Coming Together for the Holidays | Letter from the Director | December 2019

The holiday mantle at BBR campus
Telescopes, exoplanets, and Van de Graaf generators adorn the mantle at the Broad Branch Road campus 2019 Holiday Party.
Friday, December 20, 2019 

Talk about ending the year with a bang.  At the recent centennial meeting of the American Geophysical Union, Carnegie Science President Eric Isaacs announced the union of DTM and the Geophysical Laboratory (GL) in Carnegie’s new Earth and Planets Division.  This move is a step in the continuing strategic planning exercise the Institution is conducting.  The science being pursued by DTM and GL has been moving towards increasingly overlapping studies of the world around us, the manner in which planets formed and evolved, and the basic physics and chemistry of materials that control planetary dynamics.  We are excited about the opportunities for interdisciplinary science that this union will foster, and are particularly pleased that we are being allowed to conduct two searches for new staff scientists to broaden the work done on campus.

Doing Carnegie Proud at AGU

Eric Isaacs speaks to the attendees of the 2019 AGU Carnegie Science alumni reception.

At the AGU Carnegie Science alumni reception, Eric Isaacs, President of Carnegie Science, announces the union of DTM and GL in Carnegie's new Earth and Planets Division. Click here to view the full alumni reception album. Photo: Carnegie Science | Katy Cain

The annual alumni reception at AGU brings together upwards of 200 Carnegie alumni and friends and well demonstrates the important role that a small institution like Carnegie has had, and continues to play, in the science conducted by the much broader field of Earth and planetary scientists represented by AGU. As described in the accompanying story, AGU’s history is closely coupled to Carnegie’s, as many of our staff served in leadership roles at AGU not only during its formative years, but throughout its history.  We are especially proud that in the opening centennial program at AGU this year, four of the five speakers were Carnegie staff or alumni. In addition, as described in last month’s newsletter, eight of our colleagues received major awards at this year’s AGU, which well demonstrates the leadership role Carnegie scientists and alumni play in advancing our understanding of the Earth around us.

Water Out, Water In

DTM postdoctoral fellow Doug Hemingway lists the five key questions answered by his recent study, which explains the formation of Enceladus' unique "tiger stripes". This video was prepared as a teaser for his presentation at AGU

OK, now onto some of the cool science – sorry for the bad pun. DTM postdoctoral fellow Doug Hemingway just published a fascinating paper describing the origin of the “tiger stripes” on Saturn’s moon, Enceladus.  The four or five fissures that make up the tiger stripes are fractures that penetrate all the way through the icy crust of Enceladus and allow the inner liquid ocean to erupt huge streams of water into space, forming one of the rings of Saturn in the process.  Doug’s paper attributes the opening of these fractures to the gradual cooling of the moon which initiated the first crack, after which the weight of the snow falling from the erupting ocean caused additional fracturing at regular distances from the first fissure.

Closer to home we have two new reports involving water going into, instead of out of, Earth’s interior. In these studies, Carnegie staff scientists Steve Shirey, Mike Walter, Lara Wagner, Peter van Keken, and colleagues explore the mechanisms through which water can be taken from Earth’s surface deep into its interior.

Stishovite Sponge

A tiny sample of stishovite used by the researchers in the lab. Photo is provided by GL postdoctoral fellow Yanhao Lin.

Some rocks can contain as much as 10 weight percent water, which means that if you could squeeze the water out of 10 pounds of such a rock, you could refill a pint glass emptied by consumption of your favorite beverage.  You can’t squeeze water out of a rock, but the Earth’s interior can, so getting that water into Earth’s interior is not as easy as it sounds. The increasing pressure and temperature experienced by a subducting plate as it descends into the mantle essentially squeezes out the water, which among other consequences, fuels the volcanism that occurs along convergent plate boundaries such as in the Cascades, Alaska, Japan, and the Andes. The study by Walter, former GL staff scientists David Mao, and colleagues documents the ability of the high-pressure crystalline form of the common low-pressure mineral quartz, known as stishovite, to carry substantial quantities of water in its mineral structure and hence allow the transport of water to at least mid-mantle depths.

Deep Fault Lubrication

Steve Shirey presents his poster titled, "Deep Focus Earthquakes, Deep Slab Fluids, and Superdeep Diamonds" to an interested attendee at AGU. Photo: Carnegie Science | Katy Cain

During an AGU presentation, Shirey and colleagues showed how they used superdeep diamonds, those that derive from depths as great as 400-500 km, to track the release of such water as various water-bearing minerals in subducting oceanic crust change structure in response to increasing pressure and temperature during subduction. They note that the depths of maximum water release match up with where deep-focus earthquakes occur.  While the crustal and upper mantle earthquakes that are more familiar, and more dangerous, to humans are clearly driven by tectonic stresses along faults driving them to brittle failure, the origin of the deeper quakes is less well understood.  At the depths where they occur, temperatures are hot enough that rocks soften to the point where brittle failure is less likely to occur.  The correspondence of deep earthquakes with areas where mineral breakdown releases water could implicate this process as a means to change the stresses in the plate quickly enough to instigate earthquakes at depths where they are otherwise unexpected.

Thank You For a Wonderful Year

Closing out the year, I offer my thanks to all of my colleagues at DTM and to the many people who support our work in so many ways.  My best wishes go out to you all for a peaceful holiday season and a new year filled with happiness and appreciation of the marvels of the world around us.

Richard Carlson, Director, Carnegie Science Earth and Planets Division
Carnegie Institution for Science