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HIGHLIGHTS by Kelly Beatty
Mini-Asteroid Makes a House Call
|Update: The flyby of asteroid 2005 YU55 generated a lot of interest among the news media and general public. Click here for details.|
Roll out the red carpet! Earth is about to be visited by the largest close-approaching asteroid on record. Known as 2005 YU55, it comes closest to us on November 8th at 23:28 Universal Time (6:28 p.m. EST), when it passes 198,000 miles (319,000 km) from Earth's surface — closer than the Moon's orbit. It will be visible from the Americas and Europe through much of the night.
The Arecibo observations showed this asteroidal emissary to be a quarter mile (400 meters) across and remarkably round. Given its size and dimness, its surface must be quite dark and thus likely carbon-rich. Its rotation period is relatively long, 18 to 20 hours.
In the grand scheme of things it's more micro-planet than minor planet, but we've never knowingly had something this big come this close before. Were it to strike Earth, 2005 YU55 would deliver a kinetic-energy punch equivalent to several thousand megatons of TNT. It's the kind of potential threat that outer-space sentries lose sleep over.
So we might as well just enjoy this month's show. The asteroid will approach Earth from the sunward direction, so it will be a daylight object until just before the time of closest approach. A few hours later 2005 YU55 should reach a visual magnitude of 11.1, within reach of backyard telescopes with apertures of at least 6 inches under fairly dark skies — though you'll be fighting light from the nearly full Moon. (By the way, that bright thing near the Moon tonight is Jupiter.)
If you don't have a suitable scope, or if it's cloudy tonight, check out the live video webcast of asteroid 2005 YU55 from the 25-inch telescope at Clay Center Observatory in Massachuetts (continuously from about 6 p.m. to 3 a.m. EST). Another live webcast is available from Bellatrix Astronomical Observatory in Italy.
Amateur asteroid sleuths Brian Warner and Robert Stephens have mounted a campaign to obtain detailed photometry (brightness measurements) of the asteroid. You'll need at least a 10- or 12-inch scope, a CCD camera, and ideally one or more of the standard photometric filters commonly used by professional astronomers. Details.
Meanwhile, this visit by 2005 YU55 is providing an unprecedented opportunity for high-reolution radar study. Astronomers have lined up extensive radar campaigns with Arecibo and with NASA's Goldstone facility in California's Mojave Desert, using big radio dishes in West Virginia and elsewhere as receivers. "The signal-to-noise ratios will be more than 1 million for Goldstone observations on November 89," explains Lance Benner (Jet Propulsion Laboratory). This SNR is heady territory for radar work, high enough to yield thousands of pixels across the object and to achieve surface resolution "comparable to what can be obtained by a spacecraft flyby mission."
So I hope you all get a chance to spot 2005 YU55 as it zips past Earth.
Posted by Kelly Beatty, November 1, 2011