After Curiosity (whew!), Thoughts on Enceladus

by Paul Gilster on August 6, 2012

At $2.5 billion, NASA’s Curiosity rover didn’t cost quite as much as Cassini ($3 billion), but what a relief to Solar System exploration both near and far to have it safely down at Gale Crater. This Reuters story tells me that 79 different pyrotechnic detonations were needed to release ballast weights, open the parachute, separate the heat shield, detach the craft’s back shell and perform the rest of the functions needed to make this hair-raising landing a success. All of this with a 14-minute round-trip radio delay that left mission engineers as no more than bystanders.

Congratulations to the entire Curiosity team on this triumphant event! As we now move into the next several weeks checking the six-wheeled rover and its instruments out for exploration, let’s ponder future targets beyond the Red Planet. For at some point, no matter what we find on Mars, we’re going to want to push on to the outer planets, where intriguing moons like Titan, Europa and Enceladus await. The latter’s stock seems to be rising, as witness this recent article in The Guardian forwarded by Andy Tribick. Although they face major challenges, astrobiological missions to Enceladus offers rich prospects indeed. Two are being studied, and it’s easy to see why.

Increasingly, Enceladus seems to be a natural for astrobiology. Cassini has already shown us that the geysers spewing out of the Saturnian moon’s south pole contain complex organic compounds, and I like what NASA astrobiologist Chris McKay has to say about the place:

“It just about ticks every box you have when it comes to looking for life on another world. It has got liquid water, organic material and a source of heat. It is hard to think of anything more enticing short of receiving a radio signal from aliens on Enceladus telling us to come and get them.”

A subterranean ocean with complex organic chemicals of the sort suggested by the Cassini findings should be an interesting place indeed, especially since it seems to rise close to the surface at the south pole, accounting for the material being vented into space along the ‘tiger stripes,’ long cracks in the crust. All this material is feeding Saturn’s E-ring which, if Enceladus were suddenly to switch off, would likely disappear. McKay calls the venting of water and organics into space ‘an open invitation to go there.’

Image: Geysers at the south pole of Enceladus, as seen by Cassini in a November, 2009 flyby. Credit: NASA.

Answering the invitation would be the Enceladus Sample Return mission, a concept NASA scientists including McKay are putting together that would involve another Saturn orbiter, one that would make periodic flybys of Enceladus to collect plume samples that would eventually be returned to Earth. With Enceladus already pumping sub-surface material into space, a landing there becomes unnecessary. The Enceladus Sample Return mission builds on missions like Stardust, from which we gained expertise in retrieving sample materials from a comet’s tail. The mission is being designed to fit within the parameters of NASA’s Discovery program, which keeps the cost (without launch) at $500 million or below, about a fifth the price tag for Curiosity.

But not everyone agrees that a landing on Enceladus isn’t necessary. The German Aerospace Center (DLR) has been exploring concepts involving landing at the south pole and drilling through the ice. Its Enceladus Explorer would use an ice drill probe that would melt its way down to a depth of 100 to 200 meters to reach a water-bearing crevasse, sampling the liquid found there for microorganisms. A prototype of the device DLR is calling an IceMole has been used at the Morteratsch glacier in Switzerland and is soon to be tested in the Antarctic.

The complicated landing and drilling operation — not to mention the navigation issues faced by the IceMole as it moves through sub-surface ice — make operating the Enceladus Explorer look as risky as Curiosity’s landing on Mars. This excerpt from its project description online explains why the German team is anxious to put instrumentation on the moon’s surface and below:

…water rises to the surface through crevasses and fissures in the ice where it evaporates explosively and freezes instantly. The resulting ice fountains can shoot up to altitudes of several hundred kilometres before the ice particles slowly fall back to the moon’s surface. The microorganisms that could have evolved in the hypothetical ocean of liquid salt water under Enceladus’ icy crust, and have been swept away by the water spouting through the crevasses in the ice, would be extremely unlikely to survive; they would explode at the surface, and all that would remain are the organic compounds whose existence was verified by the Cassini spacecraft.

In other words, forget about microorganisms once they are exposed to the vacuum — all you will see are organic compounds. DLR’s IceMole, in contrast, would examine its samples in situ, sending results back to a base station on the surface that would also serve as the power source for the probe.

Would the chance to study actual living organisms give the edge to DLR’s proposal, or is a flyby the safer and cheaper alternative and the one we’re most likely to see achieved? Ideally we wind up with both missions funded, but no one would be so rash as to predict the mission choices likely from both NASA and ESA in a time of drastically reduced budgets. Let’s just say that Enceladus is staying in the news and that ingenious proposals are emerging for its study.

