Rocks from Vesta on Bennu?

Scientists reviewing data of Bennu from OSIRIS-REx have found six very bright boulders that have a make-up similar to that found on Vesta, which suggests they initially came from that asteroid.

The unusual boulders on Bennu first caught the team’s eye in images from the OSIRIS-REx Camera Suite. They appeared extremely bright, with some almost ten times brighter than their surroundings. They analyzed the light from the boulders using the OSIRIS-REx Visible and Infrared Spectrometer instrument to get clues to their composition. … The signature from the boulders was characteristic of the mineral pyroxene, similar to what is seen on Vesta and the vestoids, smaller asteroids that are fragments blasted from Vesta when it sustained significant asteroid impacts.

Of course it’s possible that the boulders actually formed on Bennu’s parent asteroid, but the team thinks this is unlikely based on how pyroxene typically forms. The mineral typically forms when rocky material melts at high-temperature. However, most of Bennu is composed of rocks containing water-bearing minerals, so it (and its parent) couldn’t have experienced very high temperatures. Next, the team considered localized heating, perhaps from an impact. An impact needed to melt enough material to create large pyroxene boulders would be so significant that it would have destroyed Bennu’s parent-body. So, the team ruled out these scenarios, and instead considered other pyroxene-rich asteroids that might have implanted this material to Bennu or its parent.

The make-up of Vesta matches. While these rocks might have been flung from Vesta during an impact there, eventually to settle on the surface of Bennu, Vesta is not the only possibility. We do not have a good census of the asteroids in the solar system. Others whose make-up is not yet determined could be a source, as well as an asteroid that no longer exists, destroyed by a collision long ago.

Regardless, these rocks confirm that in the process of formation in the early days of the solar system, asteroids of all types exchanged material.

Dawn’s chief engineer reviews the mission

In a long and very detailed post, the chief engineer and mission director of Dawn gives us a very detailed update on the successful state of the spacecraft’s mission.

Not only does he describe what has been gathered at Ceres since the spacecraft arrived a year ago, he gives us this crucial information about the state of this paradigm-shattering ion engine spacecraft, the first to travel to two different objects in the solar system:

Dawn has faced many challenges in its unique voyage in the forbidding depths of space, but it has surmounted all of them. It has even overcome the dire threat posed by the loss of two reaction wheels (the second failure occurring in orbit around Vesta 3.5 years and 1.3 billion miles, or 2.0 billion kilometers, ago). With only two operable reaction wheels (and those no longer trustworthy), the ship’s remaining lifetime is very limited.

A year ago, the team couldn’t count on Dawn even having enough hydrazine to last beyond next month. But the creative methods of conserving that precious resource have proved to be quite efficacious, and the reliable explorer still has enough hydrazine to continue to return bonus data for a while longer. Now it seems highly likely that the spacecraft will keep functioning through the scheduled end of its primary mission on June 30, 2016.

NASA may choose to continue the mission even after that. Such decisions are difficult, as there is literally an entire universe full of interesting subjects to study, but resources are more limited. In any case, even if NASA extended the mission, and even if the two wheels operated without faltering, and even if the intensive campaign of investigating Ceres executed flawlessly, losing not an ounce (or even a gram) of hydrazine to the kinds of glitches that can occur in such a complex undertaking, the hydrazine would be exhausted early in 2017. Clearly an earlier termination remains quite possible.

Dawn has proven the value of ion engines. I would expect to see them used many more times in the future, especially missions heading to low gravity environments.

Water flows on Vesta?

Some data produced by Dawn while it was in orbit around the asteroid Vesta have suggested to some scientists that liquid water might have helped create a handful of the surface features on the asteroid.

The theory is interesting and might be true. I also wouldn’t bet a lot of money on it, because this interpretation of the data is somewhat tentative and based on a lot of assumptions.

How a big impact gave Vesta its grooves

New data suggests that when a large impact hit Vesta’s Rheasilvia basin sometime in the past, the entire asteroid was shaken up, producing ripples that eventually surfaced as the giant grooves that circle the asteroid’s equator.

“Vesta got hammered,” said Peter Schultz, professor of earth, environmental, and planetary sciences at Brown and the paper’s senior author. “The whole interior was reverberating, and what we see on the surface is the manifestation of what happened in the interior.”

The research suggests that the Rheasilvia basin on Vesta’s south pole was created by an impactor that came in at an angle, rather than straight on. But that glancing blow still did an almost unimaginable amount of damage. The study shows that just seconds after the collision, rocks deep inside the asteroid began to crack and crumble under the stress. Within two minutes major faults reached near the surface, forming deep the canyons seen today near Vesta’s equator, far from the impact point.

