[Badyalectlawl]

You're beautiful, Vesta
by Staff Writers
Los Angeles CA (SPX) May 11, 2012

The study of Vesta, however, is only half of Dawn's mission. The spacecraft will also conduct a detailed study of the structure and composition of the dwarf planet Ceres. Vesta and Ceres are the most massive objects in the main asteroid belt between Mars and Jupiter. Dawn's goals include determining the shape, size, composition, internal structure, and tectonic and thermal evolution of both objects, and the mission is expected to reveal the conditions under which each of them formed.



When UCLA's Christopher T. Russell looks at the images of the protoplanet Vesta produced by NASA's Dawn mission, he talks about beauty as much as he talks about science.

"Vesta looks like a little planet. It has a beautiful surface, much more varied and diverse than we expected," said Russell, a professor in UCLA's Department of Earth and Space Sciences and the Dawn mission's principal investigator. "We knew Vesta's surface had some variation in color, but we did not expect the diversity that we see or the clarity of the colors and textures, or their distinct boundaries. We didn't find gold on Vesta, but it is still a gold mine."

Dawn has been orbiting Vesta and collecting data on the protoplanet's surface since July 2011. Vesta, which is in the doughnut-shaped asteroid belt between Mars and Jupiter, is currently some 321 million miles from Earth.

The journal Science publishes six papers about Vesta on May 11. Russell is a co-author on all of them.

Russell and his scientific team expected to find a large crater on Vesta, but they were surprised to find two, with the larger one essentially on top of the smaller. The smaller crater covers roughly the distance from Los Angeles to Monterey, Calif.; the larger one would stretch from L.A. to San Francisco.

"When we got to Vesta, we found two very large impacts, both in the southern region," Russell said. "One dates at about a billion years ago, and the other at least 2 billion years ago. Seeing two was a real discovery, and getting their ages is even better. The ages look like they correspond to the dates when we think rocks were blasted off Vesta; some came all the way to Earth. The large size of the craters can easily account for the material that came off, to fall as meteorites and many smaller 'Vestoids' that are like very large boulders."

Many of the so-called Vestoids are approximately one-half mile to five miles across, and there may be thousands of them throughout the asteroid belt, Russell said. Named for the ancient Roman goddess of the hearth, Vesta has been bombarded by comets, meteoroids and its smaller siblings for 4.5 billion years.

Among the other new discoveries reported in Science:

+ Vesta has large mountains - the largest is more than twice the size of Mount Everest - which were formed by a major impact to the protoplanet's surface. Scientists thought most of Vesta outside the south polar region might be flat like the moon, yet some of the craters outside that region formed on very steep slopes and have nearly vertical sides, with landslides often occurring in the regolith, the deep layer of crushed rock on the surface.

+ The Dawn mission has witnessed a pattern of minerals exposed by deep gashes created by space-rock impacts to Vesta. This might support the idea that Vesta was once molten inside and had a sub-surface magma ocean.

+ Vesta has an iron core, formed during the period in which the protoplanet was molten, at the earliest epoch of the solar system; Dawn's measurements of Vesta's gravitational field have confirmed this. This finding was expected because meteorites from Vesta have less iron than the solar nebula from which planetary building blocks formed. That the iron is indeed sequestered in Vesta's core confirms thinking that Vesta separated into layers when it formed, and this starting composition allows scientists to constrain early solar system models.

+ Vesta's surface contains many bright spots of varying size. A real surprise is that Vesta also has some areas as dark as coal. The dark and light markings form intricate patterns suggesting the dominance of impact processes in creating mixed layers in Vesta's regolith.

"It looks like an artist has painted the craters in fancy patterns," Russell said. "It is beautiful, and surprising."

Dawn has obtained more than 20,000 images of Vesta and millions of spectra, or data collected from different wavelengths of radiation.

"Everything is working," Russell said proudly.

Studies of meteorites found on Earth that are linked to Vesta suggest that Vesta formed from interstellar gas and dust during the solar system's first 2 to 5 million years.

"Vesta has been recording the history of the solar system from the beginning," Russell said. "We are going back to the beginning of the solar system - more than 4.5 billion years ago. We're going back further than ever before on the surface of a body."

New images and videos of Vesta are available at http://www.nasa.gov/mission_pages/da...n20120510.html.

The Dawn mission, which launched in September 2007, has been as close as 125 miles from the surface of Vesta, which has an average diameter of approximately 330 miles.

Dawn has a high-quality camera, along with a back-up; a visible and near-infrared mapping spectrometer to identify minerals on the surface; and a gamma ray and neutron spectrometer to reveal the abundance of elements such as iron and hydrogen, possibly from water, in the soil. Dawn also probes Vesta's gravity using extremely precise navigation.

The study of Vesta, however, is only half of Dawn's mission. The spacecraft will also conduct a detailed study of the structure and composition of the dwarf planet Ceres. Vesta and Ceres are the most massive objects in the main asteroid belt between Mars and Jupiter. Dawn's goals include determining the shape, size, composition, internal structure, and tectonic and thermal evolution of both objects, and the mission is expected to reveal the conditions under which each of them formed.

Dawn, the second scientific mission to be powered by an advanced NASA technology known as ion propulsion, is the first NASA mission to orbit two solar system targets beyond the moon.

After orbiting Vesta, Dawn will leave for its nearly three-year journey to Ceres, which could harbor substantial water or ice beneath its rock crust - and possibly life. The spacecraft will rendezvous with Ceres and begin orbiting in 2015, conducting studies and observations for at least five months.

