March 2017 Letter from the Director

Normally March brings warming temperatures and bountiful flowers to the campus, but this year Spring was marked with snow and sadness on the passing of our long-time colleague Sandy Keiser.  Former Director Sean Solomon hired Sandy as a Scientific Computer Programmer in 1993.  She served this role exquisitely for 24 years at DTM, always willing and happy to help those in need of her expertise. Her dedication and skill allowed her job at DTM to expand considerably over time. Most recently she was collaborating with Alan Boss and Alycia Weinberger in remote observing using the Carnegie du Pont Telescope in Chile. Besides her wide-ranging support for astronomy computing at DTM, and her own scientific pursuits, Sandy will be remembered for the quality and imagination of her contribution to lunch club and other campus social events.  Two memorable examples of her culinary creativity are the time she prepared for lunch club the whole last dinner menu served on the Titanic, and her mud pie dessert, complete with abundant gummy worms embedded. Above all else, Sandy was a kind soul, always seeing the best in the world around her.  Her life was cut unfairly short, but her unfailingly calm and positive spirit will long be remembered by her colleagues at DTM.

DTM Astronomy Group Photo, August 2000. Seated (L-R): Dan Kelson, Vera Rubin, Sandy Keiser, George Wetherill, Steve Desch. Standing (L-R): Rob Swaters, Harri Vanhala, Alan Boss, Ken Chick, Satoshi Inaba, John Graham, Paul Butler.

On a happier note, the Spring Neighborhood Lecture series started off strong with Carnegie President Matt Scott packing the Greenewalt Auditorium with his talk entitled “Jumping Genes: What They Mean for Evolution and Medicine.”  The talk highlighted the contributions of Carnegie scientists Barbara McClintock, Nina Fedoroff, and Maxine Singer in developing our understanding of the function and mechanisms of evolution of the genetic code that controls the development of complex life on Earth.  Matt engaged the audience with questions and answers throughout that talk, turning the lecture into a classroom-like learning experience for 120 of our BBR neighbors, much to their delight. The next Neighborhood Lecture will be April 27 by our own Conel Alexander who will be talking about “Rocks from Space: Be Grateful and a Little Afraid.”
March was a good month for seeing the work of DTM scientists in the news.  Kicking off the month was Jonathan Gagné’s article in the Astrophysical Journal describing the likelihood that there are a large number of brown dwarfs and giant free-floating planets in the TW Hya association waiting to be discovered.  Later in the month was the report by Erik Hauri and colleagues at Woods Hole Oceanographic Institution of careful work precisely documenting the role of even small amounts of water on the melting temperature of rock in Earth’s interior.  This topic has been a subject of study for decades, in particular by workers at the Geophysical Laboratory.   Controlling the amount of water in this type of high-pressure experiment is not easy, mostly because Earth’s atmosphere, including that in the laboratory, has enough water vapor present that even “dry” experimental charges pick up enough atmospheric water by adsorption that they obtain water concentrations not too different from the low abundances in the upper mantle.  Using both an imaginative approach to introduce known quantities of water into the experimental material, and the ability to measure water at low concentrations on the DTM ion probe, the team was able to determine the melting temperature of rocks with the low, but not zero, water content of the mantle that produces volcanism along ocean ridges. Their results suggest this mantle is some 60oC hotter than previously suspected, with important implications for the dynamic behavior of Earth’s interior given the strong dependence of rock strength on temperature.



Back to the astronomical world, DTM postdoc Erika Nesvold explored how a distant planet can influence the shape of a dusty debris disk between the planet and its central star.  The work addresses the question of how such a distant planet can shape the disk, and in turn, whether the shape of the disk can be used to determine whether the planet formed outside the disk, or formed inside and migrated outside.  Though a theoretical examination of the problem, Erika made the direct comparison of her results with the imaged HD106906 debris disk, explaining several important aspects of the shape of this disk with her model.  Being a fan of the L.A. Thunderbirds when I was growing up in southern California, I found her description of the work as a “Debris Disk Roller Derby” quite appropriate, and funny. 

A photograph of the ancient crust along the eastern shores of Hudson Bay.  Photo courtesy of Rick Carlson, DTM

My own work, or mostly that of former Carnegie postdoc Jonathan O’Neil, now an assistant professor at the University of Ottawa, provided evidence that a good portion of the old crust in north eastern Canada was produced by the recycling of really old crust.  As a geologist, I suspect that my use of the word “old” might be unfamiliar to many readers of this letter, so let me be precise, by “old” I mean 2.7 billion years, and by “really old,” I am talking about older than 4.3 billion years, so quite possibly some of the first crust formed on Earth.  Finding really old crust seems to be a topic of interest for the press as the paper, published in Science, was covered with articles in NOVANext, the BBC, and even the International Business Times.  Reading more than one of these articles will mostly illustrate the difficulty we have in explaining to the non-geologist the difference between “old” rocks that contain the chemical signature of being made by the remelting of “really old” rocks, as opposed to simply finding “really old” rocks. 

For all these press releases, we have to offer a huge “Thank You” to Natasha Metzler, science writer at Carnegie Headquarters.  Not only does Natasha do a great job, often on short notice, of translating our work into something that can be understood by the non-expert and make it sound interesting to the press, but she also is the prime tweeter for science events at both P-Street and the Neighborhood Lectures, bringing, in real time, our science to the huge audience for social media. 

Richard Carlson, Director, DTM
Carnegie Institution for Science
March 2017 Newsletter

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