Category: Asteroids

Image credit: NASA
In an article published today in the journal Nature, a team led by Robert Jedicke of the University of Hawaii?s Institute for Astronomy provides convincing evidence that asteroids change color as they age.

David Nesvorny, a team member from the Southwest Research Institute in Boulder, CO, used a variety of methods to estimate asteroid ages that range from 6 million up to 3 billion years. Accurate color measurements for over 100,000 asteroids were obtained by the Sloan Digital Sky Survey (SDSS), and catalogued by team members Zeljko Ivezic from the University of Washington and Mario Juric from Princeton University.

Robert Whiteley, a team member from the USAF Space and Missile Systems Center in Los Angeles, points out that ?the age-color correlation we found explains a long-standing discrepancy between the colors of the most numerous meteorites known as ordinary chondrites (OC) and their presumed asteroid progenitors.? Meteorites are chips of asteroids and comets that have fallen to Earth?s surface.

According to Jedicke, ?If you were given a piece of rock from the Grand Canyon, you might expect that it would be red, like the colorful pictures in travel magazines. You?d be forgiven for questioning its origin if the rock had a bluish color. But if you were then told that the rocks turn from blue to Grand Canyon red because of the effects of weather, then everything might make sense. Your gift is simply a fresh piece of exposed rock, whereas the pictures you?ve seen show weathered cliff faces millions of years old.?

Nesvorny explains that this is similar to the situation experienced by asteroid astronomers. ?The meteorites are gifts of the solar system to scientists on Earth?pieces of asteroids delivered to their own backyard. The mystery is that the OC meteorites have a bluish color relative to the reddish color of the asteroids from which they were supposedly released.? Jedicke asks, ?How could they possibly be related??

About thirty years ago, a ?space weathering? effect was proposed to explain the color change. Meteorites, whose surface is affected by their fall through Earth?s atmosphere, are usually studied in laboratories by observing their freshly cut and exposed interiors. Billions of years of exposure of the same material on the surface of an asteroid to solar and cosmic radiation and the heating effect of impacts of tiny asteroids might alter the surface color of asteroids in exactly the manner required to match the color of asteroids.

Jedicke said that they found that ?asteroids get more red with time in exactly the right manner and at the right rate to explain the mystery of the color difference between them and OC meteorites.? He added, ?Even though we have found a link between the two types of objects, we still don?t know what causes space weathering.?

Once these researchers refine their analysis by obtaining more colors of the youngest-known asteroid surfaces, it will be possible to determine the age of any asteroid from its surface color. They are currently searching for a space weathering effect on other types of asteroids in the solar system.

The Institute for Astronomy at the University of Hawaii conducts research into galaxies, cosmology, stars, planets, and the sun. Its faculty and staff are also involved in astronomy education, deep space missions, and in the development and management of the observatories on Haleakala and Mauna Kea. Refer to http://www.ifa.hawaii.edu/ for more information about the Institute.

Funding for the creation and distribution of the SDSS Archive has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Aeronautics and Space Administration, the National Science Foundation, the U.S. Department of Energy, the Japanese Monbukagakusho, and the Max Planck Society. The SDSS Web site is http://www.sdss.org/.

The SDSS is managed by the Astrophysical Research Consortium (ARC) for the Participating Institutions. The Participating Institutions are The University of Chicago, Fermilab, the Institute for Advanced Study, the Japan Participation Group, The Johns Hopkins University, Los Alamos National Laboratory, the Max-Planck-Institute for Astronomy (MPIA), the Max-Planck-Institute for Astrophysics (MPA), New Mexico State University, University of Pittsburgh, Princeton University, the United States Naval Observatory, and the University of Washington.

Original Source: University of Hawaii News Release

Image credit: NASA
An impact crater believed to be associated with the “Great Dying,” the largest extinction event in the history of life on Earth, appears to be buried off the coast of Australia. NASA and the National Science Foundation (NSF) funded the major research project headed by Luann Becker, a scientist at the University of California, Santa Barbara (UCSB). Science Express, the electronic publication of the journal Science, published a paper describing the crater today.

Most scientists agree a meteor impact, called Chicxulub, in Mexico’s Yucatan Peninsula, accompanied the extinction of the dinosaurs 65 million years ago. But until now, the time of the Great Dying 250 million years ago, when 90 percent of marine and 80 percent of land life perished, lacked evidence and a location for a similar impact event. Becker and her team found extensive evidence of a 125-mile-wide crater, called Bedout, off the northwestern coast of Australia. They found clues matched up with the Great Dying, the period known as the end-Permian. This was the time period when the Earth was configured as one primary land mass called Pangea and a super ocean called Panthalassa.

During recent research in Antarctica, Becker and her team found meteoric fragments in a thin claystone “breccia” layer, pointing to an end-Permian event. The breccia contains the impact debris that resettled in a layer of sediment at end-Permian time. They also found “shocked quartz” in this area and in Australia. “Few Earthly circumstances have the power to disfigure quartz, even high temperatures and pressures deep inside the Earth’s crust,” explains Dr. Becker.

