The First Europa Lander, What can be done first, cheapest & best? Options

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I think that many people in this forum would agree that somebody's going to have to land on Europa someday before the rather elaborate schemes to penetrate the outer ice layer will ever fly, if for no other reason than to get some relevant ground truth before committing to such an elaborate, expensive, and risky mission.

EO seems to have ruled out any surface science package for that mission (though it would be nice to change their minds! ), but I think that there is a valid requirement at some point to directly assess the surface properties of Europa in an inexpensive yet creative way. Some candidate instrument payloads might be:

1. A sonar transducer/receiver set embedded within a penetrometer to determine crust density and examine the uniformity of the ice layer within the operational radius of the instrument (looking for cracks and holes, in other words).

2. A conductivity sensor again embedded inside a penetrometer to measure the native salinity of the surrounding material and possibly derive some constraints on the composition of metallic salts in the European crust (saltiness has a major effect on ice properties, in addition to the obvious need to derive the salt content of any underlying ocean).

3. A seismometer for all sorts of reasons.


How does this sound? Any critiques, additions, or subtractions? I omitted a surface imager not only because of bandwidth/extra complexity considerations but also because it seems desirable to penetrate the crust in order to minimize as much as possible reading any contaminants from Io during surface measurements. The orbiter data could be used to sense and subtract this from the penetrometer readings.

[Guest_BruceMoomaw_*]

JPL's study of useful instruments for a small Europa lander listed, in order of priority:

(1 & 2): A surface GCMS (or, better, a mass spectrometer combined with some kind of liquid chromatography) to look for organics and other interesting compounds; and a seismometer to try to sound the thickness of the total ice layer.

(3) A magnetometer to make induced-field measurements simultaneously with an orbiter to obtain data on the thickness of both the ice layer AND the underlying liquid-water layer.

(4) A surface panoramic camera.

There was, as I've noted, a knockdown debate on this subject at the November COMPLEX meeting -- including an unbelievably dreary and nitpicking debate over the usefulness of seismometers and magnetometers, culminating in the general conclusion that you'd need at least 1 or 2 weeks of data from them, which requires powering the lander with a small RTG rather than batteries.

But the trouble, again, is that the most important measurement by far would be a search for possibly biological organic compounds buried deeply enough in the ice that Jupiter's radiation won't have scrambled them unrecognizably -- and such a small lander probably can't drill the 1 or 2 meters necessary for that purpose. Any of the other measurements that a small lander could make can just as well be delayed and then put on the first dedicated larger Europa Astrobiological Lander mission to look for near-subsurface organics, at a site selected by Europa Orbiter.

The obvious possible solution to this problem would be a penetrator, and in fact at the meeting I spoke up and suggested just that. (It has other major advantages, too -- elimination of the need for a heavy final braking or shock-absorption system, shielding of the lander from Jupiter's destructive radiation by the ice itself, and better coupling of the seismometer to Europa's surface.) Unfortunately, Torrance Johnson was one step ahead of me. He said that just this possibility was examined in depth by the JIMO science definition team, and it turned out that penetrators on airless worlds have one huge Achilles heel -- there's no airflow to keep their nose pointed straight in their direction of travel when they hit the surface. So you need to add a big and complex attitude-control system to do this, or your penetrator will hit the surface slightly skewed, at which point you're screwed.

Still, Paul Lucey of the University of Hawaii is proposing "Thunderbolt" -- a Europa penetrator to look for subsurface organics (a descendant of his "Polar Night" Discovery proposal that would launch three small penetrators from a lunar orbiter to look for polar ice). The COMPLEX people actually suggested that I should get in touch with him to see if he's found a possible solution to the attitude-control problem, and while I haven't been able to contact him yet I intend to do so after New Year.

By the way, I'm telling you guys all this because every crumb of it had to be cut out of the shortened version of my upcoming article on the COMPLEX meeting for "Astronomy".