"Thrust is engaged, and we are now climbing away from Vesta atop a blue-green pillar of xenon ions," said Marc Rayman, Dawn's chief engineer and mission director, at NASA's Jet Propulsion Laboratory, Pasadena, Calif. "We are feeling somewhat wistful about concluding a fantastically productive and exciting exploration of Vesta, but now have our sights set on dwarf planet Ceres."
Say: "a blue-green pillar of xenon ions" (or "sights set on Ceres") 5 times fast.
Mission controllers received confirmation today that NASA's Dawn spacecraft has escaped from the gentle gravitational grip of the giant asteroid Vesta. Dawn is now officially on its way to its second destination, the dwarf planet Ceres.
Dawn departed from Vesta at about 11:26 p.m. PDT on Sept. 4 (2:26 a.m. EDT on Sept. 5). Communications from the spacecraft via NASA's Deep Space Network confirmed the departure and that the spacecraft is now traveling toward Ceres.
"As we respectfully say goodbye to Vesta and reflect on the amazing discoveries over the past year, we eagerly look forward to the next phase of our adventure at Ceres, where even more exciting discoveries await," said Robert Mase, Dawn project manager, based at NASA's Jet Propulsion Laboratory, Pasadena, Calif.
Launched on Sept. 27, 2007, Dawn slipped into orbit around Vesta on July 15, 2011 PDT (July 16 EDT). Over the past year, Dawn has comprehensively mapped this previously uncharted world, revealing an exotic and diverse planetary building block. The findings are helping scientists unlock some of the secrets of how the solar system, including our own Earth, was formed.
A web video celebrating Dawn's "greatest hits" at Vesta is available at NASA's video gallery and YouTube. Two of Dawn's last looks at Vesta are also now available, revealing the creeping dawn over the north pole.
Dawn spiraled away from Vesta as gently as it arrived. It is expected to pull into its next port of call, Ceres, in early 2015.
Spring arrives to Vesta's north pole, as Dawn departs,
plus a request for citizen scientists
Posted By Emily Lakdawalla, 2012/09/11 11:08 CDT
<<Today the Dawn mission released what they said would be their last captioned daily image release until the Ceres phase of the mission begins in 2015. It shows shadowy regions of Vesta's north pole that were hidden in winter darkness when Dawn arrived last summer. Dawn managed to stick around long enough to see most of the pole before energizing its ion engines to embark on the cruise to Ceres.
This photographic look at the north pole is important for a couple of reasons. There's the obvious: it means there won't be a "here there be dragons" region on our map of Vesta. But the science team really needed to see the north pole in order to understand Vesta's interior. How does that work?
Vesta is a lumpy place, and the north polar winter was hiding some interesting topography. Dawn's science team needed to map that topography in order to develop a precise measurement of Vesta's volume and therefore its density, a crucial piece of information for guessing at the nature of its interior.
The topography is also an important input into understanding what Vesta's gravity field means about how its mass is distributed. They tracked Dawn very precisely to notice all the wiggles and bumps in Dawn's orbit that result from extra mass here and missing mass there. A planet's gravity field usually correlates well with its topography -- if you have a mountain sticking up, that's a bit of excess mass that affects the course of a spacecraft -- but if you assume a density for the planet's crust and then correct for the missing and excess mass due to topography, the residual "gravity anomaly" often shows surprising features, clues to inhomogeneous distribution of mass inside the body, places where there is unusually dense material or unusually light material hidden beneath the surface.
To pass the time during Dawn's long journey, you can help the science team out in the recently announced Vesta Mappers project. Just like Moon Mappers, Vesta Mappers requests citizen scientists' help in mapping craters and any unusual features in high-resolution images of Vesta. I gave it a shot this morning and noticed that Cosmoquest has made some subtle improvements to its interface that make it even easier to use than it was previously. But Vesta's craters are not easy to map; it's a very heavily cratered surface, and many of its craters are very subtle. I find myself using a trick I learned in drawing classes: to close my eyes most of the way while looking at the image, which has the effect of filtering out detail, leaving behind the broader patterns of bright and dark. That helps reveal subtle craters that are obscured by more recent ones.