Quartz can be fractured by extreme volcanic activity, but only in one direction. Shocked quartz is fractured in several directions and is therefore believed to be a good tracer for the impact of a meteor. Becker discovered oil companies in the early 70’s and 80’s had drilled two cores into the Bedout structure in search of hydrocarbons. The cores sat untouched for decades. Becker and co-author Robert Poreda went to Australia to examine the cores held by the Geological Survey for Australia in Canberra. “The moment we saw the cores, we thought it looked like an impact breccia,” Becker said. Becker’s team found evidence of a melt layer formed by an impact in the cores.

In the paper, Becker documented how the Chicxulub cores were very similar to the Bedout cores. When the Australian cores were drilled, scientists did not know exactly what to look for in terms of evidence of impact craters. Co-author Mark Harrison, from the Australian National University in Canberra, determined a date on material obtained from one of the cores, which indicated an age close to the end-Permian era. While in Australia on a field trip and workshop about Bedout, funded by the NSF, co-author Kevin Pope found large shocked quartz grains in end-Permian sediments, which he thinks formed as a result of the Bedout impact. Seismic and gravity data on Bedout are also consistent with an impact crater.

The Bedout impact crater is also associated in time with extreme volcanism and the break-up of Pangea. “We think that mass extinctions may be defined by catastrophes like impact and volcanism occurring synchronously in time,” Dr. Becker explains. “This is what happened 65 million years ago at Chicxulub but was largely dismissed by scientists as merely a coincidence. With the discovery of Bedout, I don’t think we can call such catastrophes occurring together a coincidence anymore,” Dr. Becker adds.

Image credit: US Department of Energy
Next time an asteroid or comet is on a collision course with Earth you can go to a web site to find out if you have time to finish lunch or need to jump in the car and DRIVE.

University of Arizona scientists are launching an easy-to-use, web-based program that tells you how the collision will affect your spot on the globe by calculating several environmental consequences of its impact.

Starting today, the program is online at http://www.lpl.arizona.edu/impacteffects .

You type in your distance from the predicted impact site, the size and type of projectile (e.g. ice, rock, or iron) and other information. Then the Earth Impact Effects Program calculates impact energies and crater size. It next summarizes thermal radiation, seismic shaking, ejecta deposition (where all that flying stuff will land), and air-blast effects in language that non-scientists understand.

For those who want to know how all these calculations are made, the web page will include “a description of our algorithm, with citations to the scientific sources used,” said Robert Marcus, a UA undergraduate in the UA/NASA Space Grant Program. He discussed the project recently at the 35th Lunar and Planetary Science Conference meeting in Houston, Texas.

Marcus developed the web site in collaboration with planetary sciences Regents? Professor H. Jay Melosh and research associate Gareth Collins of UA?s Lunar and Planetary Laboratory.

Melosh is a leading expert on impact cratering and one of the first scientists reporters call when rumors of big, Earth-smashing objects begin to circulate.

Reporters and scientists both want to know the same thing: how much damage a particular collision would wrack on communities near the impact site.

The web site is valuable for scientists because they don’t have to spend time digging up the equations and data needed to calculate the effects, Melosh said. Similarly, it makes the information available to reporters and other non-scientists who don’t know how to make the calculations.

“It seemed to us that this is something we could automate, if we could find some very capable person to help us construct the website,” Melosh said.

That person turned out to be Marcus, who is majoring in computer engineering and physics. He applied to work on the project as a paid intern through the UA/NASA Space Grant Program.

Marcus built the web-based program around four environmental effects. In order of their occurrence, they are:

1) Thermal radiation. An expanding fireball of searing vapor occurs at impact. The program calculates how this fireball will expand, when maximum radiation will occur, and how much of the fireball will be seen above the horizon.

The researchers based their radiation calculations on information found in “The Effect of Nuclear Weapons.” This 1977 book, by the U.S. Defense Department and U.S. Department of Energy, details “considerable research into what different degrees of thermal radiation from blasts will do,” Melosh noted.

“We determine at a given distance what type of damage the radiation causes,” Marcus said. “We have descriptions like when grass will ignite, when plywood or newspaper will ignite, when humans will suffer 2nd or 3rd degree burns.”

2) Seismic shaking. The impact generates seismic waves that travel far from the impact site. The program uses California earthquake data and computes a Richter scale magnitude for the impact. Accompanying text describes shaking intensity at the specified distance from the impact site using a modified Mercalli scale This is a set of 12 descriptions ranging from “general destruction” to “only mildly felt.”

Now suppose the dinosaurs had this program 65 million years ago. They could have used it to determine the environmental consequences of the 15-kilometer-diameter asteroid that smashed into Earth, forming the Chicxulub Crater.

