A strange gaseous
molecule has been discovered lurking in the atmospheres of both Mars and Venus,
scientists announced today, adding that it could affect Venus's hyperactive
greenhouse effect.
The
molecule's signature was first noticed in Venus's atmosphere in April 2006, when
the European Space Agency's Venus
Express arrived at the planet and began to measure the composition of the
atmosphere.
The
Infrared Atmospheric Spectrometer instrument aboard the spacecraft watched the
sun set behind the planet and measured the wavelengths of light absorbed by the
planet's atmosphere. Because different gases absorb at different wavelengths,
scientists can infer the composition of the atmosphere from the wavelengths that
are strongly absorbed.
While observing
Venus, scientists noted an unusual signature in the mid-infrared region of
the spectrum that they couldn't identify.
"It
was conspicuous and systematic, increasing with depth in the atmosphere during
the occultation, so we knew it was real," said study leader Jean-Loup
Bertaux of the Service d'aeronomie of France's National Center for Scientific
Research (CNRS).
Later that
year, NASA scientists observing Mars using telescopes in Hawaii notified Bertaux's
team that they had found the same unusual signature.
Because the
atmospheres of both Mars and Venus are composed of 95 percent carbon dioxide
(as compared to Earth's atmosphere which has only 0.04 percent carbon dioxide
and is composed primarily of nitrogen), the researchers thought the strange
molecule could be an isotope of carbon dioxide. (Isotopes have the same number
of protons, but a different number of neutrons than the main form of an
element.)
This exotic
form of carbon dioxide has one "normal" oxygen attached to its carbon
atom, while the other attached oxygen atom has 10 neutrons, instead of the
usual eight.
The
differently-weighted oxygen atoms let the isotope absorb more energy than
normal carbon dioxide molecules, which could mean that it contributes more to
the greenhouse effect on stifling-hot Venus, the researchers said. (Because the
isotope only accounts for about 1 percent of carbon dioxide molecules on Earth,
its contribution to our
greenhouse effect is likely very small.)
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