Floating ice on Titan may harbour exotic life
NASA scientists have discovered blocks of hydrocarbon
ice in seas and lakes on Saturn’s moon Titan that may host exotic forms
of life.
A new study by scientists on NASA’s Cassini
mission found that blocks of hydrocarbon ice might decorate the surface
of existing lakes and seas of liquid hydrocarbon on Titan.
“One of the most intriguing questions about these lakes and seas is
whether they might host an exotic form of life,” said Jonathan Lunine of
Cornell University, co-author of the study.
“And
the formation of floating hydrocarbon ice will provide an opportunity
for interesting chemistry along the boundary between liquid and solid, a
boundary that may have been important in the origin of terrestrial
life,” Mr. Lunine said in a statement.
Titan is the
only other body besides Earth in our solar system with stable bodies of
liquid on its surface. While our planet’s cycle of precipitation and
evaporation involves water, Titan’s cycle involves hydrocarbons like
ethane and methane.
Ethane and methane are organic
molecules, which scientists think can be building blocks for the more
complex chemistry from which life arose.
Up to this
point, Cassini scientists assumed that Titan lakes would not have
floating ice, because solid methane is denser than liquid methane and
would sink.
But the new model considers the
interaction between the lakes and the atmosphere, resulting in different
mixtures of compositions, pockets of nitrogen gas, and changes in
temperature.
The result, scientists found, is that
winter ice will float in Titan’s methane-and-ethane-rich lakes and seas
if the temperature is below the freezing point of methane — minus 297
degrees Fahrenheit.
The scientists realised all the
varieties of ice they considered would float if they were composed of at
least 5 per cent “air,” which is an average composition for young sea
ice on Earth.
If the temperature drops by just a few
degrees, the ice will sink because of the relative proportions of
nitrogen gas in the liquid versus the solid.
Temperatures close to the freezing point of methane could lead to both
floating and sinking ice — that is, a hydrocarbon ice crust above the
liquid and blocks of hydrocarbon ice on the bottom of the lake bed.
Scientists haven’t entirely figured out what colour the ice would be,
though they suspect it would be colourless, as it is on Earth, tinted
reddish-brown from Titan’s atmosphere.
“We now know
it’s possible to get methane-and-ethane-rich ice freezing over on Titan
in thin blocks that congeal together as it gets colder — similar to what
we see with Arctic sea ice at the onset of winter,” said Jason
Hofgartner, first author on the paper
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