Sadly, Vesta Mappers seems to be the only way that us members of the public can see Vesta camera data (other than the now-ended daily image releases), at least for the time being. The Vesta approach, suruvey, and high-altitude mapping orbit data were supposed to be available from the Planetary Data System as of last month, but they are not there. A version was actually released some time ago -- and I posted a few pictures from it -- but then it was taken down, because it was not an approved release. The holdup is a dispute between the mission and the IAU over the choice of longitude system for Vesta. You can read about that in a Nature article here.
I am actually sympathetic to the mission's point of view, but I doubt that the choice of coordinate system is the whole story; we may be exploring space with robots and computers but it's humans back on Earth that are in charge, and just occasionally, humans are not quite rational. Even scientists!
It's frustrating to me because in all of its public image releases, the Dawn mission has not yet released an approximately true color global view of Vesta. That's all I want: a color portrait of the world they've just spent more than a year exploring. Ordinarily, if a mission team doesn't produce an image I'm looking for, it's easy for me to rectify that, by going into the data myself and making the illustration I want. But I can't do that for Vesta until the data become public.>>.
NASA's Dawn mission is releasing two parting views of the giant asteroid Vesta, using images that were among the last taken by the spacecraft as it departed its companion for the last year.
The first set of images is a color-coded relief map of Vesta's northern hemisphere, from the pole to the equator. It incorporates images taken just as Dawn began to creep over the high northern latitudes, which were dark when Dawn arrived in July 2011. The other image is a black-and-white mosaic that shows a full view of the giant asteroid, created by synthesizing some of Dawn's best images.
"Dawn has peeled back the veil on some of the mysteries surrounding Vesta, but we're still working hard on more analysis," said Christopher Russell, Dawn's principal investigator at UCLA. "So while Vesta is now out of sight, it will not be out of mind."
These will be the last daily images during the cruise to Dawn's second destination, the dwarf planet Ceres. Other images will be highlighted as findings are made. Other data will be archived at http://pds.nasa.gov .
Dawn left Vesta on Sept. 4, 2012 PDT (Sept. 5, 2012 EDT). The spacecraft is using its ion propulsion system to travel to Ceres. It is expected to arrive in early 2015.
NASA's Dawn spacecraft has revealed that the giant asteroid Vesta has its own version of ring around the collar. Two new papers based on observations from the low-altitude mapping orbit of the Dawn mission show that volatile, or easily evaporated materials, have colored Vesta's surface in a broad swath around its equator.
Pothole-like features mark some of the asteroid's surface where the volatiles, likely water, released from hydrated minerals boiled off. While Dawn did not find actual water ice at Vesta, there are signs of hydrated minerals delivered by meteorites and dust evident in the giant asteroid's chemistry and geology. The findings appear today in the journal Science.
One paper, led by Thomas Prettyman, the lead scientist for Dawn's gamma ray and neutron detector (GRaND) at the Planetary Science Institute in Tucson, Ariz., describes how the instrument found signatures of hydrogen, likely in the form of hydroxyl or water bound to minerals in Vesta's surface.
"The source of the hydrogen within Vesta's surface appears to be hydrated minerals delivered by carbon-rich space rocks that collided with Vesta at speeds slow enough to preserve their volatile content," said Prettyman.
A complementary paper, led by Brett Denevi, a Dawn participating scientist based at the Johns Hopkins University Applied Physics Laboratory in Laurel, Md., describes the presence of pitted terrain created by the release of the volatiles.
Vesta is the second most massive member of the main asteroid belt. The orbit at which these data were obtained averaged about 130 miles (210 kilometers) above the surface. Dawn left Vesta earlier this month, on Sept. 4 PDT (Sept. 5 EDT), and is now on its way to its second target, the dwarf planet Ceres.
