Curator Glenn MacPherson and postdoctoral fellow Emma Bullock investigate particles in chondritic meteorites. The particles – chondrules and calcium-aluminum-inclusions – formed in the cloud of gas and dust (the solar nebula) from which the Sun, planets, asteroids and comets eventually formed. Studies of the detailed chemistry, mineralogy, and isotopic compositions of these particles provide invaluable clues to the range of chemical and physical processing and timing of events in the solar nebula.
MacPherson, Bullock and curator Ed Vicenzi have participated in the analyses of cometary dust collected by the Stardust mission. These particles provide our first returned samples of a comet and the first samples that can be related to a known comet. Their study is revealing fascinating clues to the early evolution of our Solar System.
Curator Tim McCoy investigates a wide range of processes that occurred during the melting of asteroids, using both the mineralogy and texture of meteorites and the reflectance spectra (the reflectance of light over a range of wavelengths) of asteroids to understand how asteroids composed of primitive meteorites changed to become layered worlds with cores, mantles and crusts like the Earth. His research, including study of the Antarctic meteorite Graves Nunatak 95209, has uncovered clues to the processes occurring during early partial melting of asteroids.
McCoy along with colleagues at the University of Maryland, University of Massachusetts, Applied Physics Laboratory, Carnegie Institution of Washington and UCLA, have been investigating the links between pallasites and iron meteorites. These meteorites sample the deep interiors of asteroids and offer our best clues to processes that occur during the formation of cores. Their research has uncovered a previously unknown grouping of meteorites that sample the core-mantle boundary of a little-known asteroid.
McCoy also collaborates with postdoctoral fellow Mariek Schmidt as a member of the Mars Exploration Rover mission. They are particularly interested in the volcanic features observed in Gusev Crater, Mars by the Spirit Rover. A circular feature dubbed Home Plate shares a number of similarities with small terrestrial volcanoes on Earth. Schmidt and McCoy, along with intern Megan Ennis, visited one of these in New Mexico to compare with features on Mars [Link to “Volcanoes on Earth and Mars”].
At the dawn of the 21st century, researchers in the Division of Meteorites couple access to an unparalleled collection with opportunities to visit other worlds in our own Solar System. Staff in the Division are involved in the MESSENGER mission to Mercury and actively planning for sample return from asteroids, the Moon and Mars.
How do asteroids melt?Early in the history of our Solar System, small rocky bodies began to heat up and melt. Eventually, this melting would produce layered worlds with cores, mantles and crusts like the Earth. But exactly how did primitive asteroids formed from materials accreted out of the solar nebula – space sediments, if you will – actually change into layered worlds like Earth. Tim McCoy has been trying to find out by studying meteorites that fell in Antarctica. These meteorites are different from most others in that they aren’t primitive and unheated and they aren’t fully melted. They just started to melt and then the melting stopped. These meteorites offer probably our best clues to how asteroids and planets melted. Among these meteorites, a particularly interesting one is Graves Nunatak 95209. Found in Antarctica in 1995, this meteorite has been studied intensively. One of the most interesting measurements was a computed tomography scan. Although similar to a medical CAT scanner you might find at a hospital, a CT scanner emits a more powerful beam of radiation and can reveal much finer details.
The CT scans can be viewed in a number of ways, but the most interesting is as a rotational, three-dimensional image like the one shown below. The orange material is metal and the surrounding rocky part is a semi-transparent green. You can see veins of metal. These were created more than four and a half billion years ago when the asteroid just started to heat up and the metal began to migrate along veins. If this process hadn’t been stopped, this metal may have eventually migrated to the center of the asteroid to form a core like we have on Earth.
Three-dimensional CT scan. (Quick Time movie, 6 MB)Another way to look at the data is to examine individual slices, like the one shown in black and white. The metal is the bright white material. You’ll notice that it contains a very dark round blob. Those blobs are graphite, like the material in the center of a pencil. But this graphite is amazing!
Carbon, like most elements, has isotopes – atoms that have the same number of electrons and protons, but different numbers of neutrons. In this graphite, the isotopes of carbon tell you that this material had to form not during the melting, but in the cloud of gas and dust from which the Sun and all the planets formed. Then it had to be preserved despite heating. Most remarkably, these tiny grains of graphite retain a greater range of carbon isotopic compositions than we find in the entire Earth! This remarkable rock gives us a glimpse of how the elements that make up all living things actually behaved during the melting of our planet at the birth of the Solar System.
Volcanoes on Earth and MarsBelieve it or not, not all geologists actually do field work. While most geologists love getting out and hiking around to look at rocks, an unfortunate few can’t do this. That’s because their field areas are REALLY far away. In the Dept. of Mineral Sciences, Tim McCoy and Mariek Schmidt work on volcanoes on Mars using the Mars Exploration Rover Spirit to do their field work for them. Since 2006, McCoy and Schmidt, as part of the Mars Exploration Rover mission, have studied a feature on Mars called Home Plate, which most of the team members think is formed by explosive volcanism. While the pictures and data from the rover are great, sometimes you just have to stomp around on a volcano. To do this, McCoy and Schmidt took intern Megan Ennis to New Mexico to visit the extinct Zuni Salt Lake volcanic crater. In addition to walking around the crater, they dug a trench about 6 feet long into the side of the crater to look at the layers.
Home Plate, Mars
Zuni Salt Lake, New Mexico
The team revelaed that there were numerous similarities between the volcanoes on Earth and Mars, including how the rock layers were deposited, what they contained and how big they were. One of the most remarkable similarities is the presence of bomb sags. As the volcanoes throw out both fine dust and larger rocks, occasionally one of those larger rocks hits layers of the finer-dust and “sags” that layer. The larger rock is the “bomb” and the structure produced is called a bomb sag. Amazingly, this only happens if the fine dust is wet, proving that these volcanic eruptions on Mars must have contained water. NASA is particularly interested in the presence of water, since that is a key ingredient for life and the search for life drives us to want to explore Mars.
Home Plate, Mars Zuni Salt Lake, New Mexico
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