Dawn Spacecraft offers first look at giant asteroid’s chemistry

Jan 23, 2012

(PhysOrg.com) -- The NASA Dawn spacecraft’s close-up study of the giant asteroid Vesta is offering researchers their first look at the elemental composition of this ancient protoplanet. Vesta is the second most massive body in the main asteroid belt and has remained intact since its formation more than 4.5 billion years ago.  Dawn’s Gamma Ray and Neutron Detector (GRaND) will determine the chemical composition of Vesta, providing new information about how Vesta formed and evolved.  Tom Prettyman, a Senior Scientist at the Planetary Science Institute, is the lead for GRaND as well as Dawn’s Geochemistry Team.

The NASA has been acquiring science data in orbit around Vesta since July of 2011. In December, Dawn reached its lowest altitude orbit, with an average distance of about 130 miles from Vesta’s surface.  Vesta’s diameter is about 330 miles, just a little bit larger than the width of Arizona. Dawn plans to stay in this orbit for 110 days before ascending to higher altitudes and departing to its next destination, the dwarf planet Ceres.

At low altitudes, GRaND is detecting strong neutron and gamma ray signals that we will analyze to map the elemental composition of the entire surface of Vesta, Prettyman said. Unlike Dawn’s framing camera and visible and infrared mapping spectrometer, GRaND can see in the dark, Prettyman added. Consequently, GRaND is sensitive to the composition of Vesta’s surface at high northern latitudes, presently in polar night.

GRaND measures the abundance of elements found in planetary surfaces, such as hydrogen (H), iron (Fe), magnesium (Mg) and silicon (Si). The data will help scientists determine how hydrogen was delivered to the surface of Vesta – for example, by the solar wind or by carbon-rich materials hitting the asteroid. Measurements of rock-forming elements, including Fe, Mg, and Si, will help them understand the volcanic processes that shaped Vesta.

After five weeks of mapping in the spacecraft’s low altitude orbit, global-scale variations in Vesta’s elemental composition are apparent, Prettyman said. Vesta’s varied surface distinguishes it from smaller asteroids, which are typically uniform in composition. Vesta, which underwent complex geochemical processes, forming a core, mantle, and crust, seems more like a terrestrial planet than an asteroid.

GRaND’s initial observations are tantalizing; however, their interpretation will require additional accumulation of data and further analysis by Dawn’s Geochemistry Team.  First results will be reported soon after mapping at low altitudes is complete.

Prettyman is lead author of a paper titled “Dawn’s Gamma Ray and Neutron Detector,” published recently in the journal Space Science Reviews as a chapter in a book about the Dawn Mission. The paper provides a detailed description of GRaND, including science objectives, design and construction, and measurement capabilities.  Data acquired by GRaND will be made available to the public through the Planetary Data System’s Small Bodies Node.  The paper will be a valuable resource for scientists who want to study the chemical makeup of Vesta.

PSI’s William Feldman, Jeffrey Morgenthaler, Karly Pitman and Robert Reedy are among the paper’s co-authors. PSI’s Naoyuki Yamashita, a veteran of the Japanese mission Kaguya, recently joined the GRaND team and is helping to analyze the data acquired at Vesta.

GRaND is operated by the Planetary Science institute under the leadership of Senior Scientist Tom Prettyman, who is also the lead for Geochemistry on Dawn. This work is supported by NASA under a subcontract from the Jet Propulsion Laboratory to the Planetary Science Institute. GRaND was built by Los Alamos National Laboratory under Prettyman’s direction and supervision.

The Dawn mission to Vesta and Ceres is managed by the Jet Propulsion Laboratory for NASA’s Science Mission Directorate, Washington, D.C. It is a project of the Discovery Program managed by ’s Marshall Space Flight Center, Huntsville, Ala. UCLA is responsible for overall Dawn Mission science. Orbital Sciences Corporation in Dulles, Va. designed and built the Dawn spacecraft.

Explore further: NASA team lays plans to observe new worlds

More information: Information about Dawn is available at: www.nasa.gov/dawn

Provided by Planetary Science Institute

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User comments : 10

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clandau
1 / 5 (3) Jan 23, 2012
This article tells me nothing about the geochemistry. What was the point of writing it?
Chris
Shelgeyr
1 / 5 (5) Jan 23, 2012
...and has remained intact since its formation more than 4.5 billion years ago...

They have no way of knowing if that is a true statement.

...will determine the chemical composition of Vesta, providing new information about how Vesta formed and evolved...

That implies a direct composition-to-process route where none exists. Determining what Vesta's made out of will let us know what it is made out of. Contrary to the popular refrain, knowing its composition will not in fact tell us much (or anything) about its formation. And if they're going to stand by that first quote, there wasn't much evolution going on either.

