Astronomy - USA (2020-01)

(Antfer) #1

10 ASTRONOMY • JANUARY 2020


QUANTUM GRAVITY


In October 2017, astronomers
announced the discovery of our
solar system’s first identified interstel-
lar visitor: 1I/2017 U1, also called
‘Oumuamua. Now, they’ve found a
second. Discovered August 30, 2019, by
amateur astronomer Gennady Borisov,
2I/Borisov already appears different
from ‘Oumuamua. And it’s offering
astronomers a better, longer look at an
interstellar object than its predecessor.

IT CAME FROM INTERSTELLAR SPACE
Borisov spotted the comet from the
MARGO observatory in Nauchnij,
Crimea, using a 0.65-meter telescope, as
it zipped toward the Sun and inner solar

system. By September 12, it was roughly
260 million miles (420 million kilome-
ters) from the Sun and astronomers had
clocked it moving at 93,000 mph (150,
km/h). From there, it will grow brighter
as it approaches perihelion — the point in
its orbit closest to the Sun — which will
take place December 7 at a distance of
about 2 astronomical units (1 astronomi-
cal unit [AU] is the average Earth-Sun
distance). The comet’s closest approach to
Earth will also bring it within about 2 AU
of our planet December 28. Its trajectory
will then carry it out of the solar system
again, never to return.
Unlike ‘Oumuamua, whose move-
ment indicated it was a comet but never

revealed a visible tail, 2I/Borisov has
a clear tail. A team of astronomers
announced September 30 that they’d
already detected CN gas, which is also
commonly observed in our own solar
system’s comets, from the object. Early
observations indicate 2I/Borisov is
between 1.2 and 10 miles (2 and 16 km)
in diameter — larger than ‘Oumuamua,
which was estimated to be 0.06 to
0.24 mile (100 to 400 meters) long.
“From the very early results, it’s similar
to comets in our solar system,” says Mike
Kelley of the University of Maryland, who
analyzed early observations of the object.
“It has a similar color, a very red color,
which is already an interesting result.”

MEET OUR SECOND-EVER


INTERSTELLAR VISITOR


Although it looks like a typical solar system comet,


2I/Borisov undoubtedly came from another star.


FAR-OFF FUZZBALL. Comet 2I/Borisov
appears as a fuzzy gray ball (above) in a
composite image taken September 9/10 with
the Gemini North Telescope on Hawaii’s
Mauna Kea. Stars appear as blue and red
streaks because the telescope was tracking
the comet, which moves at a different rate.
On October 9, the Hubble Space Telescope
snapped a clearer shot (left) of the object,
showing in more detail the dust around its
bright, compact icy nucleus. GEMINI OBSERVATORY/
NSF/AURA; NASA, ESA, D. JEWITT (UCLA)
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