Vesta: A Protoplanet’s Mutable Surface

by Paul Gilster on November 5, 2012

I remember having a particularly strong ‘sense of wonder’ moment when reading Poul Anderson’s “The Snows of Ganymede” when I was a kid. Anderson was good at this kind of thing, but really my reaction was not just to this story but to the whole notion of taking a distant astronomical object and placing people in it. A bright point in the telescope suddenly becomes a landscape and you feel your sense of scale – the sheer immensity of things – beginning to shift under your feet. These thoughts are triggered by the latest news from the Dawn mission about Vesta, and a UCLA news release commenting on the asteroid’s steep topography, which often leads to landslides.

Immediately I was thinking of stark drops and boulder-strewn regolith with no friendly blue/green Earth in the sky and wondering what it would be like to see Vesta in person. Thus dreams accumulate. Ray Bradbury found that attaching names to unknown places is a distinctively human enterprise, and one that when abandoned suggested deep change in the psyche (see “Dark They Were and Golden-Eyed,” one of Ray’s superb Mars stories, for more on this). We’re well along in naming features on the worlds our space probes have revealed to us, but standing in the imagination amidst these forbidding landscapes is what really makes some of the deep space imagery sing to me. That feeling is also, of course, a prime reason for reading science fiction.

Image: Vesta’s surface as imaged by the Dawn spacecraft. Credit: NASA/JPL.

The frisson of deep space brings many into the field, but thankfully the science holds just as deep a sway on the imagination. About Vesta we’ve learned the unexpected fact that the asteroid — or protoplanet, as you choose – has a range of brightness that is about as extreme as any rocky object yet found in the Solar System. The tiny world’s variation in dark and light areas has been under intense scrutiny, with the finding that the widely distributed dark areas — apparently not correlated with underlying geological features — are likely material from carbon-rich asteroids. Thus Christopher Russell (UCLA, and Dawn principal investigator):

“Ever since Dawn arrived at Vesta [in July 2011] and we saw the bright and dark streaks across the surface, we have wondered how the zebra got her stripes. Now we know that the bright streaks and spots are due to very pure early Vestan material, and the dark patches are deposits on the surface most probably due to collisions with material from the dark outer reaches of the asteroid belt.”

The estimate is that to arrive at what we see on Vesta today, approximately 300 dark asteroids between 1 and 10 kilometers in diameter have struck the protoplanet during the last 3.5 billion years. The researchers, whose work appeared on November 1 in Nature, believe that enough accumulated to produce between 1 and 2 meters of material on the surface. Because Vesta is thought to have formed at the very beginning of the Solar System, it is a place that records the system’s formation some 4.5 billion years ago, and a surface that has had plenty of time to accumulate debris from impacts.

Meanwhile, it’s interesting that while we have observed a form of ‘weathering’ on the Moon and on various asteroids, Vesta’s surface seems to be continually renewed. The weathering is thought to be the result of the accumulation of metallic particles containing iron, and we would expect these to dull the outer layers of the surface of Vesta. The researchers say, however, that Dawn’s visible and infrared mapping spectrometer (VIR) and framing camera find no such accumulation. Here the steep topography mentioned above comes into play, leading to landslides that mix surface materials. Impacts large and small should also mix the outer layers over time.

Now that Dawn is on its way to Ceres, the largest object in the main belt, keep in mind that this is one of the darkest of the asteroids, meaning we’re likely to learn more there about the dark materials that have had such an effect on Vesta. Ceres also beckons because it is thought to hold water or ice in substantial amounts under its crust, adding to its astrobiological interest. Operations around Ceres begin in 2015, at which time our imaginations will be able to seize on yet another set of deep space images showing us terrain features in need of names, out of which we can fashion a new set of dreams.

The papers are Pieters et al., “Distinctive space weathering on Vesta from regolith mixing processes,” Nature 491 (01 November 2012), pp. 79–82 (abstract) and McCord et al., “Dark material on Vesta from the infall of carbonaceous volatile-rich material,” Nature 491 (01 November 2012), pp. 83–86 (abstract).

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Alex Tolley November 5, 2012 at 11:16

Immediately I was thinking of stark drops and boulder-strewn regolith with no friendly blue/green Earth in the sky and wondering what it would be like to see Vesta in person.