The program would have told them to expect seismic shaking of magnitude 10.2 on the Richter scale. They also would have found (supposing that the continents were lined up as they are now) that the ground would be shaking so violently 1,000 kilometers (600 miles) away in Houston that dinosaurs living there would have trouble walking, or even standing up.

If the Chicxulub Crater-impact occurred today, glass in Houston would break. Masonry and plaster would crack. Trees and bushes would shake, ponds would form waves and become turbid with mud, sand and gravel banks would cave in, and bells in Houston schools and churches would ring from ground shaking.

3) Ejecta deposition. The team used a complicated ballistics travel-time equation to calculate when and where debris blown out of the impact crater would rain back down on Earth. Then they used data gathered from experimental explosions and measurements of craters on the moon to calculate how deep the ejecta blanket would be at and beyond the impact-crater rim.

They also determined how big the ejecta particles would be at different distances from impact, based on observations that Melosh and UA?s Christian J. Schaller published earlier when they analyzed ejecta on Venus.

OK, back to the dinosaurs. Houston would have been covered by an 80.8-centimeter- (32-inch-) thick blanket of debris, with particles averaging 2.8 mm (about 1/8th inch) in size. They would have arrived 8 minutes and 15 seconds after impact (meaning they got there at more than 4,000 mph).

4) Air blast. Impacts also produce a shock wave in the atmosphere that, by definition, moves faster than the speed of sound. The shock wave creates intense air pressure and severe winds, but decays to the speed of sound while it?s still close to the fireball, Melosh noted. “We translate that decreasing pressure in terms of decibels ? from ear-and-lung-rupturing sound, to being as loud as heavy traffic, to being only as loud as a whisper.”

The program calculates maximum pressures and wind velocities based on test results from pre-1960s nuclear blasts. Researchers at those blasts erected brick structures at the Nevada Test Site to study blast wave effects on buildings. The UA team used that information to describe damage in terms of buildings and bridges collapsing, cars bowled over by wind, or forests being blown down.

Dinosaurs living in Houston would have heard the Chicxulub impact as loud as heavy traffic and basked in 30 mph winds.

Original Source: UA News Release

Image credit: UA
The hunt for space rocks on a collision course with Earth has so far been pretty much limited to the Northern Hemisphere.

But last week astronomers took the search for Earth-threatening asteroids to southern skies.

Astronomers using a refurbished telescope at the Australian National University’s Siding Spring Observatory discovered their first two near-Earth asteroids (NEAs) on March 29. NEAs are asteroids that pass near the Earth and may pose a threat of collision.

Siding Spring Survey (SSS) astronomer Gordon Garradd detected a roughly 100-meter (about 300-foot) diameter asteroid and 300-meter (about 1,000-foot) diameter asteroid in images he obtained with the 0.5-meter (20-inch) Uppsala Schmidt telescope.

SSS partner Robert H. McNaught confirmed both discoveries in images he took with the Siding Spring 1-meter (40-inch) that same night.

The 100-meter asteroid, designated 2004 FH29, makes a complete orbit around the sun every 2.13 years. It missed Earth by 3 million kilometers (1.9 million miles), or 8 times the Earth-to-moon distance, yesterday, traveling at 10 km per second (22,000 mph) relative to Earth.

The 300-meter asteroid, designated 2004 FJ29, orbits the sun about every 46 weeks. It came within 20 million kilometers (12 million miles), or within 52 lunar distances of Earth, last Tuesday, March 30, traveling at 18 km per second (40,000 mph) relative to Earth.

Neither object poses a direct threat of colliding with Earth.

Had the asteroids not missed, damage from their impacts would have depended on what kind of rock they’re made of. The 100-meter object likely would mostly burn up in Earth’s atmosphere in an airblast equivalent to 10 megatons of TNT, comparable to the 1908 explosion above the Tunguska River valley in Siberia, McNaught said. The 300-meter rocky asteroid likely would reach Earth’s surface, dumping the equivalent of 1,400 megatons of TNT energy into Earth’s atmosphere, he added. That’s comparable to 200 Tunguskas, or 24 times the largest thermonuclear bomb explosion, a 58 megaton Soviet bomb exploded in 1961.

The new survey is a joint collaboration between the University of Arizona Lunar and Planetary Laboratory and ANU’s Research School of Astronomy and Astrophysics. It is funded by NASA’s Near-Earth Object Observation Program, a 10-year effort to discover and track at least 90 percent of the one kilometer (six-tenths of a mile) or larger NEOs with the potential to become impact hazards.

When astronomers detect what they suspect is an NEA, they immediately must take additional images to confirm their discovery, McNaught said. Surveys often have to suspend their NEA searches and spend observing time confirming NEAs, or they risk losing them altogether because follow-up observations were made too late, he added.

The SSS plan is to use the 1-meter (40-inch) telescope for part of the month to quickly confirm suspect asteroids detected with the Uppsala, freeing the smaller telescope to continue it searches.

“Our confirmation strategy worked beautifully on our first try,” McNaught said.

