Odds & Sods News, Australia Day 2010

Callisto & Ganymede, twin moons of Jupiter, yet so unalike. Why? Dr Amy Barr and Dr Robin Canup of the Southwest Research Institute (SwRI) believe the two moons diverged in their evolutionary paths about 3.8 million years ago, during the Late Heavy Bombardment. Here’s a scan of the news-pages…

Comets left their mark on Jovian moons …a good summary from Aunty.

SwRI researchers offer explanation for the differences between Ganymede and Callisto …from EurekaAlert, with original graphics from SwRI. Quick, condensed summary of this…

SwRI News release …with the pretty graphics on another page. Of course the real meat is in the paper…

Letter abstract

Nature Geoscience
Published online: 24 January 2010 | doi:10.1038/ngeo746

Origin of the Ganymede–Callisto dichotomy by impacts during the late heavy bombardment

Amy C. Barr1 & Robin M. Canup1

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Jupiter’s large moons Ganymede1, 2 and Callisto2, 3 are similar in size and composition. However, Ganymede has a tectonically evolved surface1 and a large rock/metal core2, whereas Callisto’s surface shows no sign of resurfacing3 and the separation of ice and rock in its interior seems incomplete2. These differences have been difficult to explain4, 5, 6, 7, 8, 9, 10, 11. Here we present geophysical models of impact-induced core formation to show that the Ganymede–Callisto dichotomy can be explained through differences in the energy received during a brief period of frequent planetary impacts about 700?million years after planet formation, termed the late heavy bombardment12, 13, 14, 15. We propose that during the late heavy bombardment, impacts would have been sufficiently energetic on Ganymede to lead to a complete separation of rock and ice, but not on Callisto. In our model, a dichotomy between Ganymede and Callisto that is consistent with observations is created if the planetesimal disk that supplied the cometary impactors during the late heavy bombardment is about 5–30 times the mass of the Earth. Our findings are consistent with estimates of a disk about 20 times the mass of the Earth as used in dynamical models that recreate the present-day architecture of the outer solar system and the lunar late heavy bombardment15, 16.
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1. Department of Space Studies; Center for Lunar Origin and Evolution, Southwest Research Institute, 1050 Walnut St, Suite 300, Boulder, Colorado 80302, USA

Correspondence to: Amy C. Barr1 e-mail: amy@boulder.swri.edu

…all behind Nature’s Pay-per-View isn’t it? Ah well, the news summaries aren’t bad.

Amy & Robin’s homepages are…

Dr. Amy Barr

Dr. Robin Canup

…basically the model is that the higher energy and more frequent LHB impacts that Ganymede would’ve taken is why Ganymede is more differentiated than Callisto. Did that cause Ganymede to totally differentiate and produce the intrinsic magnetic field it has today? A future research question, I’d hazard.

Palaeo Cuteness News. Researchers have made a flying model of Microraptor to better understand its flight potential.
Microraptor model
…reported at Physorg News. The researchers are based in China and Kansas U, led by chief BANDit Larry Martin, and given a voice on NOVA…

KSU Link and Summary of NOVA episode

…BANDit? you say. The Birds-Are-Not-Dinosaurs (+its) are a small, but loud bunch of palaeo-ornithologists who think the bird-like dinosaurs are really birds. A long, long academic debate has swirled around a few key personalities, like Alan Feduccia and Larry Martin, about the dino-ness of birds and the birdy-ness of dinos. For an opposing view there’s the Dinosaur Mailing List bunch of Dino Docs who think the BANDits are splitting hairs.

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