How to track the ‘wolves of the solar system’

Jay Barbree Correspondent

CAPE CANAVERAL, Fla. - Apophis is coming.

On April 13, 2029, an asteroid the size of two and a half football fields, a solid rock named for the Egyptian god of evil and destruction, will come out of the heavens moving at 4 miles per second (6.4 kilometers per second), streaking as close as 18,300 miles (29,300 kilometers). That's closer than the geosynchronous satellites orbiting Earth.

Some will watch in wonder. Others will pray. A few will study and marvel at the bright object moving so close over our shores.  But most will stand stunned, witnessing the closest celestial threat to our planet in our lifetime. If our luck should fail, if some force should change the asteroid's path ever so slightly, Apophis could turn an area the size of the state of New York into an instantaneous hell.

If Apophis hits — either in 2029 or during a follow-up encounter in 2036 — the sheer violence of the 900-foot-wide (270-meter-wide) rock would throw billions of tons of scorched earth and vaporized water and melting metals and glass into the atmosphere. The sun would be blotted out in the blast zone. Living things would be wiped out.

Scientists are still weighing how much of a threat Apophis actually poses. After five years of carefully calculating Apophis' path, NASA this month reduced the probability of a direct hit from a 1-in-45,000 chance to 1-in-250,000.

"I believe Apophis will miss," David Morrison, a NASA researcher specializing in asteroids and comet impact hazards, told me. "But what we really need to know is its exact orbit so we can be sure it will miss us not only in 2029 but on its return in 2036."

Morrison would like to place a transponder for precise measurements on the asteroid long before it makes its flyby.

Why so early?

Because if NASA needs to redirect Apophis, a single rocket can do the job before it arrives.

Asteroids on the radar screen
Just last week an independent panel released a report reviewing America's future in space, and near-Earth asteroids and comets were listed among suggested targets for exploration. Now it's up to President Barack Obama to turn the panel's findings into policy. Many astronomers and scientists are hopeful he will recognize the threats that near-Earth objects pose.

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The impact threat gained fresh prominence in July when the planet Jupiter took a noticeable cosmic hit for the second time in 15 years.

In 1994, Comet Shoemaker-Levy became a star attraction when it hurtled into Jupiter's oceans of gas. The giant planet's gravity tore the comet into a long strand of individual rocky chunks, a glowing "string of pearls," and on July 21 of that year, scientists had their first-ever opportunity to watch one orbiting body slam into another.

The string of comet chunks set off an unprecedented fireworks display.  Fireballs erupted on Jupiter as the huge rocks ignited almost instantly, due to friction with the upper clouds of ammonia ice.  Black smudges, each larger than our Earth, were testimony to the violence taking place in the Jovian atmosphere.

No one questioned that had the comet hit our planet, virtually all life would have perished.

What are the chances?
The bruising of the Jovian world sounded a clarion call for tracking every possible interloper that might one day strike this planet.  At a NASA symposium in Washington, astronomer Carl Sagan estimated there was one chance in a thousand that a major comet or asteroid would blast Earth sometime during the 21st century.  Sagan emphasized that these were not very good odds.  He told the symposium attendees and the press that “you would not go on a commercial airliner if the chance of it falling were one in one thousand.”

Political action for identifying space debris orbits came swiftly, and Jupiter was still sporting bruises when NASA formed the Near-Earth Object Search Committee with the goal of detecting potential killer asteroids and comets. The committee was also told to devise the means for either exploding threatening objects or deflecting their approach to Earth.

Astronomer Eugene Shoemaker — the co-discoverer of Shoemaker-Levy 9 — joined the other experts on the group who warned that at least 15 comets known to swing within Earth’s orbit were big enough to wreak global devastation if they struck this planet. The experts also warned Congress that each day an asteroid the size of a house passes between Earth and the moon, and that we must track these “wolves of the solar system.”

But because our defenses are focused on searching for near-Earth objects and not objects near the solar system’s other planets, another impact was missed in July. Astronomers peering at Jupiter's surface were surprised to see a dark blotch that served as evidence of a recent hit — a hit they never saw coming.

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