Podcast: Homing Beacon for an Asteroid

Asteroids have been roughing up the Earth since it formed 4.6 billion years ago. Hundreds of thousands of potentially devastating asteroids are still out there, and whizzing past our planet all the time. Eventually, inevitably, one is going to score a direct hit and cause catastrophic damage. But what if we could get a better idea of where all these asteroids are or even learn to shift their orbits? Dr Edward Lu is a NASA astronaut, and a member of the B612 Foundation – an organization raising awareness about the threat of these asteroids and some potential solutions.
Continue reading “Podcast: Homing Beacon for an Asteroid”

Asteroid Will Zip Past the Earth in 2029

The orbits of Earth and asteroid 2004mn4. Image credit: NASA/JPL. Click to enlarge.
Friday the 13th is supposed to be an unlucky day, the sort of day you trip on your shoe laces or lose your wallet or get bad news.

But maybe it’s not so bad. Consider this: On April 13th–Friday the 13th–2029, millions of people are going to go outside, look up and marvel at their good luck. A point of light will be gliding across the sky, faster than many satellites, brighter than most stars.

What’s so lucky about that? It’s asteroid 2004 MN4 … not hitting Earth.

For a while astronomers thought it might. On Christmas Eve 2004, Paul Chodas, Steve Chesley and Don Yeomans at NASA’s Near Earth Object Program office calculated a 1-in-60 chance that 2003 qq47 would collide with Earth. Impact date: April 13, 2029.

The asteroid is about 320 meters wide. “That’s big enough to punch through Earth’s atmosphere,” devastating a region the size of, say, Texas, if it hit land, or causing widespread tsunamis if it hit ocean, says Chodas. So much for holiday cheer.

Asteroid 2004 MN4, also known as the 2029 meteor, had been discovered in June 2004, lost, then discovered again six months later. With such sparse tracking data it was difficult to say, precisely, where the asteroid would go. A collision with Earth was theoretically possible. “We weren’t too worried,” Chodas says, “but the odds were disturbing.”

This is typical, by the way, of newly-discovered asteroids. Step 1: An asteroid is discovered. Step 2: Uncertain orbits are calculated from spotty tracking data. Step 3: Possible Earth impacts are noted. Step 4: Astronomers watch the asteroid for a while, then realize that it’s going to miss our planet.

Killer Asteroid! headlines generally appear between steps 3 and 4, but that’s another story.

Astronomers knew 2004 MN4 would miss Earth when they found pictures of the 2029 asteroid taken, unwittingly, in March 2004, three months before its official discovery. The extra data ruled out a collision in 2029.

Instead, what we’re going to have is an eye-popping close encounter:

On April 13, 2029, asteroid 2004 MN4 will fly past Earth only 18,600 miles (30,000 km) above the ground. For comparison, geosynchronous satellites orbit at 22,300 miles (36,000 km). “At closest approach, the asteroid will shine like a 3rd magnitude star, visible to the unaided eye from Africa, Europe and Asia–even through city lights,” says Jon Giorgini of JPL. This is rare. “Close approaches by objects as large as 2004 MN4 are currently thought to occur at 1000-year intervals, on average.”

The asteroid’s trajectory will bend approximately 28 degrees during the encounter, “a result of Earth’s gravitational pull,” explains Giorgini. What happens next is uncertain. Some newspapers have stated that the asteroid might swing around and hit Earth after all in 2035 or so, but Giorgini discounts that: “Our ability to ‘see’ where 2004 MN4 will go (by extrapolating its orbit) is so blurred out by the 2029 Earth encounter, it can’t even be said for certain what side of the sun 2004 MN4 will be on in 2035. Talk of Earth encounters in 2035 is premature.”

In January 2004, a team of astronomers led by Lance Benner of JPL pinged 2004 MN4 using the giant Arecibo radar in Puerto Rico. (Coincidentally, the Arecibo dish is about the same size as the asteroid.) Echoes revealed the asteroid’s precise distance and velocity, “allowing us to calculate the details of the 2029 flyby,” says Giorgini, who was a member of the team along with Benner, Mike Nolan (NAIC) and Steve Ostro (JPL).

More data are needed to forecast 2004 MN4’s motion beyond 2029. “The next good opportunities are in 2013 and 2021,” Giorgini says. The asteroid will be about 9 million miles (14 million km) from Earth, invisible to the naked eye, but close enough for radar studies. “If we get radar ranging in 2013, we should be able to predict the location of 2004 MN4 out to at least 2070.”

