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We are not alone

Trojan asteroid 2010 TK7

Trojan asteroid 2010 TK7 (circled in green) orbits the Sun ahead of the Earth. This single frame was taken by NASA's Wide-field Infrared Survey Explorer, or WISE. The majority of the other dots are stars or galaxies far beyond our Solar System.

  • Trojan asteroid found orbiting ahead of Earth
  • 80 million kilometres from our planet
  • No danger of it colliding with us

ASTRONOMERS STUDYING OBSERVATIONS taken by NASA’s Wide-field Infrared Survey Explorer (WISE) mission have discovered the first known ‘Trojan’ asteroid orbiting the Sun along with Earth.

Trojans are asteroids that share an orbit with a planet near stable points in front of or behind the planet. Because they constantly lead or follow in the same orbit as the planet, they never can collide with it.

In our Solar System, Trojans also share orbits with Neptune, Mars and Jupiter. Two of Saturn’s moons even have Trojans.

Hard to see

Scientists had predicted Earth should have Trojans, but they have been difficult to find because they are relatively small and appear near the Sun from Earth’s point of view.

“These asteroids dwell mostly in the daylight, making them very hard to see,” said Martin Connors of Athabasca University in Canada, lead author of a new paper on the discovery in the July 28 issue of the journal Nature.

“But we finally found one, because the object has an unusual orbit that takes it farther away from the Sun than what is typical for Trojans,” added Connors. “WISE was a game-changer, giving us a point of view difficult to have at Earth’s surface.”

Artist's impression of the WISE space telescope

Artist's impression of the WISE space telescope

Thousands of asteroids found

The WISE telescope scanned the entire sky in infrared light from January 2010 to February 2011.

Connors and his team began their search for an Earth Trojan using data from NEOWISE, an extension to the WISE mission that focused in part on near-Earth objects, or NEOs, such as asteroids and comets.

NEOs are bodies that pass within 45 million kilometres of Earth’s path around the Sun.

The NEOWISE project saw more than 155,000 asteroids in the main belt between Mars and Jupiter, and more than 500 NEOs, including 132 that were previously unknown.

Unusual orbit

The team’s hunt resulted in two Trojan candidates. One, called 2010 TK7, was confirmed as an Earth Trojan after follow-up observations with the Canada-France-Hawaii Telescope in Hawaii.

The asteroid is roughly 300 metres in diameter. It has an unusual orbit that traces a complex motion near a stable point in the plane of Earth’s orbit, although the asteroid also moves above and below the plane.

The object is about 80 million kilometres from Earth.

The following video shows how the asteroid continually loops above and below Earth’s orbital plane, while always remaining ahead of our planet:

No danger to Earth

The asteroid’s orbit is well-defined, and for at least the next 100 years it will not come closer to Earth than 24 million kilometres.

“It’s as though Earth is playing follow the leader,” said Amy Mainzer, the principal investigator of NEOWISE at NASA’s Jet Propulsion Laboratory in Pasadena, Calif. “Earth always is chasing this asteroid around.”

A handful of other asteroids also have orbits similar to Earth. Such objects could make excellent candidates for future robotic or human exploration.

Asteroid 2010 TK7 is not a good target because it travels too far above and below the plane of Earth’s orbit, which would require large amounts of fuel to reach it.

More information: WISE mission

Adapted from information issued by NASA / JPL-Caltech / UCLA / Paul Wiegert, University of Western Ontario.

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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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Dealing with space hazards

PEOPLE AND GOVERNMENTS rely on satellites for a growing number of crucial tasks. Any shutdown of these systems would seriously affect an enormous range of commercial and civil activities, including travel, transportation, telecommunications, information technology and broadcasting.

Europe, in particular, has no autonomous capability to watch for and warn of hazards to its vital satellites and ground infrastructure.

But in 2009, European Space Agency member states asked the Agency to embark on a new programme, known as Space Situational Awareness, or SSA. Now in its initial phase, SSA aims to develop Europe’s own scanning, detection and warning capabilities against space weather, space debris and natural near-earth objects.

Adapted from information issued by ESA.

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Asteroid rendezvous nears

Dawn and Hubble images of Vesta

Already, Dawn's images of Vesta (left) are better even than the Hubble Space Telescope can obtain (right). The protoplanet Vesta is the second-most massive object in the main asteroid belt.

