America
Comets are like deep-fried ice cream: Indian-origin scientist
Washington, Feb 11
Using an icebox-like
instrument nicknamed Himalaya, an Indian-origin researcher-led team has
revealed that fluffy ice on the surface of a comet would crystallise and
harden as the comet heads toward the Sun and warms up.
As the
water-ice crystals form, becoming denser and more ordered, other
molecules containing carbon would be expelled to the comet's surface.
The result is a crunchy comet crust sprinkled with organic dust, NASA said in a statement.
"A
comet is like deep fried ice cream. The crust is made of crystalline
ice, while the interior is colder and more porous. The organics are like
a final layer of chocolate on top," explained Murthy Gudipati of NASA's
Jet Propulsion Laboratory in Pasadena, California.
Researchers already know that comets have soft interiors and seemingly hard crusts.
In
the new study, Gudipati and Antti Lignell, post-doctoral scholar at the
California Institute of Technology, put together a model of
crystallising comet crust.
The experiments began with amorphous or porous ice -- the proposed composition of the chilliest of comets and icy moons.
In this state, water vapour molecules are flash-frozen at extremely cold temperatures of around minus 243 degrees Celsius.
Gudipati
and team used their Himalaya instrument to slowly warm their amorphous
ice mixtures to minus 123 degrees Celsius, mimicking conditions a comet
would experience as it journeys toward the sun.
The ice had been
infused with a type of organics called polycyclic aromatic hydrocarbons
(PAHs) which are seen everywhere in deep space.
"What we saw in
the lab - a crystalline comet crust with organics on top - matches what
has been suggested from observations in space," Gudipati noted.
"Deep-fried
ice cream is really the perfect analogy, because the interior of the
comets should still be very cold and contain the more porous, amorphous
ice," he pointed out.
The composition of comets is important to
understanding how they might have delivered water and organics to our
nascent, bubbling-hot Earth.
New results from the Rosetta mission show that asteroids may have been the primary carriers of life's ingredients.
For Gudipati, comets are capsules containing clues not only to our planet's history but to the birth of our entire solar system.
The study appeared in the Journal of Physical Chemistry.