Science News - October 9, 2010

10 meters

estimated diameter of asteroid exploding over Indonesia in Oct. 2009

5.56 kilograms

Approximate mass of meteorite striking Ann hodges of Sylacauga, Ala., in Nov. 1954

Close encounter
fascinates media
Small space rocks often pass
within radius of moon’s orbit

By Ron Cowen

The only thing that was particularly unusual about two asteroids that zipped past Earth September 8, astronomers say, was that anybody noticed them.

Such approaches inside the moon’s orbit — one asteroid passed within 79,000 kilometers of Earth — happen several times a week, scientists calculate. Yet some media outlets reacted as if it were a

2010 RF12 *

Two small asteroids passed within the
moon’s orbit of Earth on september 8.

2010 RX30

* Moon’s movement during encounters

brush with Armageddon. “Quite frankly,
I don’t know why they’re making such
a fuss about it,” says astronomer Brian
Marsden of the Harvard-Smithsonian
Center for Astrophysics in Cambridge,
Mass. “This is essentially nothing.”
Astronomers first spotted the asteroids
three days before the close encounter,
using the Catalina Sky Survey telescope
near Tucson, which scans the skies for
near-Earth objects. The larger asteroid
was estimated to be 10 to 20 meters in
diameter, and the smaller 6 to 14 meters
across. But subsequent observations by
Richard Binzel and Francesca DeMeo of
MIT using NASA’s Infrared Telescope
Facility in Hawaii indicated that the
objects were only about half that size.

of NASA’s Ames Research Center in Moffett Field, Calif., describe their work in an upcoming Journal of Geophysical Research–Planets. They also reported the findings September 6 in a press briefing at the National Autonomous University.

The study was inspired by a soil analysis conducted by the Mars Phoenix Lander, which arrived on Mars in 2008. Phoenix found that most of the chlorine at the landing site was in the form of perchlorate, rather than a chloride salt as had been assumed (SN: 4/11/09, p. 12).

When heated, perchlorate breaks down into fragments that destroy organic compounds. These reactions take place at the same temperatures — 200° to 500° Celsius — to which Martian soil was heated by the Viking craft. The only organic compounds found by Viking, chloromethane and dichloromethane, were interpreted as contaminants from Earth, since they are common in cleaning fluid and explosives.

But when researchers added magnesium perchlorate to soil from Chile’s Atacama Desert, known to contain organic compounds, and heated the soil as in the Viking experiments, the same chlorinated compounds were found. Most organic compounds originally in the Chilean soil were destroyed by the heat.

Similarly, the team says, the soil at the two Viking sites probably contained plenty of organics that were destroyed upon heating and were turned into chlorinated methane compounds due to the presence of perchlorate.

“The bottom line of this work is that the Viking landers did detect organics on But astrobiologist David Des Marais of NASA-Ames cautions that scientists can’t be sure that the desert soil closely resembles the Martian soil. And inorganic compounds in the Chilean samples could alter the nature of the materials released during the heating process, he notes.

“The bottom
line ... is
that the
Viking landers
did detect
organics on
Mars.”

ChRis MCKay
Mars organics were possibly missed

By Ron Cowen

Martian soil could contain the building blocks of carbon-based life after all, a new study suggests, despite the negative results of an analysis performed by the Viking missions 34 years ago.

When two Viking landers visited Mars in 1976 and scooped up soil samples, scientists were surprised that the craft failed to unearth evidence of organic compounds. The apparent lack of organic molecules helped cement the notion that Mars would not easily support life.

But a new study, relying on soil samples from Earth, now suggests that the Viking craft may have found organic compounds from Mars but failed to recognize them. The finding represents a sea change in the way many scientists think about Mars and suggests a specific strategy for searching for vestiges of life on the planet, says study coauthor Rafael Navarro-González of the National Autonomous University of Mexico in Mexico City.