Asteroid zooms in for close encounter

A rather large asteroid is about to make the closest scrape with Earth that has ever been predicted in advance. Monster space rock YU55, which is more than 400 metres wide will be nearest at 11.28 UT tomorrow, 8 November.

Smoothed Arecibo image of asteroid YU55 from 2010 (NASA)
Smoothed Arecibo image of asteroid YU55 from 2010 (NASA)

Its orbit will bring the asteroid to a distance of 324,600 km (201,700 miles) which is considerably closer than the Moon 384,000 km (240,000 miles) away from us.

The asteroid is labelled 2005 YU55, a catalogue number that also indicates the year in which it was discovered, and it is of a type called a Potentially Hazardous Object because it regularly crosses the Earth’s path through space. But there is no danger of a collision this time.

No large asteroid has been observed before to skim so close to the Earth. A closer encounter with another huge asteroid in 1976 went unnoticed at the time because that object was not discovered until last year (2010). Amateur astronomers with clear skies in the UK will be able to view tonight’s flyby through medium-sized telescopes. It will appear as a faint star but moving rapidly from the constellation of Aquila to Pegasus in just a few hours.

Robin Scagell, of the UK’s Society for Popular Astronomy, told Skymania: “Many of our members will be trying to spot the asteroid as it makes this historic close approach. It will look like a faint point of light through their telescopes but it will be striking how quickly it moves against the starry background.”

NASA experts are preparing two giant radio telescopes in its Deep Space Network – one at Goldstone, California, and the other at Arecibo, in Puerto Rico – to bounce radar signals off the asteroid and help them map its dark surface.

The Arecibo dish made similar radar observations of the asteroid last year and showed it is roughly spherical and is slowly spinning, turning once every 18 hours. A European space telescope called Herschel, positioned more than 900,000 miles from Earth, will make infrared observations of YU55 two days after its flyby to measure its temperature and tell what rocks it is made of.

The near miss is a reminder that space is a cosmic shooting gallery and that Earth faces a real threat of asteroid impacts in the future. One with Apophis in 2036, though highly unlikely, can still not be entirely ruled out.

Impact expert Dr Emily Baldwin, of Astronomy Now magazine, told Skymania: “Asteroids do sometimes make close passes of the earth but this one is nothing to worry about. The close up view will give astronomers the chance to look at the type of object that might pose a risk another time. It will also tell us more about the nature of the rocks that went into building our own planet.”

YU55, which was discovered by a robotic telescope in Arizona scanning the skies for threatening objects as part of NASA’s Spacewatch programme, orbits the Sun every 14 months or so. But its trajectory has been precisely calculated and there is absolutely no risk of it hitting us for at least 100 years.

An enounter with planet Venus in 2029 will alter the asteroid’s orbit slightly, but not enough to cause a threat at its next close approach to Earth in 2041.

In September a survey suggested that NASA has managed to discover 93 per cent of all asteroids more than 1km wide that pose a threat to the Earth. They have detected 911 of an estimated 981 big enough to collide with the force to devastate cities and cause tsunamis.

Paul Sutherland

Paul Sutherland

I have been a professional journalist for nearly 40 years. I write regularly for science magazines including BBC Sky at Night magazine, BBC Focus, Astronomy Now and Popular Astronomy. I have also authored three books on astronomy and contributed to others.
Paul Sutherland

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Paul Sutherland

I have been a professional journalist for nearly 40 years. I write regularly for science magazines including BBC Sky at Night magazine, BBC Focus, Astronomy Now and Popular Astronomy. I have also authored three books on astronomy and contributed to others.

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