@clandau said:
This article tells me nothing about the geochemistry.

You certainly got that right!
Graeme
not rated yet Jan 23, 2012
Since it seems to be a press release to keep up interest while a whole picture is established, I would assume this means there are no big surprises. So we can expect compositions similar to meteorites, and nothing truly exotic such as no silicon or iron detected.
GSwift7
1 / 5 (1) Jan 24, 2012
That implies a direct composition-to-process route where none exists.


That isn't true. Composition can tell you some things. The article didn't say that the composition would tell how it formed. It says
providing new information
about how it formed. For example, if you see an area of volcanic rock surrounding a mountain, you know that was probably a volcano. If you see a ridge and the compostion is different on each side, then it was probably two techtonic plates, and so forth. It's still a guessing game, but a map of the entire surface composition allows you to make some intelligent limited guesses. Comparing and contrasting to other things like Earth and Mars (comparative planetology) is also usefull.
Deathclock
1 / 5 (1) Jan 24, 2012
They have no way of knowing if that is a true statement.


Okay doctor, where did you get your PhD in astrophysics?

Sometimes I would really like to know the credentials of people on this site (or in general) that feel they are capable of questioning the claims of actual scientists. I would be willing to bet the vast majority of them would be blue collar laborers with zero formal education in relevant fields.
Deathclock
1 / 5 (1) Jan 24, 2012
That isn't true. Composition can tell you some things. The article didn't say that the composition would tell how it formed. It says
providing new information
about how it formed. For example, if you see an area of volcanic rock surrounding a mountain, you know that was probably a volcano. If you see a ridge and the composition is different on each side, then it was probably two tectonic plates, and so forth. It's still a guessing game, but a map of the entire surface composition allows you to make some intelligent limited guesses. Comparing and contrasting to other things like Earth and Mars (comparative palaeontology) is also useful.


Unless you've actually studied geology you have no idea how much information you can gain about the origin and history of physical features just by examining them as they exist today. Stratigraphy alone provides a wealth of reliable information.
GSwift7
1 / 5 (1) Jan 25, 2012
I would be willing to bet the vast majority of them would be blue collar laborers with zero formal education in relevant fields.


Yeah, and most of them don't even both to consult wiki or do a google search.

Comparing and contrasting to other things like Earth and Mars (comparative palaeontology) is also useful.


haha, I notice that you changed my word. You know that palaeontology is the study of ancient life forms, not geology per se. I assume you used a translator program? If there's dinosaur fossiles on Vesta, that'll be BIG news.

From the University of Washington:

Comparative Planetology

One of the most important areas of astronomy is the field of comparative planetology. By studying planets and other large bodies in the solar system, we learn about the history and possible future of our own


http://www.astro....ets.html

Deathclock
1 / 5 (1) Jan 25, 2012
haha, I notice that you changed my word. You know that palaeontology is the study of ancient life forms, not geology per se. I assume you used a translator program? If there's dinosaur fossiles on Vesta, that'll be BIG news.


That wasn't my intent. I was speaking specifically about geology and determining the origin and history of physical features. One can assume similar geological principles would apply to other planets, moons, asteroids, etc.
GSwift7
1 / 5 (1) Jan 26, 2012
One can assume similar geological principles would apply to other planets, moons, asteroids, etc.


Yes, that is exactly what they do in comparative planetology. They look at the similarities and differences, which helps us confirm or revise our theories about geology, both here on Earth and elsewhere. But comparative planetology isn't just limited to geology. They look at many different things, such as climate, weather, soil chemistry, atmospheric chemical processes, etc. Geology is part of it though.
Shelgeyr
1 / 5 (1) Jan 26, 2012
@Deathclock embarked on an "appeal to authority" fallacy when quoting me then asking:
They have no way of knowing if that is a true statement.

Okay doctor, where did you get your PhD in astrophysics?... (snip) ...that feel they are capable of questioning the claims of actual scientists.


To quote Captain Taggart/Jason Nesmith: "It doesn't take a great actor to recognize a bad one. You're sweating."

You seem to hold way too much reverence for "actual scientists".

I was saying a true fact, not an opinion. If you can't recognize that that's a fact, then logic or evidence will not convince you. By the way, they may be accidentally or coincidentally correct - but my statement doesn't address that. They have no way for them to actually KNOW the statement to be factual. If I could convince you otherwise by waving credentials in your face, I'd be taking advantage of your gullibility, so I'll refrain.

You need to be convinced - or not - based on evidence, facts, and logic.