Presence of serpentine on Vesta suggests exogenic origin

Jul 03, 2014
The Numisia crater just south of Vesta’s equator has a diameter of 30 kilometers. Images obtained by the camera system on board NASA’s spacecraft Dawn with the clear filter (left) show dark material in the crater walls and in the material ejected during impact. The camera system’s color filters can filter individual wavelengths from the reflected light and thus make further variations in the surface composition visible (right). In data like this the researchers found the characteristic fingerprints of the mineral serpentine. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

(Phys.org) —Rocks are silent storytellers: because each mineral is created only under certain conditions, they provide insight into the evolution of the body on which they are found. Scientists from the Max Planck Institute for Solar System Research (MPS) in Germany have now begun to tell such a story from the enigmatic dark material discovered on the protoplanet Vesta. Using data from the framing camera aboard NASA's Dawn spacecraft, the researchers have succeeded for the first time in identifying a mineral component of this material: serpentine. The new discovery puts an end to the discussion about the origin of the dark material: impacts of primitive asteroids must have distributed it on Vesta.

The so-called dark material that can be found scattered over the surface of the protoplanet Vesta is one of its most unusual features. Ever since Dawn's arrival in July 2011, this material, that absorbs light as efficiently as soot, has sparked discussions within the scientific community. What is it made of? How did it originate? And what does it tell us about this unique body that took the first steps towards becoming a planet, but got stuck in an early evolutionary phase approximately 4.5 billion years ago?

In their new study, the MPS researchers answer some of these questions. Almost a year ago, researchers had characterized the dark material to be rich in carbon. Now they are able to identify the silicate as one of the components of the dark material. "Identifying complex minerals instead of just individual elements and simple compounds such as OH-groups, helps us substantially", Dr. Andreas Nathues from the MPS explains.

Like any mineral, serpentine is formed only under certain conditions: pressure and temperature must be neither too high nor too low; if other elements such as hydrogen are present, different minerals are formed. "The detection of minerals as components of the dark material gives us access to a completely new type of information," says Nathues. "We are no longer restricted to answering the question, what the dark material is made of. The minerals tell us what conditions it was exposed to."

Serpentine, for example, cannot survive temperatures above 400 degrees Celsius. "The dark material can therefore not have been exposed to great heat", concludes Dr. Martin Hoffmann from the MPS. Because Vesta - unlike the much smaller asteroids - was once hot and melted, the the dark material cannot have originally belonged to the protoplanet. A volcanic origin, which some scientists had suspected, can also be ruled out.

"The only reasonable explanation is the impacts of asteroids," says Hoffmann, who points out that some primitive meteorites contain serpentine. These meteorites are regarded as fragments of carbon-rich asteroids. The impacts must have been comparatively slow, because an asteroid crashing at high speeds would have produced temperatures too high to sustain serpentine. In a previous study, scientists from the MPS had calculated how dark material would be distributed on Vesta as a result of a low-speed oblique impact. Their results are consistent with the distribution of dark material on the edge of one of the two large impact basins in the southern hemisphere.

Key to the current results was a new and more accurate analysis of the images Dawn acquired while orbiting Vesta from July 2011 to September 2012. The camera system's seven color filters can distinguish certain wavelength ranges from Vesta's reflected light and thus detect the characteristic fingerprints of certain materials. "The areas where the dark material are found on the slopes of steep craters are not large. Sometimes they extend only a few hundred meters", Nathues, framing camera Lead Investigator explains, highlighting the special challenges of these measurements. Only by carefully recalibrating the instrument was it possible to elicit this new information from the data. In addition, the researchers used data from Dawn's visible and infrared mapping spectrometer.

To confirm their identification of serpentine, the researchers also examined mineral mixtures and meteorites containing serpentine in the laboratory. The fingerprints from these samples are in good agreement with the data from Vesta.

Explore further: Dawn creates guide to Vesta's hidden attractions

More information: Andreas Nathues, Martin Hoffman et al.: "Detection of Serpentine in Exogenic Carbonaceous Chondrite Material on Vesta from Dawn FC Data," Icarus, in press, DOI: 10.1016/j.icarus.2014.06.003

add to favorites email to friend print save as pdf

Related Stories

Dawn creates guide to Vesta's hidden attractions

Dec 17, 2013

(Phys.org) —Some beauty is revealed only at a second glance. When viewed with the human eye, the giant asteroid Vesta, which was the object of scrutiny by the Dawn spacecraft from 2011 to 2012, is quite ...

Dawn sees new surface features on giant asteroid

Mar 21, 2012

(PhysOrg.com) -- NASA's Dawn spacecraft has revealed unexpected details on the surface of the giant asteroid Vesta. New images and data highlight the diversity of Vesta's surface and reveal unusual geologic ...

The faces of Vesta (w/ video)

Jun 24, 2011

(PhysOrg.com) -- New images of the asteroid show the first surface structures and give a preview of the Dawn mission's coming months.

Dawn reality-checks telescope studies of asteroids

Sep 30, 2013

(Phys.org) —Tantalized by images from NASA's Hubble Space Telescope and ground-based data, scientists thought the giant asteroid Vesta deserved a closer look. They got a chance to do that in 2011 and 2012, ...

Asteroid Vesta's mysterious olivine

Nov 07, 2013

(Phys.org) —Just when scientists thought they had a tidy theory for how the giant asteroid Vesta formed, a new paper from NASA's Dawn mission suggests the history is more complicated.

Recommended for you

New launch date set for ISS delivery vessel

15 hours ago

A robot ship will be launched from Kourou, French Guiana, after a five-day delay on July 29 to deliver provisions to the International Space Station, space transport firm Arianespace said Tuesday.

The heart of an astronaut, five years on

16 hours ago

The heart of an astronaut is a much-studied thing. Scientists have analyzed its blood flow, rhythms, atrophy and, through journal studies, even matters of the heart. But for the first time, researchers are ...

Image: Kaleidoscopic view of Mars

22 hours ago

Astrophotographer Leo Aerts from Belgium took advantage of the recent opposition of Mars and captured the Red Planet both "coming and going" in this montage of images taken from October 2013 to June of 2014. ...

User comments : 0