NASA’S DAWN SPACECRAFT is on track to begin the first extended visit to a large asteroid. The mission expects to go into orbit around Vesta on July 16 and begin gathering science data in early August.

Vesta is considered a protoplanet, or body that didn’t quite become a full-fledged planet. It lives in the main asteroid belt between Mars and Jupiter, and is thought to be the source of a large number of meteorites that fall to Earth.

After travelling nearly four years and 2.7 billion kilometres, Dawn is approximately 150,000 kilometres away from Vesta. When Vesta captures Dawn into its orbit on July 16, there will be approximately 16,000 kilometres between them. When orbit is achieved, they will be approximately 188 million kilometres away from Earth.

Artist's impression of the Dawn spacecraft

Artist's impression of the Dawn spacecraft

“The spacecraft is right on target,” said Robert Mase, Dawn project manager at NASA’s Jet Propulsion Laboratory. “We look forward to exploring this unknown world during Dawn’s one-year stay in Vesta’s orbit.”

Peeling back the layers

After Dawn enters Vesta’s orbit, engineers will need a few days to determine the exact time of capture. Unlike other missions where a dramatic, nail-biting propulsive burn results in orbit insertion around a planet, Dawn has been using its placid ion propulsion system to subtly shape its path for years to match Vesta’s orbit around the Sun.

Images from Dawn’s framing camera, taken for navigation purposes, show the slow progress toward Vesta. Made into a movie (below), they are about twice as sharp as the best images of Vesta from NASA’s Hubble Space Telescope, but the surface details Dawn will obtain are still a mystery.

“We can’t wait for Dawn to peel back the layers of time and reveal the early history of our Solar System,” said Christopher Russell, Dawn principal investigator, at UCLA.

During the initial reconnaissance orbit, at a distance of approximately 2,700 kilometres, the spacecraft will get a broad overview of Vesta with colour pictures and data in different wavelengths of reflected light.

The spacecraft will then move drop lower into a mapping orbit about 680 kilometres above the surface to systematically map the parts of Vesta’s surface illuminated by the Sun.

It will collect stereo images to see topographic highs and lows, acquire higher-resolution data to map rock types at the surface; and learn more about Vesta’s thermal properties.

Up close and personal

Dawn then will move even closer, to a low-altitude mapping orbit approximately 200 kilometres above the surface. The primary science goals of this orbit are to detect the by-products of cosmic rays hitting the surface and help scientists determine the many kinds of atoms there, and probe the protoplanet’s internal structure.

“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.

Following a year at Vesta, the spacecraft will depart for its second destination, the dwarf planet Ceres, in July 2012.

As Dawn spirals away from Vesta, it will pause again at the high-altitude mapping orbit. Because the Sun’s angle on the surface will have progressed, scientists will be able to see previously hidden terrain while obtaining different views of surface features.

Dawn was launched in September 2007.

More information about Dawn:

http://www.nasa.gov/dawn

http://dawn.jpl.nasa.gov/

Follow the mission on Twitter:

http://www.twitter.com/NASA_Dawn

Adapted from information issued by NASA / JPL-Caltech. Images courtesy NASA / JPL-Caltech / UCLA / MPS / DLR / PSI and NASA / ESA / STScI / Umd.

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Rocky horror show in deep space

LATE LAST YEAR, ASTRONOMERS noticed an asteroid named Scheila had unexpectedly brightened, and it was sporting short-lived plumes. Data from NASA’s Swift satellite and Hubble Space Telescope showed 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.”

Asteroids are rocky fragments thought to be debris from the formation and evolution of the solar system approximately 4.6 billion years ago. Millions of them orbit the Sun between Mars and Jupiter in the main asteroid belt. Scheila is approximately 110 kilometres wide and orbits the Sun every five years.

Astronomers have known for decades that comets contain icy material that erupts when warmed by the Sun. They regarded asteroids as inactive rocks whose destinies, surfaces, shapes and sizes were determined by mutual impacts.

However, this simple picture has grown more complex over the past few years.

During certain parts of their orbits, some objects, once categorised as asteroids, clearly develop comet-like clouds that can last for many months. Others display much shorter outbursts. Icy materials may be occasionally exposed, either by internal geological processes or by an external one, such as an impact.

