Posted on by Ken Kremer

Dawn Exceeds Wildest Expectations as First Ever Spacecraft to Orbit a Protoplanet – Vesta

Enhanced Image of Vesta Captured by Dawn on July 9, 2011. NASA's Dawn spacecraft entered orbit around Vesta on July 16, 2011. Dawn obtained the raw image of Vesta with its framing camera on July 9, 2011 - which has been enhanced and annotated. It was taken from a distance of about 26,000 miles (41,000 kilometers) away from the protoplanet Vesta. Each pixel in the image corresponds to roughly 2.4 miles (3.8 kilometers). Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA. Enhanced and annotated by Ken Kremer

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NASA’s super exciting Dawn mission to the Asteroid Belt marked a major milestone in human history by becoming the first ever spacecraft from Planet Earth to achieve orbit around a Protoplanet – Vesta – on July 16. Dawn was launched in September 2007 and was 117 million miles (188 million km) distant from Earth as it was captured by Asteroid Vesta.

Dawn’s achievements thus far have already exceeded the wildest expectations of the science and engineering teams, and the adventure has only just begun ! – so say Dawn’s Science Principal Investigator Prof. Chris Russell, Chief Engineer Dr. Marc Rayman (think Scotty !) and NASA’s Planetary Science Director Jim Green in exclusive new interviews with Universe Today.

As you read these words, Dawn is steadily unveiling new Vesta vistas never before seen by a human being – and in ever higher resolution. And it’s only made possible via the revolutionary and exotic ion propulsion thrusters propelling Dawn through space (think Star Trek !). That’s what NASA, science and space exploration are all about.

“Dawn is in orbit, remains in good health and is continuing to perform all of its functions,” Marc Rayman of the Jet Propulsion Laboratory, Pasadena, Calif., told me. “Indeed, that is how we know it achieved orbit. The confirmation received in a routine communications session that it has continued thrusting is all we needed.”

Image of Vesta Captured by Dawn on July 9, 2011. NASA's Dawn spacecraft obtained this image with its framing camera on July 9, 2011. It was taken from a distance of about 26,000 miles (41,000 kilometers) away from the protoplanet Vesta. Each pixel in the image corresponds to roughly 2.4 miles (3.8 kilometers). Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

Dawn entered orbit at about 9900 miles (16000 km) altitude after a nearly 4 year journey of 1.73 billion miles.

Over the next few weeks, the spacecrafts primary task is to gradually spiral down to its initial science operations orbit, approximately 1700 miles above the pock marked surface.

Vesta is the second most massive object in the main Asteroid Belt between Mars and Jupiter. Dawn is the first probe to orbit an object in the Asteroid Belt.

I asked Principal Investigator Chris Russell from UCLA for a status update on Dawn and to describe what the team can conclude from the images and data collected thus far.

“The Dawn team is really, really excited right now,” Russell replied.

“This is what we have been planning now for over a decade and to finally be in orbit around our first ‘protoplanet’ is fantastic.”

“The images exceed my wildest dreams. The terrain both shows the stress on the Vestan surface exerted by 4.5 billion years of collisions while preserving evidence [it seems] of what may be internal processes. The result is a complex surface that is very interesting and should be very scientifically productive.”

NASA's Dawn spacecraft, illustrated in this artist's concept, is propelled by ion engines to Protoplanets Vesta and Ceres. Credit: NASA/JPL

“The team is looking at our low resolution images and trying to make preliminary assessments but the final answers await the higher resolution data that is still to come.”

Russell praised the team and described how well the spacecraft was operating.

“The flight team has been great on this project and deserves a lot of credit for getting us to Vesta EARLY and giving us much more observation time than we had planned,” Russell told me.

“And they have kept the spacecraft healthy and the instruments safe. Now we are ready to work in earnest on our science observations.”

Dawn will remain in orbit at Vesta for one year. Then it will fire its ion thrusters and head for the Dwarf Planet Ceres – the largest object in the Asteroid Belt. Dawn will then achieve another major milestone and become the first spacecraft ever to orbit two celestial objects.