The closest encounter of all, Friday the 13th, 2029, will be a spectacular opportunity to explore this asteroid via radar. During this encounter, says Giorgini, “radar could detect the distortion of 2004 MN4’s shape and spin as it passes through Earth’s gravity field. How the asteroid changes (or not) would provide information about its internal structure and material composition.” Beautifully-detailed surface maps are possible, too.

The view through an optical telescope won’t be so impressive. The asteroid’s maximum angular diameter is only 2 to 4 arcseconds, which means it will be a starlike point of light in all but the very largest telescopes.

But to the naked eye–wow! No one in recorded history has ever seen an asteroid in space so bright.

Friday the 13th might not be so bad after all.

Original Source: Science@NASA

Spitzer Sees an Alien Asteroid Belt

NASA’s Spitzer Space Telescope has spotted what may be the dusty spray of asteroids banging together in a belt that orbits a star like our Sun. The discovery offers astronomers a rare glimpse at a distant star system that resembles our home, and may represent a significant step toward learning if and where other Earths form.

“Asteroids are the leftover building blocks of rocky planets like Earth,” said Dr. Charles Beichman of the California Institute of Technology, Pasadena, Calif. Beichman is lead author of a paper that will appear in the Astrophysical Journal. “We can’t directly see other terrestrial planets, but now we can study their dusty fossils.”

Asteroid belts are the junkyards of planetary systems. They are littered with the rocky scraps of failed planets, which occasionally crash into each other, kicking up plumes of dust. In our own solar system, asteroids have collided with Earth, the moon and other planets.

If confirmed, the new asteroid belt would be the first detected around a star about the same age and size as our Sun. The star, called HD69830, is located 41 light-years away from Earth. There are two other known distant asteroid belts, but they circle younger, more massive stars.

While this new belt is the closest known match to our own, it is not a perfect twin. It is thicker than our asteroid belt, with 25 times as much material. If our solar system had a belt this dense, its dust would light up the night skies as a brilliant band.

The alien belt is also much closer to its star. Our asteroid belt lies between the orbits of Mars and Jupiter, whereas this one is located inside an orbit equivalent to that of Venus.

Yet, the two belts may have one important trait in common. In our solar system, Jupiter acts as an outer wall to the asteroid belt, shepherding its debris into a series of bands. Similarly, an unseen planet the size of Saturn or smaller may be marshalling this star’s rubble.

One of NASA’s future planet-hunting missions, SIM PlanetQuest, may ultimately identify such a planet orbiting HD 69830. The mission, which will detect planets as small as a few Earth masses, is scheduled to launch in 2011.

Beichman and colleagues used Spitzer’s infrared spectrograph to observe 85 Sun-like stars. Only HD 69830 was found to possibly host an asteroid belt. They did not see the asteroids themselves, but detected a thick disk of warm dust confined to the inner portion of the star system. The dust most likely came from an asteroid belt in which dusty smash-ups occur relatively frequently, about every 1,000 years.

“Because this belt has more asteroids than ours, collisions are larger and more frequent, which is why Spitzer could detect the belt,” said Dr. George Rieke, University of Arizona, Tucson, co-author of the paper. “Our present-day solar system is a quieter place, with impacts of the scale that killed the dinosaurs occurring only every 100 million years or so.”

To confirm that the dust detected by Spitzer is indeed ground-up asteroids, a second less-likely theory will have to be ruled out. According to the astronomers, it is possible a giant comet, almost as big as Pluto, got knocked into the inner solar system and is slowly boiling away, leaving a trail of dust. This hypothesis came about when the astronomers discovered the dust around the star consists of small silicate crystals like those found in comet Hale-Bopp. One of these crystals is the bright green-colored gem called forsterite.

“The ‘super comet’ theory is more of a long shot,” Beichman said, “but we’ll know soon enough.” Future observations of the star using Spitzer and ground-based telescopes are expected to conclude whether asteroids or comets are the source of the dust.

Other authors of this study include G. Bryden, T. Gautier, K. Stapelfeldt and M. Werner of NASA’s Jet Propulsion Laboratory, Pasadena, Calif.; and K. Misselt, J. Stansberry and D. Trilling of the University of Arizona.

