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Parting shots from the asteroid

Bill Merline / SwRI / W.M. Keck Observatory

An infrared image produced by the W.M. Keck Observatory in Hawaii shows the asteroid 2005 YU55 as it receded on Nov. 8. Measurements suggest that the space rock was not as wide as originally thought.

The asteroid that had everybody excited on Tuesday is just another space rock today, but 2005 YU55 brought a surprise or two to scientists as it passed by.

As expected, YU55 zoomed harmlessly past our planet at a distance of roughly 198,000 miles (319,000 kilometers) on Tuesday, and made its closest approach to the moon hours afterward.

If the asteroid were on a collision course, Tuesday would have been a very bad day, marked by a cosmic blast equivalent to a 4,000-megaton super-duper nuclear bomb. Instead, it was a very good day for astronomers. They can use the insights gained during this flyby to figure out how near-Earth objects might behave during closer, potentially more dangerous encounters to come.


Scientists tracked the receding asteroid from the Keck Observatory in Hawaii, using an adaptive-optics imaging system, and produced some great infrared pictures (including the one you see above).

Over the next few days, the full data set will be analyzed and perhaps turned into a time-lapse movie, similar to the sequence created from radar imagery during YU55's approach, said Larry O'Hanlon, spokesman for the Keck Observatory. The pictures confirm that the asteroid looks more like an elongated potato than a beach ball, with its side-to-side diameter estimated at 240 meters (787 feet).

"Note that this puts the asteroid at about half the diameter of what previous researchers thought it was," O'Hanlon wrote in an email.

'Puzzling' readings
Meanwhile, researchers are analyzing the radar readings gathered by the Goldstone radio antenna in California.

"The animation reveals a number of puzzling structures on the surface that we don't yet understand," radar astronomer Lance Benner, the principal investigator for the YU55 observations, said in a news release from NASA's Jet Propulsion Laboratory. "To date, we've seen less than one-half of the surface, so we expect more surprises."

Radar observations from the Arecibo Observatory in Puerto Rico will be factored in as well.

Well-equipped amateurs captured some great shots in the visible-light spectrum. Mike Renzi combined hundreds of images from his Starhoo Observatory in Massachusetts to create this video, showing YU55 as a fast-moving dot among the stars:

Asteroid 2005 YU55 captured at the Starhoo Observatory.

Rick Fienberg, press officer for the American Astronomical Society, snapped this time-exposure picture of YU55's track through the night sky:

Richard Tresch Fienberg / AAS

This time-exposure picture from Rick Fienberg shows 2005 YU55's track through the star field. The contrast has been boosted to emphasize the track.

Here's what Fienberg said about the picture:

"I shot this at Phillips Academy in Andover, MA, using my Canon DSLR and the school's 80mm Orion refractor piggybacked on a 16-inch telescope. Asteroid (in Pegasus) is moving lower right to upper left (north is up, east is left), and each streak is 1 minute long, separated by 1-minute gaps (during which the camera was making dark frames). This is a stack of three 1-minute exposures."

For more pictures of YU55, check out SpaceWeather.com's post-encounter roundup — and mark your calendar for June 26, 2028, when an even bigger asteroid, 2001 WN5, is due to even come closer to Earth.

Update for 10:15 p.m. Nov. 9: Asteroid-hunting can be hazardous to your health, even if the space rock is 198,000 miles away from causing a catastrophic cosmic collision. Just ask the six teenagers who said they were held at gunpoint in Marion, Ohio, while trying to catch a glimpse of YU55.

Update for 2:30 a.m. Nov. 11: A member of the Cosmic Log Facebook community, John Giroux, sent along this time-lapse picture of YU55 streaking across the sky. "Thirty-seven images stacked, contrast and brightness adjusted, color removed," Giroux writes. "Seven minutes worth of tracking, from right to left. Note how the brightness periodically varied. The time frame is from approximately 21:23 EST until 21:30 EST, in the constellation Pegasus."

John Giroux

Asteroid 2005 YU55 shows up as a series of short streaks in this picture from John Giroux.

More about the encounter:


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