Dawn launch on September 27, 2007 by a Delta II rocket from Cape Canaveral Air Force Station, Florida. Credit: Ken Kremer

Jim Green, Director of Planetary Science for the Science Mission Directorate (SMD) at NASA HQ in Washington, DC, summed up his feelings about Dawn in this way;

“Getting Dawn into orbit is an amazing achievement,” Green told me.

“Instead of the ‘fire the thrusters full blast’ we just sort of slid into orbit letting gravity grab the spacecraft with a light tug. This gives us great confidence that the big challenge down the road of getting into orbit around Ceres can also be accomplished just as easily.”

Sharper new images from Vesta will be published by NASA in the next day or so.

“We did take a few navigation images in this last sequence and when they get through processing they should be put on the web this week,” Russell informed. “These images are from a similar angle to the last set and with somewhat better resolution and will not reveal much new.”

However, since Dawn is now orbiting Vesta our upcoming view of the protoplanet will be quite different from what we’ve seen in the approach images thus far.

“We will be changing views in the future as the spacecraft begins to climb into its science orbit,” stated Russell.

“This may reveal new features on the surface as well as giving us better resolution. So stay tuned.”

Marc Rayman explained how and why Dawn’s trajectory is changing from equatorial to polar:

“Now that we are close enough to Vesta for its gravity to cause a significant curvature in the trajectory, our view is beginning to change,” said Rayman. “That will be evident in the pictures taken now and in the near future, as the spacecraft arcs north over the dark side and then orbits back to the south over the illuminated side.”

“The sun is over the southern hemisphere right now,” added Russell. “When we leave we are hoping to see it shine in the north.”

Dawn is an international mission with significant participation from Germany and Italy. The navigation images were taken by Dawn’s framing cameras which were built in Germany.

Exploring Vesta is like studying a fossil from the distant past that will immeasurably increase our knowledge of the beginnings of our solar system and how it evolved over time.

Dawn Infographic Poster - click to enlarge. Credit: NASA

Vesta suffered a cosmic collision at the south pole in the distant past that Dawn can now study at close range.

“For now we are viewing a fantastic asteroid, seeing it up close as we zero in on its southern hemisphere, looking at the huge central peak, and wondering how it got there,” explained Jim Green

“We know Vesta was nearly spherical at one time. Then a collision in its southern hemisphere occurred blowing off an enormous amount of material where a central peak now remains.”

That intriguing peak is now obvious in the latest Dawn images from Vesta. But what does it mean and reveal ?

“We wonder what is that peak? replied Green. “Is it part of the core exposed?

“Was it formed as a result of the impact or did it arise from volcanic action?”

“The Dawn team hopes to answer these questions. I can’t wait!” Green told me.

As a result of that ancient south pole collision, about 5% of all the meteorites found on Earth actually originate from Vesta.

Keep your eyes glued to Dawn as mysterious Vesta’s alluring secrets are unveiled.

Dawn Trajectory and Current Location in orbit at Vesta on July 18, 2011. Credit: NASA/JPL

Read my prior features about Dawn
Dawn Closing in on Asteroid Vesta as Views Exceed Hubble
Revolutionary Dawn Closing in on Asteroid Vesta with Opened Eyes

Posted on by Nancy Atkinson

Latest Image from Dawn: View of Vesta Getting Sharper

The Dawn spacecraft took this image of Vesta on July 1, 2011. Image credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

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The Dawn spacecraft is getting closer to asteroid/protoplanet Vesta, and the view is getting better! Here’s the latest image, which was obtained with Dawn’s framing camera on July 1, 2011 and just released today. It was taken from a distance of about 62,000 miles (100,000 kilometers). Each pixel in the image corresponds to roughly 5.8 miles (9.3 kilometers). Features like craters are starting to sharpen as the spacecraft moves closer, as well as the lumps, bumps and variations in color.

The most exciting part of this mission will be finally figuring out what Vesta really is. Here, it’s looking more like a squished version of our own Moon; a little smoother than I was expecting from some of the earlier images.

Some astronomers classify Vesta as an asteroid, some a protoplanet, and some are on the fence. It’s not really considered a dwarf planet, but the classification could be re-evaluated when Dawn gets in orbit of Vesta and studies it in detail.