The Jet Propulsion Laboratory manages the Spitzer Space Telescope mission for NASA’s Science Mission Directorate, Washington. Science operations are conducted at the Spitzer Science Center, at the California Institute of Technology in Pasadena. Caltech manages JPL for NASA. Spitzer’s infrared spectrograph was built by Cornell University, Ithaca, N.Y. Its development was led by Dr. Jim Houck of Cornell.

For artist’s concepts and more information, visit: www.spitzer.caltech.edu/spitzer.

Original Source: Spitzer News Release

Torino Scale Revised

Astronomers led by an MIT professor have revised the scale used to assess the threat of asteroids and comets colliding with Earth to better communicate those risks with the public.

The overall goal is to provide easy-to-understand information to assuage concerns about a potential doomsday collision with our planet.

The Torino scale, a risk-assessment system similar to the Richter scale used for earthquakes, was adopted by a working group of the International Astronomical Union (IAU) in 1999 at a meeting in Torino, Italy. On the scale, zero means virtually no chance of collision, while 10 means certain global catastrophe.

“The idea was to create a simple system conveying clear, consistent information about near-Earth objects [NEOs],” or asteroids and comets that appear to be heading toward the planet, said Richard Binzel, a professor in MIT’s Department of Earth, Atmospheric and Planetary Sciences and the creator of the scale.

Some critics, however, said that the original Torino scale was actually scaring people, “the opposite of what was intended,” said Binzel. Hence the revisions.

“For a newly discovered NEO, the revised scale still ranks the impact hazard from 0 to 10, and the calculations that determine the hazard level are still exactly the same,” Binzel said. The difference is that the wording for each category now better describes the attention or response merited for each.

For example, in the original scale NEOs of level 2-4 were described as “meriting concern.” The revised scale describes objects with those rankings as “meriting attention by astronomers”–not necessarily the public.

Equally important in the revisions, says Binzel, “is the emphasis on how continued tracking of an object is almost always likely to reduce the hazard level to 0, once sufficient data are obtained.” The general process of classifying NEO hazards is roughly analogous to hurricane forecasting. Predictions of a storm’s path are updated as more and more tracking data are collected.

According to Dr. Donald K. Yeomans, manager of NASA’s Near Earth Object Program Office, “The revisions in the Torino Scale should go a long way toward assuring the public that while we cannot always immediately rule out Earth impacts for recently discovered near-Earth objects, additional observations will almost certainly allow us to do so.”

The highest Torino level ever given an asteroid was a 4 last December, with a 2 percent chance of hitting Earth in 2029. And after extended tracking of the asteroid’s orbit, it was reclassified to level 1, effectively removing any chance of collision, “the outcome emphasized by level 4 as being most likely,” Binzel said.

“It is just a matter of the scale becoming more well known and understood. Just as there is little or no reason for public concern over a magnitude 3 earthquake, there is little cause for public attention for NEO close encounters having low values on the Torino scale.” He notes that an object must reach level 8 on the scale before there is a certainty of an impact capable of causing even localized destruction.

The Torino scale was developed because astronomers are spotting more and more NEOs through projects like the Lincoln Near Earth Asteroid Research project at MIT’s Lincoln Laboratory. “There’s no increase in the number of asteroids out there or how frequently they encounter our planet. What’s changed is our awareness of them,” Binzel notes.

As a result, astronomers debated whether they should keep potential NEO collisions secret or “be completely open with what we know when we know it,” Binzel said. The IAU working group, of which Binzel is secretary, resoundingly decided on the latter.

The revised wording of the scale was published last fall in a chapter of “Mitigation of Hazardous Comets and Asteroids” (Cambridge University Press). The revisions were undertaken through consultation with astronomers worldwide for nearly a year before being published.

Binzel concludes that “the chance of something hitting the Earth and having a major impact is very unlikely. But although unlikely, it is still not impossible. The only way to be certain of no asteroid impacts in the forecast is to keep looking.”

For more information on the revised Torino scale go to: neo.jpl.nasa.gov/torino_scale.html.

Original Source: MIT News Release

Asteroid Created a Rain of Rock

Scientists at the American Museum of Natural History and the University of Chicago have explained how a globe-encircling residue formed in the aftermath of the asteroid impact that triggered the extinction of the dinosaurs. The study, which will be published in the April issue of the journal Geology, draws the most detailed picture yet of the complicated chemistry of the fireball produced in the impact.