Scientists thought it might be possible for water ice to survive near the surface around the giant asteroid's poles. Unlike Earth's moon, however, Vesta has no permanently shadowed polar regions where ice might survive. The strongest signature for hydrogen in the latest data came from regions near the equator, where water ice is not stable.
In some cases, other space rocks crashed into these deposits later at high speed. The heat from the collisions converted the hydrogen bound to the minerals into water, which evaporated. The holes that were left as the water escaped stretch as much as 0.6 miles (1 kilometer) across and go down as deep as 700 feet (200 meters). Seen in images from Dawn's framing camera, this pitted terrain is best preserved in sections of Marcia crater.
"The pits look just like features seen on Mars, but while water was common on Mars, it was totally unexpected on Vesta in these high abundances," said Denevi. "These results provide evidence that not only were hydrated materials present, but they played an important role in shaping the asteroid's geology and the surface we see today."
GRaND's data are the first direct measurements describing the elemental composition of Vesta's surface. Dawn's elemental investigation by the instrument determined the ratios of iron to oxygen and iron to silicon in the surface materials. The new findings solidly confirm the connection between Vesta and a class of meteorites found on Earth called the Howardite, Eucrite and Diogenite meteorites, which have the same ratios for these elements. In addition, more volatile-rich fragments of other objects have been identified in these meteorites, which supports the idea that the volatile-rich material was deposited on Vesta.
Elemental Mapping by Dawn Reveals Exogenic H in Vesta's Regolith - Thomas H. Prettyman et al
The mechanism that incorporates water into the terrestrial planets is a matter of extensive debate for planetary scientists. Now, observations of the giant asteroid Vesta by NASA's Dawn mission suggest that hydrated materials were delivered to it mainly through a buildup of small particles during an epoch when the solar system was rich in dust. This is a radically different process from the way hydrated materials have been deposited on the moon and may have implications for the formation of terrestrial planets, including the delivery of the water that formed Earth's ocean. Maria Cristina De Sanctis and the Dawn team present the scenarios today at the European Planetary Science Congress in Madrid, Spain.
"Vesta's surface shows distinct areas enriched with hydrated materials," said De Sanctis, of the Italian National Institute for Astrophysics in Rome. "These regions are not dependent on solar illumination or temperature, as we find in the case of the moon. The uneven distribution is unexpected and indicates ancient processes that differ from those believed to be responsible for delivering water to other airless bodies, like the moon."
A team led by De Sanctis studied data from Dawn's visible and infrared mapping spectrometer, which complement recently reported data on hydrogen distribution from Dawn's gamma ray and neutron detector. Their analysis showed large regional concentrations of hydroxyl - a hydrogen and an oxygen atom bound together - clearly associated with geological features, including ancient, highly-cratered terrains and a crater named Oppia.
Hydroxyl on the surface of the moon is thought to be created continuously by the interaction of protons from the solar wind with the top 10 feet (few meters) of the lunar surface, or regolith. Highest concentrations are found in areas near the lunar poles and in permanently shadowed craters where it is very cold. By contrast, the distribution of hydroxyl on Vesta is not dependent on significant shadowing or unusual cold temperatures. It is also stable over time, so its origin does not appear to be due to short-term processes.
The hydroxyl-rich regions on Vesta broadly correspond to its oldest surfaces. Around relatively large and young impact craters, hydroxyl detections are weak or absent, suggesting that the delivery of the substance is not an ongoing process.
The evidence from Dawn's visible and infrared mapping spectrometer suggests that much of Vesta's hydroxyl was delivered by small particles of primitive material, less than a few centimeters in diameter, over a time-limited period. This period may have occurred during the primordial solar system, around the time water is believed to have accumulated on Earth, or during the Late Heavy Bombardment, when collisions with space rocks would have produced a significant amount of dust.
However, this is not the whole story of hydrated materials on Vesta. The Oppia Crater is hydroxyl-rich, but not covered with the primitive dark material. This suggests there is more than one mechanism at work for depositing hydroxyl on Vesta's surface.
