LPSC: Outer Planet Satellites, Not Titan, Not Enceladus

Clearly, I should attend all the sessions in the amphitheatre regardless of their topic. It has better chairs, better audio/mic control, a better (tiered) layout and tables – which make my computer so much easier to use than when it’s sitting on my lap.

So I attended this session, and as with all the sessions I will go to, most of the science was way over my head. But, this is what I learned from the talk I understood best – though I’ll supplement it with background information from Google, as soon as I get the mobile broadband internet dongle from Pamela.

Unresolved Characteristics of Europa’s Crater Population – Bierhaus E.B., Zahnle K. Chapman C.R.

Cratering research has answered a lot of questions. How many large craters (diameter >30km) does Europa have? 6. How young is Europa’s surface? Really, really young – we’re talking less than 2% the age of the solar system.

There are two impactor models for what creates craters. The first model says that comets from the Kuiper Belt are the dominant impactors in the Jovian system. The second says that asteroids from the asteroid belt are the dominant impactors.

In plotting characteristics of craters on Europa, they expected to see a crater size-frequency distribution of craters consistent with that of the inner solar system, for example the Moon. Using data sets from two independent researchers, they found that no amount of correction for impact depth, velocity, etc. could match them to the same plots of lunar craters. This means that asteroids are not the dominant impactors at least in this region.

When observing hemispheric differences, it was expected that heliospheric impactors create a higher crater density on the leading side. This was found to be true – there are 31 craters with diameters greater than 2km on the leading side, versus 12 on the trailing side. That’s almost three times as many.

Additionally, they expected to see a dominant sesquinary effect on the leading hemisphere, and none on the trailing hemisphere. Instead, what they observed were possible sesquinaries from Io (using dark rays as marker), but they were at the resolution limit so to confirm these findings they need more higher-resolution data. (Note: sesquinaries they are talking about sesquinary craters which are created by impact ejecta from Io that went into orbit about Jupiter. Sesquinary craters’ character is between primary craters and standard secondary craters).

Finally, they learned that the chaos regions on Europa are the stratigraphically youngest terrains. It was expected then, that they would have the lowest crater density, but this is not the case. In fact, they generally have a higher crater density (secondaries cannot account for the difference they found).

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