The residue consists of sand-sized droplets of hot liquid that condensed from the vapor cloud produced by an impacting asteroid 65 million years ago. Scientists have proposed three different origins for these droplets, which scientists call ?spherules.? Some researchers have theorized that atmospheric friction melted the droplets off the asteroid as it approached Earth?s surface. Still others suggested that the droplets splashed out of the Chicxulub impact crater off the coast of Mexico?s Yucatan Peninsula following the asteroid?s collision with Earth.

But analyses conducted by Denton Ebel, Assistant Curator of Meteorites at the American Museum of Natural History, and Lawrence Grossman, Professor in Geophysical Sciences at the University of Chicago, provide new evidence for the third proposal. According to their research, the droplets must have condensed from the cooling vapor cloud that girdled the Earth following the impact.

Ebel and Grossman base their conclusions on a study of spinel, a mineral rich in magnesium, iron and nickel contained within the droplets.

?Their paper is an important advance in understanding how these impact spherules form,? said Frank Kyte, adjunct associate professor of geochemistry at the University of California, Los Angeles. ?It shows that the spinels can form within the impact plume, which some researchers argued was not possible.?

When the asteroid struck approximately 65 million years ago, it rapidly released an enormous amount of energy, creating a fireball that rose far into the stratosphere. ?This giant impact not only crushes the rock and melts the rock, but a lot of the rock vaporizes,? Grossman said. ?That vapor is very hot and expands outward from the point of impact, cooling and expanding as it goes. As it cools the vapor condenses as little droplets and rains out over the whole Earth.?

This rain of molten droplets then settled to the ground, where water and time altered the glassy spherules into the clay layer that marks the boundary between the Cretaceous and Tertiary (now officially called the Paleogene) periods. This boundary marks the extinction of the dinosaurs and many other species.

The work that led to Ebel and Grossman?s Geology paper was triggered by a talk the latter attended at a scientific meeting approximately 10 years ago. At this talk, a scientist stated that spinels from the Cretaceous-Paleogene boundary layer could not have condensed from the impact vapor cloud because of their highly oxidized iron content. ?I thought that was a strange argument,? Grossman said. ?About half the atoms of just about any rock you can find are oxygen,? he said, providing an avenue for extensive oxidation.

Grossman?s laboratory, where Ebel worked at the time, specializes in analyzing meteorites that have accumulated minerals condensed from the gas cloud that formed the sun 4.5 billion years ago. Together they decided to apply their experience in performing computer simulations of the condensation of minerals from the gas cloud that formed the solar system to the problem of the Cretaceous-Paleogene spinels.

UCLA?s Kyte, who himself favored a fireball origin for the spinels, has measured the chemical composition of hundreds of spinel samples from around the world.

Ebel and Grossman built on on Kyte?s work and on previous calculations done by Jay Melosh at the University of Arizona and Elisabetta Pierazzo of the Planetary Science Institute in Tucson, Ariz., showing how the asteroid?s angle of impact would have affected the chemical composition of the fireball. Vertical impacts contribute more of the asteroid and deeper rocks to the vapor, while impacts at lower angles vaporize shallower rocks at the impact site.

Ebel and Grossman also drew upon the work of the University of Chicago?s Mark Ghiorso and the University of Washington?s Richard Sack, who have developed computer simulations that describe how minerals change under high temperatures.

The resulting computer simulations developed by Ebel and Grossman show how rock vaporized in the impact would condense as the fireball cooled from temperatures that reached tens of thousands of degrees. The simulations paint a picture of global skies filled with a bizarre rain of a calcium-rich, silicate liquid, reflecting the chemical content of the rocks around the Chicxulub impact crater.

Their calculations told them what the composition of the spinels should be, based on the composition of both the asteroid and the bedrock at the impact site in Mexico. The results closely matched the composition of spinels found at the Cretaceous-Paleogene boundary around the world that UCLA?s Kyte and his associates have measured.

Scientists had already known that the spinels found at the boundary layer in the Atlantic Ocean distinctly differed in composition from those found in the Pacific Ocean. ?The spinels that are found at the Cretaceous-Paleogene boundary in the Atlantic formed at a hotter, earlier stage than the ones in the Pacific, which formed at a later, cooler stage in this big cloud of material that circled the Earth,? Ebel said.