The Uppsala Schmidt telescope was built in the 1950s for Uppsala Observatory in Sweden. It was sited at Stromlo as the Uppsala Southern Station to make wide field photographs of the southern sky. Increasing light pollution from Canberra led to its relocation to Siding Spring, near Coonabarabran in New South Wales, in 1982. Despite its high quality optics, the telescope drifted into disuse because it used photographic film rather than modern electronic detectors and had to be operated manually.

In 1999, McNaught and Stephen M. Larson of UA?s Lunar and Planetary Laboratory joined in an effort to refurbish and upgrade the Uppsala telescope. Larson had similarly just overhauled a manually operated, photographic wide-field Schmidt telescope in the Santa Catalina Mountains north of Tucson for his Catalina Sky Survey (CSS), part of the NASA-funded program to spot and track asteroids headed toward Earth.

The SSS builds on telescope control, detector technology and software developed for the CSS in Tucson. During the upgrade, the Uppsala was completely reconditioned, and fitted with computer control, a large format (16 megapixel) solid state detector array, and extensive support computers and software that detects objects moving against background stars.

Larson said his reaction to the SSS milestone was “one of relief, since it took several years to make the telescope and facility modifications. Now the real work begins.”

Larson and Catalina Sky Survey team member Ed Beshore worked on commissioning the Uppsala telescope during the past few months. Commissioning a telescope is like commissioning a ship: You have to get all the parts working and working together, and adjust things so they perform as expected.

“We actually achieved ‘first light’ last summer, with good images from the start,” Larson said.

McNaught and Garradd will operate SSS about 20 nights each month. They suspend operations when the week around full moon brightens the sky, making faint object detection difficult.

The Catalina telescope, which Larson and his team upgraded again in May 2000, features new optics that give it a 69 centimeter (27-inch) aperture and a new, more sensitive camera. In addition to Larson and Beshore, Eric Christensen, Rik Hill, David McLean, and Serena Howard operate CSS.

Both CSS and SSS telescopes can detect objects as faint as 20th magnitude, close to sky background level generated by scattered city light and auroral glow that brightens Earth?s upper atmosphere.

Original Source: UA News Release

Image credit: NASA
A small near-Earth asteroid (NEA), discovered Monday night by the NASA-funded LINEAR asteroid survey, will make the closest approach to Earth ever recorded. There is no danger of a collision with the Earth during this encounter.

The object, designated 2004 FH, is roughly 30 meters (100 feet) in diameter and will pass just 43,000 km (26,500 miles, or about 3.4 Earth diameters) above the Earth’s surface on March 18th at 5:08 PM EST (2:08 PM PST, 22:08 UTC).

On average, objects about the size of 2004 FH pass within this distance roughly once every two years, but most of these small objects pass by undetected. This particular close approach is unusual only in the sense that scientists know about it. The fact that an object as small as asteroid 2004 FH has been discovered now is mostly a matter of perseverance by the LINEAR team, who are funded by NASA to search for larger kilometer-sized NEAs, but also routinely detect much smaller objects.

Asteroid 2004 FH’s point of closest approach with the Earth will be over the South Atlantic Ocean. Using a good pair of binoculars, the object will be bright enough to be seen during this close approach from areas of Europe, Asia and most of the Southern Hemisphere.

Scientists look forward to the flyby as it will provide them an unprecedented opportunity to study a small NEA asteroid up close.

Original Source: NASA News Release

Image credit: ESA
Today the Rosetta Science Working Team has made the final selection of the asteroids that Rosetta will observe at close quarters during its journey to Comet 67P/Churyumov-Gerasimenko. Steins and Lutetia lie in the asteroid belt between the orbits of Mars and Jupiter.

Rosetta’s scientific goals always included the possibility of studying one or more asteroids from close range. However, only after Rosetta’s launch and its insertion into interplanetary orbit could the ESA mission managers assess how much fuel was actually available for fly-bys. Information from the European Space Operations Centre (ESOC) in Germany enabled Rosetta’s Science Working Team to select a pair of asteroids of high scientific interest, well within the fuel budget.

The selection of these two excellent targets was made possible by the high accuracy with which the Ariane 5 delivered the spacecraft into its orbit. This of course leaves sufficient fuel for the core part of the mission, orbiting Comet 67P/Churyumov-Gerasimenko for 17 months when Rosetta reaches its target in 2014.

Asteroids are primitive building blocks of the Solar System, left over from the time of its formation about 4600 million years ago. Only a few asteroids have so far been observed from nearby. They are very different in shape and size, ranging from a few kilometres to over 100 kilometres across, and in their composition.

The targets selected for Rosetta, Steins and Lutetia, have rather different properties. Steins is relatively small, with a diameter of a few kilometres, and will be visited by Rosetta on 5 September 2008 at a distance of just over 1700 kilometres. This encounter will take place at a relatively low speed of about 9 kilometres per second during Rosetta’s first excursion into the asteroid belt.