Essentially, for a very very short period of time, immediately after the impact, the solid material of the asteroid acted more like a liquid, producing ripples that immediately settled down as the solid deep equatorial grooves we see today.

An update on Dawn in its journey from the asteroids Vesta to Ceres.

An update on Dawn in its journey from the asteroids Vesta to Ceres. Bottom line:

Dawn is 18 million kilometers (11 million miles) from Vesta and 50 million kilometers (31 million miles) from Ceres. It is also 3.47 AU (519 million kilometers or 322 million miles) from Earth, or 1,310 times as far as the moon and 3.42 times as far as the sun today. Radio signals, traveling at the universal limit of the speed of light, take 58 minutes to make the round trip.

NASA scientists in a battle with astronomers over who gets to name things on Vesta and Mars.

A rose by any other name: NASA scientists are in a battle with astronomers over who gets to name things on Vesta and Mars.

This is not a new problem. The International Astronomical Union (IAU) has maintained its power over naming everything in space since the 1960s, even though the IAU has sometimes ignored the wishes of the actual discoverers and explorers and given names to things that no one likes. For example, even though the Apollo 8 astronauts wanted to give certain unnamed features on the Moon specific names, the IAU refused to accept their choices, even though those astronauts were the first human beings to reach another world and see these features up close.

Eventually, the spacefarers of the future are going to tell the IAU where to go. And that will begin to happen when those spacefarers simply refuse to use the names the IAU assigns.

The mysterious dark streaks on Vesta

dark material on Vesta

In a preprint paper published today at the Los Alamos astro-ph website, scientists have taken a detailed look at the mysterious dark streaks seen by Dawn on the surface of the asteroid Vesta and have concluded that the material comes from impacts, not from volcanic activity.

The scientists also concluded that

the majority of the spectra of [dark material] are similar to carbonaceous chondrite meteorites mixed with materials indigenous to Vesta.

Carbonaceous chondrite meteorites are considered to be the most primeval material in the solar system. This means that Vesta has the potential to give scientists a convenient laboratory for studying that primeval material and the early formation of the solar system. Ideally, the best way to do this would of course be to go there.

The scientists also theorize that much of this material was brought to Vesta by a single large impact.
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One of Dawn’s reaction wheels, used to orient the spacecraft, shut down last week.

Uh-oh: One of Dawn’s reaction wheels, used to orient the spacecraft, shut down last week.

During a planned communications pass on Aug. 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.

That the spacecraft can get to Ceres without reaction wheels is good. However, can it be oriented precisely to do science without these wheels? The JPL press release does not say.

Dawn has begun its slow departure from Vesta in anticipation of its journey to the solar system’s largest asteroid, Ceres.

Dawn has begun its slow departure from Vesta in anticipation of its journey to the solar system’s largest asteroid, Ceres.

The departure was actually announced two weeks ago, but since this is a very slow process it isn’t like we have missed anything. Dawn’s ion engines are very efficient, but they work at a very leisurely pace. It will take a month for the engine’s thrusters to push Dawn out of its orbit around Vesta.

A global view of Vesta


The accumulating data from Dawn has now allowed scientists to compile a global picture of the varied surface makeup of the asteroid Vesta.

The colors were chosen to highlight differences in surface composition that are too subtle for the human eye to see. Scientists are still analyzing what some of the colors mean for the composition of the surface. But it is clear that the orange material thrown out from some impact craters is different from the surrounding surface material. Green shows the relative abundance of iron. Parts of the huge impact basin known as Rheasilvia in Vesta’s southern hemisphere, for instance, have areas with less iron than nearby areas.

It also makes for a very nice image of the giant asteroid.

New close-up photos of the asteroid Vesta from Dawn have discovered numerous bright spots scattered across the face of the asteroid Vesta.

New close-up photos of the asteroid Vesta from Dawn have discovered numerous bright spots scattered across the face of the asteroid Vesta.

The photos show surprisingly bright spots all over Vesta, with the most predominant ones located inside or around the asteroid’s many craters. The bright areas range from large spots (around several hundred feet across) to simply huge, with some stretching across 10 miles (16 kilometers) of terrain.

The scientists believe the bright spots might be the asteroid’s oldest material, excavated from below by impacts.

Colorful Vesta

False color of Vesta

Tonight’s press conference at the American Geophysical Union conference focused on the latest results from Dawn, orbiting the giant asteroid Vesta. Or to put it as scientist Vishnu Reddy put it, “Vesta is the most colorful asteroid in the solar system.”

At least, in geological terms. To our human eye the asteroid wouldn’t be so spectacular. However, the false color images released by the scientists show the global geological diversity of Vesta. From the press release:
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