The event would have dwarfed the enormous volcanic eruptions of Krakatoa and Mount St. Helens, Ebel said. ?These kinds of things are just very difficult to imagine,? he said.

The results in this paper strengthen the link between the unique Chicxulub impact and the stratigraphic boundary marking the mass extinction 65 million years ago that ended the Age of Dinosaurs. The topic will be explored further in a new groundbreaking exhibition, ?Dinosaurs: Ancient Fossils, New Discoveries,? set to open at the American Museum of Natural History on May 14. After it closes in the New York, the exhibition will travel to the Houston Museum of Natural Science (March 3-July 30, 2006); the California Academy of Sciences, San Francisco (Sept. 15, 2006-Feb. 4, 2007); The Field Museum, Chicago (March 30-Sept. 3, 2007); and the North Carolina State Museum of Natural Sciences, Raleigh (Oct. 26, 2007-July 5, 2008).

Original Source: University of Chicago News Release

New Theory on Meteor Crater

Scientists have discovered why there isn’t much impact-melted rock at Meteor Crater in northern Arizona.

The iron meteorite that blasted out Meteor Crater almost 50,000 years ago was traveling much slower than has been assumed, University of Arizona Regents’ Professor H. Jay Melosh and Gareth Collins of the Imperial College London report in Nature (March 10).

“Meteor Crater was the first terrestrial crater identified as a meteorite impact scar, and it’s probably the most studied impact crater on Earth,” Melosh said. “We were astonished to discover something entirely unexpected about how it formed.”

The meteorite smashed into the Colorado Plateau 40 miles east of where Flagstaff and 20 miles west of where Winslow have since been built, excavating a pit 570 feet deep and 4,100 feet across – enough room for 20 football fields.

Previous research supposed that the meteorite hit the surface at a velocity between about 34,000 mph and 44,000 mph (15 km/sec and 20 km/sec).

Melosh and Collins used their sophisticated mathematical models in analyzing how the meteorite would have broken up and decelerated as it plummeted down through the atmosphere.

About half of the original 300,000 ton, 130-foot-diameter (40-meter-diameter) space rock would have fractured into pieces before it hit the ground, Melosh said. The other half would have remained intact and hit at about 26,800 mph (12 km/sec), he said.

That velocity is almost four times faster than NASA’s experimental X-43A scramjet — the fastest aircraft flown — and ten times faster than a bullet fired from the highest-velocity rifle, a 0.220 Swift cartridge rifle.

But it’s too slow to have melted much of the white Coconino formation in northern Arizona, solving a mystery that’s stumped researchers for years.

Scientists have tried to explain why there’s not more melted rock at the crater by theorizing that water in the target rocks vaporized on impact, dispersing the melted rock into tiny droplets in the process. Or they’ve theorized that carbonates in the target rock exploded, vaporizing into carbon dioxide.

“If the consequences of atmospheric entry are properly taken into account, there is no melt discrepancy at all,” the authors wrote in Nature.

“Earth’s atmosphere is an effective but selective screen that prevents smaller meteoroids from hitting Earth’s surface,” Melosh said.

When a meteorite hits the atmosphere, the pressure is like hitting a wall. Even strong iron meteorites, not just weaker stony meteorites, are affected.

“Even though iron is very strong, the meteorite had probably been cracked from collisions in space,” Melosh said. “The weakened pieces began to come apart and shower down from about eight-and-a-half miles (14 km) high. And as they came apart, atmospheric drag slowed them down, increasing the forces that crushed them so that they crumbled and slowed more.”

Melosh noted that mining engineer Daniel M. Barringer (1860-1929), for whom Meteor Crater is named, mapped chunks of the iron space rock weighing between a pound and a thousand pounds in a 6-mile-diameter circle around the crater. Those treasures have long since been hauled off and stashed in museums or private collections. But Melosh has a copy of the obscure paper and map that Barringer presented to the National Academy of Sciences in 1909.

At about 3 miles (5 km) altitude, most of the mass of the meteorite was spread in a pancake shaped debris cloud roughly 650 feet (200 meters) across.

The fragments released a total 6.5 megatons of energy between 9 miles (15 km) altitude and the surface, Melosh said, most of it in an airblast near the surface, much like the tree-flattening airblast created by a meteorite at Tunguska, Siberia, in 1908.

