Astronomers
have found the first signature of complex organic molecules in the dust cloud
around a distant star, suggesting that these building blocks of life may be a
common feature of planetary systems.
In our
solar system, the large carbon molecules, called tholins,
have been found in comets and on Saturn's moon, Titan,
giving its atmosphere a red tinge.
Tholins are
thought to be precursors to the biomolecules that make up living organisms on
Earth (though they are no longer found on our planet because the oxygen in our
atmosphere would quickly destroy them).
A new study,
detailed in a recent issue of Astrophysical Journal Letters, features observations
of the spectrum of the dust disk surrounding the star HR4796A that indicate the
presence of tholins there.
The
spectrum of scattered visible and infrared light from the disk looks very red,
the researchers report, a color known to be produced by tholins. (The
spectrum's signature doesn't seem to match other red substances, such as iron
oxides.)
"Until
recently it's been hard to know what makes up the dust in a disk from scattered
light, so to find tholins this way represents a great leap in our
understanding," said study team member John Debes of the Carnegie
Institution.
HR4796A,
located in the constellation Centaurus, is a massive 8-million-year-old star
about 220 light-years from Earth. Its dust disk, discovered in 1991, is
considered a prime example of a planetary system in formation.
The dust is
generated by the collisions of small bodies, perhaps similar to our own comets and asteroids, which could
deliver these tholins to planets that might be orbiting the distant star.
Because the
star is twice as massive and nearly twice as hot as the sun, it provides clues
into the different conditions under which planets, and life, might potentially
evolve.
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