With so much detail known about the topography of these worlds, I’m surprised that so little artwork seems to exist showing actual views from surface features. With its small diameter and rugged surface features, the landscape would seem oddly distorted compared to Earth. What would navigating the surface feel like? Could you walk or bounce, make jet assisted hops in the low g, or use tethers to allow some semblance of walking? Would the short rotation period make the shadow movements even more obvious than on Earth? Given the low g, would the best human outpost be a rotating station in orbit, with easy trips to and from the surface, rather than a surface location?

computronium November 5, 2012 at 21:00

If I was king of the internet, I would ban all space photos that don’t include some sort of scale indicator :)

Seriously, what sort of scale are we looking at there?

Paul Gilster November 6, 2012 at 11:00

That’s a good point, and the source doesn’t give that information. Let me see if I can dig it up.

jkittle November 6, 2012 at 11:28

SOOOO… is Vesta or ceres stacking up to be a good target for a human mission?

Alex Tolley November 6, 2012 at 15:39

@computronium – you can identify the craters from the whole map of Vesta (Wikipedia has one) and infer the scale from that.

tom November 9, 2012 at 12:42

I was frankly surprised about what kind of world is 4 Vesta. There really needs to be a manned presence on that asteroid. The moon & Mars are territory that can sharpen our exploration & colonization skills; but considering the sheer number of large space bodies within a 2 light-year radius of our Sun… how humanity will move into the local solar system & ultimately through out the Milky Way could come from ‘vaulting’ from asteroid to asteroid? It might be easier to ‘terraform’ Ceres than dome up Mars? What a brave, new world and such marvelous beings who will inhabit it?

ljk November 12, 2012 at 12:59

tom said on November 9, 2012 at 12:42:

“I was frankly surprised about what kind of world is 4 Vesta. There really needs to be a manned presence on that asteroid.”

LJK replies:

What kind of manned presence are you looking for? A scientific expedition base? A mining company? A permanent colony? Other than using Vesta for resources, what can be gained by these scenarios that a robotic mission could not accomplish much more cheaply and with virtually no potential for loss of life?

I am not against space colonization, I just want to know if you know a good reason to put people on that little airless world other than just because it is there and having human explorers is the traditional way of doing such things?

Tom then said:

“The moon & Mars are territory that can sharpen our exploration & colonization skills; but considering the sheer number of large space bodies within a 2 light-year radius of our Sun… how humanity will move into the local solar system & ultimately through out the Milky Way could come from ‘vaulting’ from asteroid to asteroid?

“It might be easier to ‘terraform’ Ceres than dome up Mars? What a brave, new world and such marvelous beings who will inhabit it?”

LJK replies:

While living on planetoids at least for a while will certainly sharpen our skills for dwelling and working in space, I am not quite sure how terraforming even Ceres will work if you want our future astronauts to live on an Earthlike planet there. Maybe science can find a way to grow whole forests on that space rock, but unless you can increase its mass, you are dealing with a world smaller than Texas. An average adult would weigh only a few pounds on its surface. Space agencies are still working on how to adapt human bodies to microgravity conditions.

Something tells me there will be better uses for Ceres and the other planetoids than just colonizing them for the sake of doing so.

ljk January 4, 2013 at 10:08

3 January 2013

** Contacts are listed below. **

Text & Images:

http://www.dawn.mps.mpg.de/index.php?id=17&L=1&tx_ttnews%5Btt_news%5D=172&cHash=fb71c4cb2dd3810fdc8752db4e4dcf3e

VESTA: GIANT IMPACTS DELIVERED CARBON

** Synopsis: Large collisions between asteroids transferred carbonaceous material in the inner solar system. **

The protoplanet Vesta has been witness to an eventful past: images taken by the framing camera onboard NASA’s space probe Dawn show two enormous craters in the southern hemisphere. The images were obtained during Dawn’s year-long visit to Vesta that ended in September 2012. These huge impacts not only altered Vesta’s shape, but also its surface composition.

Scientists under the lead of the Max Planck Institute for Solar System Research (MPS) in Germany have shown that impacting small asteroids delivered dark, carbonaceous material to the protoplanet. In the early days of our solar system, similar events may have provided the inner planets such as Earth with carbon, an essential building block for organic molecules. These results were published in the November-December issue of the journal Icarus.