The intact half of the Meteor Crater meteorite exploded with at least 2.5 megatons of energy on impact, or the equivalent of 2.5 million tons of TNT.

Elisabetta Pierazzo and Natasha Artemieva of the Planetary Science Institute in Tucson, Ariz., have independently modeled the Meteor Crater impact using Artemieva’s Separated Fragment model. They find impact velocities similar to that which Melosh and Collins propose.

Melosh and Collins began analyzing the Meteor Crater impact after running the numbers in their Web-based “impact effects” calculator, an online program they developed for the general public. The program tells users how an asteroid or comet collision will affect a particular location on Earth by calculating several environmental consequences of the impact.

Original Source: University of Arizona News Release

Dawn Will Show How Different Two Asteroids Can Be

Although they’re both enormous asteroids, protoplanets really, and lie within the asteroid belt between Mars and Jupiter, Vesta and Ceres couldn’t be more different.

Vesta formed closer to the Sun, and probably shares many features of the inner planets. Scientists believe it formed in a hot, dry environment and will probably have layers of volcanic flows and a solid metallic core. But even the best photos from Hubble show a blurry gray world, bringing more questions than answers. It’s the brightest asteroid in the Solar System, measuring 530 km (329 miles) across. You can even see it with the unaided eye; in fact, it’s the only main belt asteroid you can see. Traveling to Vesta could be a little dangerous. “We know very little about Vesta’s internal structure,” explained Chief Engineer Dr. Marc Rayman, “it
has an unpredictable and possibly very irregular gravity field.”

Just a little further out – across an invisible line that separates the inner rocky planets from the outer planets – is Ceres; the largest asteroid in the Solar System, measuring 957 km (595 miles) across. Unlike Vesta, Ceres is believed to have formed in a cool, wet environment, and in the presence of water. This water is probably still there, in the form of ice caps, a thin water vapour atmosphere, or even as a liquid underneath the surface.

While most of the objects in the asteroid belt are pulverized chunks of rock, accumulations of material from different bodies, Vesta and Ceres remain largely unchanged from when they first formed 4.6 billion years ago. Revelations about the early history of the Solar System could be written on their surfaces.

The $370 million US spacecraft is scheduled for liftoff in June, 2006. After 4 or 5 years of travel time (depending on whether or not it’ll be making a flyby of Mars first) Dawn will arrive at Vesta in 2010 or 2011, studying it for almost a year before flying off to rendezvous with Ceres three years later. It has a suite of scientific instruments on board to study the two asteroids in great detail: their mass, volume, spin rate, chemical and elemental composition, and gravity. Oh, and it’ll be taking pretty pictures too.

Dawn will be the first spacecraft ever to orbit two separate objects in the solar system (and no, orbiting the Earth doesn’t count here). A feat that wouldn’t even be possible without its ion engine. A very similar engine helped Deep Space 1 set speed and duration records, and served as a model for Dawn’s development. It uses solar electricity to ionize xenon atoms and then hurl them out the back of the spacecraft. The thrust is tiny but fuel efficient, and the engine can keep running for months or even years providing a tremendous velocity.

And an ion engine gives controllers flexibility. “It gives us a very long launch window. We’re launching in June 2006 because that’s when the spacecraft will be ready. But we could still make it in November or even after that,” said Dr. Rayman. So far, though, the project is right on schedule. The completed spacecraft shipped this week from NASA’s Jet Propulsion Laboratory to Orbital Sciences for the next stage of assembly and testing.

If you’re interested in finding out more about this mission, stay tuned. Dr. Rayman is planning on keeping the world well informed, through the Internet. He learned how important this can be while working on Deep Space 1, taking the unusual step – at the time – of maintaining a web log to describe his experiences working with the spacecraft. “I was in the airport when I realized that we needed to get the word out. I dictated my first entry over the phone,” recalled Dr. Rayman. Rayman continued maintaining his popular DS1 blog, giving armchair mission controllers a unique insight into the day-to-day challenges and decisions that go into managing a spacecraft half a solar system away.

Expect more of the same with Dawn. “These missions belong to more than just NASA, or the United States. They’re humanity’s emissaries to the cosmos, and we want everyone to come along for the ride,” explained Rayman. But this time, he’ll get started earlier, bringing an Internet audience into the development stages as well as post-launch.