HST image of asteroid Scheila

The Hubble Space Telescope imaged asteroid Scheila on December 27, 2010, when it was about 350 million kilometres away. The C-shaped cloud of particles and dust tail suggest the asteroid was struck by another object.

Asteroid or comet?

On December 11, 2010, images from the University of Arizona’s Catalina Sky Survey, a project of NASA’s Near Earth Object Observations Program, revealed 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 November 11 and December 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.

But none of the emissions most commonly identified in comets, such as hydroxyl or cyanogen, show up in the UVOT spectrum. The absence of gas around Scheila led the Swift team to reject scenarios where exposed ice accounted for the activity.

Images show the asteroid was flanked by dual plumes formed as small dust particles excavated by the impact were pushed away from the asteroid by sunlight.

The teams found the observations were best explained by a small asteroid hitting Scheila’s surface at an angle of less than 30 degrees, leaving a crater 300 metres across. The researchers estimate the crash ejected more than 660,000 tons of dust.

Adapted from information issued by NASA’s Goddard Space Flight Centre. Images courtesy NASA / ESA / D. Jewitt (UCLA) / Goddard Space Flight Centre /Conceptual Image Lab.

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Space rock winks as it passes by

Asteroid 2011 GP59

Asteroid 2011 GP59 as imaged on the night of April 11, 2011 by amateur astronomer Nick James of Chelmsford, Essex, England. At the time, the asteroid was approximately 3,356,000 kilometres distant.

VIDEO IMAGING OF NEWLY DISCOVERED asteroid 2011 GP59 shows it appearing to blink on and off about once every four minutes.

2011 GP59 was discovered the night of April 8/9 by astronomers with the Observatorio Astronomico de Mallorca in Andalusia, Spain.

At the time, the asteroid was approximately 3,356,000 kilometres away. Since then, the space rock has become something of a darling of the amateur astronomy community, with many videos available.

Amateur astronomers around the world captured video of the interesting object, such as this one:

“Usually, when we see an asteroid strobe on and off like that, it means that the body is elongated and we are viewing it broadside along its long axis first, and then on its narrow end as it rotates,” said Don Yeomans, manager of NASA’s Near-Earth Object Program Office at the Jet Propulsion Laboratory.

“GP59 is approximately 50 metres long, and we think its period of rotation is about seven-and-a-half minutes. This makes the object’s brightness change every four minutes or so.”

GP59 made its closest approach to Earth on April 15 at a distance just beyond the Moon’s orbit—about 533,000 kilometres.

“Although newly discovered, the near-term orbital location of asteroid 2011 GP59 can be accurately plotted,” said Yeomans. “There is no possibility of the small space rock entering Earth’s atmosphere during this pass or for the foreseeable future.”

NASA detects, tracks and characterises asteroids and comets passing close to Earth using both ground- and space-based telescopes. The Near-Earth Object Observations Program, commonly called “Spaceguard,” discovers these objects, characterises a subset of them, and plots their orbits to determine if any could be potentially hazardous to our planet.

Adapted from information issued by NASA.

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Tracking a dangerous asteroid

Illustration of a spacecraft heating part of Apophis' surface using mirrors

One way to tackle an errant asteroid is to heat part of its surface. Material will be expelled one way, and the asteroid will move slightly in the opposite direction. Done far enough ahead of any potential collision, it will keep a rocky body from coming near Earth.

  • Asteroid Apophis will make a close approach to Earth in 2029
  • Has the potential to strike our planet later this century
  • More observations are needed to clarify its orbit

ASTRONOMERS HAVE TAKEN THE FIRST new images in over three years of the potentially dangerous near-Earth asteroid Apophis as it emerged into view from behind the Sun.

The object became famous in late 2004, when it appeared to have a 1-in-37 chance of colliding with Earth in 2029, but additional data eventually ruled out that possibility.

However, on April 13, 2029, the asteroid, which is 270 metres in diameter, will come closer to Earth than the geosynchronous communications satellites that orbit Earth at an altitude of about 36,000 kilometres. Apophis will then be briefly visible to the naked eye as a fast-moving starlike object.

This close encounter with Earth will significantly change Apophis’s orbit, which could lead to a collision with Earth later this century. For that reason, astronomers have been eager to obtain new data to further refine the details of the 2029 encounter.

