OF
NOTE
of the data suggested biological activity in
the Red Planet’s soil, the chemical analyses
didn’t turn up organic compounds, expected
to be present if there were life there.
The data became the basis for arguments
against current or past life on Mars, says
Rafael Navarro-González, a chemist at the
National Autonomous University of Mexico in Mexico City.
The Viking landers used a technique
called thermal volatilization–gas chromatography–mass spectrometry (
TV-GC-MS) to analyze the soil. In that process, an
instrument vaporizes a soil sample, separates the chemical fragments produced, and
then identifies those constituents.
To review the technique’s effectiveness,
Navarro-González and his colleagues used
TV-GC-MS on Earth soils that share features with soil on Mars.
They tested arid samples
from Chile, Egypt, and
Antarctica and iron-rich
soils from Spain and
Hawaii. The researchers
also tested all the samples
with a different technique
for measuring organic
matter.
In tests of the arid-soil
ON THE WAY Satellite photo samples, the latter tech-
shows dust (arrow), bound for nique revealed small
the Amazon, blowing away from amounts of organic com-
the Sahara's Bodélé depression. pounds. But a TV-GC-
MS analysis done accord-
ing to the landers’ protocol failed to detect
those compounds.
The iron-rich soils also contained organic
compounds. However, the researchers
found that the iron causes a reaction during TV-GC-MS analysis that converts the
compounds’ carbon to carbon dioxide. This
could explain why the landers detected carbon dioxide but not organic material, notes
Navarro-González.
“The question of whether there is life on
Mars remains open,” he adds.
The researchers describe their work in
the Oct. 31 Proceedings of the National
Academy of Sciences. —A. C.
EARTH SCIENCE
The African source
of the Amazon’s
fertilizer
In the winter months in the Northern
Hemisphere, massive dust storms from
the African Sahara waft southwest across
the Atlantic to drop tons of vital minerals
on the Amazon basin in South America.
Now, scientists have pinpointed the source
of many of those dust
storms and estimated
their dust content.
The Amazonian rainforest depends on Saharan
dust for many of its nutrients, including iron and
phosphorus (SN: 9/29/01,
p. 200). “If it weren’t for
those nutrients, the Amazon would be a wet desert,”
says Ilan Koren, an atmospheric scientist at the
Weizmann Institute in
Rehovot, Israel.
Using satellite measurements of dust clouds, Koren and his
colleagues estimate that 40 million tons of
Saharan dust reaches South America each
year. The images indicate that more than
half of that dust originates from the Bodélé
depression, a now-dry basin on the southern edge of the Sahara that in wetter times
held a body of water the size of Lake Erie.
Although the depression is only 0.2 percent of the Sahara’s surface area, it’s a prodigious dust source, the researchers report in
the October–December Environmental
Research Letters. Dust storms arise from
the area on 40 percent of winter days. On
average, the storms loft more than 700,000
tons of dust each day, says Koren. —S. P.
in British Columbia and his colleagues previously reported that sea lice spread readily
between these groups of fish (SN: 4/2/05,
p. 212). The team proposed that fish farms
imperil wild salmon, which must swim past
the farms as they migrate to the sea.
Farms, Volpe says, are “point sources of
lice, pumping out tremendous quantities
of infectious larvae.”
But some researchers questioned that
assertion because there was limited evidence that the lice cause substantial harm
to wild fish.
In the Oct. 17 Proceedings of the National
Academy of Sciences, Volpe’s team confirms
its earlier findings and reports further that
sea lice that have spread from fish farms
kill 9 to 95 percent of migrating wild
salmon, depending on the season and local
circumstances.
Volpe says, “Salmon farms are far and
away the major contributor to lice on out-migrating salmon [and] the most significant driver of mortality” in the wild fish
during their migration.
As part of the new study, the researchers
captured migrating salmon and recorded
how many lice were attached. Subsequent
mortality was significantly higher among
salmon that had at least one louse attached
than among fish with none. Death of the
fish, says Volpe, was “effectively assured
with two lice or more.” —B. H.
ASTRONOMY
Black hole survey
CHEMISTRY
Were Viking landers
blind to life?
ANIMAL SCIENCE
Farm salmon
spread deadly lice
The Viking landers may have missed potential signs of life when they explored Mars in
1976, an international research team asserts.
NASA
NASA’s two unmanned Viking craft
landed on Mars, took pictures, and conducted a variety of experiments. While some
In the Pacific Northwest, sea lice that spread
from cultivated salmon to their wild counterparts have become major parasites affecting the wild population. The lice, which are
visible to the naked eye, attach to fish and
draw blood and nutrients.
John Volpe of the University of Victoria
Scanning the sky for high-energy X rays,
NASA’s Swift satellite has completed the
first comprehensive census of active
supermassive black holes that lie within
400 million light-years of Earth. The
study, reported in October at a meeting of
the American Astronomical Society in San
Francisco, found more than 200 supermassive black holes, including several that
had been overlooked in previously studied galaxies.
Each black hole, millions to billions times
as massive as the sun, lurks at the center of
a galaxy but in visible light may lie hidden
behind thick layers of dust. However,
because X rays penetrate the dust,
astronomers can detect black holes by looking for the energetic X rays emitted by the
gas swirling around and into them.
Dormant black holes, like the one at the
center of the Milky Way, emit too little radiation to be part of the new census.
The Swift satellite was built to record
gamma-ray bursts, the most energetic
explosions in the universe. But between
bursts, Swift’s Burst Alert Telescope
