estimated diameter of
asteroid exploding over
Indonesia in Oct. 2009
Approximate mass of meteorite
striking Ann hodges of
Sylacauga, Ala., in Nov. 1954
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.
* Moon’s movement
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.
line ... is
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.
Navarro-González and collaborators,
including astrobiologist Chris McKay
October 9, 2010 | science news | 9