Below is an “enhanced” view by Stu Atkinson:

The latest Vesta image from Dawn, with enhancements by Stu Atkinson.

Stu sent us this image with the caveat that he created it for his own amusement/entertainment, and that it’s not a scientifically enhanced image — i.e., it’s not to be 100% relied upon for feature identification, etc. But some of the craters show up a tad better.

Vesta is pretty much an enigma: too big for an asteroid and more evolved than other asteroid. But it is kind of too small for a planet (even a dwarf one). But that’s why it is so interesting so scientists and getting Dawn in orbit will be exciting.

Stay tuned for more!

Posted on by Ken Kremer

Dawn Closing in on Asteroid Vesta as Views Exceed Hubble

Hubble and Dawn Views of Vesta. These views of the protoplanet Vesta were obtained by NASA's Dawn spacecraft and NASA's Hubble Space Telescope. The image from Dawn, on the left, is a little more than twice as sharp as the image from Hubble, on the right. The image from Hubble, which is in orbit around the Earth, was obtained on May 14, 2007, when Vesta was 109 million miles (176 million kilometers) away from Earth. Dawn's image was taken on June 20, 2011, when Dawn was about 117,000 miles (189,000 kilometers) away from Vesta. The framing cameras were developed and built under the leadership of the Max Planck Institute for Solar System Research in Katlenburg-Lindau, Germany. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/PSI and NASA/ESA/STScI/UMd

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A new world in our Solar System is about to be unveiled for the first time – the mysterious protoplanet Vesta, which is the second most massive object in the main Asteroid Belt between Mars and Jupiter.

NASA’s Dawn Asteroid orbiter has entered its final approach phase to Vesta and for the first time is snapping images that finally exceed those taken several years ago by the iconic Hubble Space Telescope.

“The Dawn science campaign at Vesta will unveil a mysterious world, an object that can tell us much about the earliest formation of the planets and the solar system,” said Jim Adams, Deputy Director, Planetary Science Directorate at NASA HQ at a briefing for reporters.

Vesta holds a record of the earliest history of the solar system. The protoplanet failed to form into a full planet due to its close proximity to Jupiter.

Check out this amazing NASA approach video showing Vesta growing in Dawn’s eyes. The compilation of navigation images from Dawn’s framing camera spans about seven weeks from May 3 to June 20 was released at the NASA press briefing by the Dawn science team.

Dawn’s Approach to Vesta – Video

Best View from Hubble – Video

Be sure to notice that Vesta’s south pole is missing due to a cataclysmic event eons ago that created a massive impact crater – soon to be unveiled in astounding clarity. Some of that colossal debris sped toward Earth and survived the terror of atmospheric entry. Planetary Scientists believe that about 5% of all known meteorites originated from Vesta, based on spectral evidence.

After a journey of four years and 1.7 billion miles, NASA’s revolutionary Dawn spacecraft thrusting via exotic ion propulsion is now less than 95,000 miles distant from Vesta, shaping its path through space to match the asteroid.

The internationally funded probe should be captured into orbit on July 16 at an initial altitude of 9,900 miles when Vesta is some 117 million miles from Earth.

After adjustments to lower Dawn to an initial reconnaissance orbit of approximately 1,700 miles, the science campaign is set to kick off in August with the collection of global color images and spectral data including compositional data in different wavelengths of reflected light.

Dawn Approaching Vesta
Dawn obtained this image on June 20, 2011. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/PSI and NASA/ESA/STScI/UMd

Dawn will spend a year investigating Vesta. It will probe the protoplanet using its three onboard science instruments – provided by Germany, Italy and the US – and provide researchers with the first bird’s eye images, global maps and detailed scientific measurements to elucidate the chemical composition and internal structure of a giant asteroid.

“Navigation images from Dawn’s framing camera have given us intriguing hints of Vesta, but we’re looking forward to the heart of Vesta operations, when we begin officially collecting science data,” said Christopher Russell, Dawn principal investigator, at the University of California, Los Angeles (UCLA). “We can’t wait for Dawn to peel back the layers of time and reveal the early history of our solar system.”

