The IAU will have a problem now...asteroid or dwarf planet--VESTA

Like Earth and other terrestrial planets, Vesta has ancient basaltic lava flows on the surface and a large iron core. It also has tectonic features, troughs, ridges, cliffs, hills and a giant mountain. False colors in this montage represent different rock and mineral types.

"Is Vesta the "Smallest Terrestrial Planet?""

by

Dauna Coulter

December 9th, 2011

NASA

Vesta was discovered over two hundred years ago but, until Dawn, has been seen only as an indistinct blur and considered little more than a large, rocky body. Now the spacecraft's instruments are revealing the true complexity of this ancient world.

"We're seeing enormous mountains, valleys, hills, cliffs, troughs, ridges, craters of all sizes, and plains," says Chris Russell, Dawn principal investigator from UCLA. "Vesta is not a simple ball of rock. This is a world with a rich geochemical history. It has quite a story to tell!"

In fact, the asteroid is so complex that Russell and members of his team are calling it the "smallest terrestrial planet."

Vesta has an iron core, notes Russell, and its surface features indicate that the asteroid is "differentiated" like the terrestrial planets Earth, Mercury, Mars, and Venus.

Differentiation is what happens when the interior of an active planet gets hot enough to melt, separating its materials into layers. The light material floats to the top while the heavy elements, such as iron and nickel, sink to the center of the planet.

Researchers believe this process also happened to Vesta.

The story begins about 4.57 billion years ago, when the planets of the Solar System started forming from the primordial solar nebula. As Jupiter gathered itself together, its powerful gravity stirred up the material in the asteroid belt so objects there could no longer coalesce. Vesta was in the process of growing into a full-fledged planet when Jupiter interrupted the process.

Although Vesta’s growth was stunted, it is still differentiated like a true planet.

"We believe that the Solar System received an extra slug of radioactive aluminum and iron from a nearby supernova explosion at the time Vesta was forming," explains Russell. "These materials decay and give off heat. As the asteroid was gathering material up into a big ball of rock, it was also trapping the heat inside itself."

As Vesta’s core melted, lighter materials rose to the surface, forming volcanoes and mountains and lava flows.

"We think Vesta had volcanoes and flowing lava at one time, although we've not yet found any ancient volcanoes there," says Russell. "We're still looking. Vesta's plains seem similar to Hawaii's surface, which is basaltic lava solidified after flowing onto the surface.

Vesta has so much in common with the terrestrial planets, should it be formally reclassified from "asteroid" to "dwarf planet"?

"That's up to the International Astronomical Union, but at least on the inside, Vesta is doing all the things a planet does."

If anyone asks Russell, he knows how he would vote.

Dawn snaps Vesta's "snowman"

Using its framing camera, Dawn obtained this image of Vesta on July 24, 2011, from a distance of about 3,200 miles (5,200 kilometers). The three vertically-aligned craters on the left have been nicknamed "the snowman" by camera team members.

"Dawn's Smooth Move"

August 1st, 2011

NASA

When a NASA spacecraft goes into orbit around a new world for the first time, the control room is usually packed to capacity with scientists, engineers, and dignitaries ready to leap and shout when the retro-rockets fire. It's a big, noisy event.

July 15, 2011, was one of those days. NASA's Dawn spacecraft approached Vesta and became the first probe from Earth to orbit a main belt asteroid. Dawn's cameras revealed a desolate world of transcendent beauty, thrilling everyone who worked on the project.

Needless to say, the control room was .... silent?

"Actually it was empty," says Dawn Chief Engineer Marc Rayman of JPL. "Dawn entered orbit on a Friday night; I myself was out dancing with my wife and friends."

What gives? Rayman, an avid folk dancer, explains: "Our mission has a unique choreography."

Indeed, Dawn has its own way of doing things. While most spacecraft blast off Earth atop a firestorm of conventional rocket exhaust, then coast to their destinations with engines turned off to conserve fuel, Dawn was able to continue thrusting throughout its voyage. Fuel-efficient ion engines gently propelled the spacecraft toward Vesta for more than three years, never exerting more force than the weight of a feather held in your open palm yet, over time, gathering enough speed to catch an asteroid racing halfway across the solar system.

