Europa Explorer (9:56 AM): Absolutely. Their relative positions keep repeating
and enhancing their gravitational effects on one another, in effect making their
orbits eccentric.
This is ultimately why tides caused by Jupiter change periodically. The
resonance is the key to everything that is interesting about the Galilean
satellites, including the volcanoes on Io and the ocean on Europa.
As for how long? Most likely there has been a lot of tidal heat for billions of
years; at time more heat, at other times less.
Certainly plenty of heat for a long enough time for life to develop. That's a
necessary condition -- but by itself not sufficient for life, of course.
Dave on Earth (10:00 AM): Thanks!
There's
been some recent news related to Europa; I offer an entry Discovery Space
blogger Irene Klotz posted posted.
The words "new idea"
stuck out to me.
Having read some of "Unmasking Europa," it seems
like tides on Europa aren't a new idea. So what is new here?
Europa Explorer (10:01 AM): Robert Tyler's work suggests that a lot of
heat is generated by friction in the ocean.
It's comparable to what my students and I estimated might be generated in the
rock below, so an extra source of heat means that the ice crust over the ocean
is even thinner than we had expected.
Dave on Earth (10:02 AM): How thick might the ice on the surface be, then?
Europa Explorer (10:05 AM): The conventional view: Europa's ice is greater than 20
kilometers thick.
However, our research indicates
that the character of the ice -- and the nature of the processes that continually
modify the surface -- involve direct connections between the surface and the
ocean below.
The new estimate of heating in the
ocean supports this idea that the ice is thin enough to be permeable at around 10 km (on average).
Our view
has been considered controversial, but evidence continues to build that it is
correct.
Dave on Earth (10:06 AM): Permeable by what --a spacecraft?
Europa Explorer (10:08 AM): By permeability I mean geological processes that
rapidly, continually modify the moon's surface.
The tidal stress causes
cracking and all sorts of related tectonic displacements, and the heat causes
disruptions that probably melt through to the surface.
There
are hardly any craters, because the surface is so young.
Dave on Earth (10:10 AM): Reminds me of Earth's plate tectonics... on steroids. Big sections of the crust recycled at one end while regenerated at the other.
Europa Explorer (10:10 AM): There are many similarities. There are spreading
zones, like the long rift in the Atlantic sea floor, and converging sites
like the Himalayas.
As I note in my book, however, the "Himalayas of Europa" are only a
couple of hundred feet high. Lots of images of all these things are in the book, of course.
Dave on Earth (10:11 AM): And to return to the controversy you mentioned earlier:
How much would
you say the "popular" view (thick ice) has eroded since
you and your team have stood up for the thin-ice model with tides?
Europa Explorer (10:12 AM): Well, one thing I find gratifying is that NASA and the Jet Propulsion Laboratory's future Europa mission is framed in terms of exploring the thickness of the ice -- which is a big advance from simply assuming that the ice
is very thick.
My team and others have been able to produce hard-to-ignore evidence
that points to permeable ice!
To test the popular view, I just asked my family and they
all think the ice is permeable. Which goes to say that I have no idea what the popular view
is or even the consensus among scientists.
But I do have a sense that it is
swinging our way, especially based on the comments from people who have
read the book.
Dave on Earth (10:14 AM): Thanks. Before I let you get back to that family of yours, a couple more questions.
The Cassini spacecraft has been milling around Saturn for a
few years now, and there are some pretty exciting moons out there -- in
particular, Enceladus.
As someone
who's studied Europa extensively, what do you think about this icy moon? Any prospects for life there or on Europa?
(One thing that strikes me, by the way: Enceladus is 240
times smaller than Europa by volume, and Europa is about 68 times smaller than the Earth.)
Europa Explorer (10:17 AM): Enceladus is really wonderful. It's a small icy moon
with this fantastic, visible, on-going activity.
Right now, its big mystery
is where the heat behind that activity comes from. There's a
resonance (with moon Dione) but most estimates of tidal heating are too
small to explain much.
So, we really don't know what's going on inside.
We know a lot about Europa, and it all adds up to some
very good prospects for life. One key is the permeability we talked about -- it's necessary to get critical substances into the ocean. Life would be
very limited at best if there weren't breaches in the crust.
If there are such direct
connections, then extensive -- even advanced -- life becomes quite plausible.
As
for Enceladus? Everyone seems to want it to be the new Europa, but we'll have to
wait and see.
Dave on Earth (10:20 AM): My last question, though it might be a dead-giveaway: What's your favorite place in the solar system, and
why?
Europa Explorer (10:22 AM): Besides my favorite places on Earth? I love Europa!
The water just below the surface is only a bit colder than
NYC was this morning, so wear a wet suit and bring a light!
If there is a
biosphere on Europa, it probably extends up to within inches of the surface. And that's exciting.
Dave on Earth (10:23 AM): Thanks for chatting Richard!
Europa Explorer (11:03 AM): I'm always glad to chat about my favorite moon.
Article posted January 8, 2008.
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