Because Dawn is now so close to Vesta, the frequency of imaging will be increased to twice a week to achieve the required navigational accuracy to successfully enter orbit., according to Marc Rayman, Dawn Chief Engineer at the Jet Propulsion Laboratory (JPL) in Pasadena, Calif.

“By the beginning of August, it will see Vesta with more than 100 times the clarity that Hubble could ever obtain,” says Rayman.

Vesta in Spectrometer View
On June 8, 2011, the visible and infrared mapping spectrometer aboard NASA's Dawn spacecraft captured the instrument's first images of Vesta that are larger than a few pixels, from a distance of about 218,000 miles (351,000 kilometers). The image was taken for calibration purposes. An image obtained in the visible part of the light spectrum appears on the left. An image obtained in the infrared spectrum, at around 3 microns in wavelength, appears on the right. The spatial resolution of this image is about 60 miles (90 kilometers) per pixel. Credit: NASA/JPL-Caltech/UCLA/ASI/INAF

Dawn will gradually edge down closer to altitudes of 420 miles and 120 miles to obtain ever higher resolution orbital images and spectal data before spiraling back out and eventually setting sail for Ceres, the largest asteroid of them all.

Dawn will be the first spacecraft to orbit two celestial bodies, only made possible via the ion propulsion system. With a wingspan of 65 feet, it’s the largest planetary mission NASA has ever launched.

“We’ve packed our year at Vesta chock-full of science observations to help us unravel the mysteries of Vesta,” said Carol Raymond, Dawn’s deputy principal investigator at JPL.

“This is an unprecedented opportunity to spend a year at a body that we know almost nothing about,” added Raymond. “We are very interested in the south pole because the impact exposed the deep interior of Vesta. We’ll be able to look at features down to tens of meters so we can decipher the geologic history of Vesta.”

Possible Piece of Vesta
Scientists believe a large number of the meteorites that are found on Earth originate from the protoplanet Vesta. A cataclysmic impact at the south pole of Vesta, the second most massive object in the main asteroid belt, created an enormous crater and excavated a great deal of debris. Some of that debris ended up as other asteroids and some of it likely ended up on Earth. Image Credit: NASA/JPL-Caltech
Dawn Trajectory and Current Location on June 29, 2011. Credt: NASA/JPL
Dawn launch on September 27, 2007 by a Delta II rocket from Cape Canaveral Air Force Station, Florida. Credit: Ken Kremer

Read my prior feature about Dawn here

Posted on by Nancy Atkinson

Close Approach: Images and Animations of Asteroid 2011 MD

Animation of 2011 MD on Monday, June 27, 2011 at 09:30 UTC. Credit: Ernesto Guido, Nick Howes and Giovanni Sostero at the Faulkes Telescope South. Click for original larger version.

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Today, Monday June 27 at about 17:00 UT, asteroid designated as 2011 MD will pass only 12,300 kilometers (7,600 miles) above the Earth’s surface. Here are some images and an animation of the asteroid’s close approach taken around 09:30 UT taken by Ernesto Guido, Nick Howes and Giovanni Sostero at the Faulkes Telescope South through a 2.0-m f/10.0 Ritchey-Chretien and a CCD. The trio of astronomers say that at the time these images were taken, the asteroid had a magnitude of about 14.5. At the moment of its close approach, 2011 MD will be bright as magnitude ~11.8.

The animation above shows the object’s movement in the sky. Each image was 20-second exposure.

See more below from Guido, Howes and Sostero.

Below is a single 20-second exposure also taken by the 2 meter telescope at Faulkes Telescope South, and just below that is another image using a RGB filter.

2011 MD on Monday, June 27, 2011 at 09:30 UTC. Credit: Ernesto Guido, Nick Howes and Giovanni Sostero at the Faulkes Telescope South
2011 MD on Monday, June 27, 2011 at 09:30 UTC with RBG filter. Credit: Ernesto Guido, Nick Howes and Giovanni Sostero at the Faulkes Telescope South.