With engines firing almost constantly, mission controllers were able to actively steer the probe, gradually reshaping Dawn's orbit around the sun until it matched the orbit of Vesta itself. Meeting Vesta for orbital insertion wasn't a jarring encounter of mismatched velocities. It was more like two dancers merging in practiced rhythm to a familiar tune.

"Dawn did not miss a beat as it flew into Vesta's grasp," says Rayman. "The spacecraft moved gently into orbit with the same grace it has displayed during its nearly 1000 days of ion propulsion through the solar system."

The capture was so smooth, so low-key, that personnel felt no particular need to monitor the probe's operation. "I really was out dancing," says Rayman, "confident that the pas de deux being performed 188 million kilometers away would be executed with graceful beauty and flawless precision."

Calculations show that the moment of "orbit insertion" occurred on Friday night, July 15th, around 9:47 pm PDT. At that moment, Dawn's orbit around the sun finally was so close to that of Vesta that the protoplanet's gravity could take hold of it. Radio signals picked up on schedule by the Deep Space Network later confirmed that the spaceship and asteroid were truly a pair.

Dawn will spend the next year circling Vesta in a series of descending passes, bringing the giant asteroid's ancient surface ever closer to Dawn's cameras and other science instruments. Because Vesta is a relic of long-ago planet formation, the history of our solar system could be revealed under Dawn's careful scrutiny.

"This really beautiful dance," says Rayman, "is just getting started."

Dawn JPL

Another Dawn snap of Vesta

NASA's Dawn spacecraft obtained this image with its framing camera on July 18, 2011. It was taken from a distance of about 6,500 miles (10,500 kilometers) away from the protoplanet Vesta. The smallest detail visible is about 1.2 miles (2.0 km).

"Image: Vesta's South Pole As Seen From Orbit"

July 24th, 2011

Jet Propulsion Laboratory

Dawn took this image while it was orbiting around Vesta, traveling from the day side to the night side. The large structure near the south pole that showed up so prominently in previous images is visible in the center of the illuminated surface. Compared to other images, more of the surface beneath the spacecraft is in the shadow of night. Vesta turns on its axis once very five hours and 20 minutes.

Dawn entered orbit around Vesta on July 15, 2011, and will spend a year orbiting the body. Next stop on its itinerary will be an encounter with the dwarf planet Ceres. 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. 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.

Check with NASA's home page for further developments and images.

NASA

1st snap of asteroid Vesta

"NASA Dawn Spacecraft Returns Close-Up Image of Asteroid Vesta"

July 18th, 2011

Jet Propulsion Laboratory

NASA's Dawn spacecraft has returned the first close-up image after beginning its orbit around the giant asteroid Vesta. On Friday, July 15, Dawn became the first probe to enter orbit around an object in the main asteroid belt between Mars and Jupiter.

The image taken for navigation purposes shows Vesta in greater detail than ever before. When Vesta captured Dawn into its orbit, there were approximately 9,900 miles (16,000 kilometers) between the spacecraft and asteroid. Engineers estimate the orbit capture took place at 10 p.m. PDT Friday, July 15 (1 a.m. EDT Saturday, July 16).

Vesta is 330 miles (530 kilometers) in diameter and the second most massive object in the asteroid belt. Ground- and space-based telescopes have obtained images of Vesta for about two centuries, but they have not been able to see much detail on its surface. "We are beginning the study of arguably the oldest extant primordial surface in the solar system," said Dawn principal investigator Christopher Russell from the University of California, Los Angeles. "This region of space has been ignored for far too long. So far, the images received to date reveal a complex surface that seems to have preserved some of the earliest events in Vesta's history, as well as logging the onslaught that Vesta has suffered in the intervening eons."

Vesta is thought to be the source of a large number of meteorites that fall to Earth. Vesta and its new NASA neighbor, Dawn, are currently approximately 117 million miles (188 million kilometers) away from Earth. The Dawn team will begin gathering science data in August. Observations will provide unprecedented data to help scientists understand the earliest chapter of our solar system. The data also will help pave the way for future human space missions.