Astronomer David Tholen (University of Hawaii (UH) at Manoa), one of the co-discoverers of Apophis, and graduate students Marco Micheli and Garrett Elliott obtained the new images on January 31 using the UH 2.2-metre telescope on Mauna Kea, Hawaii.

Composite image of Apophis

Apophis (circled) in a composite of five exposures taken on January 31 with the University of Hawaii 2.2-metre telescope. (The blemish in the upper left corner is an artefact caused by a dust speck on the camera.)

At the time, the asteroid was less than 44 degrees from the Sun and about a million times fainter than the faintest star that the average human eye can see without optical aid.

“The superb observing conditions that are possible on Mauna Kea made the observations relatively easy,” said Tholen.

Out of the glare

Astronomers measure the position of an asteroid by comparing it with the known positions of stars that appear in the same image as the asteroid. As a result, any tiny error in the catalogue of star positions—due, for example, to the very slow motions of the stars around the centre of our Milky Way galaxy—can affect the measurement of the position of the asteroid.

“We will need to repeat the observation on several different nights using different stars to average out this source of imprecision before we will be able to significantly improve the orbit of Apophis and therefore the details of the 2029 close approach and future impact possibilities,” noted Tholen.

Apophis’s elliptical orbit around the Sun will take it back into the Sun’s glare in the middle of 2011, inhibiting the acquisition of additional position measurements.

However, in 2012, Apophis will again become observable for approximately nine months. In 2013, the asteroid will pass close enough to Earth for ultra-precise radar signals to be bounced off its surface.

Adapted from information issued by the University of Hawaii at Manoa. Apophis image courtesy D. Tholen, M. Micheli, G. Elliott, UH Institute for Astronomy. Apophis illustration courtesy SpaceWorks Engineering, Inc.

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How Kleopatra gave birth to twins

  • Asteroid Kleopatra is a rubble pile shaped like a dog bone, 217km long
  • Found to have twin 8km-wide moons that orbit it
  • Moons have been named after queen Cleopatra’s twins

ASTRONOMERS STUDYING two mini-moons orbiting an asteroid called Kleopatra have confirmed that the dog bone-shaped asteroid is probably a pile of rocky rubble instead of a solid body.

The French and American team, which includes Franck Marchis (University of California, Berkeley) and Pascal Descamps (Institut de Mecanique Celeste et de Calculs des Ephemerides, Observatoire de Paris), report their findings in the journal Icarus.

Kleopatra was discovered in 1880. Observations made in 2000 showed it to have an unusual, elongated shape reminiscent of a dog bone.

Subsequent radar observations confirmed the shape, but Marchis and his colleagues wanted higher resolution images to determine whether the two lobes of the dog bone are touching or are two separate bodies, and also to calculate its density.

The video above is a rotation of a computer model produced from the radar data.

Using the Keck II telescope in Hawaii, in 2008 the astronomers obtained the best images yet and confirmed that the asteroid is a double-lobed body. They also discovered the two small moons.

Space rubble

The team charted the orbits of the moons (diameters 3 and 5 kilometres), from which they could calculate the mass of the asteroid. Given its size, shape and mass, the astronomers then calculated the asteroid’s density—3.6 grams per cubic centimetre. (As a comparison, Earth’s average density is 5.5 grams per cubic centimetre.)

If the bulk of the asteroid is made of iron—a common component with a density of about 5 grams per cubic centimetre—then it must be between 30 and 50 percent empty space, the team concludes.

“Our observations of the orbits of the two satellites of … Kleopatra imply that this large metallic asteroid is a rubble pile, which is a surprise,” said Marchis, who is also a planetary scientist at the SETI Institute. “Asteroids this big are supposed to be solid, not rubble piles.”

Asteroid Kleopatra and its two tiny moons

Asteroid Kleopatra (overexposed in the left-hand image) and its two tiny moons. The image on the right has been processed to reduce the glare and more easily show the moons, which are now called Alexhelios and Cleoselene.

Kleopatra, about 217 kilometres long, is one of several large asteroids recently found to be composed of rocky rubble held together by mutual gravitational attraction. Others are Sylvia (280 kilometres in diameter), Antiope (86km), Hermione (190km) and 22 Kalliope (166km). Each of these has one or more moons, or in the case of Hermione, is itself a double asteroid.