Lutetia is a much bigger object, about 100 kilometres in diameter. Rosetta will pass within about 3000 kilometres on 10 July 2010 at a speed of 15 kilometres per second. This will be during Rosetta’s second passage through the asteroid belt.

Rosetta will obtain spectacular images as it flies by these primordial rocks. Its onboard instruments will provide information on the mass and density of the asteroids, thus telling us more about their composition, and will also measure their subsurface temperature and look for gas and dust around them.

Rosetta began its journey just over a week ago, on 2 March, and is well on its way. Commissioning of its instruments has already started and is proceeding according to plan.

“Comets and asteroids are the building blocks of our Earth and the other planets in the Solar System. Rosetta will conduct the most thorough analysis so far of three of these objects,” said Prof. David Southwood, Director of ESA?s Science Programme. “Rosetta will face lots of challenges during its 12-year journey, but the scientific insights that we will gain into the origin of the Solar System and, possibly, of life are more than rewarding.”

Original Source: ESA News Release

Image credit: NASA
H.R. 912, the Charles “Pete” Conrad Astronomy Awards Act, named for the third man to walk on the moon, establishes awards to encourage amateur astronomers to discover and track near-earth asteroids. The bill directs the NASA Administrator to make awards, of $3,000 each, based on the recommendations of the Smithsonian Minor Planet Center. Earth has experienced several near misses with asteroids that would have proven catastrophic, and the scientific community relies heavily on amateur astronomers to discover and track these objects.

“Given the vast number of asteroids and comets that inhabit Earth’s neighborhood, greater efforts for tracking and monitoring these objects are critical. That is why I introduced H.R. 912, the Charles ‘Pete’ Conrad Astronomy Awards Act, which is a tribute to Pete Conrad for his tremendous contributions to the aerospace community over the last four decades,” said bill sponsor, Space and Aeronautics Subcommittee Chairman Dana Rohrabacher (R-CA). “Asteroids deserve a lot more attention from the scientific community. The first step is a thorough tracking of all sizeable Near Earth Objects, and H.R. 912 is a modest step towards this goal.”

Original Source: House Committee On Science News Release

Image credit: NASA
For a few hours on January 13, 2004, astronomers thought a 30-meter wide asteroid might hit the Earth. The asteroid AL00667 seemed to be on a direct course for the Northern Hemisphere, due to strike in less than two days.
A 30-meter asteroid is larger than a tennis court. An asteroid of this size would have broken up in the atmosphere, creating a one-megaton blast. If it exploded high enough, the asteroid probably wouldn’t have caused any damage. The shock wave from the blast would have become a sonic boom by the time it reached the ground. But an explosion lower in the atmosphere could have caused considerable damage.

Astronomers who knew about the asteroid believed an impact was not likely, but they couldn’t rule out the possibility, either. So they faced a dilemma – should they warn others about something that could end up passing us by?

President Bush was preparing to make a speech at NASA headquarters the next day. He planned to talk about sending a man back to the moon and then on to Mars, but news of an approaching asteroid may have caused him to make a very different kind of announcement.

The asteroid, which has since been renamed 2004 AS1, actually passed by at about 12 million kilometers away, or 32 times the Earth-moon distance. The asteroid also turned out to be 10 times larger than first thought (about 300 meters wide – or about the height of the Eiffel Tower).

Some recent news reports say that Clark Chapman, an astronomer with the Southwest Research Institute, was moments away from calling President Bush and warning him about the asteroid. Chapman, however, adamantly denies this.

“It is absurd to think that any of us in the loop would have called the White House,” states Chapman. “Hell, we wouldn’t even have gotten through. All I was thinking about was recommending to Don Yeomans, who is in charge of JPL’s [the Jet Propulsion Laboratory’s] Near Earth Object Program office, that he inform people at NASA. It would have had to go through several layers of hierarchy before it got to anyone who would have been in a position to go higher than NASA. And Yeomans says that he wouldn’t have acted on my advice, preferring to wait for further confirmation of the object.”

The difference between the initial estimates and the final result highlights the difficulty of monitoring the skies for small Near Earth Objects (NEOs). For 2004 AS1, astronomers knew the asteroid could be either big and far away, or small and close by.

“It’s rather like noticing something in the sky out of your car window that appears to be moving along with you,” explains Alan Harris of the Space Science Institute. “It could be a bird close to your car flying along at close to the same speed, or it could be a plane in the distance that only seems to be pacing your car.”

Over the next few weeks after January 13, the asteroid came even closer to Earth, but it still passed many times farther away than the moon. There are many asteroids that routinely pass much closer to the Earth, says Harris, and asteroids the size and distance of 2004 AS1 are “a dime a dozen.”

“I think we all realized the odds were in favor of the larger, more distant object, rather than a real impactor on its way in,” says Harris.

Chapman first discussed these events in a paper presented on February 22 at the Planetary Defense workshop for the American Institute of Aeronautics and Astronautics (AIAA).