"I want to squeeze every last image out of Vesta before we leave," Russell said. "We will be analyzing Vesta's surface properties at least until we get to Ceres."





http://www.spacedaily.com/reports/Yo...Vesta_999.html

[Badyalectlawl]

Dawn easing into its final science orbit
June 15, 2012 By Priscilla Vega and Jia-Rui Cook




(Phys.org) -- After successfully completing nearly five months scrutinizing the giant asteroid Vesta at its lowest orbit altitude, NASA's Dawn spacecraft will begin its final major science data-gathering phase at Vesta on June 15, at an average altitude of 420 miles (680 kilometers) above the surface.




Over the past six weeks, Dawn has been gently spiraling up from its lowest orbit - 130 miles, or 210 kilometers, above the surface - to the final planned science orbit, known as high-altitude mapping orbit 2. Observations obtained from this orbit will provide a companion set of data and images to those obtained during the first high-altitude mapping orbit phase, completed in October 2011. A key difference will be that the angle of sunlight hitting Vesta has changed, illuminating more of its northern region. The principal science observations planned in this new orbit will be obtained with the framing camera and the visible and infrared mapping spectrometer.

Following this final science data gathering phase, Dawn will then spend almost five weeks spiraling out from the giant asteroid to the point at which Vesta will lose its gravitational hold on the spacecraft. That departure day is expected to be around Aug. 26. Dawn will turn to view Vesta as it leaves and acquire more data. Then, Dawn will set its sights on the dwarf planet Ceres, and begin a two-and-a-half year journey to investigate the largest body in the main asteroid belt. Dawn will enter orbit around Ceres in 2015.




http://phys.org/news/2012-06-dawn-ea...nce-orbit.html

[Vikonbarius]

IIRC, this is the fourth of four stages. The third is the most interesting and exciting because it was intended to give us both the mineralogy and internal structure of Vesta. The First stage was primarily a distant all-over view and the second and fourth stages concentrate on topography. The difference between the second and fourth stages is lighting - Vesta is in a different part of its orbit so is lit differently because of its axis inclination. This gives a much better way to distinguish between changes in light level due to topography and those due to intrinsic colour.

We've now finished the third stage so I eagerly await the mineralogy and internal structure results.

I should also add here that the third stage is the closest. Dawn is now moving away from Vesta.

[Badyalectlawl]

Asteroid probe loses another pointing system wheel
DAWN MISSION STATUS REPORT
Posted: 15 August 2012



Engineers working on NASA's Dawn spacecraft are assessing the status of a reaction wheel – part of a system that helps the spacecraft point precisely – after onboard software powered it off on August 8. Dawn's mission is to study the geology and geochemistry of the giant asteroid Vesta and dwarf planet Ceres, the two most massive objects in the main asteroid belt. Dawn is now using its thrusters to point at Earth for communications. The rest of the spacecraft is otherwise healthy.

During a planned communications pass on August 9, the team learned that the reaction wheel had been powered off. Telemetry data from the spacecraft suggest the wheel developed excessive friction, similar to the experience with another Dawn reaction wheel in June 2010. The Dawn team demonstrated during the cruise to Vesta in 2011 that, if necessary, they could complete the cruise to Ceres without the use of reaction wheels.

The spacecraft has been orbiting Vesta since July 15, 2011. Dawn concluded its primary science observations of Vesta on July 25, 2012, and has been spiraling slowly away from the giant asteroid using its ion propulsion system. Ion thrusting was halted to accommodate the reaction wheel investigation, which may briefly delay the escape from Vesta.

"The Vesta mission has been spectacularly successful, and we are looking forward to the exciting Ceres mission ahead of us," said Robert Mase, Dawn project manager, of NASA's Jet Propulsion Laboratory, Pasadena, California.

JPL manages the Dawn mission for NASA's Science Mission Directorate in Washington. Dawn is a project of the directorate's Discovery Program, managed by NASA's Marshall Space Flight Center in Huntsville, Alabama. The University of California at Los Angeles (UCLA) is responsible for overall Dawn mission science. Orbital Sciences Corp. in Dulles, Viginia., designed and built the spacecraft. The German Aerospace Center, the Max Planck Institute for Solar System Research, the Italian Space Agency and the Italian National Astrophysical Institute are international partners on the mission team.

For more information about Dawn, visit: http://www.nasa.gov/dawn and http://dawn.jpl.nasa.gov .





http://www.astronomynow.com/news/n1208/15dawn/

[Vikonbarius]

> Engineers working on NASA's Dawn spacecraft are assessing the status of a reaction wheel after onboard software powered it off on August 8

Drat. After the trouble with Hubble's gyroscopes you think that somebody would have learnt. Was Dawn launched before or after the latest Hubble servicing mission? Hubble's gyroscopes have behaved themselves since the most recent servicing mission.

I care a lot more about Dawn's visit to Ceres than I do about Vesta. Ceres is a dwarf planet. Vesta is not, it's just a big asteroid.

For news items and images from Dawn see http://dawn.jpl.nasa.gov/multimedia/...wn_gallery.asp
eg.


Meteorites from Vesta

May 10, 2012 - PASADENA, Calif. -- This image shows three slices of a class of meteorites that fell to Earth that NASA's Dawn mission has confirmed as originating from the giant asteroid Vesta. The meteorites, known as howardite, eucrite and diogenite meteorites, were viewed through a polarizing microscope, where different minerals appear in different colors. The texture of the rocks reveals that they crystallized at different rates. The image on the left comes from a meteorite named QUE 97053 (Antarctica), which is basaltic eucrite. The image in the middle comes from the Moore County (North Carolina) cumulate eucrite. The image on the right comes from a diogenite meteorite named GRA 98108 (Antarctica).