ESO Observations Show First Interstellar Asteroid is Like Nothing Seen Before
VLT reveals dark, reddish and highly-elongated object
20 November 2017
For the first time ever astronomers have
studied an asteroid that has entered the Solar System from interstellar
space. Observations from ESO’s Very Large Telescope in Chile and other
observatories around the world show that this unique object was
traveling through space for millions of years before its chance
encounter with our star system. It appears to be a dark, reddish,
highly-elongated rocky or high-metal-content object. The new results
appear in the journal Nature on 20 November 2017.
On 19 October 2017, the Pan-STARRS
1 telescope in Hawai`i picked up a faint point of light moving across
the sky. It initially looked like a typical fast-moving small asteroid,
but additional observations over the next couple of days allowed its
orbit to be computed fairly accurately. The orbit calculations revealed
beyond any doubt that this body did not originate from inside the Solar
System, like all other asteroids or comets ever observed, but instead
had come from interstellar space. Although originally classified as a
comet, observations from ESO and elsewhere revealed no signs of cometary
activity after it passed closest to the Sun in September 2017. The
object was reclassified as an interstellar asteroid and named 1I/2017 U1
(`Oumuamua) [1].
“We had to act quickly,” explains team member Olivier Hainaut from ESO in Garching, Germany. “`Oumuamua had already passed its closest point to the Sun and was heading back into interstellar space.”
ESO’s Very Large Telescope
was immediately called into action to measure the object’s orbit,
brightness and colour more accurately than smaller telescopes could
achieve. Speed was vital as `Oumuamua was rapidly fading as it headed
away from the Sun and past the Earth’s orbit, on its way out of the
Solar System. There were more surprises to come.
Combining the images from the FORS instrument
on the VLT using four different filters with those of other large
telescopes, the team of astronomers led by Karen Meech (Institute for
Astronomy, Hawai`i, USA) found that `Oumuamua varies dramatically in brightness by a factor of ten as it spins on its axis every 7.3 hours.
Karen Meech explains the significance: “This unusually
large variation in brightness means that the object is highly elongated:
about ten times as long as it is wide, with a complex, convoluted
shape. We also found that it has a dark red colour, similar to objects
in the outer Solar System, and confirmed that it is completely inert,
without the faintest hint of dust around it.”
http://www.eso.org/public/news/eso1737/
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