Some early observers have suggested that 2011 MD — which is only 5-20 meters in diameter — could possibly be a piece of space junk, such as a rocket booster. However, additional observations and further calculations show that this asteroid could not have been close enough to Earth any time during the space age to have started off as a rocket booster.

Trajectory of 2011 MD from the general direction of the Sun. Credit: NASA

Thanks to Ernesto Guido, Nick Howes and Giovanni Sostero for sharing their image with Universe Today. See more of their work, as well as more information about asteroid 2011 MD at their Remanzacco Observatory website. See here for more information on the Faulkes Telescope.

Again, scientists at NASA’s Asteroid Watch program at JPL say there is no danger of the asteroid hitting Earth. “There is no chance that 2011 MD will hit Earth but scientists will use the close pass as opportunity to study it w/ radar observations,” they said on the the @AsteriodWatch Twitter feed. “Asteroid 2011 MD measures about 10 meters. Stony asteroids less than 25 m would break up in Earth’s atmosphere and not cause ground damage.”

Posted on by Nancy Atkinson

Getting Closer: Images, Video of Asteroid 2011 MD

Asteroid 2011 MD. Credit: Peter Lake

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Accomplished amateur astronomer and blogger Peter Lake, a.k.a “AstroSwanny” from Australia captured some of the first images of what will be a very close pass of Earth by asteroid 2011 MD. He actually took the image at 07:00 UTC on June 26th with a 20 inch telescope in New Mexico controlled via his iPhone, through the Global Rent-A-Scope program. Ahh, the wonders of technology! As Peter says, “Its not every day, that an asteroid misses by less than 3-5 earth Radii.”

The asteroid, which was only detected last week, is about 25 to 55 feet (8 to 18 m) across, is expected to pass less than 8,000 miles above Earth’s surface around 1 p.m. EDT (17:00 UT) on Monday, June 27th. The time of closest approach will be observable from South Africa and parts of Antarctica, but the approach will be visible across Australia, New Zealand, southern and eastern Asia, and the western Pacific.

Below is a video he compiled of the his observations of the pass, and used ten 120-second images for the video.

Peter also noted that “Its close approach is being followed with great interest, more for honing the skills and techniques of the Minor Planet Center and the network of asteroid hunting astronomers, rather than because it poses any real danger.”

Thanks to Peter and his Aartscope Blog for sharing these views with Universe Today.

Posted on by Nancy Atkinson

Another Asteroid To Give Earth a Close Shave June 27, 2011

2011 MD's orbital parameters. Credit: JPL Small-Body Database Browser

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A newly discovered house-sized asteroid will miss the Earth by less than 17,700 km (11,000 miles) on Monday June 27, 2011. That’s about 23 times closer than the Moon. The size and location of the asteroid, named 2011 MD, should allow observers in certain locations to take a look at the space rock, even with small telescopes. It’s closest approach will be at 13:26 UTC on June 27.

UPDATE 6/25: According to the latest info on JPL’s Solar System Dynamics website, the closest approach has been updated to be Monday, June 27, at about 17:00 UTC. At that time it will be about 0.0001247 AU, or 18,665 km from the planet’s center and about 12,280 km (about 7,500 miles) from its surface.

According to Skymania, 2011 MD was found just yesterday, June 22, by LINEAR, a pair of robotic telescopes in New Mexico that scan the skies for Near Earth Asteroids.

As of now, asteroid 2011 MD is estimated to be between 9 to 45 meters (10 to 50 yards) wide. Dr. Emily Baldwin, of Astronomy Now magazine, said there is no danger of the asteroid hitting Earth, and even if it did enter the atmosphere, an asteroid this size would “mostly burn up in a brilliant fireball, possibly scattering a few meteorites.”

JPL scientists agree. NASA’s Asteroid Watch program at JPL wrote in a Twitter post on June 23rd saying, “There is no chance that 2011 MD will hit Earth but scientists will use the close pass as opportunity to study it w/ radar observations,” adding later, “Asteroid 2011 MD measures about 10 meters. Stony asteroids less than 25 m would break up in Earth’s atmosphere & not cause ground damage.”

