From ESO: “ESO Observations Show First Interstellar Asteroid is Like Nothing Seen Before”

ESO 50 Large

European Southern Observatory

20 November 2017
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

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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.

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This very deep combined image shows the interstellar asteroid ‘Oumuamua at the centre of the picture. It is surrounded by the trails of faint stars that are smeared as the telescopes tracked the moving asteroid. This image was created by combining multiple images from ESO’s Very Large Telescope as well as the Gemini South Telescope. The object is marked with a blue circle and appears to be a point source, with no surrounding dust. Credit: ESO/K. Meech et al.


Gemini South telescope, Cerro Tololo Inter-American Observatory (CTIO) campus near La Serena, Chile, at an altitude of 7200 feet

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This diagram shows the orbit of the interstellar asteroid ‘Oumuamua as it passes through the Solar System. Unlike all other asteroids and comets observed before, this body is not bound by gravity to the Sun. It has come from interstellar space and will return there after its brief encounter with our star system. Its hyperbolic orbit is highly inclined and it does not appear to have come close to any other Solar System body on its way in. Credit: ESO/K. Meech et al.

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This plot shows how the interstellar asteroid ‘Oumuamua varied in brightness during three days in October 2017. The large range of brightness — about a factor of ten (2.5 magnitudes) — is due to the very elongated shape of this unique object, which rotates every 7.3 hours. The different coloured dots represent measurements through different filters, covering the visible and near-infrared part of the spectrum. The dotted line shows the light curve expected if ‘Oumuamua were an ellipsoid with a 1:10 aspect ratio, the deviations from this line are probably due to irregularities in the object’s shape or surface albedo. Credit: ESO/K. Meech et al.


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 travelling 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 video is available in 4K UHD. Credit: ESO


This animation shows the path of the interstellar asteroid 1I/2017 (‘Oumuamua) through the Solar System. Observations with ESO’s Very Large Telescope and others have shown that this unique object is dark, reddish in colour and highly elongated. Credit:ESO, M. Kornmesser, L.Calcada. Music: Azul Cobalto

On 19 October 2017, the Pan-STARRS 1 telescope in Hawai`i picked up a faint point of light moving across the sky.

Pann-STARS telescope, U Hawaii, Mauna Kea, Hawaii, USA, 4,207 m (13,802 ft) above sea level

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.

ESO/FORS1

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.”

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

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 Karen 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).

See the full article here .

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