No one yet has a photo of the fireball that occurred as the asteroid (dubbed 2008 TC3) broke up in the atmosphere, and meteorite fragments will be difficult to find — the impact spot is in northern Sudan near Darfur. But Russian stargazers S. Korotkiy and T. Kryachko, of the Kazan State University Astrotel Observatory, released an animated picture of 2008 TC3's path toward Earth:

Nature reports that NASA was able to give out early warnings of the impact:

On Monday, once Yeomans' office had confirmed the incoming asteroid, he called NASA headquarters in Washington DC, which publicized the impact about seven hours before it occurred. If, however, the incoming object had been 50 to 100 times bigger than it was, the warnings would have been very different. "We would have found out several days sooner," Yeomans says, and arrangements would have been made to get people out of the area of impact.

Alerted of 2008 TC3's proximity and the possibility of seeing a fireball, a Dutch pilot with KLM reported seeing a quick flash in the sky from 1400 kilometers away. An astronomer from Western Ontario even managed to estimate the size of 2008 TC3:

... astronomer Peter Brown of the University of Western Ontario in London, Canada, was able to confirm that the space rock hit the atmosphere at around 02:45 GMT on Tuesday, within minutes of the predicted time and at the predicted location. Brown used data from a Kenya-based array of seven microbarometers, which record atmospheric sound waves to monitor countries' compliance with the Comprehensive Nuclear Test Ban Treaty. The infrasound signals show that the asteroid hit the atmosphere with an energy equivalent to detonating one to two kilotonnes of TNT.

"We can infer from that energy that 2008 TC3 was about three metres in diameter," Brown says.

Though 2008 TC3 was never listed as a potentially hazardous asteroid, its pre-impact discovery and analysis is still an encouraging development for NASA/JPL. Before 2008 TC3 ever entered Earth's atmosphere, astronomers were tracking its progress, and as far as they can tell it burned up just where they said it would. If we can predict the impact of objects this small, it bodes well for our ability to mitigate the imagined disaster scenarios of major impacts.

Great balls of fire [Nature News]
News and information about asteroid impact [Spaceweather.com]

Image from NASA/JPL.

This week, the United Nation's Association of Space Explorers (ASE) held a panel on Asteroid Threat Mitigation to discuss the threat posed by near-Earth objects (NEOs). An asteroid strike would have devastating and lasting consequences:

A hit by even one of the smaller [asteroid] rocks, say the size of a convenience store, would have the impact of 400,000 Hiroshima nuclear bombs exploding at once, he says. The larger varieties (a mile or more in diameter) could hit with as much force as millions of Hiroshima bombs, with devastating planet-wide effects, such as tsunamis, damage to the atmosphere, and radical climate change, with the magnitude of the damage depending on how big it the object is, its composition and if it hits land or water.

Several space programs do currently track NEOs to identify asteroids on a possible collision course with Earth, but these programs are not well coordinated and do not have the funding to track a sufficient number of objects. The ASE plans to deliver a proposal to the UN for a coordinated network of telescopes to better identify and track these asteroids. Although it is not the ASE's role to develop action plans in the event an asteroid threat is detected, its members have contemplated ways to avoid a collision:

In addition to telescopes to detect an incoming rock, that technology could include flying a spacecraft alongside an asteroid that is on course to impact our world. [NEO committee chairman Rusty] Schweickart says the gravitational attraction between the vessel and the space rock would tug on the latter just enough to alter its course and miss Earth. Another, less appealing option would be to shatter or blow up an approaching asteroid.

But is the risk of such an impact real, or is it just movie-engendered hype?

"It's real," says John Pike, director of Globalsecurity.org, an informational Web site focused on security issues, including space. "It's not a question of whether it's going to happen, it's just a question of when it's going to happen."

What 'Deep Impact' might an asteroid make on Earth, astronauts ask and Will an asteroid destroy Earth? Time for UN to keep tabs, say experts [Scientific American]

We already know that Apophis is due for a close pass by Earth in 2029, and if things go just right (or wrong), April 13, 2036 could be a very bad day for us.

But before we go running for cover, there's a lot we still need to figure out about this mean-looking space rock. From the article:

One problem, says [Jon Giorgini of NASA's Near-Earth Object Program], is that our calculations do not include effects arising from the fact that Earth is not a perfect sphere. This slightly alters its gravitational field and could make a difference to the asteroid's path when it swings close to Earth.

Yet the most powerful steer could come from the way the sunlit asteroid radiates heat, says Giorgini. Radiation gives rise to a small thrust, and since warmer areas of the asteroid radiate more than cooler ones, there is a net force on the asteroid. This phenomenon - the Yarkovsky effect - means our calculations of Apophis's path could be out by millions of kilometres, according to Giorgini, who will present his results at the Asteroid, Comets, and Meteors conference in Baltimore, Maryland, on 17 July.

Of course it's possible that refining the calculations will cause the odds to drop beyond their already minuscule levels. But it's also possible that in a couple of years we are going to be *very* interested in former astronaut Rusty Schweickart's idea of a asteroid-avoidance gravity tractor that just the other week barely scraped up $50,000 of funding.

Source: New Scientist