And it’s interesting to speculate on whether the IceMole technology being examined for DLR’s Enceladus Explorer might be adaptable to other interesting moons like Europa, Callisto or Ganymede. Each presents more problems than Enceladus, but a first-generation IceMole might some day grow into a far more powerful probe that could get a look at Europa’s deep ocean.

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{ 20 comments }

Alex Tolley August 6, 2012 at 10:33

The microorganisms that could have evolved in the hypothetical ocean of liquid salt water under Enceladus’ icy crust, and have been swept away by the water spouting through the crevasses in the ice, would be extremely unlikely to survive; they would explode at the surface,…

What basis is there for thinking this? Bacteria are freeze dried under vacuum and remain viable. They certainly don’t “explode”. The water erupting from Enceladus includes ice, not just water vapor, so we might well expect any bacteria or other microorganisms to be preserved, even viable.

Brie A. August 6, 2012 at 11:56

Congratulations, Curiosity, JPL, and NASA! It’s exciting to see our ideas for robotic missions get more advanced as we get better at sending probes. The idea of drilling through meters of ice on Enceladus (or another moon) sounds incredibly challenging- but after accomplishing an amazingly difficult Mars landing last night, why not dream bigger!

Tim Kendall August 6, 2012 at 12:08

Fascinating. It would be maybe interesting just to investigate the surface at the south pole to see if there is anything like unusual life-suggesting chemistry there – like loads of the end-product of some weird hydrocarbon-dissolved biochemistry.

ljk August 6, 2012 at 12:37

I thought folks might enjoy this early shot of Curiousity parachuting to the Martian surface via MRO’s HIRISE camera:

http://www.planetary.org/blogs/emily-lakdawalla/2012/08060824-hirise-curiosity-parachute.html

As for an easy way to grab geyser particles from Enceladus, I again present this idea that was originally planned for Europa back in 1997 (except that we probably won’t need the crashing copper ball this time):

http://www.astrobiology.com/europa/ice.clipper.html

It is very thoughful of Enceladus to shoot pieces of itself up to us for collection for a change.

Antonio August 6, 2012 at 13:28

Ma anche Tritone, potrebbe essere un luogo di esplorazione interessante.

E chissà, di non avere ulteriori “sorprese” dai satelliti di Urano e Nettuno…

In attesa dei dati che ci darà, la “New Horizons Mission”…

Saluti da Antonio

Via Google Translate

But Triton, could be an interesting place to explore.

And who knows, have no more “surprises” from the satellites of Uranus and Neptune …

Waiting for data that will give us the “New Horizons Mission” …

Greetings from Antonio

Michael August 6, 2012 at 15:49

There may be no need to drill into the surface, the explusion velocity of any water/organics/’Organisms’ is high enough to throw them into orbit for collection by an orbiting craft for examination.

Bill Higgins-- Beam Jockey August 6, 2012 at 18:56

“…It is hard to think of anything more enticing short of receiving a radio signal from aliens on Enceladus telling us to come and get them.” [...]McKay calls the venting of water and organics into space “an open invitation to go there.”

Maybe the mixture of water and other chemicals in a spray is a message– the inhabitants of Enceladus communicate by spit-takes, so this is their idea of interplanetary messaging.

Earth’s ambassador will need to be a qualified graduate of The Albert Brooks Famous School for Comedians.

JohnHunt August 6, 2012 at 22:31

If a mission were to go to Enceledus and find organic chemicals but not complex organic chemicals indicating life, then would it have been worth the billions spent on the mission? If this happens with curiosity, at least it will be able to get the geologic history of Mars. Is there any similar secondary value to going to Enceledus if the evidence for life there turns out negative?

Mark August 6, 2012 at 22:45

It was awesome to watch Curiosity land via the java App on eyes.nasa.gov. Amazing how the whole thing appeared to go off without a hitch.

Got me to thinking, why reinvent the wheel every time? If Curiosity checks out on Mars for say 90 days or so and seems to work OK, why not use the same mechanics and electronics, same power supply, and just refit it with Enceladus-tailored instruments. Equip the robotic arm with the ability to grasp an external drill. Put life-detection astrobio experiments inside the body of the craft instead of geological experiments. Then send it on to the outer solar system and repeat what happened at Mars last night. This instead of designing a new spacecraft from the ground up. We ought to be asking ourselves what other planets can we explore with a rover exactly like Curiosity but with a different science instrument payload? How much cheaper could they be if most of the spacecraft engineering were already done and they just needed to design new onboard experiments and possibly tweak the landing equipment a bit?

spaceman August 7, 2012 at 2:17

Congrajulations to the scientists and engineers who made this truly amazing feat a reality! And, yes, the lack of a successful landing would have immediately unleashed the ever present anti-space critics– those who contend that spending money on space science and exploration is a terrible waste of resources. So, there were no ‘I told you so’ moments here and hopefully there won’t be any as the exciting experiment progresses on the red planet.

