Cigar-shaped interstellar visitor
'Oumuamua classified as comet
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[June 30, 2018]
By Will Dunham
WASHINGTON (Reuters) - The reddish
cigar-shaped object called 'Oumuamua spotted last year tumbling through
space is a comet, scientists said on Wednesday, solving the mystery over
how to classify the first interstellar object found passing through our
solar system.
Astronomers said they closely examined the trajectory of 'Oumuamua,
which measures about a half-mile (800 meters) long, as it speeds through
our cosmic neighborhood after being evicted somehow from a distant star
system.
They found that it is deviating slightly from a path that would be
explained purely by the Sun's gravitational pull because of what
apparently is a very small emission of gas from its surface, indicative
of a comet.
'Oumuamua (pronounced oh-MOO-uh-MOO-uh) initially was pegged as a comet,
but it lacks the tail of gas and dust characteristic of many comets, and
some scientists argued that it was perhaps a dry asteroid.
"It does not display any tail in any observation we obtained," said
astronomer Marco Micheli of the European Space Agency's SSA-NEO
Coordination Centre in Italy, who led the study, published in the
journal Nature.
"However, our analysis shows that the amount of emitted gas that is
needed to generate this extra force we see would have been so small as
to be invisible in our observations," he said in an email.
This "extra force" acting on the object's trajectory amounts to only
about 0.1 percent of the Sun's gravitational attraction.
'Oumuamua was first detected last October by the University of Hawaii's
Pan-STARRS1 telescope. Its name refers in the native Hawaiian language
to a messenger arriving from a great distance.
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This artist’s impression shows the first interstellar asteroid,
`Oumuamua as it passes through the solar system after its discovery
in October 2017. European Southern Obervatory/M. Kornmesser/Handout
via REUTERS
It previously slingshot past the Sun traveling at roughly 196,000
miles per hour (315,000 km per hour) and is heading out of the solar
system in the direction of the constellation Pegasus. 'Oumuamua as
of last month was roughly the same distance from the Sun as Jupiter.
Astronomers suspect that more visitors from other star systems will
be discovered passing through our solar system.
"The discovery of 'Oumuamua is an absolute first in the field, and
it provided our first opportunity to study an object coming from
another star and planetary system," Micheli said. "The existence of
these objects was expected, but seeing one for the first time, and
being able to study it in detail, is a unique chance to know more on
these distant systems, and how they formed."
(Reporting by Will Dunham; Editing by Steve Orlofsky)
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