Comments on: Is the current plan for seeking evidence of life on Europa on thin ice?

By: Sigmund

Sigmund — Fri, 08 Apr 2011 15:10:38 +0000

Europa is not the only non-Earth body that is suspected of having liquid water present. Enceladus, one of Saturn’s moons is also believed to have large bodies of water close to its icy surface and, in contrast to Europa, that water may be accessible without drilling – or even landing on the moon. Enceladus regularly releases jets of water vapor from these liquid water bodies under its surface. These jets travel through space and end up in Saturn’s rings. Would it not be more ethical (and scientifically achievable) to try to collect and analyze some of this water from the jets of Enceladus before we try for the difficult to reach waters of Europa?

By: JesseS

JesseS — Thu, 07 Apr 2011 19:27:27 +0000

The comments here seem to focus on hitchhiking earth based organisms as ‘contamination’ but when I read the article my first thoughts were ‘pollution’. Aside from the new hole in the ice letting significantly more radiation through there’s all the chemicals the lander and drill will bring with them.

Not a Europa-wide problem but still an ethical question.

By: Mu

Mu — Thu, 07 Apr 2011 16:11:26 +0000

While a nice philosophic argument, the idea that a single probe will somehow change Europe’s ecosystem on a planetary scale is ridiculous. What Earth-bound organism would survive long enough in the environment described (100K, oxidizing, high radiation)to outcompete any local species adapted to the environment? And the likelihood that the lander will land on the head of the leader is negligible on simple geometry ground alone.
You might argue that impacters or detonation charges to measure ice thickness are unethical before we’ve determined the sterility of the surface, but that doesn’t make the lander itself “forbidden”.
So you might back off if you find any large black monolith orbiting.

By: Richard Greenberg

Richard Greenberg — Tue, 05 Apr 2011 16:10:56 +0000

Interesting discussion! Let me try to clarify a few points. First, Europa does not have much of an atmosphere. Radiation produces oxidants (oxygen and hydrogen peroxide), which get mixed into the water ice. I have calculated that a lot of the oxidants may get into the ocean and supply a complex ecosystem. Second, the issue of “thick vs. thin” is better described as permeable vs. impermeable. I have long been a vocal advocate for the permeable ice model (with ice thinner than about 10 km), which enhances the prospects for life and also makes it more vulnerable to contamination. Finally, the likely direct linkages from the ocean to the surface (through cracks, melt-through, and impacts) mean that we might be able to sample life (or its remains) within cm of the surface, rather than waiting to drill down to the ocean. This concept has important implications for exploration strategy. For more, read my book, “Unmasking Europa, the Search for Life on Jupiter’s Ocean Moon”.

By: Alan

Alan — Tue, 05 Apr 2011 15:38:17 +0000

Although I’d love to see what’s below the ice I think the best I can hope for in my lifetime will be to find out what that reddish scum on the surface is. We expect impurities to sink, so it’s mere existance is intriging.
I also think the contamination thing is a bit over-rated, the locals will be much better adapted to the Europan environment and are likely to simply eat any Earthly hitch-hikers that somehow manage to survive the dehydration, starvation, and radiation of the journey.

By: Greg Laden

Greg Laden — Tue, 05 Apr 2011 13:59:51 +0000

Patrick: Good question.

By: Greg Laden

Greg Laden — Tue, 05 Apr 2011 13:55:18 +0000

The grizzlies TT encountered were well fed – that makes a difference because their natural food sources were satisfying them and they did not need to seek new food sources like human garbage.

At Europa’s air pressure in primarily oxygen?

Regarding ice thickiness: The life is not on the surface. (If it was, I would think there’d be a signature of that.) The standard model says the is is 20 km thick. The whole point of this discussion, though, is that Greenberg is arguing that the is is not that thick (though he does not calculate an actual value) and that the surface features of Europa indicate frequent communication between the “isolated” ocean and the surface. (The standard model interprets the surface features differently.)

By: Patrick

Patrick — Tue, 05 Apr 2011 08:48:42 +0000

This is cool stuff. Question from a non-scientist:

Doesn’t the ice on the surface of Europa originally come from deep down? If so, then even if life on Europa is deep down, couldn’t the ice on the surface contain frozen bacteria-equivalents in it? When liquid water erupted onto the surface the bacteria-equivalents would have been carried upward with it, and frozen with it too.

It seems that examining the ice on the surface skirts the potential ethical issues. The bacteria-equivalents on the surface are fair game. Messing with them cannot hurt the ecosystems from which they originate.

If we found dead (or at least dormant) bacteria-equivalents in the surface ice, then we’d have grounds for return trips to drill deeper and to look for more complex critters.

By: daedalus2u

daedalus2u — Tue, 05 Apr 2011 00:26:45 +0000

A few tens of km. I would not call that “thin”.

It has a surface gravity of 0.134 g, and a surface temperature of ~100 K.

Because ice has a lower density than water, there is always going to be a layer of ice at the surface unless there is a gigantic heat flux. The maximum density of liquid water is ~4 C, well above the freezing point, so there can be a stable film of liquid water adjacent to the ice. Ice is going to sublime unless it is very cold, -100 C or so. The heat of vaporization is ~7x the heat of vaporization, so the sublimation of one inch of ice removes enough heat to freeze 7 inches of ice. Any liquid surface will be very short lived. Freezing from the top down is going to cause impurities to migrate down.

There is probably a very large production of H2O2 in the ice from the radiation. That is heavier than ice, and H2O-H2O2 form a eutectic at ~ -55 C. In a temperature gradient, H2O2 will tend to migrate to the hotter region (that would be down).

The high radiation field will generate lots of oxidizing species, O2, O3, O2-, hydroxyl radical, H2O2. There might not be much organic on the surface, it might be all oxidized away.

By: Greg Laden

Greg Laden — Mon, 04 Apr 2011 21:38:53 +0000

You’all have to read the book.