Official Dawn Mission Page

Written by Fraser Cain

Dr. David J. Tholen Answers Your Asteroid Questions

1.) Which class of Earth-crossing asteroids do you find most interesting, Atens or Apollos? (Erimus)

Personally, I find the Atens more interesting, simply because their orbits keep them out of the opposition region for a larger fraction of the time than the Apollos, making them comparatively more difficult to find. Current population statistics are biased against Atens because of the emphasis on the opposition region by the surveys.

2.) Which particular NEO do you find most interesting? (Erimus)

Which day of the week is it? Let’s see, if it’s Friday, I’d take 2000 SG344. This object is interesting because of its low velocity relative to Earth, which argues against it having been perturbed out the main belt. We can pretty much rule out it being manmade, now that another better candidate for the Apollo 12 S-IVB has been found. So, I’m leaning toward it being a piece of lunar ejecta, which could well be unique among the known objects. Because of its relatively high impact probabilities, I’ve given the object higher priority for astrometric observation, getting it a year and a half ago when it was magnitude 26, probably the faintest NEO ever observed.

If it’s Saturday, I’d go with 2004 MN4. It’s hard to ignore an object that will pass less than 6 Earth radii from the Earth just about 24 years from now, becoming bright enough to be visible to the unaided eye.

If it’s Monday, I’d go with 2004 XZ130. With a record small semimajor axis of 0.617 AU and a record small aphelion distance of 0.898 AU, it’s the kind of asteroid I’ve been interested in finding for a long time. Because it never gets into the opposition region, it would never be found by an opposition survey. Not much is known about this population of asteroid, because of the observational bias. We’re taking the first steps toward reducing that bias.

Oh, it’s Thursday. Let’s see, choices, choices…

3) What is the impact to the Earth, if an asteroid were to hit the Earth? Will it changes the weather or give any chemical or other effects? have we prepared for that? Should ordinary people know and be aware of it? (Fari)

It all depends on the size of the object that hits. If it’s small like a meteorite, it would have no significant effect. Something larger, like the one that produced Meteor Crater in Arizona, won’t change the weather, but significant local damage would occur. An object of the kind that is believed to have wiped out the dinosaurs would indeed have a major effect on the weather. So much dust would be ejected into the Earth’s stratosphere, that sunlight would be blocked, halting photosynthesis and disrupting the food chain all the way up to humans. Some of us have personally witnessed the length of time it can take for small amounts of dust to settle out of the stratosphere, given the El Chicon and Mt. Pinatubo volcanic eruptions of the 1980s and 1990s. Imagine how long it would take for a large amount of dust to settle out of the statosphere.

Currently, humans are not prepared to deal with a major asteroid impact.

Ordinary people who wish to be scientifically literate should be aware of the situation, but it’s not something over which to lose sleep.

4) What do you believe the chances are that the earth will be hit by an asteriod/comet that could cause world wide devastation within our lifetime? (Guest_SeanO)

Very small, less than one in ten thousand. That’s based on an assumed human life span of approximately 100 years (a little long, but we’re dealing with just an order of magnitude estimate here) and an average of one such impact every million years.

5) Do you have any speculations you could share with us about the exploitation of these objects, especially the sort of required technologies and favoured strategies required? (eburacum45)

It is true that some asteroids became hot enough for a long enough time to melt internally and differentiate, with the heavy metals sinking to their cores. Once catastrophically disrupted by a collision with another asteroid, the cores have been exposed, with some of the fragments falling to Earth, producing our nickel-iron meteorites. Some entrepreneurs are very interested in these cores because of the rare metals that could be extracted from them, such as gold, silver, and platinum.

Meanwhile, others are interested in exploiting the material necessary to sustain human existence in outer space. The one item that is most essential to human life is water. That’s one reason why there is so much interest in looking for water in the permanently shaded regions of the lunar poles. But some near-Earth asteroids may be rich in hydrated minerals, so it might be possible to extract water from these objects. Now, water sounds a lot more mundane than gold, silver, or platinum, but when you consider the alternative of hauling water up from the bottom of the deep gravity well that is Earth, you begin to realize that a source of water in outer space would be worth its weight in gold.