“Just last month, perhaps the most surprising impact prediction ever came and went, this time out of the view of the round-the-clock news media,” said Chapman. “It illustrates how an impact prediction came very close to having major repercussions, even though — with hindsight — nothing was ever, in reality, threatening to impact.”

The Lincoln Near Earth Asteroid Research (LINEAR) observatories in New Mexico sends routine nightly observations to the Minor Planet Center (MPC) in Cambridge, Massachusetts. On January 13, when the MPC received the LINEAR data, they performed the usual computations, and five objects were automatically highlighted as being of potential interest. One of these objects was the asteroid that was initially named AL00667.

Information about the five objects was posted on the publicly accessible NEO Confirmation Page (NEOCP). This data is posted so that amateur and professional asteroid astronomers can follow up on the LINEAR observations each night.

The MPC didn’t notice right away that one of their highlighted objects appeared to have an interesting trajectory. But Reiner Stoss, an amateur astronomer in Germany, saw that AL00667 was predicted to get 40 times brighter over the next day. He shared this information on Yahoo’s Minor Planet Mailing List (MPML). Another amateur observer, Richard Miles in England, noticed the same thing and even took images of the predicted area in the sky (although he found nothing).

Harris was monitoring the MPML mailing list at the time, and his quick calculations indicated that the asteroid could strike as soon as one day. He hurriedly contacted his colleagues, including Don Yeomans and NASA Ames Research Center’s David Morrison, who is chair of the International Astronomical Union’s Working Group on NEOs.

The word on the potential asteroid threat was out, and members of the MPML swapped anxious speculations while the scientists swapped a flurry of e-mails and additional calculations. Steven Chesley, a researcher at JPL, sent an e-mail several hours later saying that after looking at all the available data, he estimated the asteroid had a 25 percent chance of striking the Northern Hemisphere as soon as the following night, or as late as a few days later.

To determine whether the asteroid really posed a threat to Earth, more observations were needed. But Mother Nature wasn’t cooperating. Heavy cloud cover obscured much of the night skies in both Europe and North America.

Finally, thanks to clearer skies over Colorado, amateur astronomer Brian Warner was able to use a 20-inch aperture telescope to look for the asteroid. His search covered a broader area of sky than had been searched by Miles, and it covered the entire area that the asteroid should have been within to be on a collision course with Earth. The asteroid wasn’t there, meaning it wasn’t going to strike us after all.

Chapman says part of the problem that night was that the LINEAR data was not as accurate as usual. He thinks the inaccuracy of this data may have been due to the cloudy conditions. The light from the waning quarter moon also may have been a factor.

There is a protocol set in place to prepare for a large asteroid impact, but no such plans exist for smaller asteroids that can catch us off guard. Larger asteroids would be noticed long before they approached Earth, and we would have years if not decades to make plans. But smaller asteroids can seemingly come out of nowhere, giving us much less time to plan.

If a small asteroid was going to strike the Earth in just a few days, both Chapman and Harris say there would not be enough time to deflect or destroy the asteroid. Instead, scientists would try to determine exactly where the asteroid was to hit so that the area could be evacuated, if necessary. But Chapman admits that it is not easy to figure out exactly where a small asteroid will strike the Earth.

“In the case of the 30-meter body, the danger zone would be no larger than a few tens of miles across,” says Chapman. “It is hardly certain that we would be able to predict ground-zero that accurately.”

There are thought to be more than 300,000 nearby small asteroids (asteroids about 100 meters across). Such asteroids should statistically hit Earth once every few thousand years. The most recent such asteroid strike occurred in 1908, when an asteroid measuring about 60 meters in diameter hit Russia. The “Tunguska” bolide exploded in the atmosphere and flattened about 700 square miles of Siberian forest.

Large (1 kilometer or greater) asteroids are far more rare and infrequent. There are only about 1,100 nearby large asteroids, and they are predicted to strike the Earth every half million years or so. But when these asteroids strike, they can cause catastrophic changes in the global climate. Asteroids that cause mass extinctions are thought to be 10 kilometers or greater in diameter.

The Spaceguard Survey was established to track large asteroids and comets that might pose a direct threat to Earth. So far, the Spaceguard Survey has found about half of these NEOs, and they expect to find the majority of them by 2008. The Spaceguard Survey telescopes also occasionally find smaller asteroids, such as the one discovered the night of January 13.

Although there are no current plans to establish a program to track the numerous small NEOs, Chapman says there have been proposals to do so. Such surveys would be able to track asteroids in the 150 to 500 meter range, and would find even smaller asteroids as well.

Original Source: Astrobiology Magazine

Image credit: UA

A volunteer analyzing data gathered by the University of Arizona’s Spacewatch program has discovered an 18 x 36 metre asteroid that will miss the Earth by only 2 million kilometres today. Asteroid 2004 BV18 is no risk; even if it did hit the Earth, it wouldn’t do much more than cause a bright flash in the atmosphere. The asteroid was spotted by amateur astronomer Stu Megan, who was analyzing Spacewatch data through the Internet, and demonstrates how volunteers can help the search for near Earth asteroids.

