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posted by martyb on Friday October 27 2017, @04:07PM   Printer-friendly
from the just-passing-through dept.

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.


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  • (Score: 2, Interesting) by khallow on Sunday October 29 2017, @09:55AM

    by khallow (3766) Subscriber Badge on Sunday October 29 2017, @09:55AM (#588978) Journal
    It's worth noting that it'll exit the Solar System with a lower velocity as it climbs out of the gravity well of the Sun, maybe 26 km/s at a long distance from the Sun? Even a century from now, an unmanned spacecraft would be able to catch up and match speed to the object, though it'd take significant time and engineering to do so. For example, I'd suggest an Americium 241-powered radiothermal generator (RTG) combined with ion propulsion system. The half-life of the Am-241 is roughly 432 years which would be a good time frame for a pursuit mission, a century from now. Meanwhile the ion propulsion system would have a good exhaust velocity figure (~30-60 km/s) meaning that with propellant to total mass of spacecraft of well over 50% would give ample delta-v for exceeding the velocity of A/2017 U1 and then decelerating to match the object's velocity. That's in addition to a decent bit of starting delta-v from an initial chemical engine boost in Earth orbit (perhaps passing around the Moon to get the necessary out of plane motion to the start).

    The real problem is whether we've figured out the motion of the object well enough to find it again centuries from now. There will be a considerable bit of error in the positioning of the object and it's going to be a challenge to find such a small object again in a few centuries. For example, if the error in velocity is a omnidirectional 100 m/s, in oh, 5 centuries, that would be 10 AU radius volume to search through (roughly from the orbit of Saturn on in). I think they'll do much better than that, but it's still going to be a huge stretch of space to search through.
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