How to grow a planet

The proportion of large asteroids in the Solar System that are rubble piles is unknown. But the fact that, so far, all multiple asteroids are porous collections of gravitationally bound chunks could have implications for how planets form, Marchis said.

Astronomers think planets are built up by rocks and asteroids crashing into each other and merging, with the resulting bodies gradually growing bigger and bigger.

But collisions between two asteroids are just as likely to smash both bodies to pieces ars they are to coalesce into a single large one, potentially making planet formation a slow process.

Rubble pile asteroids, however, would merge more easily during a collision.

Asteroid Kleopatra

Radar image of dog bone-shaped Kleopatra. The asteroid is thought be made of rocky rubble held together under its own weak gravitational field.

“If a large proportion of asteroids in the early Solar System were rubble-pile, then the formation of the cores of planets would be much faster,” Marchis said.

The twins leave home

Kleopatra probably coalesced from the remains of a rocky, metallic asteroid smashed to smithereens after a collision with another asteroid, which could have occurred any time since the origin of the Solar System 4.5 billion years ago.

Based on a theory of “binary asteroid” formation, the rubble pile would have been set spinning faster by another, oblique impact 100 million years ago. The spinning asteroid would have slowly elongated and eventually split off the most distant of its moons.

The inner moon was likely shed more recently, perhaps 10 million years ago.

The International Astronomical Union’s Committee on Small Body Nomenclature has accepted the proposal of Marchis and his collaborators to name the moons after Cleopatra’s twin children—Cleopatra Selene II and Alexander Helios.

The outermost moon has been named Alexhelios and the innermost moon Cleoselene. In Greek mythology, Helios and Selene represented the Sun and Moon, respectively.

Adapted from information issued by the University of California, Berkeley / NSSDC / NASA / Stephen Ostro et al. (JPL) / Arecibo Radio Telescope / NSF.

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Another close shave for Earth

Artist's impression of an asteroid.

Artist's impression of an asteroid. A new telescope called Pan-STARRS has just discovered one that will come within 6.5 million kilometres of Earth in mid-October 2010.

The Panoramic Survey Telescope & Rapid Response System (Pan-STARRS) PS1 telescope has discovered an asteroid that will come within 6.5 million kilometres of Earth in mid-October.

The object is about 45 metres in diameter and was discovered in images acquired on September 16, when it was about 32 million kilometres away.

It is the first “potentially hazardous object” (PHO) to be discovered by the Pan-STARRS survey and has been given the designation “2010 ST3.”

“Although this particular object won’t hit Earth in the immediate future, its discovery shows that Pan-STARRS is now the most sensitive system dedicated to discovering potentially dangerous asteroids,” said Robert Jedicke, a University of Hawaii member of the PS1 Scientific Consortium, who is working on the asteroid data from the telescope.

2010 ST3

Two images of asteroid 2010 ST3 (circled in green) taken by PS1 about 15 minutes apart on the night of September 16 show the asteroid moving against the background field of stars and galaxies.

“This object was discovered when it was too far away to be detected by other asteroid surveys,” Jedicke noted.

Most of the largest PHOs have already been catalogued, but scientists suspect that there are many more under a kilometre across that have not yet been discovered. These could cause devastation on a regional scale if they ever hit our planet.

Such impacts are estimated to occur once every few thousand years.

Pan-STARRS expects to discover tens of thousands of new asteroids every year with sufficient precision to accurately calculate their orbits around the Sun.

Any sizable object that looks like it may come close to Earth within the next 50 years or so will be labelled “potentially hazardous” and carefully monitored.

NASA experts believe that, given several years warning, it should be possible to organise a space mission to deflect any asteroid that is discovered to be on a collision course with Earth.

Pan-STARRS has broader goals as well. PS1 and its bigger brother, PS4, which will be operational later in this decade, are expected to discover a million or more asteroids in total, as well as more distant targets such as variable stars, supernovae, and mysterious energy bursts from galaxies across more than half the universe. PS1 became fully operational in June 2010.

Adapted from information issued by the Harvard-Smithsonian Centre for Astrophysics / Rob Ratkowski / PS1SC / NASA, ESA, and G. Bacon (STScI).

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