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takyon writes:

The solar system's first "interstellar interloper" has been named 1I/ʻOumuamua. It is the first known "hyperbolic asteroid" from outside the solar system:

The first known asteroid to visit our Solar System from interstellar space has been given a name. Scientists who have studied its speed and trajectory believe it originated in a planetary system around another star.

The interstellar interloper will now be referred to as 'Oumuamua, which means "a messenger from afar arriving first" in Hawaiian. The name reflects the object's discovery by a Hawaii-based astronomer using an observatory on Maui. It was discovered on 19 October this year by Rob Weryk, a postdoctoral researcher at the University of Hawaii Institute for Astronomy.

[...] Scientists who have made observations of 'Oumuamua, say that despite its exotic origins, the asteroid is familiar in appearance. In a paper submitted to Astrophysical Journal Letters, they argue that its size, rotation, and reddish colour are similar to those of asteroids in our Solar System. Measuring about 180m by 30m, it resembles a chunky cigar.

"The most remarkable thing about ['Oumuamua'] is that, except for its shape, how familiar and physically unremarkable it is," said co-author Jayadev Rajagopal from the US National Optical Astronomy Observatory (NOAO).

Also at the National Optical Astronomy Observatory and Scientific American.

Previously: Possible Interstellar Asteroid/Comet Enters Solar System

Original Submission

"exec" writes:

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."

... [1] The Pan-STARRS team’s proposal to name the interstellar objet[sic] 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.

http://eso.org/public/news/eso1737

-- submitted from IRC. See also here.

Original Submission

takyon writes:

The interstellar asteroid 'Oumuamua's likely movements have been tracked based on the relative positions of nearby stars. Observations of 'Oumuamua indicate that it has only been subjected to interstellar conditions (cosmic rays, gas, dust) for hundreds of millions of years rather than billions. There are likely to be around 46 million such interstellar objects entering the solar system every year, most of which are too far away to be seen with current telescopes, and are quickly ejected:

[My (Fabo Feng)] latest study gives us a glimpse of exactly where 'Oumuamua may have come from. Reconstructing the object's motion, my research suggests it probably came from the nearby "Pleiades moving group" of young stars, also known as the "Local Association". It was likely ejected from its home solar system and sent out to travel interstellar space.

Based on 'Oumuamua's trajectory, I simulated how it has probably travelled through the galaxy and compared this to the motions of nearby stars. I found the object passed 109 stars within a distance of 16 light years. It went by five of these stars from in the Local Association (a group of young stars likely to have formed together), at a very slow speed relative to their movement.

It's likely that when 'Oumuamua was first ejected into space, it was travelling at just enough speed to break away from the gravity of its planet or star of origin, rather than at a much faster speed that would require even more energy. This means we'd expect the object to move relatively slowly at the start of its interstellar journey, and so its slow encounters with these five stars suggests it was ejected from one of the group.

Pleiades star cluster. "Code and results" for the arXiv paper.

We should capture as many interstellar asteroids as possible and smash them together to create a new dwarf planet near the Earth.

Previously: Possible Interstellar Asteroid/Comet Enters Solar System
Interstellar Asteroid Named: Oumuamua
ESO Observations Show First Interstellar Asteroid is Like Nothing Seen Before
Breakthrough Listen to Observe Interstellar Asteroid 'Oumuamua for Radio Emissions (none were found)

Original Submission

takyon writes:

Tracking the interstellar object 'Oumuamua to its home

A team of astronomers led by Coryn Bailer-Jones of the Max Planck Institute for Astronomy has tracked the interstellar object 'Oumuamua to several possible home stars. The object was discovered in late 2017 – this was the first time astronomers have been able to observe an astronomical object from another star system visiting our own Solar System. Bailer-Jones and his colleagues used data from the ESA astrometry satellite Gaia to find four plausible stars where 'Oumuamua could have begun its long journey, more than a million years ago. [...] Earlier studies had attempted similar reconstructions of 'Oumuamua's origin, but had not come up with plausible candidates.

These earlier studies were missing a crucial ingredient: in June 2018, a group led by ESA astronomer Marco Micheli had shown that 'Oumuamua's orbit within the Solar System is not that of an object in free fall, that is, of an object moving exclusively under the influence of gravity. Instead, there was some additional acceleration when the object was close to the Sun. The likely explanation is that 'Oumuamua has some similarity to a comet – with ice that, when sufficiently heated by sunlight, produces gas that will in turn accelerate the source object like an exceedingly weak rocket engine. Although weak - the outgassing was not visible on images like it is with comets close to the Sun - it is too large to be ignored when back-tracking the orbit. The new study by Bailer-Jones and colleagues takes into account how 'Oumuamua's orbit has changed as the object passed close to the Sun, giving the astronomers a precise estimate of the direction the object came from originally, as well as the speed at which it entered our Solar System.

[...] Bailer-Jones and his colleagues found four stars that are possible candidates for 'Oumuamua's home world. All four of them are dwarf stars. The one that came closest to 'Oumuamua, at least about one million year ago, is the reddish dwarf star HIP 3757. It approached within about 1.96 light-years. Given the uncertainties unaccounted for in this reconstruction, that is close enough for 'Oumuamua to have originated from its planetary system (if the star has one). However, the comparatively large relative speed (around 25 km/s) makes it less probable for this to be 'Oumuamua's home. The next candidate, HD 292249, is similar to our Sun, was a little bit less close to the object's trajectory 3.8 million years ago, but with a smaller relative speed of 10 km/s. The two additional candidates met 'Oumuamua 1.1 and 6.3 million years ago, respectively, at intermediate speeds and distances. These stars have been previously catalogued by other surveys, but little is known about them.

'Oumuamua.

Also at Space.com.

Plausible home stars of the interstellar object 'Oumuamua found in Gaia DR2

Previously: 'Oumuamua Likely Originated in the Local Association (Pleiades Moving Group)
'Oumuamua Outgasses Like a Comet

Original Submission