Unexpected connections: LPSC 2015

It’s a bit overwhelming really. So much new stuff to take on board. And now there’s less than a week to go. Nerves are getting frayed and a bit of panic is starting to set in. Well, it’s only natural. Next week sees the start of the 46th Lunar and Planetary Science Conference (LPSC) in Houston, Texas. And with special sessions on the latest results from the Rosetta and Dawn missions it promises to be a vintage meeting. Fascinating, stimulating, even exciting at times, but just a bit daunting too. So to start making sense of all the new results being presented out research group here at the Open University got together earlier this week to discuss some of the items on offer.

But how do you spot what is going to be new and exciting ahead of the formal conference presentation. Well, it’s not easy. What we did was to invite each member of the group to trawl through the online conference program and select a couple of abstracts that they thought stood out from the pack. The process was co-ordinated By Jess Barnes, who collected in everyone’s suggestions and then circulated copies of the all the choices to the group as a whole.

So at 9.30 am coffee in hand I headed to the ground floor Robert Hooke building seminar room for the LPSC special. Things got off to a bad start. No cake! An essential ingredient of our Tuesday morning meetings, it had just failed to turn up and no one knew why. OK, let’s move on.

Overnight Jess had pulled together an impressive PowerPoint presentation with a summary slide listing the key aspects of each abstract. The person who had chosen the abstract then briefly explained their reasons for selecting it and led a short discussion looking at the merits of the results to be presented at the forthcoming conference.

The members of a research group inevitably have diverse scientific backgrounds and interests. So one of the nice aspects of our LPSC discussions was that we were able to identify unexpected connections between what at first appeared to be a pretty diverse bunch of presentations.

So, first up we looked at new data on the silicon isotopic composition of an ancient group of meteorites known as the angrites. This might sound like a very specialist study and in a sense it is. But because the Earth and angrites have such similar silicon isotopic compositions the study has potentially important implications for the interpretation of the processes involved in the formation of our planet. The Earth and angrites formed under very different conditions, so the author’s of the study suggest that their similar silicon isotopic compositions must reflect that of their precursor materials and not later planetary differentiation processes. So, in the case of the Earth its heavy silicon isotope composition is normally related to core formation. If Nicolas Dauphas and his co-author’s are correct their data suggests that none of the known chondrite groups could have been parental to the Earth. It’s not an interpretation that will please everyone.

We stayed with angrites for our second abstract, which discussed new analyses relevant to the composition of the water that was incorporated into these very ancient rocks. The deuterium/hydrogen ratio (D/H) of angrites is higher than that of the Earth and similar to that measured in some comets. The authors, led by Adam Sarafian, examine possibility that comets were the source of water on the angrites, but point out that this is by no means the only interpretation of their data. They suggest that volcanic degassing could also account for the angrite’s elevated D/H ratio. Science is rarely cut and dry! (oops, sorry about that)

Next we headed to Mars, or more precisely to the study of a meteorite that came from Mars, the now legendary NWA 7034 a.k.a. Black Beauty. Santos and co-workers have been looking at a curious set of fragments in this breccias known as iron-titanium-phosphate clasts and draw analogues to similar rocks found on Earth. We also looked at an abstract by Leroux and others that presented the results of a detailed mineralogical study of fine-grained material along the boundaries of clasts in the paired  Black Beauty meteorite NWA 7533. It seems that this material is either martian or less glamorously may have formed during desert weathering.

The formation of the Earth-Moon system as a result of a giant impact remains a controversial topic in planetary science and there is a significant number of talks and posters at LPSC that examine different aspects of this problem. We looked at three of these. A study again by Dauphas and co-workers looked at the isotopic composition of calcium in lunar samples and finds it to be identical within error to that of the Earth. The authors suggest that , due to its refractory character, calcium would not have been completely homogenized during the giant impact and therefore the identical isotopic composition of the Earth and the Moon reflects the fact that the impactor, referred to in the trade as “Theia”, and the pre-impact Earth had an essentially identical isotopic composition.  Somewhat in contrast, a study published last year in the magazine Science claimed to have found a subtle difference between the Earth and Moon with respect to oxygen isotopes. It was suggested that this difference was inherited from Theia, which some dynamic models indicate contributed a higher proportion of material to the Moon than the Earth.  However, a new study by Kohl and others has been unable to detect a significant difference between terrestrial and lunar rocks with respect to oxygen isotopes. These are extremely challenging measurements and there is no doubt that this controversy is a long way from being settled. The possibility that not all of the proto-Earth was melted during the giant impact has been looked at by Stewart and co-workers. Based on the results of computer simulations, they conclude that as impact energy is deposited unevenly during large-scale collisions some parts of the Earth mantle may have remained at least partially solid. This study has implications for the preservation of chemical and isotopic signatures formed during the earliest stages of Earth formation.

Other abstracts we discussed looked at faulting on Vesta, new chromium isotope data for various recently discovered achondritic meteorites and isotopic mapping of Mars by satellite.

So we came to the end of our meeting having only discussed a fraction of the talks and posters that will be presented at LPSC. But at least we had made a start.


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