|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.
This radar image of asteroid 2005 YU55 was generated from radar data taken on November 7, 2011, using NASA's giant radio dishes in California. At the time the asteroid was 860,000 miles (1,380,000 km) from Earth. Radar illumination is from the top, so only half of the asteroid is apparent.
NASA / JPL
Discovered nearly six years ago by Robert McMillan at Steward Observatory's Spacewatch Telescope in Arizona, 2005 YU55
has been this way before. In April 2010 it passed close enough for detailed radar probing by the giant radio dish at Arecibo, Puerto Rico.
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.
This six-frame movie of asteroid 2005 YU55 was generated from data obtained by NASA's Goldstone tracking station on November 7, 2011. At the time the asteroid was 860,000 miles (1,380,000 km) from Earth. Radar illumination is from the top, so only half of the asteroid is apparent. Note the hint of a large crater to the right of center in the later frames.
But fear not: the Arecibo observations allowed dynamicists to recompute the big rock's orbit with enough accuracy to ensure that it won't strike Earth within the next 100 years. (That said, it will pass just 175,000 miles from Venus in 2029, close enough to alter its orbit slightly. This adds uncertainty to predictions for its next close encounter with Earth in 2041, when the minimum distance could be anywhere from 200,000 to 30 million miles.)
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.)
Best seen from North America, the little asteroid 2005 YU55 will race far across the constellations in just 11 hours. Click here
for a more detailed chart and instructions.
Sky & Telescope illustration
The pass's track is especially favorable for western Europe and North America. But you'll need to know exactly where to look at exactly what time: the object will traverse the 70° of sky eastward from Aquila to central Pegasus in just 10 hours, clipping along at 7 arcseconds per second. Use the chart here to get a sense of what part of the sky it's in, then download our detailed finder chart
for use between 9 and 10 p.m. November 8th Eastern Standard Time (2:00 and 3:00 November 9th Universal Time).
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
Part of the Goldstone Deep Space Communication Network, the Mars 70-meter antenna is often used for radio and radar astronomy. It serves a dual purpose as a communication receiver for interplanetary spacecraft.
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