To find out updated information on 2011 MD’s ephemeris, physical parameters and more, including an orbit diagram and close-approach data, see this page on JPL’s Solar System Dynamics website.

Posted on by Ken Kremer

Dawn Begins Approach to Asteroid Vesta and Snaps First Images

Dawn's First Glimpse of Vesta – Processed. This image, processed to show the true size of the giant asteroid Vesta, shows Vesta in front of a spectacular background of stars. It was obtained by the framing camera aboard NASA's Dawn spacecraft on May 3, 2011, from a distance of about 1.2 million kilometers (750,000 miles). Since Vesta is so bright that it outshines its starry background, Dawn team members commanded a long exposure time to make the stars visible. They corrected the resulting exaggerated size of Vesta by superimposing a short exposure image of the target asteroid, showing its true size. Vesta is the small, bright pearl in the middle of the image. Image credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

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NASA’s revolutionary Dawn Asteroid Orbiter has begun the final approach phase to the giant asteroid Vesta and snapped its first science image. The image was taken on May 3, when Dawn was approximately 1.21 million kilometers (752,000 miles) distant from Vesta using the science imager known as the Framing Camera.

Besides the pure delight of seeing Vesta up close for the first time, the images play a crucial role in navigating Dawn precisely through space and successfully achieve orbit around the protoplanet that nearly formed into a full fledged planet.

Vesta is the second most massive object in the Asteroid Belt and is 530 kilometers (330 miles) in diameter.

Dawn launch on September 27, 2007 by a Delta II rocket from Cape Canaveral Air Force Station, Florida. Credit: Ken Kremer

Dawn should be captured into orbit about Vesta around July 16 as the engineering team works to maneuver the spacecraft to match the asteroids path around the sun using the exotic ion thrusters. Using the background stars in the framing camera images, they will be able to determine Dawn’s location in space relative to the stars in order to precisely navigate the spacecrafts trajectory towards Vesta.

“After plying the seas of space for more than a billion miles, the Dawn team finally spotted its target,” said Carol Raymond, Dawn’s deputy principal investigator at NASA’s Jet Propulsion Laboratory in Pasadena, Calif. “This first image hints of detailed portraits to come from Dawn’s upcoming visit.”

The best images of Vesta to date were taken by the Hubble Space Telescope. Jim Adams, Deputy Director of Planetary Science, told me that the images from Dawn’s Framing Camera will exceed those from Hubble in a few weeks.

Dawn will initially enter a highly elliptical polar orbit around Vesta and start collecting science data in August from an altitude of approximately 1,700 miles (2,700 kilometers). The orbit will be lowered in stages to collect high resolution data as Dawn spends about a year collecting data from its three science instruments.

Dawn's First Glimpse of Vesta -- Unprocessed
This image shows the first, unprocessed image obtained by NASA's Dawn spacecraft of the giant asteroid Vesta in front of a background of stars. It was obtained by Dawn's framing camera on May 3, 2011, from a distance of about 1.2 million kilometers (750,000 miles). Vesta is inside the white glow at the center of the image. The giant asteroid reflects so much sunlight that its size is dramatically exaggerated at this exposure. Image credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

Thereafter Dawn will be targeted to Ceres, the largest object in the Asteroid Belt which it will reach in 2015.

Dawn is an international mission.

The 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 the German Aerospace Center (DLR) 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.

The Visible and Infrared mapping camera was provided by the Italian Space Agency. The Gamma Ray Detector was supplied by Los Alamos National Labotatory.

Read more about Dawn in my prior story:
Revolutionary Dawn Closing in on Asteroid Vesta with Opened Eyes

Dawn spacecraft under construction in cleanroom. Picture shows close up view of two science instrument; the twin Framing Cameras at top (white rectangles) and VIR Spectrometer at right. Credit: Ken Kremer

Posted on by Nancy Atkinson

Astronomy Cast EP. 220: Mass Extinction Events

The Earth seems like a safe place, most of the time. But we have evidence of terrible catastrophes in the ancient past, times when almost all life on Earth was wiped out in a geologic instant. What could have caused so much devastation? And will something like this happen again?

Click here to download the episode.
Or subscribe to: astronomycast.com/podcast.xml with your podcatching software.

