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NASA to keep watch on asteroid

2012 DA14 trajectory past Earth

Asteroid 2012 DA14 will pass close to the Earth on February 15 (February 16, Australian time) – so close in fact, that it will be nearer to us than the ring of communications and weather satellites that orbit our planet.

THE RECORD-SETTING CLOSE APPROACH of an asteroid on February 15 (early morning February 16, Australian time) is an exciting opportunity for scientists, and a research team will use US National Radio Astronomy Observatory (NRAO) and NASA telescopes to gain a key clue that will help them predict the future path of this nearby cosmic neighbour.

A 45-metre-wide asteroid called 2012 DA14, discovered just a year ago, will pass only 28,000 kilometres above the Earth’s surface. That’s closer than the geosynchronous communication and weather satellites. While the object definitely will not strike the Earth, this is a record close approach for an object of this size. Astronomers around the world are preparing to take advantage of the event to study the asteroid.

A team including NRAO astronomer Michael Busch will use a novel observing technique to determine which way the space rock is spinning as it speeds on its orbit through the solar system. The direction of its spin is an important factor in predicting how the object’s orbit will change over time.

“Knowing the direction of spin is essential to accurately predicting its future path, and thus determining just how close it will get to Earth in the coming years,” Busch said.

Radar observations

Busch’s team will use the Karl G. Jansky Very Large Array (VLA) and the Very Long Baseline Array (VLBA) antennae at Pie Town and Los Alamos, New Mexico, along with a radar on NASA’s 70-metre-diameter antenna at Goldstone, California.

The Goldstone antenna will transmit a powerful beam of radio waves toward the asteroid, and NRAO’s New Mexico antennae will receive the waves reflected from the asteroid’s surface.

Because of the asteroid’s uneven surface and the different reflectivity of portions of the surface, the reflected radar signal will have a characteristic signature, or ‘speckles,’ as seen from Earth. By measuring which antenna in a widely-separated pair receives the speckle pattern first, the astronomers can learn which way the asteroid is spinning.

This way of using the telescopes is significantly different to their normal astronomical observing, and the research team has developed special techniques for processing the data.

Yarkovsky Effect graphic

How the Yarkovsky Effect slows an asteroid’s orbital motion; opposite rotation direction would speed up the orbital motion.

Asteroid’s ‘afternoon’ heat

How does this tell anything about the asteroid’s orbital changes? Just as the afternoon is the warmest part of the day on Earth, the space rock develops a warm region that radiates infrared light in its maximum amount during ‘afternoon’ on the asteroid. That outgoing infrared radiation provides a gentle but firm jet-like push to the asteroid.

The direction of the asteroid’s spin determines whether ‘afternoon’ is either forward or rearward of its direction of motion.

If the hot spot is forward of the direction of motion, the infrared push will slow the asteroid’s orbital speed, and if the hot spot is rearward of the direction of motion, it will speed up the orbital motion. This effect, over time, can make a significant change in the orbit. This is called the Yarkovsky Effect, after the engineer who first identified it.

“When the asteroid passes close to the Earth or another large body, its orbit can be changed quickly by the gravitational effect of the larger body, but the Yarkovsky Effect, though smaller, is at work all the time,” Busch said.

Adapted from information issued by the National Radio Astronomy Observatory. Yarkovsky Effect graphic by Alexandra Bolling, NRAO / AUI / NSF. Orbit graphic by P. Chodas, NASA / JPL.

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Sentinel telescope to protect Earth

IN A PRESS CONFERENCE at the California Academy of Sciences Thursday Morning (US time), the B612 Foundation unveiled its plans to build, launch, and operate the first privately funded deep space mission.

Called Sentinel, the a space telescope will be placed in orbit around the Sun, ranging up to 270 million kilometres from Earth, for a mission of discovery and mapping.

The Foundation leadership and technical team includes some of the most experienced professionals in the world to lead this effort.

“The orbits of the inner Solar System where Earth lies are populated with a half million asteroids larger than the one that struck Tunguska (June 30, 1908), and yet we’ve identified and mapped only about one percent of these asteroids to date, said Ed Lu, space shuttle, Soyuz, and International Space Station astronaut, now Chairman and CEO of the B612 Foundation.

The asteroid that entered Earth’s atmosphere over Tunguska, Russia, was only about 40 metres across (less than the length of an Olympic swimming pool) yet destroyed an unpopulated area roughly the size of the San Francisco Bay area.

“During its 5.5-year mission survey time, Sentinel will discover and track half a million near Earth asteroids, creating a dynamic map that will provide the blueprint for future exploration of our Solar System, while protecting the future of humanity on Earth,” says Lu.

Trees flattened at Tunguska in 1908

A 40-metre-wide meteroid exploded in the air over Tunguska, Russia, in 1908, flattening over 2,000 square kilometres of forest.

