I read the Canup and Asphaug paper (yes, Robin is a woman), as well as the Melosh News and Views article. In short, for computer modelling Canup and Asphaug used an SPH (smooth particle hydrodynamics) code, which to first order can track both shock physics and gravity. Conventional hydrocodes, used by early impact modellers, were limited to modelling only the early phases of the impact because the technique uses "central gravity" and not "self-gravity." Canup and Asphaug's model benefits from increased computer processing capability that was not available to the early modellers. The import of of Canup and Asphaug's work is that they show a plausible model for the impact to have occured *after* the Earth was fully formed (ca. 50-70 million years after the first meteorites), not during the protoplanetary stages, which was the conventional wisdom. Melosh does hint, however, that the issue is far from settled and to expect more work to published shortly.

One may also wish to read:

http://www.space.com/searchforlife/new_jupplanet_010815.html
http://www.swri.org/9what/releases/canupmoon.htm

P.S. To answer Justin about online access to Nature: I actually check the Nature website in advance of the email TOC notification, which I received about the same time as you apparently did. I have online access to almost all of the journals in my field, so if anyone wishes a copy of the Canup and Asphaug paper and/or the Melosh article, let me know. On a limited basis, I could email it to you, or if the facility exists, perhaps place it online here at habitablezone.com for a LIMITED time. I normally wouldn't offer this, as the journals have fairly strict policies in this regard, but for this discussion group most people seem fairly reasonable, interested, and more importantly, DISCREET ;-)

P.P.S. I mounted a goodwill foray in MSNBC BBS yesterday on an issue that is important to me and my current research: Water on Mars. I don't if I got through to some of the posters or not, but some did seem to come around to logic. Robert's posts below in the "Some 'Hoagland and Bara strike out' followups" thread were persuasive - up to a certain point :-)

Alex R. Blackwell
University of Hawaii