"The origin of Vesta's hydroxyl is certainly complex and possibly not unique: there could be various sources, like formation of hydroxyl actually on Vesta, in addition to the primordial impactors," said De Sanctis. "Vesta is providing new insights into the delivery of hydrous materials in the main asteroid belt, and may offer new scenarios on the delivery of hydrous minerals in the inner solar system, suggesting processes that may have played a role in the formation of terrestrial planets."
Enormous troughs that wrap around the giant asteroid Vesta may actually be dropped blocks of terrain bounded by fault lines, suggesting a geologic complexity beyond that of most asteroids. Since the discovery of the troughs last year in data from NASA's Dawn spacecraft, scientists have been working to determine the story behind these unusual features. The research reinforces the claim that Vesta has a core, mantle and crust, a structure normally reserved for larger bodies, such as planets and large moons.
An extensive system of troughs encircles Vesta's equatorial region. The biggest of those troughs, named Divalia Fossa, surpasses the size of the Grand Canyon. It spans 289 miles (465 kilometers) in length, 13.6 miles (22 kilometers) in width and 3 miles (5 kilometers) in depth. The complexity of the troughs' morphology can't be explained by small collisions. New measurements from Dawn indicate that a large collision could have created the asteroid's troughs, said Debra Buczkowski, a Dawn participating scientist based at the Johns Hopkins University Applied Physics Laboratory in Laurel, Md., who is the lead author of a new paper in Geophysical Research Letters, a journal of the American Geophysical Union. The crustal layer at the surface appeared to stretch to the breaking point and large portions of the crust dropped down along two faults on either side of the downward-moving block, leaving the giant troughs we see today.
The scale of the fracturing would only have been possible if the asteroid is differentiated - meaning that it has a core, mantle and crust. "By saying it's differentiated," said Buczkowski, "we're basically saying Vesta was a little planet trying to happen."
<<Enormous troughs that wrap around the giant asteroid Vesta may actually be dropped blocks of terrain bounded by fault lines, suggesting a geologic complexity beyond that of most asteroids. Since the discovery of the troughs last year in data from NASA's Dawn spacecraft, scientists have been working to determine the story behind these unusual features. The research reinforces the claim that Vesta has a core, mantle and crust, a structure normally reserved for larger bodies, such as planets and large moons. An extensive system of troughs encircles Vesta's equatorial region. The biggest of those troughs, named Divalia Fossa, surpasses the size of the Grand Canyon. It spans 2465 kilometers in length, 22 kilometers in width and 5 kilometers in depth. The complexity of the troughs' morphology can't be explained by small collisions. New measurements from Dawn indicate that a large collision could have created the asteroid's troughs, said Debra Buczkowski. The crustal layer at the surface appeared to stretch to the breaking point and large portions of the crust dropped down along two faults on either side of the downward-moving block, leaving the giant troughs we see today. The scale of the fracturing would only have been possible if the asteroid is differentiated - meaning that it has a core, mantle and crust. "By saying it's differentiated," said Buczkowski, "we're basically saying Vesta was a little planet trying to happen."
Re: Dawn: Journey to the Asteroid Belt
Posted: Wed Oct 17, 2012 1:05 pm
by dougettinger
How are the ages of the two largest crater systems, one billion and two billion years, determined ?
About 4.6 billion years ago, the solar system was little more than a tenuous disk of gas and dust. In the span of merely 10 million years, this soup evolved to form today’s massive, complex planets. In the intervening period, however, the solar system contained a mixture of intermediary bodies — small chunks of rock, the remnants of which today are known as asteroids.
Although not much is known about the early composition of asteroids, some scientists suspect that such information may reveal an unexpected diversity of planetary bodies within the early solar system.
Now a new study published this week in Science has found evidence that Vesta, the second-most-massive asteroid in the solar system, once harbored a dynamo — a molten, swirling mass of conducting fluid generating a magnetic field — resembling that in much larger planets like Earth. Researchers at MIT say the findings suggest that asteroids like Vesta may have been more than icy chunks of space debris.
