Near miss no big deal
- By Megan Lisagor
- Mar 31, 2002
Like a car zooming past a driver's blind spot, a space rock whizzed near Earth last month without anyone noticing.
Asteroid 2002 EM7 passed the planet March 8 within 1.2 times the distance to the moon. Because the object flew from the direction of the sun, scientists didn't detect it until four days later.
"It wasn't discovered earlier because it's hard to see," said Steven Prav.do, project man.ager and co-principal investigator of the Near-Earth Asteroid Tracking Program (NEAT) at NASA's Jet Propulsion Laboratory. "You can't look with telescopes at the sun."
However, astronomers do look with telescopes in the dark in the hope of catching glimpses of asteroids and comets — rocky and icy bodies left from the formation of the solar system — that could approach Earth.
NEAT, a cooperative effort between NASA and the Air Force, is an automated system designed to take comprehensive sweeps of the sky. The first camera and telescope were installed in 1995 on Mount Haleakala in Hawaii. Since 2000, they have been mounted on the Maui Space Surveillance Site.
Another setup in California began working last year. Powered by computers, the system searches for asteroids and comets during the night and analyzes the data collected.
Only those within 30 million miles are considered near-Earth and are reported to the Minor Planet Center, a nonprofit organization that keeps track of asteroids and comets, according to Pravdo.
Statistically, scientists are more likely to observe an asteroid on a crash course years in advance rather than months before — giving them time, theoretically, to deflect the object from its current orbit.
The stakes are high. If it had hit the Earth, asteroid 2002 EM7 could have caused serious damage. Depending on its landing point, the 50-meter rock could have created a tidal wave in the ocean or wiped out a city, according to Pravdo.
But people have about the same chance of dying in a commercial aircraft as they do by an asteroid, he added.
"I didn't consider it of any particular significance at all," said Edward Bowell, an astronomer at Lowell Observatory in Arizona. "Those sort of objects come close to the Earth several times a year. The fact that we're missing them is neither here nor there. They may or may not be precursors to an impact."
To date, about 1,873 near-Earth objects have been discovered, with 414 classified as potentially hazardous asteroids.
But others, such as asteroid 2002 EM7, evade early detection, slipping by in the sun's blinding rays. A satellite is needed to use telescopes that block out the light, astronomers said.
"If it becomes enough of an importance in people's minds, it would be a possibility," Pravdo said. "It's kind of out of the ballpark."
NASA's asteroid program has a $3 million budget, and the cheapest satellite costs about $50 million, he noted.
As for this month's space visitor, scientists were pleased to spot it at all.
"The significant thing was that it was seen," Bowell said. "The name of the game is to cover as much area of the sky as you can."