Because I actually bought the book (what was I thinking ), I wrote a review for my blog last year:

http://volcanopele.blogspot.com/2005/06/re...search-for.html

Your hatred for Europa is bit disturbing.

Or is it the possibility for life on Europa that you dislike!?









Werid.

Jason:

Glad to hear you're blogging again!

And Titan is *much* nicer than Europa!

Bob Shaw

Bah. Jason just prefers orange stuff...

I imagine he's spot-on about Greenberg, though -- I have yet to see a convincing explanation from him about how Europa's ice crust could be so thin right now without any visible changes or geysers being seen by Voyager and Galileo. I think the cyclical tidal heating theory of Europan history is probably right: the thickness of its crust varies over cycles of several tens of millions of years as its degree of tidal heating changes. It last became thin enough for all the surface features from its previous cycle to be totally erased roughly 30-60 million years ago, and since then it's been gradually chilling and re-thickening -- more in some regions than others, which has allowed Pappalardo-type solid-ice diapirs to form up to this time only in the thicker areas of its crust, where they have erased the Greenberg-style cracks and ridges formed during its thinner period.

I don't think anyone wants to hear my astrobiology rant again... I just prefer places that don't have the taint of astrobiology.

As for Europa, it is a world trying to be cool like Io but failed miserably, and gave up.

And Bruce, I've warmed up to Enceladus and it isn't orange. Neither is Triton for the most part.

I'm not sure I can explain why, but that is one of the funnier things I've read lately. I do get a little tired of the implication that 'if we could conclusively prove that there were no life in the solar system outside of Earth, anywhere, ever, then that proves the system is boring and we should just go home and forget about exploring it.' I think it would be fun to find extraterrestrial life, but I don't think that that's the whole ball game, or even most of the ball game. But then my space-related obsession is planetary geography, not exobiology.



I thought it was a world trying to be hot, like Io, but gave up?

My point is that astrobiology and the search for life beyond earth is not a goal. A goal (to me) is something that if you put enough effort toward achieving it, it can be achieved. Building a colony on Mars is a goal because if we put enough money and man-power into it, we can put a person on Mars and build a colony. Yes, it would be a lot of money, but it something that can be achieved. Finding life on another world is not a goal. If there is no life on Mars or in Europa's ocean, then no matter how much money you pour into achieving that goal, you can never succeed, no matter how hard you try. My other beef is that it is used to sell missions to congress and the public far more often than it should.

So I essentially agree with you, while finding life on another world would be great, we, as a community, should be careful how much we advertise astrobiology, lest it become the noose we hang our selves with.

I don't want to hijack this thread any more than I already have so I'll stop there.

true

We still have to "discover" what the rocky surface of Europa looks like. It might be Io, but smoking into an ocean instead of spraying into a vacuum.

The map of Europa's "other" surface will be interesting to see, sometime in the 23rd century when we have it.

Interesting turn of a phrase. I didn't know searching for life beyond Earth or even
just thinking about it was an abomination to science. Just like the astronomers of
the early Twentieth Century who focused on distant galaxies for "respectability".

When extraterrestrial life is found, the bandwagon will be practically crushed by
all the scientists who won't hesitate to jump on it. Just like with exoplanets,
which were ignored and sometimes outright put down as rarities by many
mainstream astronomers until they were proven in 1995.

My problems with astrobiology have nothing to do with my opinions on whether there is or is not life on other worlds in this solar system. In fact I think it is quite possible on Europa, a slightly more distant possibility on Mars, and maybe a few other places. I just have a problem with using astrobiology as a rationale for missions that will not actually search for life. I have a problem with using astrobiology to have some future missions jump to the front of the line while missions to non-astrobiologically interesting worlds, but are important for other reasons, are subjugated to the back.

All I am saying is that we shouldn't put all our eggs in the astrobiology basket. Okay, I have really steered this thread in a wrong direction. If someone wants to start a thread in Policy and Strategy, I'll join in.

John that's a rather pessimistic view of our future in planetary exploration. Certainly we'll have a spacecraft that can penetrate the ice on Europa this century.
Are you saying this because of the pressures at the bottom of this deep ocean would be immense? How much would you estimate the pressure would be given the depth of this ocean but Europa's weaker gravity?

- Bob Clark

I actually agree with you in certain cases here. As much as I want us
to find extraterrestrial life, I also think the worlds of our Sol system
certainly justify exploration and study in and of themselves, whether
they have life or none. I would not want any place left untouched
just because someone thinks it may not have organisms.

Case in point: The Viking mission. They were actually called failures
by some because the landers did not find any conclusive evidence of
Martian life. The whole point was that they went there to see if the
planet had life, not to confirm what some thought they already knew.

Both landers and orbiters made it to the Red Planet intact and returned
information and images that has only been surpassed in the last few
years. Hardly a failure just because little bugs didn't dance around in
the biology equipment saying Here We Are! And thanks in large part
to the Vikings, we have a much better idea of how and where to really
look for Martian life.

I know I am preaching to most of the choir here, but I felt it had to
be said.

JOVIAN DREAMS

- New Recipe For Oxygen On Icy Moons

http://www.spacedaily.com/reports/New_Reci..._Icy_Moons.html

Richland WA (SPX) Mar 27, 2006 - Researchers at Pacific Northwest National
Laboratory said they have uncovered the most detailed picture to date of how
oxygen could be manufactured on water-rich but frigid moons in the outer solar
system.

Outer irregular satellites of the planets and their relationship with
asteroids, comets and Kuiper Belt objects

Authors: Scott S. Sheppard (Carnegie Institution of Washington)

http://arXiv.org/abs/astro-ph/0605041

What a belated reply on my part! I lost track of this thread, obviously.

Anyway, with the water+ice depth being 100 km, Europa's seafloor isn't going to be mapped from orbiting spacecraft to any but the crudest degree (like the identification of mascons).

Supposing a craft did penetrate the ice and ocean, the chore of mapping more than a tidbit of the surface would be gargantuan. And returning results to the surface (and on to Earth) yet more difficult. I imagine a straight-shot descent from a hole to the seafloor could be done this century (although I can't prove it... and note that "century" doesn't look so long when you see that the delay between Voyager 2 and the *second* subsequent Europa mission from then (with Galileo being the next subsequent) is going to be perhaps 40 years.

So, when (if) a submarine does make the trip, an obvious, yet still dazzlingly difficult, mission scope would be to descend straight down, communicate via something left in the melt-path all the way through the crust, and to have its lateral mobility (easy in water) made irrelevant by the need to keep the craft near the antenna. I suppose it could wander a circle 10 km in radius or so, but that's still a small pinpoint of Europa's area. And -- this is painful, light would be nonexistant, so it's not like it could "fly" over the ocean floor and map away from an altitude of several km -- it would have to get very close to the floor and map with sonar (semi useful) or VERY close and map a room-sized area at a time with a flood lamp.

Now imagine how many submarines it would take to cut lots of razor-thin swaths around Europa, recording their flood-lamp-lit swaths, and beaming the results back to Earth (but through the ice: apparently impossible).

At this point, several uber-expensive solutions come to mind (a massive network of communication antennas in the ice?)... c'mon, this isn't going to happen. It almost seems like it would be easier to develop a flyby craft for exploring other stars than it would be to produce a global map of Europa's seafloor of anything like the resolution and coverage of the maps we have of, geez, even Pluto.