“We’re filling in the story of basically what happened during those first few million years of the solar system, when an entire solar system was dominated by objects like this,” says Roger Fu, a graduate student in MIT’s Department of Earth, Atmospheric and Planetary Sciences (EAPS), and the study’s first author. “These bodies are really like miniature planets.”
“Vesta becomes now the smallest known planetary object to have generated a dynamo,” says co-author Benjamin Weiss, an associate professor of planetary sciences in EAPS. “You can imagine many asteroids in the early solar system were doing this.” ...
Now a new study published this week in Science has found evidence that Vesta, the second-most-massive asteroid in the solar system, once harbored a dynamo — a molten, swirling mass of conducting fluid generating a magnetic field — resembling that in much larger planets like Earth. Researchers at MIT say the findings suggest that asteroids like Vesta may have been more than icy chunks of space debris.
Thank you for referencing the above articles. The two articles "gsa" and "adsabs" differ in their dating of the largest impact craters on Vesta. Owlice, do you have any resolution to these different dating criteria of the Vesta impact craters. The "gsa" article states that Rheasilvia is estimated to be 1 Gyr in age and the crater underneath, Veneneia, is 2 Gyr in age. The "adsabs" article states that the Rheasilvia basin is 3.70 Ga and the older basin underneath is 3.81 Ga with a general re-surfacing event occurring 4.00 Ga. The two articles have a large conflict. The "adsabs" article is more credible and agrees with what I would expect in the main belt.
Is the "gsa" still under review or dis-credited?
Doug
Dawn Sees 'Young' Surface on Giant Asteroid
Posted: Thu Nov 01, 2012 12:21 pm
by bystander
Dawn Sees 'Young' Surface on Giant Asteroid
NASA | JPL-Caltech | Dawn | 2012 Oct 31
Like a Hollywood starlet constantly retouching her makeup, the giant asteroid Vesta is constantly stirring its outermost layer to present a young face. Data from NASA's Dawn mission show that a form of weathering that occurs on the moon and other airless bodies we've visited in the inner solar system does not alter Vesta's outermost layer in the same way. Carbon-rich asteroids have also been splattering dark material on Vesta's surface over a long span of the body's history. The results are described in two papers released today in the journal Nature.
"Dawn's data allow us to decipher how Vesta records fundamental processes that have also affected Earth and other solar system bodies," said Carol Raymond, Dawn deputy principal investigator at NASA's Jet Propulsion Laboratory, Pasadena, Calif. "No object in our solar system is an island. Throughout solar system history, materials have exchanged and interacted."
Over time, soils on Earth's moon and asteroids such as Itokawa have undergone extensive weathering in the space environment. Scientists see this in the accumulation of tiny metallic particles containing iron, which dulls the fluffy outer layer. Dawn's visible and infrared mapping spectrometer (VIR) and framing camera detected no accumulation of such tiny particles on Vesta, and this particular protoplanet, or almost-planet, remains bright and pristine.
Nevertheless, the bright rays of the youngest features on Vesta are seen to degrade rapidly and disappear into background soil. Scientists know frequent, small impacts continually mix the fluffy outer layer of broken debris. Vesta also has unusually steep topography relative to other large bodies in the inner solar system, which leads to landslides that further mix surface material.
"Getting up close and familiar with Vesta has reset our thinking about the character of the uppermost soils of airless bodies," said Carle Pieters, one of the lead authors and a Dawn team member based at Brown University, Providence, R.I. "Vesta 'dirt' is very clean, well mixed and highly mobile."
Early pictures of Vesta showed a variety of dramatic light and dark splotches on Vesta's surface. These light and dark materials were unexpected and now show the brightness range of Vesta is among the largest observed on rocky bodies in our solar system.
Dawn scientists suspected early on that bright material is native to Vesta. One of their first hypotheses for the dark material suggested it might come from the shock of high-speed impacts melting and darkening the underlying rocks or from recent volcanic activity. An analysis of data from VIR and the framing camera has revealed, however, that the distribution of dark material is widespread and occurs both in small spots and in diffuse deposits, without correlation to any particular underlying geology. The likely source of the dark material is now shown to be the carbon-rich material in meteoroids, which are also believed to have deposited hydrated minerals from other asteroids on Vesta.
