Nasa Picks "juno" As Next New Frontiers Mission Options

[Guest_BruceMoomaw_*]

http://www.nasa.gov/home/hqnews/2005/jun/H...rontiers_2.html

Yeah, I know it ain't Saturn, but we don't seem to have any proper slot for Jovian news -- including yesterday's totally unexpected announcement that Amalthea's density is so low as to suggest that it's a highly porous ice object; maybe a captured Kuiper Belt Object reduced to rubble by infalling meteoroids. As Jason Perry says, this might explain those previously mysterious light-colored patches on Amalthea -- they may be its underlying ice, exposed by impacts that punched through the layer of sulfur spray-painted onto it by Io.

Scott Bolton has been pretty talkative to me already about the design of Juno. It certainly won't be as good in the PR department as Galileo or Cassini, but it DOES carry a camera -- as much for PR as for Jovian cloud science, according to Bolton. And since the latitude of periapsis of its highly elliptical orbit will change radically during the primary mission, I wonder if they might be able to set up at least one close photographic flyby of Io and/or Amalthea? (I believe, by the way, that this selection is a bit ahead of schedule -- and it certainly indicates that NASA's science program under Griffin won't be a complete slave to Bush's Moon-Mars initiative.)

[Guest_BruceMoomaw_*]

[quote=tedstryk,Jun 4 2005, 12:27 PM]
I don't think getting to Europa is the biggest hurdle to overcome. I think one of most difficult challenges will be to get there without contaminating the moon with terrestrial organisms. I don't think that it is possible to completely sterilize a spacecraft and allow it to impact the moon. Enough fuel would have to be brought to allow it to leave the orbit of Europa when the mission is over and de-orbit into Jupiter the same way that Galileo did.

My apologies for getting OT.

[/quote]

I don't think the crashing of Galileo to "protect" Europa was worth it. I am extremely skeptical of the idea that the place might have life, and I think NASA's hyping of the idea distracts from the truly interesting aspects of Europa and the Jovian system.

[/quote]

That possibility ain't "hyping": the science community itself has taken the idea extremely seriously for a couple of decades. Europa, after all, has lots of liquid water -- something which Mars has in tremendously more limited amounts.

And there's another factor, which I haven't seen mentioned in print although the scientists I've mentioned it to seem to agree: even if we find proof of present or fossil Martian life, we may have hell's own time proving that it didn't just descend from ancient Earth germs blasted to Mars via meteorites from Earth during the Solar System's earliest days (or, for that matter, vice versa). On the other hand, if we find Europan life, the odds will be overwhelming that it's native -- which means, since two worlds in a single Solar System will have separately developed life, that we'll know life must be common in the Universe as a whole, rather than being just an extremely rare chance development that happened to make one of its rare appearances in our own Solar System. For this reason, I have for years regarded the search for Europan life as MORE important scientifically than the search for Martian life.

As for the danger of contaminating Europa: the science community takes that very seriously, too. See the 2000 report by the National Academy of Sciences ( http://www7.nationalacademies.org/ssb/europamenu.html ) -- which points out that, since Europa has a unified liquid-water ocean, terrestrial microbes could spread all over that world far more quickly than terrestrial microbes could if they got loose on Mars. Proper sterilization of Europa spacecraft is extremely important, even given the fact that Jupiter's savage radiation environment will give us a lot of help in that regard.

That being said, providing Europa Orbiter with enough fuel to break back out of Europa orbit is simply impractical -- it will be hard to carry enough even to put it into Europa orbit in the first place. This is a difficult mission. We will, instead, just have to make sure it's properly sterilized (as we'll have to do in any case with all Europa landers).

[garybeau]

That being said, providing Europa Orbiter with enough fuel to break back out of Europa orbit is simply impractical -- it will be hard to carry enough even to put it into Europa orbit in the first place.  This is a difficult mission.  We will, instead, just have to make sure it's properly sterilized (as we'll have to do in any case with all Europa landers).

Thanks for all the info you provided. I hadn't heard about a Nasa/ESA cooperative effort for a Europa orbiter That's great news I hope the plans don't get stalled.

If leaving a Eurpan orbit is not practical, I guess the next best thing to do is leave it in orbit and let the intense radiation sterilize the craft. Once in orbit, how long would a spacecraft remain in an orbit around Europa? With little or no atmosphere, I would think a spacecraft would remain there for quite a few years. Are there other factors that would cause the orbit to decay such as tidal forces or resonant forces from the other moons?

I read the link that you provided from The National Academies on Preventing the Forward Contamination of Europa. I'm not sure if I share their optimism on the ability to satisfactorily sterilize a spacecraft. Even by their admission, a spacecraft will never be 100% free of biological organisms or spores, but only reduced to an acceptable level. I remember the surprise and disbelief when a piece of the Surveyor lander was brought back and Streptococcus bacteria were found to be still alive inside the camera. They were exposed to the vacuum of space, zero moisture, extreme temperature swings (night and day on the moon are 14 days long) and they were there for almost three years.
The biggest fear would be if the spacecraft missed it's orbital insertion target (i.e. Mars Climate Orbiter) and impacted directly into the moon. Without an atmosphere to slow it down, it would impact hard and pieces would most likely be buried under a protective layer of ice. I am still 100% for a Europa orbiter, but I think that we have an obligation to keep the risk of contamination as close to zero as we can. At least until we can confirm if any life currently resides there.

[JRehling]

Three miscellaneous comments for this thread, from the concrete to the fanciful:

1) Orbits around Europa are very unstable due to the presence of other gravitational sources in the vicinity (the same is true of the Moon, but of course, Jupiter is much pushier than Earth gravitationally). So whenever the craft dies, it will not be long in impacting Europa's surface. Months, not years.

2) It is not believed that a europan ocean would have enough energy to support advanced life. That is surely somewhat speculative, but take that for what it is. The suspicions lean towards bacteria or nothing.

3) If (2) were wrong, the presence of, eg, fish would not point to a common origin. Earthly biota have reinvented key phylogeny properties many times. For example, "tree"ness has evolved very many times, on separate family branches. I think we can be dead certain (NPI) that fish would not make the ride from/to Earth to/from Europa on meteorites, in any form whatsoever.
If we do find life elsewhere, macroscopic resemblance would be a much less convincing evidence of common origin than molecular resemblance. Chirality to start with, use of the DNA codons vs. RNA codons in equivalent roles next. Someone with biology training past ninth grade could comment on others.