Astronomers Spot Pass of First-Known Interstellar Asteroid

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Lorenzo von Matterhorn
Jan 31, 2009
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Astronomers Spot Pass of First-Known Interstellar Asteroid object swept up just a week ago by observers using the PanSTARRS 1 telescope atop Haleakala on Maui has an extreme orbit — it's on a hyperbolic trajectory that doesn't appear to be bound to the Sun. Preliminary findings, published earlier today by the International Astronomical Union's Minor Planet Center (MPC), suggest that we are witnessing a body that escaped from another star.

Initially designated C/2017 U1, this interloper was a dim, 20th-magnitude blip when first spotted on October 18th, after having zipped within 37,600,000 km (23,400,000 miles) of the Sun on September 9th. Such a close approach to the Sun's searing heat would ordinarily spell doom for a small comet. Based on its apparent brightness, dynamicist Bill Gray calculates that it would have a diameter of about 160 meters (525 feet) if it were a rock with a surface reflectivity of 10%. "It went past the Sun really fast," Gray notes, "and may not have had time to heat up enough to break apart."

Now it's headed out of the solar system, never to return. It passed closest to Earth on October 14th at a distance of about 24,000,000 km (15,000,000 miles), and astronomers worldwide have been tracking it in the hopes of divining its true nature — especially whether it's displaying any cometary activity.

Its true character became clearer after Karen Meech (University of Hawaii) recorded a series of images with the Very Large Telescope that, when stacked, showed a perfectly starlike object. So it's a deep-space asteroid, not a comet, and consequently officials at the MPC changed its designation to A/2017 U1.

Dynamicists had previously calculated how often comets and asteroids from other stars should be in our midst. However, the only other object suspected to have an interstellar origin was Comet Bowell (C/1980 E1), which had an eccentricity near 1.05. However, notes S&T Senior Contributing Editor Roger Sinnott, "Comet Bowell apparently was not hyperbolic on the way in, but only as it left" because that object passed within 35,000,000 km (0.23 a.u.) of Jupiter, whose gravity gave it a boost in speed.

According to Gray, the PanSTARRS "comet" appears to have entered the solar system from the direction of the constellation Lyra, within a couple of degrees of right ascension 18h 50m, declination +35° 13′. That's tantalizingly close to Vega — and eerily reminiscent of the plot of the movie Contact — but its exact path doesn't (yet) appear to link any particular star.

Enhanced Hubble image of asteroid A/2017 U1:

Update on ‘Oumuamua, Our First Interstellar Object
By: Kelly Beatty | November 10, 2017

...there's been a flurry of speculation about where 'Oumuamua came from. Dynamicist Eric Mamajek (Jet Propulsion Laboratory) points out that the object's incoming velocity (26 km per second) is within 5 km/s of the mean galactic velocity of stars that lie within 25 parsecs (80 light-years) of the Sun, but it does not match the relative velocity of any of the dozen nearest systems. These characteristics all suggest that 'Oumuamua has been drifting among the stars for a very long time, perhaps billions of years.
Weird, very elongated shape, so not a Borg Cube. Perhaps a Babylon 5 Sunhawk class?