure trove which is the Cassini spacecraft orbiting the Saturn system continues to produce fascinating discoveries. Now it appears that Saturn’s moon Enceladus has a subsurface ocean, one which is likely responsible for the geysers which Enceladus is jetting into space.

It is important to note that after the end of the Cassini mission, NASA has nothing else planned for this amazing system, one which offers an ever widening number of targets worthy of further exploration. Much the same could be said for Jupiter’s system as well, which will at least be visited by the short lived Juno orbiter, even as notional funding for a Europa mission is barely enough to keep the lights on.

One wonders what it would take to inspire a new major outer planets mission.

The full text of the NASA press release is below:

NASA’s Cassini spacecraft and Deep Space Network have uncovered evidence Saturn’s moon Enceladus harbors a large underground ocean of liquid water, furthering scientific interest in the moon as a potential home to extraterrestrial microbes.

Researchers theorized the presence of an interior reservoir of water in 2005 when Cassini discovered water vapor and ice spewing from vents near the moon’s south pole. The new data provide the first geophysical measurements of the internal structure of Enceladus, consistent with the existence of a hidden ocean inside the moon. Findings from the gravity measurements are in the Friday April 4 edition of the journal Science.

“The way we deduce gravity variations is a concept in physics called the Doppler Effect, the same principle used with a speed-measuring radar gun,” said Sami Asmar of NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, Calif., a coauthor of the paper. “As the spacecraft flies by Enceladus, its velocity is perturbed by an amount that depends on variations in the gravity field that we’re trying to measure. We see the change in velocity as a change in radio frequency, received at our ground stations here all the way across the solar system.”

The gravity measurements suggest a large, possibly regional, ocean about 6 miles (10 kilometers) deep, beneath an ice shell about 19 to 25 miles (30 to 40 kilometers) thick. The subsurface ocean evidence supports the inclusion of Enceladus among the most likely places in our solar system to host microbial life. Before Cassini reached Saturn in July 2004, no version of that short list included this icy moon, barely 300 miles (500 kilometers) in diameter.

“This then provides one possible story to explain why water is gushing out of these fractures we see at the south pole,” said David Stevenson of the California Institute of Technology, Pasadena, one of the paper’s co-authors.

Cassini has flown near Enceladus 19 times. Three flybys, from 2010 to 2012, yielded precise trajectory measurements. The gravitational tug of a planetary body, such as Enceladus, alters a spacecraft’s flight path. Variations in the gravity field, such as those caused by mountains on the surface or differences in underground composition, can be detected as changes in the spacecraft’s velocity, measured from Earth.

The technique of analyzing a radio signal between Cassini and the Deep Space Network can detect changes in velocity as small as less than one foot per hour (90 microns per second). With this precision, the flyby data yielded evidence of a zone inside the southern end of the moon with higher density than other portions of the interior.

The south pole area has a surface depression that causes a dip in the local tug of gravity. However, the magnitude of the dip is less than expected given the size of the depression, leading researchers to conclude the depression’s effect is partially offset by a high-density feature in the region, beneath the surface.

“The Cassini gravity measurements show a negative gravity anomaly at the south pole that however is not as large as expected from the deep depression detected by the onboard camera,” said the paper’s lead author, Luciano Iess of Sapienza University of Rome. “Hence the conclusion that there must be a denser material at depth that compensates the missing mass: very likely liquid water, which is seven percent denser than ice. The magnitude of the anomaly gave us the size of the water reservoir.”

There is no certainty the subsurface ocean supplies the water plume spraying out of surface fractures near the south pole of Enceladus, however, scientists reason it is a real possibility. The fractures may lead down to a part of the moon that is tidally heated by the moon’s repeated flexing, as it follows an eccentric orbit around Saturn.

Much of the excitement about the Cassini mission’s discovery of the Enceladus water plume stems from the possibility that it originates from a wet environment that could be a favorable environment for microbial life.

“Material from Enceladus’ south polar jets contains salty water and organic molecules, the basic chemical ingredients for life,” said Linda Spilker, Cassini’s project scientist at JPL. “Their discovery expanded our view of the ‘habitable zone’ within our solar system and in planetary systems of other stars. This new validation that an ocean of water underlies the jets furthers understanding about this intriguing environment.”

