Martians, Look Out Above!

December 22, 2007

Scientists estimate that a newly-discovered asteroid has a 1-in-75 chance of colliding with Mars on January 30, 2008.

If it strikes the planet, I may need to add a chapter to my book for young readers Collision Course! Cosmic Impacts and Life on Earth, which includes chapters about the Tunguska event (see below) and the collision of Comet Shoemaker-Levy 9 with Jupiter. The Jupiter collision is also a major part of two of my other books, To the Young Scientist: Reflections on Doing and Living Science and Beyond Jupiter: The Story of Planetary Astronomer Heidi Hammel.

According to a news release from the University of Arizona (from which most of this article is drawn), Catalina Sky Survey team member Andrea Boattini discovered the asteroid, designated 2007 WD5, with UA's Mount Lemmon 60-inch telescope in the Santa Catalina Mountains north of Tucson on Nov. 20.

Astronomers monitoring the trajectory of the asteroid estimate it to be 164 feet wide. Observations provided by the astronomers and analyzed by NASA's Near-Earth Object Office at the Jet Propulsion Laboratory in Pasadena, Calif., indicate the object may pass within 30,000 miles of Mars at about 6 a.m. EST on Jan. 30, 2008.

According to survey team member Ed Beshore, the Mars-approaching asteroid is about the size of the object that blasted out Meteor Crater, Ariz., 50,000 years ago. That object that is believed to be a metallic asteroid - more like a ball bearing than a rock. The newly found Mars-approaching asteroid is probably a stony asteroid, as are most asteroids, Beshore said.

Scientists calculate it is traveling at eight miles a second, or 15 times faster than a rifle bullet, he added.

Beshore notes that Asteroid 2007 WD5 is also being compared to the object that exploded over Tunguska, Siberia, with the energy of a three megaton bomb in 1908. The Tunguska object is believed to be the midair explosion of a cometary fragment.

In the unlikely event that 2007 WD5 does hit Mars, it would hit somewhere within a broad swath across the planet north of where the Opportunity rover is, according to NASA.

"We estimate such impacts occur on Mars every thousand years or so," Steve Chesley, an astronomer with the Near Earth Object Program at NASA's Jet Propulsion Laboratory, said in a NASA news release. "If 2007 WD5 were to thump Mars on Jan. 30, we calculate it would hit at about 30,000 miles per hour and might create a crater more than a half-a-mile wide."

The Mars Reconnaissance Orbiter, which is mapping the planet, would have a front-row seat, Chesley added.

The orbiter's science payload includes the High Resolution Imaging Experiment, or HiRISE, which operates the most powerful camera ever to orbit another planet.

"If the asteroid hits Mars we'll get a great look at the crater within a few days of impact," HiRISE principal investigator Alfred S. McEwen of UA's Lunar and Planetary Laboratory said.

HiRISE images of recent Martian impact craters can be found on the HiRISE Website.

Besides the Mount Lemmon Survey in the northern hemisphere, the CSS includes a southern hemisphere component, the Siding Spring Survey near Coonabarabran, New South Wales, Australia.

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