Mass Extinction Events shownotes and transcript.

Posted on by Nancy Atkinson

Hit and Run Asteroid Caused Scheila’s Comet-like Behavior

Faint dust plumes bookend asteroid (596) Scheila, which is overexposed in this composite. Visible and ultraviolet images from Swift's UVOT (circled) are merged with a Digital Sky Survey image of the same region. The UVOT images were acquired on Dec. 15, 2010, when the asteroid was about 232 million miles from Earth. Credit: NASA/Swift/DSS/D. Bodewits (UMD)

Asteroid or comet? That was the question astronomers were asking after an asteroid named Scheila had unexpectedly brightened, and seemingly sprouted a tail and coma. But follow-up observations by the Swift satellite and the Hubble Space Telescope show that these changes likely occurred after Scheila was struck by a much smaller asteroid.

“Collisions between asteroids create rock fragments, from fine dust to huge boulders, that impact planets and their moons,” said Dennis Bodewits, an astronomer at the University of Maryland in College Park and lead author of the Swift study. “Yet this is the first time we’ve been able to catch one just weeks after the smash-up, long before the evidence fades away.”

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On Dec. 11, 2010, images from the University of Arizona’s Catalina Sky Survey, a project of NASA’s Near Earth Object Observations Program, revealed the Scheila to be twice as bright as expected and immersed in a faint comet-like glow. Looking through the survey’s archived images, astronomers inferred the outburst began between Nov. 11 and Dec. 3.

Three days after the outburst was announced, Swift’s Ultraviolet/Optical Telescope (UVOT) captured multiple images and a spectrum of the asteroid. Ultraviolet sunlight breaks up the gas molecules surrounding comets; water, for example, is transformed into hydroxyl (OH) and hydrogen (H). But none of the emissions most commonly identified in comets — such as hydroxyl or cyanogen (CN) — showed up in the UVOT spectrum. The absence of gas around Scheila led the Swift team to reject the idea that Scheila was actually a comet and that exposed ice accounted for the brightening.

Hubble observed the asteroid’s fading dust cloud on Dec. 27, 2010, and Jan. 4, 2011. Images show the asteroid was flanked in the north by a bright dust plume and in the south by a fainter one. The dual plumes formed as small dust particles excavated by the impact were pushed away from the asteroid by sunlight.

The science teams from the two space observatories found the observations were best explained by a collision with a small asteroid impacting Scheila’s surface at an angle of less than 30 degrees, leaving a crater 1,000 feet across. Laboratory experiments show a more direct strike probably wouldn’t have produced two distinct dust plumes. The researchers estimated the crash ejected more than 660,000 tons of dust–equivalent to nearly twice the mass of the Empire State Building.

The Hubble Space Telescope imaged (596) Scheila on Dec. 27, 2010, when the asteroid was about 218 million miles away. Scheila is overexposed in this image to reveal the faint dust features. The asteroid is surrounded by a C-shaped cloud of particles and displays a linear dust tail in this visible-light picture acquired by Hubble's Wide Field Camera 3. Because Hubble tracked the asteroid during the exposure, the star images are trailed. Credit: NASA/ESA/D. Jewitt (UCLA)

“The Hubble data are most simply explained by the impact, at 11,000 mph, of a previously unknown asteroid about 100 feet in diameter,” said Hubble team leader David Jewitt at the University of California in Los Angeles. Hubble did not see any discrete collision fragments, unlike its 2009 observations of P/2010 A2, the first identified asteroid collision.

Scheila is approximately 113 km (70 miles) across and orbits the sun every five years.

“The dust cloud around Scheila could be 10,000 times as massive as the one ejected from comet 9P/Tempel 1 during NASA’s UMD-led Deep Impact mission,” said co-author Michael Kelley, also at the University of Maryland. “Collisions allow us to peek inside comets and asteroids. Ejecta kicked up by Deep Impact contained lots of ice, and the absence of ice in Scheila’s interior shows that it’s entirely unlike comets.”

The studies will appear in the May 20 edition of The Astrophysical Journal Letters.

Source: NASA Goddard