Spotting dangerous asteroids

Asteroids are a scientific and economic opportunity in that they contain the original building blocks of the Solar System. They are targets for future human exploration, and may contain valuable raw materials for mining.

But these asteroids are also a threat in that they can pose great risk to humanity here on Earth. Taking advantage of these opportunities and dealing with these threats require not only knowing where each of these individual asteroids is now, but also projecting where they will be in the future.

“For the first time in history, B612’s Sentinel mission will create a comprehensive and dynamic map of the inner Solar Systemin which we live—providing vital information about who we are, who are our neighbours, and where we are going,” says Rusty Schweickart, Chairman Emeritus of B612, and Apollo 9 astronaut.

Diagram of the Sentinel telescope

The solar-powered Sentinel telescope will be equipped with a special camera to spot asteroids.

“We will know which asteroids will pass close to Earth and when, and which, if any of these asteroids actually threaten to collide with Earth,” adds Schweickart. “The nice thing about asteroids is that once you’ve found them and once you have a good solid orbit on them you can predict a hundred years ahead of time whether there is a likelihood of an impact with the Earth.”

Sentinel to launch in five years

Advances in space technology, including advances in infrared sensing and on-board computing, as well as low-cost launch systems, have opened up a new era in exploration where private organisations can now carry out grand and audacious space missions previously only achievable by governments.

The B612 Foundation is working with Ball Aerospace, Boulder, Colorado, which has designed and will be building the Sentinel Infrared (IR) Space Telescope with the same expert team that developed the Spitzer and Kepler space telescopes. It will take approximately five years to complete development and testing to be ready for launch in 2017-2018. The launch vehicle of choice is the SpaceX Falcon9.

Sentinel will scan the entire night half of the sky every 26 days to identify every moving object, with repeated observations in subsequent months. Data collected by Sentinel will be sent back to the Earth via NASA’s Deep Space Network, which also will be used for tracking and navigation.

More information: B612 Foundation

Adapted from information issued by the B612 Foundation.

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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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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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Near misses for Earth today

Asteroid Itokawa

This is asteroid Itokawa, which was visited in recent years by a Japanese spacecraft. The two asteroids due to pass by Earth today are much smaller than Itokawa.

Two small asteroids are due to pass close to Earth within the next 24 hours. So close, in fact, that they’ll be close to us than the Moon is.

Discovered on Sunday by astronomer Andrea Boatini at the Mount Lemmon Observatory in Arizona, they are known only by their catalogue names: 2010 RX30 and 2010 RF12.

2010 RX30 is thought to be 32 to 65 feet (10 to 20 metres) in width. It’ll pass within 0.6 of the distance between the Moon and the Earth (about 154,000 miles, or 248,000 kilometres) at 5:51am US EDT on Wednesday…that’s 7:51pm Sydney time on Wednesday).

The second object, 2010 RF12, estimated to be 20-46 feet (6 to 14 metres) in size, will pass within 0.2 of the Moon-Earth distance (about 49,088 miles or 79,000 kilometres) at 5:12pm US EDT on Wednesday…that’s 7:12am Sydney time on Thursday.

Asteroid orbit diagrams

Orbits of the inner planets (white circles) and the asteroids (light blue lines). Arrows show where the orbit of Earth and the asteroids' trajectories almost intersect.

Experienced amateur astronomers will have a chance of seeing them, depending upon where the observer is located on the Earth (eg. whether it is daylight or night-time at the observing location). Details are available on the Fawkes Telescope web site.

But the two small space rocks won’t be visible to the unaided eye—they’ll be hundreds of times fainter than the naked eye can see.

Neither of the objects have any chance of hitting us during these close approaches, nor indeed at any reasonable time into the future.

So why weren’t they discovered earlier?

Asteroids don’t give off any light of their own…all they do is reflect sunlight. And being made of rock, they aren’t very reflective. Add this dullness to the fact that small asteroids don’t reflect as much light as big ones do (because of their smaller surface area), and you can see that small ones are dim. And this makes them harder to spot.

They have to be almost upon us before they can be seen. Indeed, some have been spotted only once they’ve gone past!

Small asteroids such as these don’t pose much of a risk to anyone on Earth. If they hit, they would explode in the upper atmosphere—due to the tremendous deceleration forces experienced during atmospheric entry—with some small fragments probably surviving to fall to the ground as meteorites.

This is what happened in October 2008, when a small asteroid that had been spotted only a few days before, entered the atmosphere over Sudan in Africa and exploded. Searchers went out and found some fragments a few days later.

And we’re probably being buzzed by them all the time. NASA says that a “10-metre-sized near-Earth asteroid from the undiscovered population of about 50 million would be expected to pass almost daily within a lunar distance, and one might strike Earth’s atmosphere about every 10 years on average.”

Adapted from information issued by NASA / JAXA.

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