A volunteer who analyzes online images for the University of Arizona Spacewatch program has discovered a 60-to-120-foot diameter asteroid that will miss Earth by about 1.2 million miles tomorrow, Jan. 22.

While the asteroid is no cause for alarm, its discovery marks a milestone in a new project that relies on volunteers to spot fast-moving objects, or FMOs, in Spacewatch images.

Even if asteroid 2004 BV18 hit Earth head-on, it would only create a bright flash of light in the upper atmosphere, and possibly streaks of light as asteroid fragments heat to incandescence while they rocket across the sky. “In other words, a bright meteoric display known as a bolide,” said Robert S. McMillan, who directs UA’s Spacewatch.

The asteroid appeared in images taken by Spacewatch astronomer Miwa Block with the 0.9-meter telescope at 1:49 UT on Jan. 19, which is 6:49 p.m. MST on Jan. 18. Volunteer Stu Megan reviewed the images on the Internet, and spotted the asteroid’s light trail. Megan is part of a Web-based program that Spacewatch made public last October through a grant from the Paul G. Allen Charitable Foundation.

“It’s hard to explain the excitement when you find a fast-moving asteroid,” Megan said in an E-mail message.

Megan is semi-retired from a 35-year career in information technology and an amateur astronomer who is interested in finding potentially hazardous asteroids. A resident of Tucson, he has reviewed close to 6,500 Spacewatch images during the past three months.

“When I saw (this light trail), it just sat there screaming at me. It was very, very bright and a perfect length. I knew it could be nothing else.”

Three observatories made follow-up observations of the asteroid, so scientists at the Minor Planet Center could compute its orbit. The Minor Planet Center gave Asteroid 2004 BV18 its provisional designation yesterday. (A provisional designation is one that’s adopted until the asteroid’s orbit is known well enough that astronomers won’t lose it.) The center also published the discovery and follow-up studies in the Minor Planet Electronic Circular yesterday.

The asteroid is classified as an “Apollo” asteroid because it is on average slightly farther from the sun than the Earth is, but its modest orbital eccentricity causes it to occasionally cross Earth’s orbit.

At the time Megan discovered the asteroid, it was six times farther from Earth than the Earth is from the moon. Seen from Earth, it appeared to move across the sky at about 6.5 degrees per day, or about the diameter of 13 full moons. At closest approach tomorrow, it will be five times the distance between Earth and the moon.

Spacewatch operates 1.8-meter and 0.9-meter CCD-equipped telescopes on Kitt Peak, about 45 miles southwest of Tucson, Ariz. The project studies solar system dynamics through the movements of asteroids and comets. Spacewatch also finds potential targets for interplanetary spacecraft missions and hunts for objects that might pose a threat to Earth.

The 0.9-meter telescope typically takes two-minute-long exposures, and objects closest to Earth move so quickly through the telescope’s field of view that they trace a line on the sky image. Objects orbiting farther from Earth appear to move more slowly, just as an airplane flying at 40,000 feet appears to move slower than it does at takeoff.

Computer software has a hard time detecting FMO light trails because they vary greatly in length and direction.

Human observers are still much better than computers at finding FMOs in Spacewatch images. But the work is too time intensive for on-duty Spacewatch observers. So the astronomers have turned to 30 volunteers for help. FMO project volunteers are based in the United States, Germany, and Finland.

They would gladly accept more.

The only requirements are interest, sharp eyes, and access to a computer when astronomers are operating Spacewatch telescopes on Kitt Peak. More details on how to volunteer for the FMO Project are on the Web at FMO Project.

“Our reviewers are students, people with full-time jobs, retired ? they run the gamut,” McMillan said. “While our most dedicated volunteers tend to be members of the amateur astronomy community or at least have a strong interest and knowledge of astronomy, we have members who have just begun to climb the learning curve.

“We hope that our Website helps fuel curiosity and participation in science in general, as well as provide a productive outlet for those eager to apply their computer skills,” McMillan said.

McMillan’s Spacewatch team protects the privacy of its volunteers, releasing volunteers’ names only to the Minor Planet Center when discoveries are to be published.

Astronomers want to study small asteroids to know how many there are, their spin rates and surface properties, McMillan said.

Spin rate tells observers if the asteroid is a single solid piece or a loose aggregate of rocks.

The distribution of asteroid sizes tells scientists about the effects of asteroid collisions during the lifetime of the solar system.

The smallest asteroids are free of regoliths, the blanket of loose dust or dirt that obscures the bare rock surfaces of larger asteroids. And the smallest asteroids are useful for studying non-gravitational forces that work on very long time scales, such as the Yarkovsky Effect, a phenomenon where heat propels objects through space.

The Spacewatch Project was begun in 1980 at the UA Lunar and Planetary Laboratory. More information about Spacewatch can be found on the Web at Spacewatch.

