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takyon writes:

Astronomer Rob Weryk has identified what appears to be the first interstellar object to enter (and soon exit) the solar system. The object, provisionally designated A/2017 U1, is estimated to be 400 meters in diameter:

A/2017 U1 was discovered Oct. 19 by the University of Hawaii's Pan-STARRS 1 telescope on Haleakala, Hawaii, during the course of its nightly search for near-Earth objects for NASA. Rob Weryk, a postdoctoral researcher at the University of Hawaii Institute for Astronomy (IfA), was first to identify the moving object and submit it to the Minor Planet Center. Weryk subsequently searched the Pan-STARRS image archive and found it also was in images taken the previous night, but was not initially identified by the moving object processing.

[...] "This is the most extreme orbit I have ever seen," said Davide Farnocchia, a scientist at NASA's Center for Near-Earth Object Studies (CNEOS) at the agency's Jet Propulsion Laboratory in Pasadena, California. "It is going extremely fast and on such a trajectory that we can say with confidence that this object is on its way out of the solar system and not coming back."

The CNEOS team plotted the object's current trajectory and even looked into its future. A/2017 U1 came from the direction of the constellation Lyra, cruising through interstellar space at a brisk clip of 15.8 miles (25.5 kilometers) per second.

The object approached our solar system from almost directly "above" the ecliptic, the approximate plane in space where the planets and most asteroids orbit the Sun, so it did not have any close encounters with the eight major planets during its plunge toward the Sun. On Sept. 2, the small body crossed under the ecliptic plane just inside of Mercury's orbit and then made its closest approach to the Sun on Sept. 9. Pulled by the Sun's gravity, the object made a hairpin turn under our solar system, passing under Earth's orbit on Oct. 14 at a distance of about 15 million miles (24 million kilometers) -- about 60 times the distance to the Moon. It has now shot back up above the plane of the planets and, travelling at 27 miles per second (44 kilometers per second) with respect to the Sun, the object is speeding toward the constellation Pegasus.

"We have long suspected that these objects should exist, because during the process of planet formation a lot of material should be ejected from planetary systems. What's most surprising is that we've never seen interstellar objects pass through before," said Karen Meech, an astronomer at the IfA specializing in small bodies and their connection to solar system formation.

Here is a direct link to an animation of the object's passage.

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:

'Oumuamua's interstellar origin and unusually elongated shape has been enough to convince the billionaire-backed Breakthrough Listen to observe it to look for signs of alien technology:

The team's efforts will begin on Wednesday, with astronomers observing the asteroid, which is currently speeding away from our Solar System, across four different radio frequency bands. The first set of observations is due to last for 10 hours.

[...] Mr Milner's Breakthrough Listen programme released a statement which read: "Researchers working on long-distance space transportation have previously suggested that a cigar or needle shape is the most likely architecture for an interstellar spacecraft, since this would minimise friction and damage from interstellar gas and dust."

Andrew Siemion, director of the Berkeley SETI Research Center, who is part of the initiative, said: "'Oumuamua's presence within our Solar System affords Breakthrough Listen an opportunity to reach unprecedented sensitivities to possible artificial transmitters and demonstrate our ability to track nearby, fast-moving objects." He added: "Whether this object turns out to be artificial or natural, it's a great target for Listen."

Previously: Possible Interstellar Asteroid/Comet Enters Solar System
Interstellar Asteroid Named: Oumuamua
ESO Observations Show First Interstellar Asteroid is Like Nothing Seen Before

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:

Astronomers have posited an interstellar origin for (514107) 2015 BZ₅₀₉, the first example of a retrograde co-orbital asteroid with one of the solar system's planets (Jupiter):

An asteroid in Jupiter's orbit [Note: actually orbiting the Sun and crossing the orbit of Jupiter] may have come from outside our Solar System, according to a new study. Unlike 'Oumuamua, the interstellar object which briefly visited the Solar System earlier this year, 2015 BZ509 (affectionately known as BZ) seems to have been here for 4.5 billion years. This makes it the first known interstellar asteroid to have taken up residence orbiting the Sun.

It is not yet known where the object came from. "That's what we need to figure out next," laughs Dr Fathi Namouni from the Universite Cote d'Azur, one of the study's authors. "Because 'Oumuamua was just passing by... it's not that difficult to go back and pinpoint where it came from," he told BBC News. "BZ reached the Solar System when it was forming, when the planets themselves were not exactly where they are now. So it's a little more tricky to figure out where it came from."

Also at Scientific American, Science News, EarthSky, and CNN.

An interstellar origin for Jupiter's retrograde co-orbital asteroid (open, DOI: 10.1093/mnrasl/sly057) (DX)

Related: 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)
'Oumuamua Likely Originated in the Local Association (Pleiades Moving Group)

Original Submission

takyon writes:

The interstellar space rock that mystified astronomers is actually a comet

A mysterious space rock, first spotted in 2017, bewildered astronomers — was it an icy comet, a rocky asteroid, or something entirely new? As the object, called 'Oumuamua, hurtles away from us, the mystery may be solved: it's accelerating like a comet.

Researchers tracked the space rock's trajectory on its way out of this solar system, using telescopes on the ground and the powerful Hubble Space Telescope to keep watch even as the interstellar visitor faded out of [sight]. They discovered that 'Oumuamua's speed couldn't just be the result of gravity. It was accelerating — which could be explained by gas puffing out of the sun-warmed end of a comet, the team reports today in the journal Nature [DOI: 10.1038/s41586-018-0254-4] [DX].

'Oumuamua.

Also at ESA and ESA/Hubble.

Previously: Interstellar Asteroid Named: Oumuamua
ESO Observations Show First Interstellar Asteroid is Like Nothing Seen Before
Oumuamua Likely Originated in the Local Association (Pleiades Moving Group)

Original Submission