In both cases, a source of energy would be needed for the extraction process, but the Sun provides ample amounts of that. We just need to find an efficient way of harnessing that power. Some people want to change the orbit of an asteroid and park it around the Earth, sort of like a second moon, so that it is easier to get to on a routine basis. Needless to say, most of this work is very speculative in nature. Some scientists are probably actively thinking about ways to do the job, but I’m not aware of any major development of infrastructure at this time. One challenge is to work in the weak gravity field of an asteroid. Many terrestrial approaches simply won’t work very well on an asteroid because of the weak gravity.

6) Why is the asteroid belt so far away, in relation to the rocky planets? Why for instance do we not have an asteroid belt between Earth and Venus? (Guest)

The rocky planets range from 0.4 to 1.5 AU from the Sun, and the main asteroid belt extends from roughly 2.1 to 3.2 AU. Practically next door neighbors considering the scale of the Solar System, which extends to roughly 50 AU when you think of the trans-Neptunian objects, and even farther when you think of the Oort cloud comets, like 50,000 AU. So the asteroid belt doesn’t seem all that far away to me.

Asteroids between Venus and Earth do not have particularly stable orbits, at least compared to the 2 to 3 AU region of the Solar System. Nevertheless, some asteroids are believe to inhabit this region of space. Because they never reach the opposition region, they are harder to find. Looking in the part of the sky close to the Sun has been a research interest of mine for over a decade, and we’re just now finding the first inhabitants of this region. The numbers are too small at this time to be thinking in terms of a “belt”, but who knows what we’ll find after an extended investigation?

7) Are two (or more) asteroids ever found in orbit around each other, or will objects that small inevitably drift apart? (gnosys)

There are approximately four dozen asteroids known to have satellites in orbit around them. In some cases, the primary is large and the secondary is small, as in the case of Dactyl orbiting Ida, as imaged by the Galileo spacecraft while en route to Jupiter. In other cases, the two components are more nearly equal in size, such as 90 Antiope. Satellites of asteroids have been found among the near-Earth population, the main belt between Mars and Jupiter, and among the trans-Neptunian objects.

As long as the satellite is in a bound orbit, a source of energy would be necessary to cause them to separate.

Asteroid Threat Ruled Out

Over the past week, several independent efforts were made to search for pre-discovery observations of 2004 mn4. These efforts proved successful today when Jeff Larsen and Anne Descour of the Spacewatch Observatory near Tucson, Arizona, were able to detect and measure very faint images of asteroid 2004mn4 on archival images dating to 15 March 2004. These observations extended the observed time interval for this asteroid by three months allowing an improvement in its orbit so that an Earth impact on 13 April 2029 can now be ruled out.

As is often the case, the possibility of future Earth impacts for some near-Earth objects cannot be entirely ruled out until the uncertainties associated with their trajectories are reduced as a result of either future position observations, or in this case, heretofore unrecognized, pre-discovery observations. When these additional observations were used to update the orbit of 2004 MN4, the uncertainties associated with this object’s future positions in space were reduced to such an extent that none of the object’s possible trajectories can impact the Earth (or Moon) in 2029.

In the accompanying diagram, the most likely position of asteroid 2004 MN4 is shown at the end of the blue line near the Earth on 13 April 2029. However, since the asteroid’s position in space is not perfectly known at that time, the white dots at right angles to the blue line are possible alternate positions of the asteroid. Neither the nominal position of the asteroid, nor any of its possible alternative positions, touches the Earth, indicating that an Earth impact in 2029 is ruled out.

The passage of the asteroid by the Earth in 2029 alters its subsequent trajectory and expands the asteroid’s position uncertainty region (i.e., the line of white dots increases in extent) so the asteroid’s subsequent motion is less certain than it was prior to the 2029 close Earth approach. However, our current risk analysis for 2004 MN4 indicates that no subsequent Earth encounters in the 21st century are of any concern.

Original Source: NASA News Release

Asteroid Threat Upgraded to 1 in 45

The probability that Asteroid 2004 MN4 will strike the Earth on April 13, 2029 has actually been upgraded to a 1-in-43 chance now that more observations have been made. The asteroid has reached an uprecedented 4 on the Torino scale. Of course, this still means that there’s a 98% chance that it’ll completely miss the Earth. The space rock is 400 metres (1,300 feet) across, so a direct impact with our planet would cause a significant amount of damage on a regional level. Update: as of Dec. 28th, the probability has been significantly downgraded thanks to further observations. It’ll definitely miss.