The huge asteroid 2005 YU55 will sweep closely past the Earth – missing us by 319,000 kilometers (about 200,000 miles) – tomorrow. It’ll be the closest known passage of an asteroid this big – but there was an even closer passage to Earth of this same asteroid in 1976, which went undetected. This time, astronomers spotted it ahead of time. Does it make you feel safer – or more vulnerable? I’m not sure how it makes me feel!
On this November 8, 2011 passage, 2005 YU55 will come closer than the moon’s distance from Earth, but it will not strike Earth or the moon.
The time of closest passage will be November 8 at 5:28 p.m. CST (23:28 UTC).
The asteroid is 1,300 feet (400 meters) wide. In contrast, the moon is 3,476 kilometers wide. That’s 3,476,000 meters for the moon’s diameter in contrast to 400 meters for YU55. That’s why you don’t need to worry about YU55 raising tides on Earth, or causing earthquakes, volcanoes or tsunamis. It’s big for an asteroid, but much much smaller than our moon.
2005 YU55 will reach a visual brightness of 11th magnitude. That’s very faint for most of us. The asteroid will be visible only to amateur or professional astronomers as it plunges past us and moves on.
Known asteroids come close pretty often. To prove it to yourself, check out this link to passages of near-Earth asteroids in November 2011, from Jet Propulsion Laboratory’s Space Calendar. An “AU” is an Earth-sun distance, by the way, or about 93 million miles (150 million km).
Asteroids also come within the moon’s distance every so often, but 2005 YU55 is the biggest known asteroid to do so for about the next 17 years, until the year 2028. Still, the asteroid 2005 YU55 poses no immediate threat to Earth. Its orbit is well known to astronomers – so well known that we can rule out an impact for at least the next century.
According to NASA’s Near Earth Object Program:
Although classified as a potentially hazardous object, 2005 YU55 poses no threat of an Earth collision over at least the next 100 years. However, this will be the closest approach to date by an object this large that we know about in advance and an event of this type will not happen again until 2028 when asteroid (153814) 2001 WN5 will pass to within 0.6 lunar distances.
The animation below, from NASA’s Jet Propulsion Laboratory, shows this asteroid’s sweep past Earth on November 8 and 9.
In this animated diagram, Earth appears at the center, with the diagonal line representing Earth’s orbit around the sun. The moon is shown orbiting Earth, and you can see that the path of YU55 carries the asteroid inside the moon’s orbit. The imagine the scale, remember that the moon’s orbit is roughly 770,000 kilometers (475,000 miles) wide. YU55 will miss Earth by 319,000 kilometers (about 200,000 miles) – a nice safe margin.
Robert McMillan of the Spacewatch Program near Tucson, Arizona discovered YU55 on December 28, 2005. It appears to be a very dark, nearly spherical object.
The closest approach to Earth and the moon will be respectively 0.00217 AU and 0.00160 AU on 2011 November 8 at 23:28 UTC (5:28 p.m. CST) and November 9 at 07:13 UTC (1:13 a.m. CST).
I remember in the 1970s when astronomers were speculating that the Tunguska event in Russia in 1908 was probably caused by a small comet striking Earth. That event – in a remote part of Siberia – killed reindeer and flattened many miles of forest, but essentially did little harm. In the 1970s, the consciousness was just arising that objects in space might strike us. Astronomers began programs to watch for near-Earth asteroids, and it was inevitable that they would find some passing as closely as 2005 YU55 will on November 8.
One of the first programs to watch for near-Earth asteroids, by thew way, was Spacewatch – founded in 1980 by Robert McMillan, who discovered this asteroid 2005 YU55. Spacewatch did what it was supposed to do! It found an asteroid sweeping near us. Presumably, if an asteroid is ever headed straight for us, we’ll have some advance warning. But let me emphasize that 2005 YU55 is not a doomsday asteroid. So relax, everyone.
Bottom line: The huge asteroid 2005 YU55 will sweep within the moon’s distance from Earth on November 8, 2011. Its orbit is well known to astronomers, and it will not strike Earth or the moon. 2005 YU55 is the largest asteroid ever known to sweep this closely to Earth. There is no danger. It will not raise tides, or cause earthquakes, volcanoes or tsunamis. Both amateur and professional are very curious about this close asteroid passage, which they will be watching with telescopes.
Deborah Byrd created the EarthSky radio series in 1991 and EarthSky.org in 1994. Today, she serves as Editor-in-Chief of this website. She has won a galaxy of awards from the broadcasting and science communities, including having an asteroid named 3505 Byrd in her honor. A science communicator and educator since 1976, Byrd believes in science as a force for good in the world and a vital tool for the 21st century. "Being an EarthSky editor is like hosting a big global party for cool nature-lovers," she says.