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. JPL manages the mission for NASA’s Science Mission Directorate in Washington. For more information about Cassini, visit:

http://www.nasa.gov/cassini

New Discovery at the Edge of Solar System Suggest Planet X May Still Be Out There

Image Credit: Scott Sheppard/Carnegie Institution for Science

Image Credit: Scott Sheppard/Carnegie Institution for Science

Time lapse photo showing movement

On the third episode of the re-tooled COSMOS, Neil deGrasse Tyson took his ship of the imagination to the Oort cloud to discover the origin of comets. He may have to go back.

Astronomers have discovered a second dwarf planet orbiting in the far reaches of the solar system, well beyond the boundary of the Kuiper Belt, where poor Pluto orbits,  demoted to minor planet status in part by Tyson himself.  The new object, designated 2012 VP113,  is estimated to have a diameter of 450 km, and makes its closest approach to the sun at a very distant 80 astronomical units.   Its only known companion is the dwarf planet Sedna.

The interesting part is that it quite likely has a great deal of company, as many as a thousand more celestial bodies, including some according to the team which discovered 2012 VP113, that “could rival the size of Mars or even Earth.”

And that’s not all, not by a long shot.  The similarity in orbits displayed by 2012 VP113 and Sedna suggests that the long hypothesized Planet X, sometimes called Nemesis, could still be a possibility. Rather than a very dim red dwarf star, or a Jupiter sized object, it could be roughly 10 times the size of Earth,  orbiting so far out and radiating so little heat, that nothing in the current tool box is capable of detecting it.

The timing is almost comical. Earlier this month, results of a search by NASA’s Wide-Field Infrared Survey Explorer were interpreted to suggest Planet X did not exist.

The NASA report on the new Dwarf Planet is here, and a Sky and Telescope article on the implications for Planet X is here.

We really need to start cranking out the PU-238, there is an awful lot of solar system to explore.

Cassini Looks at Saturn’s Moon Dione

Dione as imaged by Cassini Credit: NASA

Dione as imaged by Cassini
Credit: NASA

With at least 53 confirmed Moons, it’s a little difficult to keep track of everything going on in Saturn’s system, but the amazing Cassini probe which has been on duty there since 2004 is still doing a remarkable job. Overshadowed by methane rich and surprisingly Earth-like Titan, and showy Enceladus, which is jetting ice crystals into space in a plume three higher than its diameter, Dione got a chance to shine this week.

In this image released by NASA,  and taken on September 10th, Dione reveals long geologic fault lines caused by fractures in its icy outer surface.  Dione is 698 miles in diameter, tidally locked to Saturn, and has two smaller moons, Helene and Polydeuces,  phase locked in its orbit, at 60 degrees ahead and behind respectively.

The Water Geysers of Enceladus

Fries with That? Credit : JPL

Fries with That?
Credit : JPL

Forget about the Bellagio,  the best dancing water fountain in this solar system isn’t in Vegas, its in orbit around Saturn’s moon Enceladus.  In the latest series of a series of images released by JPL from the remarkable Cassini spacecraft still on duty in the Saturn system, NASA has captured the simply stunning spectacle of water ice  being  shot from the Moon’s subsurface ocean into space.  Based on observations, it appears the phenomenon occurs due to regular variation in its orbits as it reaches a peak distance from Saturn. The full press release from JPL is here.

There is another aspect to this story which almost beggars belief.  Thanks to this historic mission, we now have documented evidence of water from another planetary body, including apparently organics, being shot out of a gravity well and into space. It is the solar system’s equivalent of a drive through window for a scientific treasure trove. And Enceladus isn’t even the most interesting moon in the system, a distinction which clearly goes to Titan. However, as NASA’s Planetary Division Director Jim Green glumly  assessed earlier this year,  despite all that has been learned about both the Saturnian and Jovian systems in recent years, there is no room in the budget for new Flagship missions to either of these two destinations.

While the U.S. is participating in the European Space Agency’s JUICE, Jupiter Icy Moon’s Explorer Mission, the total contribution of $100 million, or about the rolling 38 day average for the Orion capsule.

Europa: A Salty Piece of Land?

Europa: A Salty Piece of Land?Credit : JPL

Europa: A Salty Piece of Land?
Credit : JPL

 

A team of scientists working at NASA’s JPL and Cal-Tech studying Jupiter’s moon Europa, have found evidence of a chemical exchange between the frozen, radiation swept surface and a liquid ocean which is believed to exist beneath an ice pack nearly 60 miles thick.

