Yahoo – AFP,
Marlowe Hood, 28 Oct 2015
 |
In a
"big surprise," scientists have found lots of oxygen on Comet
67P/Churyumov–Gerasimenko, captured by the European space
probe Rosetta
an hour before its closest approach to the sun on August 13, 2015
(AFP Photo)
|
Paris (AFP)
- Stunned scientists announced Wednesday the unexpected discovery of large
quantities of oxygen on a comet which streaked past the Sun in August with a
European spacecraft in tow.
The find
came as a "big surprise" and challenges mainstream theories on the
formation of our Solar System, said scientist Andre Bieler of the University of
Michigan.
Measurements
made by the Rosetta probe suggested that oxygen molecules in the 67P comet's
gassy halo must have existed "before or at" its formation, he told
journalists.
This may
have implications for mankind's understanding of the chemistry involved in the
formation of the Solar System some 4.6 billion years ago.
"We
believe this oxygen is primordial, which means it is older than our Solar
System," said Bieler.
Scientists
had previously ruled out the presence of oxygen (O2) on comets such as
67P/Churyumov-Gerasimenko, the subject of intensive prodding and probing by a
European robot lab.
As O2 mixes
easily with other elements, "we never thought that oxygen could 'survive'
for billions of years" in a pristine state, said Kathrin Altwegg of the
University of Bern, who co-authored a study in the journal Nature.
"This
evidence of oxygen as an ancient substance will likely discredit some
theoretical models of the formation of our Solar System," she said.
The comet
is being tracked on its deep-space journey around the Sun by the European Space
Agency's Rosetta spacecraft.
The
historic mission seeks to unlock the mystery of the origins of life on Earth.
Scientists
believe that comets "seeded" early Earth with some of the ingredients
for life.
The team
monitored the ratio of oxygen to water on the comet for several months to see
if the gas molecules would dissipate as solar winds ripped away layers of
surface.
They did
not -- proving the oxygen was embedded in the comet, not just hanging around
its surface.
Prevailing
theories of the Solar System's birth posit a chaotic, collision-strewn mixing
of matter flowing toward and away from the newly formed Sun.
Pristine, icy
grains containing oxygen would not have made it through such violence intact,
the scientists said, leading them to speculate that the process was, in fact,
"gentler".
The oxygen
molecules must have "survived from the dark molecular clouds from which they
were probably formed into comets as we have them today," said Altwegg.
Only twice
before -- on the icy moons of Jupiter and Saturn -- have oxygen molecules been
found in the Solar System beyond Earth's atmosphere, and never before on a
comet.
Oxygen is
difficult to detect with Earth-bound telescopes.
'Don't
jump to conclusions'
Rosetta
offered a rare opportunity to study 67P's "coma" -- the envelope of
dust, gas and ice that forms as it nears the Sun on an elliptical orbit.
The new
data suggests that water on comets is probably the rule rather than the
exception, the scientists said.
Scientists
not involved in this study underlined its importance, but said more time was
needed to assess the implications.
The
discovery "imposes a severe constraint on the mechanism for the formation
of the Solar System," said French astrophysicist Francis Rocard.
"But
we shouldn't jump to conclusions," he cautioned.
Oxygen
molecules were the fourth-most common gas detected in 67P's debris halo --
after water, carbon monoxide and carbon dioxide.
Their
presence did not tell us anything about the origins of life on Earth, of the
possibility of finding it elsewhere in the universe, Altwegg said.
In looking
at exo-planets, "the combination of O2 and methane has been taken as a
sign that you might have life underneath," she said.
"On
this comet we have both, but we don't have life. So having oxygen may not be a
very good bio-signature."
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