快猫短视频

THE surface of Mars could be littered with the chemical residues of life.
Previous missions to the planet were simply not equipped to detect them,
researchers claim.

The Viking spacecraft, which landed on Mars nearly 25 years ago, failed to
find any signs of organic molecules, dashing hopes of detecting traces of
life鈥攎odern or ancient鈥攐n the surface. 快猫短视频s have since assumed
that the harsh oxidising environment on the surface would destroy such molecules
and that future missions will have to drill into the ground to find them.

But the chemistry of Mars could have altered organic molecules in a number of
complex ways, says Steven Benner, a chemist and Mars exploration consultant at
the University of Florida in Gainesville. 鈥淭here are some people who can look at
music scores and see the chords,鈥� he says, 鈥渁nd there is a similar talent for
guessing what the products of organic reactions will be under certain
肠辞苍诲颈迟颈辞苍蝉.鈥�

The Martian surface is thought to be highly oxidising because it is exposed
to the Sun鈥檚 ultraviolet rays. This high-energy bombardment splits water
molecules into hydrogen, and hydroxyl radicals which can oxidise organic
compounds directly or combine to form hydrogen peroxide, a powerful oxidising
agent.

Far from destroying all organic molecules, however, these agents may react
with some of them to form stable compounds, say Benner and his colleagues. They
considered how hydroxyl radicals and peroxides would react with the five most
abundant types of organic compound found in meteorites, including aromatic
compounds such as naphthalene and kerogen, as well as alcohols and simple
hydrocarbons.

Although these compounds undergo different reactions, the researchers found
that the first relatively stable product of each is a carboxylic acid. These
could accumulate in the soil鈥攁cetic acid, for example, should oxidise 100
times more slowly than ethanol under the assumed Martian soil conditions. Even
complex carboxylic acids containing benzene rings should be much more stable
than anything preceding them, they say.

But even if carboxylic acids were abundant, the two Viking landers would not
have detected them. To look for organics, the spacecraft heated a scoop of soil
to 500 掳C for 30 seconds and ran the volatile products through a gas
spectrometer. But carboxylic acids take longer to vaporise.

鈥淚f they had heated it for 10 to 20 minutes, they would have seen what we are
predicting is there,鈥� Benner claims. And if traces of organic compounds from
non-living sources such as meteorites can survive on Mars, then so might
traces of compounds created by life.

鈥淭he question of organics is not closed,鈥� agrees Christopher McKay, a space
scientist at NASA鈥檚 Ames Research Center in California. Even if the missing
Polar Lander had reached its destination safely, it would not have been able to
heat its oven for much longer than Viking, he says.

McKay says Martian soil samples should be brought back to Earth so ideas like
Benner鈥檚 can be tested quickly. 鈥淚鈥檓 a big fan of bringing the dirt home.鈥