Using spectrographic analysis of surface ice taken from the Keck II telescope in Hawaii, the pair found a clear signature of magnesium sulfate, believed to be formed from a combination of sulfur emanating from Jupiter’s innermost moon Io, and magnesium chloride salt welling up from the Europan ocean below. The find is significant because if the exchange is actually taking place it is a sign that the subsurface ocean is richer and more diverse than it otherwise would be, and could in fact be quite similar to Earth’s own oceans, and thus an ideal candidate for life. But then again if you read Arthur C. Clarke’s 2010: Odyssey Two, you already know that, and are probably smart enough to stay away, heeding the warning ” All these world are yours except Europa, attempt no landing there”

The full story (not the book) can be found here.

Epilogue:  Apparently following advice for once, Russia announced today that it is planning a landing mission for Europa’s sister moon, Ganymede in 2023,  which may or may not be part of the European Space Agency’s  Jucy Icy Moon Explorer (Juice) mission scheduled for 2022. The JUICE mission will spend several years in orbit around the gas giant before finally settling into an orbit (wisely) around Ganymede.

On Titan: Icebergs Really Could Be Dead Ahead

Artists Impression of "Titanic" IcebergsCredit : JPL

Artists Impression of “Titanic” Icebergs
Credit : JPL

Source: JPL

One of the most promising potential locations for eventual human settlement in the outer solar system is Saturn’s fascinating moon, Titan.

Bigger than innermost planet Mercury, half again as large as our own Moon, and second only to Ganymede in total size,  Titan possesses a thick nitrogen atmosphere, which blankets a bizarre frigid landscape  dominated by the hydrocarbons  methane and ethane.  Perhaps the most unusual feature however, is that the hydrocarbons exist in the form of a vast network of seas and large lakes, making it the only other planetary body in our solar system known to have stable liquids on its surface.

Eight years ago, on January 14, 2005, the European Space Agency built Huygens probe, carried to Titan by the Cassini spacecraft, became the first man-made spacecraft to land on a planetary body in the outer solar system.   Based on descent analysis and some of the 350 pictures send back to Earth, it apparently landed in a dry area not far from the shoreline of one of the many seas.

Now,  scientists studying data from the Cassini probe orbiting the Saturnian system have concluded that many of those seas likely contain floating “icebergs” of  methane and ethane made buoyant by a small percentage of nitrogen “air” in their composition. According to the theory,  the hydrocarbon ice could float or sink depending on seasonal variations in temperature.  As Titan’s northern lakes warm slighty with the coming spring, Cassini’s radar should be able to detect first increased reflection as submerged ice comes to the surface, followed by a decrease as it melts into the seas.

While it is a truly cold world,  -179 degrees Centigrade,  the organic components comprising the surface  environment  mean it is a possible abode of microbial life. It is also a veritable planetary filling station for rocket fuel, which though far too distant to have any bearing on an Earth-Moon-Mars   transportation infrastructure, at least offers a ready-made supply for local operations, particularly ascent and descent from Titan itself.  Titan’s greatest asset however, may be what it doesn’t have,  which is an abundance of fatal radiation due to both its thick atmosphere, as well as the overall weaker magnetic field of Saturn, meaning the entire system is  not constantly awash in high doses of radiation like that found around  Jupiter.

As compelling as Saturn’s system is, which contains at last 62 moons, most of which are tiny, but also the brilliantly reflective water ice world of Enceladus which is dominated by ice geysers shooting into space, it may be quite some time before we can build on the fantastical knowledge base provided by Cassini.  Besides limited budgets and two very expensive flagship programs in SLS and JWST, the U.S. has allowed its capacity to produce nuclear fuel for space reactors, of the type which powers Cassini,  and critical for missions beyond Mars, to fade to essentially nothing.

For all the talk of the importance of STEM education initiatives, it is difficult to reconcile the lack of any follow-up on a major success story such as provided by Cassini with the potential for engaging successive generations of engineers and scientists to dig deeper into the mysteries being revealed, particularly given the long time frame between any project start, transit time, and the arrival of the first bits of data.

While both NASA and the Department of Energy are working to develop a more efficient type of space reactor, the Advanced Stirling Radioisotope Generator,   which would require fewer PU- 238 pellets but provide a higher yield, the need for renewed production is a real problem which is being studiously ignored by Congress.