MOLECULE ICONS: GREGG DINDERMAN /
S&TORGANICS
Anorganiccompound is any molecule that contains
carbon bonded to hydrogen. The molecule can
contain other elements, too. Hydrocarbons are
a type of organic compound and consist ofonly
hydrogen and carbon. Most carbon-bearing
molecules are organic.as we know it produced the large amount of molecular
oxygen (O 2 ) we now breathe. It might even give us the
tools to recognise habitable planets around other stars.A hydrocarbon laboratory
After molecular nitrogen, methane is the most abundant
gas in Titan’s atmosphere (2% to nitrogen’s 98%).
Ultraviolet photons from the Sun break N 2 and CH 4
molecules into pieces that react with each other to
produce heavier byproducts, which eventually form
Titan’s thick organic haze. This photochemistry is similar
to the way that sunlight spurs the formation of smog here
on Earth.
Some of the molecules formed by Titan’s
photochemistry are very familiar to us — molecules such
as propane (C 3 H 8 ) or hydrogen cyanide (HCN) — and
they fall into broad categories of chemical compounds
called hydrocarbons (molecu les w it h
hydrogen atoms attached to carbon
atoms) and nitriles (molecu les w it h
a carbon atom triple-bonded to a
nitrogen atom). More broadly, we
refer to the compounds in Titan’s
atmosphere (and, eventually, on its
surface) as organic, which simply means
the molecules contain hydrogen atoms
bonded to carbon atoms.
Prior to the arrival of the Cassini-
Huygens spacecraft, the heaviest
molecule that scientists had ever
detected in Titan’s atmosphere was
benzene (C 6 H 6 ), discovered using data
from ESA’s Infrared Space Observatory
in the late 1990s. Benzene is a pretty
complicated molecule to result from
atmospheric chemistry, although we do also see it at
Jupiter’s poles, where it is made via energetic-particle
chemistry in the aurorae. Thus we knew that the organic
chemistry in Titan’s atmosphere was very complicated
even before Cassini-Huygens. Indeed this is one of the
reasons why we have been interested in Titan since the
Voyager encounters first revealed that complex organic
reactions are happening in its atmosphere.#1
Hydrogen
STOP 10 Here and
on the following
pages are the 10
most abundant
photochemically
made molecules in
the stratosphere
above Titan’s
equatorial regions.
White is hydrogen,
black is carbon,
red is oxygen and
blue is nitrogen.http://www.skyandtelescope.com.au 27