Original Source: UA News Release

Image credit: NASA/JPL

NASA scientists have measured a tiny force for the first time which is known to act on asteroids; subtly changing their orbits and speed of rotation. The force, called the Yarkovsky Effect, is produced by the way an asteroid absorbs energy from the Sun, and then radiates it back into space as heat – the force is tiny, only a few grams, but over time it can make a significant change. Asteroid 6489 has been tracked by astronomers since 1991, and they’ve found that it’s shifted its orbit 15 km since then.

NASA scientists have for the first time detected a tiny but theoretically important force acting on asteroids by measuring an extremely subtle change in a near-Earth asteroid?s orbital path. This force, called the Yarkovsky Effect, is produced by the way an asteroid absorbs energy from the sun and re-radiates it into space as heat. The research will impact how scientists understand and track asteroids in the future.

Asteroid 6489 “Golevka” is relatively inconspicuous by near- Earth asteroid standards. It is only one half-kilometer (.33 mile) across, although it weighs in at about 210 billion kilograms (460 billion pounds). But as unremarkable as Golevka is on a celestial scale it is also relatively well characterized, having been observed via radar in 1991, 1995, 1999 and this past May. An international team of astronomers, including researchers from NASA’s Jet Propulsion Laboratory in Pasadena, Calif., have used this comprehensive data set to make a detailed analysis of the asteroid?s orbital path. The team’s report appears in the December 5 issue of “Science.”

“For the first time we have proven that asteroids can literally propel themselves through space, albeit very slowly,” said Dr. Steven Chesley, a scientist at NASA?s Jet Propulsion Laboratory and leader of the study.

The idea behind the Yarkovsky Effect is the simple notion that an asteroid?s surface is heated by the sun during the day and then cools off during the night. Because of this the asteroid tends to emit more heat from its afternoon side, just as the evening twilight on Earth is warmer than the morning twilight. This unbalanced thermal radiation produces a tiny acceleration that has until now gone unmeasured.

“The amount of force exerted by the Yarkovsky Effect, about an ounce in the case of Golevka, is incredibly small, especially considering the asteroid?s overall mass,” said Chesley. “But over the 12 years that Golevka has been observed, that small force has caused a shift of 15 kilometers (9.4 miles). Apply that same force over tens of millions of years and it can have a huge effect on an asteroid?s orbit. Asteroids that orbit the Sun between Mars and Jupiter can actually become near-Earth asteroids.”

The Yarkovsky Effect has become an essential tool for understanding several aspects of asteroid dynamics. Theoreticians have used it to explain such phenomena as the rate of asteroid transport from the main belt to the inner solar system, the ages of meteorite samples, and the characteristics of so-called “asteroid families” that are formed when a larger asteroid is disrupted by collision. And yet, despite its profound theoretical significance, the force has never been detected, much less measured, for any asteroid until now.

“Once a near-Earth asteroid is discovered, radar is the most powerful astronomical technique for measuring its physical characteristics and determining its exact orbit,” said Dr. Steven Ostro, a JPL scientist and a contributor to the paper. “To give you an idea of just how powerful ? our radar observation was like pinpointing to within a half inch the distance of a basketball in New York using a softball-sized radar dish in Los Angeles.”

To obtain their landmark findings, the scientists utilized an advanced model of the Yarkovsky Effect developed by Dr. David Vokrouhlick? of Charles University, Prague. Vokrouhlick? led a 2000 study that predicted the possibility of detecting the subtle force acting on Golevka during its 2003 approach to Earth.

“We predicted that the acceleration should be detectable, but we were not at all certain how strong it would be,” said Vokrouhlick?. “With the radar data we have been able to answer that question.”

Using the measurement of the Yarkovsky acceleration the team has for the first time determined the mass and density of a small solitary asteroid using ground-based observations. This opens up a whole new avenue of study for near-Earth asteroids, and it is only a matter of time before many more asteroids are “weighed” in this manner.

In addition to Chesley, Ostro and Vokrouhlick?, authors of the report include Jon Giorgini, Dr. Alan Chamberlin and Dr. Lance Benner of JPL; David ?apek, Charles University, Prague, Dr. Michael Nolan, Arecibo Observatory, Puerto Rico, Dr. Jean-Luc Margot, University of California, Los Angeles, and Alice Hine, Arecibo Observatory, Puerto Rico.

Arecibo Observatory is operated by Cornell University under a cooperative agreement with the National Science Foundation and with support from NASA. NASA?s Office of Space Science, Washington, DC supported the radar observations. JPL is managed for NASA by the California Institute of Technology in Pasdena.

More information about NASA’s planetary missions, astronomical observations, and laboratory measurements are available on the Internet at: http://neo.jpl.nasa.gov/

Information about NASA programs is available on the Internet at: www.nasa.gov

JPL is managed for NASA by the California Institute of Technology in Pasadena

Original Source: NASA/JPL News Release