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Giant asteroid’s secrets revealed

View of Vesta's southern regions

NASA's Dawn mission has begun to reveal Vesta's complex history. The 110-kilometre-wide dwarf planet is the second-largest body in the asteroid belt.

NASA’s DAWN SPACECRAFT has provided researchers with the first close-up analysis of the giant asteroid Vesta, yielding new insights into its creation and kinship with terrestrial planets and Earth’s Moon.

Vesta now has been revealed as a special fossil of the early Solar System with a more varied, diverse surface than originally thought. Scientists have confirmed a variety of ways in which Vesta more closely resembles a small planet or Earth’s Moon than another asteroid.

“Dawn’s visit to Vesta has confirmed our broad theories of this giant asteroid’s history, while helping to fill in details it would have been impossible to know from afar,” said Carol Raymond, deputy principal investigator at NASA’s Jet Propulsion Laboratory in Pasadena, Calif.

“Dawn’s residence at Vesta of nearly a year has made the asteroid’s planet-like qualities obvious and shown us our connection to that bright orb in our night sky.”

Complex history

Scientists now see Vesta as a layered, planetary building block with an iron core—the only one known to survive the earliest days of the Solar System.

The asteroid’s geologic complexity can be attributed to a process that separated the asteroid into a crust, mantle and iron core with a radius of approximately 110 kilometres about 4.56 billion years ago. The terrestrial planets and Earth’s Moon formed in a similar way.

Graphic showing size comparisons of Mars, Mercury, the Moon and Ceres

Family history: Mars, Mercury, Earth's Moon and the dwarf planet Ceres.

Dawn observed a pattern of minerals exposed by deep gashes formed by space rock impacts, which may support the idea the asteroid once had a subsurface magma ocean.

A magma ocean occurs when a body undergoes almost complete melting, leading to layered building blocks that can form planets. Other bodies with magma oceans ended up becoming parts of Earth and other planets.

Meteorite matches

Data also confirm that a distinct group of meteorites found on Earth did, as theorised, originate from Vesta. The signatures of pyroxene—an iron- and magnesium-rich mineral—in those meteorites match those of rocks on Vesta’s surface.

These objects account for about 6 percent of all meteorites seen falling on Earth.

Three slices of meteorites

Chunks of Vesta have fallen on Earth as meteorites. These are slices of some of them.

This makes the asteroid one of the largest single sources for Earth’s meteorites. The finding also marks the first time a spacecraft has been able to visit the source of samples after they were identified on Earth.

Similarity to moons

Scientists now know Vesta’s topography is quite steep and varied. Some craters on Vesta formed on very steep slopes and have nearly vertical sides, with landslides occurring more frequently than expected.

Another unexpected finding was that the asteroid’s central peak in the Rheasilvia basin in the southern hemisphere is much higher and wider, relative to its crater size, than the central peaks of craters on bodies like our Moon.

Vesta also bears similarities to other low-gravity worlds like Saturn’s small icy moons, and its surface has light and dark markings that don’t match the predictable patterns on Earth’s Moon.

“We know a lot about the Moon and we’re only coming up to speed now on Vesta,” said Vishnu Reddy, a framing camera team member at the Max Planck Institute for Solar System Research in Germany and the University of North Dakota in Grand Forks.

Topographic map of Vesta

Vesta was clobbered by impacts that left huge scars. The largest is called Rheasilvia.

“Comparing the two gives us two storylines for how these fraternal twins evolved in the early Solar System.”

A battered world

Dawn has revealed details of ongoing collisions that battered Vesta throughout its history. Scientists now can date the two giant impacts that pounded Vesta’s southern hemisphere and created the basin Veneneia approximately 2 billion years ago and the Rheasilvia basin about 1 billion years ago. Rheasilvia is the largest impact basin on Vesta.

“The large impact basins on the Moon are all quite old,” said David O’Brien, a Dawn participating scientist from the Planetary Science Institute in Tucson, Arizona. “The fact that the largest impact on Vesta is so young was surprising.”