After traveling nearly four years and 1.7 billion miles (2.8 billion kilometers), Dawn also accomplished the largest propulsive acceleration of any spacecraft, with a change in velocity of more than 4.2 miles per second (6.7 kilometers per second), due to its ion engines. The engines expel ions to create thrust and provide higher spacecraft speeds than any other technology currently available.

"Dawn slipped gently into orbit with the same grace it has displayed during its years of ion thrusting through interplanetary space," said Marc Rayman, Dawn chief engineer and mission manager at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "It is fantastically exciting that we will begin providing humankind its first detailed views of one of the last unexplored worlds in the inner solar system."

Although orbit capture is complete, the approach phase will continue for about three weeks. During approach, the Dawn team will continue a search for possible moons around the asteroid; obtain more images for navigation; observe Vesta's physical properties; and obtain calibration data.

In addition, navigators will measure the strength of Vesta's gravitational tug on the spacecraft to compute the asteroid's mass with much greater accuracy than has been previously available. That will allow them to refine the time of orbit insertion.

Dawn will spend one year orbiting Vesta, then travel to a second destination, the dwarf planet Ceres, arriving in February 2015. The mission to Vesta and Ceres is managed by JPL for the agency's Science Mission Directorate in Washington. Dawn is a project of the directorate's Discovery Program, which is managed by NASA's Marshall Space Flight Center in Huntsville, Ala.

UCLA is responsible for Dawn mission science. Orbital Sciences Corp. of Dulles, Va., 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 part of the mission's team.

Asteroid Vesta today

Image taken from a distance of about 26,000 miles (41,000 kilometers).

More science here that ISS and shuttles.

"NASA Spacecraft to Enter Asteroid's Orbit on July 15"

Julj 15th, 2011

NASA

On July 15, NASA's Dawn spacecraft will begin a prolonged encounter with the asteroid Vesta, making the mission the first to enter orbit around a main-belt asteroid.

The main asteroid belt lies between the orbits of Mars and Jupiter. Dawn will study Vesta for one year, and observations will help scientists understand the earliest chapter of our solar system's history.

Engineers expect the spacecraft to be captured into orbit at approximately 10 p.m. PDT Friday, July 15 (1 a.m. EDT Saturday, July 16). They expect to hear from the spacecraft and confirm that it performed as planned during a scheduled communications pass that starts at approximately 11:30 p.m. PDT on Saturday, July 16 (2:30 a.m. EDT Sunday, July 17).

When Vesta captures Dawn into its orbit, engineers estimate there will be approximately 9,900 miles (16,000 kilometers) between them. At that point, the spacecraft and asteroid will be approximately 117 million miles (188 million kilometers) from Earth.

"It has taken nearly four years to get to this point," said Robert Mase, Dawn project manager at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "Our latest tests and check-outs show that Dawn is right on target and performing normally."

Engineers have been subtly shaping Dawn's trajectory for years to match Vesta's orbit around the sun. Unlike other missions, where dramatic propulsive burns put spacecraft into orbit around a planet, Dawn will ease up next to Vesta. Then the asteroid's gravity will capture the spacecraft into orbit. However, until Dawn nears Vesta and makes accurate measurements, the asteroid's mass and gravity will only be estimates. So the Dawn team will need a few days to refine the exact moment of orbit capture.

Launched in September 2007, Dawn will depart for its second destination, the dwarf planet Ceres, in July 2012. The spacecraft will be the first to orbit two solar system destinations beyond Earth.

Dawn's mission to Vesta and Ceres is managed by JPL for NASA's Science Mission Directorate in Washington. Dawn is a project of the directorate's Discovery Program, which is managed by NASA's Marshall Space Flight Center in Huntsville, Ala. UCLA is responsible for overall Dawn mission science. Orbital Sciences Corp. of Dulles, Va., 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 part of the mission team.

Asteroids in fiction [Wikipedia]