Unusual object likely originated outside the solar system

First interstellar object to pass through solar system is now on one-way trip out.
By Laurel Kornfeld | Oct 27, 2017
A small object in an extreme orbit that flew closest to the Sun in September likely originated outside the solar system, according to astronomers who have observed its trajectory over the last few weeks.

Less than a quarter of a mile (400 meters) wide and either an asteroid or comet, the object, designated A/2017 U1, is traveling at 27 miles (44 km) per second and is now on its way out of the solar system.

Worldwide, scientists are aiming telescopes at the object as it departs, in the hope of obtaining data that might provide clues as to its origin.

Using the Pan-STARRS 1 telescope in Hawaii, which searches for near-Earth asteroids and comets, Rob Weryk of the University of Hawaii's Institute for Astronomy (IfA) first observed A/2017 U1 on the night of October 19.

While searching Pan-STARRS archives, he found images of it captured the previous night but more importantly discovered its highly unusual orbit.

"Its motion could not be explained using either a normal solar system asteroid or comet orbit," he noted.

Fellow IfA graduate Marco Micheli, who took his own followup images of the object using the European Space Agency's (ESA) Canary Islands telescope on Tenerife when contacted by Weryk, agreed that it originated from beyond the solar system.

Scientists at NASA's Center for Near-Earth Object Studies (CNEOS) at the Jet Propulsion Laboratory (JPL) analyzed the path taken by the object and found it is leaving the solar system and will not return.

"This is the most extreme orbit I have ever seen. 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," noted CNEOS scientist Davide Farnocchia.

Having come toward our solar system from almost directly above the plane of Earth's orbit, known as the ecliptic, A/2017 U1 originated from the direction of the constellation Lyra, travelling at 15.8 miles (25.5 km) per second.

It did not interact with any solar system planets, and on September 2, within the orbit or Mercury, it dipped beneath the ecliptic, coming closest to the Sun one week later.

Tugged at by the Sun's gravity, A/2017 U1 then essentially made a U-turn, flying within 15 million miles (24 million km) of the Earth beneath its orbit, before heading back above the ecliptic. It is currently traveling in the direction of 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," said IfA astronomer Karen Meech, who specializes in small objects such as comets and asteroids.

"What's most surprising is that we've never seen an interstellar object pass through before," she emphasized.

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