Adam Crowl August 7, 2012 at 5:34

The putative near-surface lakes just under Europa’s skin would make an “Ice Rover”, able to melt a tunnel of its own, an enticing mission concept. Enceladus would then be the test-bed – easier to land and lift off from – for the Main Event. Remember the possible macro-fauna of Europa!

Although there’s also the acidic ocean issue, also raised by Richard Greenberg, long-time Europan-Life advocate.

ljk August 7, 2012 at 9:36

In case you were wondering about Curiousity’s computer “brain”:

http://whyevolutionistrue.wordpress.com/2012/08/07/what-kind-of-computer-does-the-mars-rover-use/

And when MRO imaged Curiousity parachuting down to the planet Mars, they also captured the falling heat shield in the same shot:

http://blogs.discovermagazine.com/badastronomy/2012/08/06/curiosity-update-heat-shield-spotted/

When the Vikings landed on Mars in 1976, the only functioning craft in the vicinity were the two Viking orbiters. Both landers came down without any control other than parachutes and retrorockets. Mission control did not even know they made it until after the landing. By comparison Curiousity and even the MERs had a virtual support staff at Mars.

Viking 1 landed just 9 feet away from a large boulder later nicknamed Big Joe. Had the robot come down upon the rock, we would never have known about its fate for decades.

Communications were actually lost with the Viking 2 lander after it separated from its orbiter. The lander was not recovered until after its landing on the Red Planet. Viking 2 came down on a pretty even field of similar size boulders, though it was tilted about 8 degrees having landed atop one of the rocks.

Michael August 7, 2012 at 13:44

If geyser ‘Organisms’ are ejected from Enceladus they could have been flung all across the solar system by now. We might all be ancestors of Enceladinians.

FrankH August 7, 2012 at 14:52

@JohnHunt – A mission to sample the plumes may not cost billions. If it takes several samples and finds simple organics (but no life) in any of the samples, it would still be important:
The lakes/oceans/wet ice cracks under Enceladus may be transient, short lived, recent (or a combination of) and life hasn’t had a chance to develop.

The theory that life will develop given sufficient water, organics and energy would have to be expanded or modified. Maybe other environmental factors are involved. This would be instructive for the truly expensive mission to drill into the ice of Europa (to whatever depth – a few meters into an ice cave or several km). Maybe a surface mission to sample a young ice upwelling would be a better step.

ljk August 8, 2012 at 9:03

Curiousity and the various parts that got it to Mars, scattered across the alien landscape as seen by MRO:

http://www.universetoday.com/96666/rover-sky-crane-heat-shield-and-parachute-located-from-orbit-by-hirise/

When we go to explore places like Enceladus and Europa, I presume and hope we will be able to do so with less terrestrial debris if possible. I also presume these items were thoroughly cleansed of Earthly microbes, but you cannot be too careful when it comes to exobiological exploration.

Astronist August 9, 2012 at 18:26

Worth remembering, perhaps, that when we get around to launching the first robotic interstellar probes in a century or so, they’ll need to carry a number of probes of the sort we’re discussing here to explore the target planetary system. Clearly by then they’ll need to be completely autonomous and utterly reliable.

Eniac August 10, 2012 at 0:05

Astronist is right, and I think that successes such as Voyager and the Mars rovers are going quite far in proving that we are up to the challenge. We have gone a non-negligible distance in the right direction. Let’s keep moving!

ljk August 10, 2012 at 16:23

Apparently Percival Lowell had proof of life on Mars back in 1908!

http://philosophyofscienceportal.blogspot.com/2012/08/martian-life-proven.html

Rob Henry August 11, 2012 at 21:34

ljk, perhaps Lowell did find powerful evidence of a thriving Martian ecosphere. The seasonal wave of darkening on Mars has never been properly explained. The last attempts to do so were in the seventies where wind blown dust was shown to have much promise in this regard. Unfortunately peer reviewed publication on such matters seemed to have stopped at the stage were the fit to data was so bad that the colour change often seemed to be occurring in the opposite direction to that expected if dust really was the cause.

We will only really find out if reopen that file and use better modern data.

Klaus February 17, 2013 at 10:25

On the subject of Enceladus, if the water geysers have been spouting water into space for millions, if not billions of years, surely the reservoir of liquid water held by this 300 mile wide satellite would have long ago been depleted? I’d love an answer to this question…Anyone?

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