Artist’s impression of the interstellar asteroid `Oumuamua
Combined deep image of `Oumuamua from the VLT and other telescopes (annotated)
The Orbit of ‘Oumuamua
Combined deep image of ‘Oumuamua from the VLT and other telescopes (unannotated)
Artist’s impression of the interstellar asteroid `Oumuamua
Light curve of interstellar asteroid `Oumuamua
Videos
ESOcast 138 Light: VLT Discovers First Interstellar Asteroid is like Nothing Seen Before (4K UHD)
Animation of `Oumuamua passing through the Solar System
Animation of `Oumuamua passing through the Solar System (annotated)
Animation of artist's concept of `Oumuamua
VLT reveals dark, reddish and highly-elongated object
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 it.
These properties suggest that `Oumuamua is dense, possibly
rocky or with high metal content, lacks significant amounts of water or
ice, and that its surface is now dark and reddened due to the effects of
irradiation from cosmic rays over millions of years. It is estimated to
be at least 400 metres long.
Preliminary orbital calculations suggested that the object had come from the approximate direction of the bright star Vega, in the northern constellation of Lyra.
However, even travelling at a breakneck speed of about 95 000
kilometres/hour, it took so long for the interstellar object to make the
journey to our Solar System that Vega was not near that position when
the asteroid was there about 300 000 years ago. `Oumuamua may well have
been wandering through the Milky Way, unattached to any star system, for
hundreds of millions of years before its chance encounter with the
Solar System.
Astronomers estimate that an interstellar asteroid similar
to `Oumuamua passes through the inner Solar System about once per year,
but they are faint and hard to spot so have been missed until now. It is
only recently that survey telescopes, such as Pan-STARRS, are powerful
enough to have a chance to discover them.
“We are continuing to observe this unique object,” concludes Olivier Hainaut, “and we hope to more accurately pin
down where it came from and where it is going next on its tour of the
galaxy. And now that we have found the first interstellar rock, we are
getting ready for the next ones!”
Notes
[1] The Pan-STARRS team’s proposal to name the interstellar objet was accepted by the International Astronomical Union,
which is responsible for granting official names to bodies in the Solar
System and beyond. The name is Hawaiian and more details are given here.
The IAU also created a new class of objects for interstellar asteroids,
with this object being the first to receive this designation. The
correct forms for referring to this object are now: 1I, 1I/2017 U1,
1I/`Oumuamua and 1I/2017 U1 (`Oumuamua). Note that the character before
the O is an okina.
So, the name should sound like H O u mu a mu a. Before the
introduction of the new scheme, the object was referred to as A/2017 U1.
More Information
More Information
This research was presented in a paper entitled “A brief visit from a red and extremely elongated interstellar asteroid”, by K. Meech et al., to appear in the journal Nature on 20 November 2017.
The team is composed of these J. Meech (Institute for
Astronomy, Honolulu, Hawai`i, USA [IfA]) Robert Weryk (IfA), Marco
Micheli (ESA SSA-NEO Coordination Centre, Frascati, Italy;
INAF–Osservatorio Astronomico di Roma, Monte Porzio Catone, Italy), Jan
T. Kleyna (IfA) Olivier Hainaut (ESO, Garching, Germany), Robert Jedicke
(IfA) Richard J. Wainscoat (IfA) Kenneth C. Chambers (IfA) Jacqueline
V. Keane (IfA), Andreea Petric (IfA), Larry Denneau (IfA), Eugene
Magnier (IfA), Mark E. Huber (IfA), Heather Flewelling (IfA), Chris
Waters (IfA), Eva Schunova-Lilly (IfA) and Serge Chastel (IfA).
ESO is the foremost intergovernmental astronomy
organisation in Europe and the world’s most productive ground-based
astronomical observatory by far. It is supported by 16 countries:
Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland,
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Switzerland and the United Kingdom, along with the host state of Chile
and by Australia as a strategic partner. ESO carries out an ambitious
programme focused on the design, construction and operation of powerful
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scientific discoveries. ESO also plays a leading role in promoting and
organising cooperation in astronomical research. ESO operates three
unique world-class observing sites in Chile: La Silla, Paranal and
Chajnantor. At Paranal, ESO operates the Very Large Telescope and its
world-leading Very Large Telescope Interferometer as well as two survey
telescopes, VISTA working in the infrared and the visible-light VLT
Survey Telescope. ESO is also a major partner in two facilities on
Chajnantor, APEX and ALMA, the largest astronomical project in
existence. And on Cerro Armazones, close to Paranal, ESO is building the
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world’s biggest eye on the sky”.
Links
Links
Contacts
Olivier Hainaut
ESO
Garching, Germany
Tel: +49 89 3200 6752
Email: ohainaut@eso.org
Karen Meech
Institute for Astronomy
Honolulu, Hawai`i, USA
Cell: +1-720-231-7048
Email: meech@IfA.Hawaii.Edu
Richard Hook
ESO Public Information Officer
Garching bei München, Germany
Tel: +49 89 3200 6655
Cell: +49 151 1537 3591
Email: rhook@eso.org
Source: ESO