Vesta is remarkable in many respects. With a diameter of approximately 530 kilometers, Vesta is the one of the few protoplanets in our solar system still intact today. Like other protoplanets, Vesta underwent complete melting approximately 4.5 billion years ago. However, most of the volcanic activity on Vesta is thought to have ceased within a few million years, making it a time capsule from the early solar system. Dawn observations of Vesta have shown a surface with diverse brightness variations and surface composition. There is bright material on Vesta that is as white as snow and dark material on Vesta as black as coal.

The enigmatic dark material holds the key to understanding the impact environment around Vesta early in its evolution. Research led by scientists at the MPS has shown that this dark material is not native to Vesta but was delivered by impacting asteroids. “The evidence suggests that the dark material on Vesta is rich in carbonaceous material and was brought there by collisions with smaller asteroids,” explains Prof. Dr. Vishnu Reddy from the MPS and the University of North Dakota, the lead author of the paper. In the journal Icarus, he and his colleagues now present the most comprehensive analysis of this material so far. Compositional analysis, mapping, and modeling of dark material distribution on Vesta suggests that it was delivered during the formation of giant impact basins on Vesta.

“First, we created a map showing the distribution of dark material on Vesta using the framing camera data and found something remarkable,” explains Dr. Lucille Le Corre from the MPS, one of the lead authors of the study. Dark material was preferentially spread around the edges of the giant impact basins in the southern hemisphere of Vesta suggesting a link to one of the two large impact basins. A closer examination showed that the dark material was most probably delivered during the formation of the older Veneneia basin when a slow impacting asteroid collided with Vesta. Dark material from this two to three billion year old basin was covered up by the impact that subsequently created the Rheasilvia basin. “We believe that the Veneneia basin was created by the first of two impacts two to three billion years ago,” says Reddy. In fact, impact modeling presented in the paper reproduces the distribution of dark material from such a low velocity impact.

Evidence for dark material is also found in the HED meteorites that come from Vesta. Some of the meteorites show dark inclusions that are carbon-rich. Color spectra of dark material on Vesta are identical to these carbon-rich inclusions in HED meteorites. The link between dark material on Vesta and dark clasts in HED meteorites provides us with direct evidence that these meteorites are indeed from Vesta. “Our analysis of the dark material on Vesta and comparisons with laboratory studies of HED meteorites for the first time proves directly that these meteorites are fragments from Vesta”, says Le Corre.

“The aim of our efforts was not only to reconstruct Vesta’s history, but also to understand the conditions in the early solar system,” says Dr. Holger Sierks, co-investigator of the Dawn mission at the MPS.

PIO Contact:

Dr. Birgit Krummheuer
Max Planck Institute for Solar System Research
+49 5556 979-462, cell: +49 173 3958625
krummheuer@mps.mpg.de

Science Contacts:

Prof. Dr. Vishnu Reddy
Max Planck Institute for Solar System Research
+49 5556 979-550
reddy@mps.mpg.de

Dr. Lucille Le Corre
Max Planck Institute for Solar System Research
+49 5556 979-143
lecorre@mps.mpg.de

Dr. Holger Sierks
Max Planck Institute for Solar System Research
+49 5556 979-242
sierks@mps.mpg.de

Original publication:

Vishnu Reddy, Lucille Le Corre et al., “Delivery of dark material to Vesta via carbonaceous chondritic impacts,” Icarus, Volume 221, Issue 2, November-December 2012. http://dx.doi.org/10.1016/j.icarus.2012.08.011

The Dawn mission was launched approximately five years ago and entered orbit around Vesta on July 16th, 2011. In 2015, Dawn will arrive at its second destination, the dwarf planet Ceres, that like Vesta orbits the Sun between the orbits of Mars and Jupiter within the so-called asteroid belt. The Dawn mission to Vesta and Ceres is managed by NASA’s Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, for NASA’s Science Mission Directorate, Washington. The University of California, Los Angeles, is responsible for overall Dawn mission science. The Dawn framing cameras have been developed and built under the leadership of the Max Planck Institute for Solar System Research, Katlenburg-Lindau, Germany, with significant contributions by DLR German Aerospace Center, Institute of Planetary Research, Berlin, and in coordination with the Institute of Computer and Communication Network Engineering, Braunschweig. The Framing Camera project is funded by the Max Planck Society, DLR, and NASA/JPL.

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