To get the amount of darkening we now see on Vesta, scientists on the Dawn team estimate about 300 dark asteroids with diameters between 0.6 to 6 miles (1 and 10 kilometers) likely hit Vesta during the last 3.5 billion years. This would have been enough to wrap Vesta in a blanket of mixed material about 3 to 7 feet (1 to 2 meters) thick.
"This perpetual contamination of Vesta with material native to elsewhere in the solar system is a dramatic example of an apparently common process that changes many solar system objects," said Tom McCord, the other lead author and a Dawn team member based at the Bear Fight Institute, Winthrop, Wash. "Earth likely got the ingredients for life - organics and water - this way."
dougettinger wrote:Thank you for referencing the above articles. The two articles "gsa" and "adsabs" differ in their dating of the largest impact craters on Vesta. Owlice, do you have any resolution to these different dating criteria of the Vesta impact craters. The "gsa" article states that Rheasilvia is estimated to be 1 Gyr in age and the crater underneath, Veneneia, is 2 Gyr in age. The "adsabs" article states that the Rheasilvia basin is 3.70 Ga and the older basin underneath is 3.81 Ga with a general re-surfacing event occurring 4.00 Ga. The two articles have a large conflict. The "adsabs" article is more credible and agrees with what I would expect in the main belt.
Is the "gsa" still under review or dis-credited?
Doug
I have yet to receive any answer regarding what the current, popular age is for the Rheasilvia and Veneneia impact basins. The two referenced articles post different ages. Can anyone confirm that the ages of the two subject crater basins is NOT a difference of 1 billion years? Thanks.
Doug
Re: Dawn: Journey to the Asteroid Belt
Posted: Sat Nov 03, 2012 3:34 am
by owlice
Doug, I'm not an astronomer. I don't even play one on TV. So no, I do not have any resolution to the dating criteria. The GSA item is for a session that will be given next week. It cites two papers for the age of Rheasilvia. Did you look up and read those two papers? If I were to research this question, I'd start by reading the relevant research. I've pointed you to the abstracts for some recent/upcoming presentation of findings; these can lead you to additional research to read. Neither the item from the GSA meeting nor the item from ADS are research papers; these are just abstracts, descriptions of the papers/research that was/will be presented. Likely good places to start to find research that has been presented in peer-reviewed journals.
New findings can shed new light on a question, changing an earlier answer developed when there was less information. That's how science works. There are no canals on Mars after all, and Pluto is now a dwarf planet.
Re: Dawn: Journey to the Asteroid Belt
Posted: Sun Nov 04, 2012 10:43 pm
by dougettinger
Owlice, thank you. I am not very good at following the "threads" of abstracts and short articles. I will try to improve. I thought that someone would know already if this matter was sorted out.
Besides being the Guardian of Codes what is your background that brings you to the forum?
Are "minor" and "dwarf" planet considered interchangeable for Pluto and Ceres ?
Doug
Re: Dawn: Journey to the Asteroid Belt
Posted: Wed Nov 14, 2012 1:46 am
by neufer
Nov. 13, 2012
------------------------------------------------------------
Dawn spacecraft 1 million kilometers from Vesta
& 58 million kilometers from Ceres.
dougettinger wrote:Are "minor" and "dwarf" planet considered interchangeable for Pluto and Ceres ?
Doug
Is Doug still out there in the blogosphere, or did he give out since his questions weren't being answered?
Anyway, as modifiers of the noun "planet" the words "minor" and "dwarf" are not interchangeable. I'll be corrected if I'm wrong (and maybe even if I'm not wrong ) but dwarf planets are the smallest objects that actually are planets by virtue of the fact that their mass is large enough to have pulled themselves into a round shape. Minor "planets" aren't planets, at least in many (most?) people's (persons?) opinions. Minor planets refer to all the irregularly shaped leftover (natural) junk that's orbiting the Sun.