Launched in 2007, Dawn began exploring Vesta in mid-2011. The spacecraft will depart Vesta on August 26 for its next study target, the dwarf planet Ceres, in 2015.

More information:

NASA’s Dawn mission page

JPL’s Dawn mission page

Adapted from information issued by NASA / JPL-Caltech. Images courtesy NASA / JPL-Caltech / UCLA / University of Tennessee / MPS / DLR / IDA / PSI.

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Latest Dawn image of Vesta

Dawn image of the surface of the asteroid Vesta

Craters large and small litter the surface of the 530-kilometre-wide asteroid Vesta. This image was taken by the Dawn's spacecraft's framing camera. Dawn will spend the next 12 months in orbit around Vesta.

NASA’S DAWN SPACECRAFT obtained this image of Vesta with its framing camera on July 31, 2011. It was taken from a distance of about 3,700 kilometres from the giant asteroid.

Vesta is one of the largest of the asteroids, and orbits the Sun in the main asteroid belt between Mars and Jupiter.

The smallest visible detail, which is about 2 pixels, corresponds to roughly 70 metres.

Dawn arrived at Vesta on July 16 after a journey of almost four years. It is now in orbit around the 530-kilometre-wide asteroid and will spend the next 12 months investigating it.

At the end of those 12 months, it will depart Vesta and voyage to the even-larger main belt body, the dwarf planet Ceres, and spend a further 12 months studying that object.

The aim of the Dawn mission is to shed light on the origins of the Sun and the planets by examining these two asteroids, which are thought to be amongst the oldest surviving bodies in the Solar System.

More information:

First close-up images from Vesta

NASA’s Dawn mission pages

Adapted from information issued by NASA / JPL-Caltech / UCLA / MPS / DLR / IDA.

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Vesta vistas streaming in

Full-frame image of Vesta

NASA's Dawn spacecraft obtained this image of the giant asteroid Vesta with its framing camera on July 24, 2011. It was taken from a distance of about 5,200 kilometres. Dawn will spend a year orbiting the body. After that, the next stop on its itinerary will be an encounter with the dwarf planet Ceres.

  • Vesta is one of the largest asteroids
  • Dawn mission will spend a year investigating it
  • First close-up images now coming in

AFTER TRAVELLING NEARLY FOUR YEARS and 2.8 billion kilometres, NASA’s Dawn spacecraft has been captured by the Vesta’s gravity. The giant asteroid and its new companion are currently approximately 184 million kilometres from Earth.

The first spacecraft to orbit an object in the main asteroid belt, Dawn is now spiralling down towards its first of four intensive science orbits. That initial orbit of the rocky world—to begin on August 11, at an altitude of nearly 2,700 kilometres—will provide in-depth analysis of the asteroid.

Vesta, 530 kilometres wide, is the brightest object in the asteroid belt as seen from Earth and is thought to be the source of a large number of meteorites that fall to Earth.

Snowman craters on Vesta

A set of three craters, informally nicknamed 'Snowman' by the camera's team members, is located in the northern hemisphere of Vesta.

Craters on Vesta

Various craters are visible in this image of part of the southern equatorial region of the giant asteroid Vesta.

The smallest rocky ‘planet’

Images from Dawn’s framing camera, taken for navigation purposes and as preparation for scientific observations, are revealing the first surface details of the giant asteroid. These images go all the way around Vesta, since the giant asteroid turns on its axis once every five hours and 20 minutes.

“Now that we are in orbit around one of the last unexplored worlds in the inner Solar System, we can see that it’s a unique and fascinating place,” said Marc Rayman, Dawn’s chief engineer and mission manager at NASA’s Jet Propulsion Laboratory.

Download a Vesta wallpaper image, 1024 x 1024 pixels.

“We have been calling Vesta the smallest terrestrial planet,” said Chris Russell, Dawn’s principal investigator at UCLA. “The latest imagery provides much justification for our expectations.”

“They show that a variety of processes were once at work on the surface of Vesta and provide extensive evidence for Vesta’s planetary aspirations.”

Here’s a short video showing the different faces of Vesta as it rotates:

“The new observations of Vesta are an inspirational reminder of the wonders unveiled through ongoing exploration of our Solar System,” said Jim Green, planetary division director at NASA Headquarters in Washington.

Dawn launched in September 2007. Following a year at Vesta, the spacecraft will depart in July 2012 for Ceres, where it will arrive in 2015.

More information: NASA’s Dawn mission pages

Adapted from information issued by NASA. Images courtesy NASA / JPL-Caltech / UCLA / MPS / DLR / IDA.

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Dawn mission is a rock star

Latest Image of Vesta Captured by Dawn

NASA's Dawn spacecraft obtained this image with its framing camera on July 17, 2011. It was taken from a distance of about 15,000 kilometres from the protoplanet Vesta. Each pixel in the image corresponds to roughly 1.4 kilometres.

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 16,000 kilometres between the spacecraft and asteroid.

Vesta is 530 kilometres in diameter and the second most massive object in the asteroid belt. Vesta and Dawn are currently approximately 188 million kilometres from Earth.

The onslaught of eons

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,” he added. “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.”

Comparative sizes of eight asteroids

This composite image shows the comparative sizes of eight asteroids visited by spacecraft. Until now, Lutetia, with a diameter of 130 kilometres, was the largest asteroid visited, which occurred during a flyby of the Rosetta spacecraft in July 2010.

High thrust

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 travelling nearly four years and 2.8 billion kilometres, Dawn accomplished the largest propulsive acceleration of any spacecraft, with a change in velocity of more than 6.7 kilometres per second, courtesy of its ion engines. The engines expel ions (electrically charged atoms) to create continuous 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.

“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.”

Searching for moons

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.

More information

Dawn mission

Dawn on Twitter

Adapted from information issued by NASA / JPL. Images courtesy NASA / JPL-Caltech / UCLA / MPS / DLR / IDA / JAXA / ESA.

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Dawn mission reaches asteroid Vesta

Artist's impression of the Dawn mission

The Dawn spacecraft has spent almost four years tracking down the asteroid Vesta, located in the main asteroid belt between Mars and Jupiter. (Note that this artist's impression is not intended to be accurate, as it shows both Vesta and Dawn's next destination, Ceres, in the one frame, as well as many other small asteroids. In reality, these rocky bodies are nowhere near each other.)

NASA’S DAWN SPACECRAFT has become the first probe ever to enter orbit around an object in the main asteroid belt between Mars and Jupiter.

Dawn will study the asteroid, named Vesta, for a year before departing for a second destination, a dwarf planet named Ceres, in July 2012. 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.

“Today, we celebrate an incredible exploration milestone as a spacecraft enters orbit around an object in the main asteroid belt for the first time,” NASA Administrator Charles Bolden said.

“Dawn’s study of the asteroid Vesta marks a major scientific accomplishment and also points the way to the future destinations where people will travel in the coming years.”

“President Obama has directed NASA to send astronauts to an asteroid by 2025, and Dawn is gathering crucial data that will inform that mission,” he added.

Dawn image of Vesta

This image of Vesta was taken with Dawn's navigation camera on July 9, 2011, from a distance of 41,000 kilometres. Once science operations begin, we will see very high-resolution images of the asteroid's surface.

Entering orbit

The spacecraft relayed information to confirm it entered Vesta’s orbit, but the precise time this milestone occurred is unknown at this time.

The time of Dawn’s capture depended on Vesta’s mass and gravity, which only has been estimated until now. The asteroid’s mass determines the strength of its gravitational pull.

If Vesta is more massive, its gravity is stronger, meaning it pulled Dawn into orbit sooner. If the asteroid is less massive, its gravity is weaker and it would have taken the spacecraft longer to achieve orbit.

According to the Dawn Twitter feed, the spacecraft has achieved an orbit about 16,000 kilometres from Vesta.

With Dawn now in orbit, the science team can take more accurate measurements of Vesta’s gravity and gather more accurate timeline information.

More information — see our earlier story on the Dawn mission, complete with videos.

Adapted from information issued by NASA / JPL. Images courtesy NASA / JPL-Caltech / UCLA / MPS / DLR / IDA.

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