Giant Asteroid On Course For Earth

A huge asteroid a quarter of a mile wide (400m) is currently headed on a direct course for the Earth-Moon system and will be with us in six months. Thankfully it will miss both potential targets, passing inside the orbit of our natural satellite on November 8 and 9 before speeding back off into space.

An asteroid called Gaspra, photographed by the Galileo spaceprobe in 1991. (NASA).

But it will be a remarkable near miss, with asteroid 2005 YU55 becoming the largest space missile ever recorded to come anywhere near as close to us. It will pass just 201,700 miles from Earth at 11.28pm on November 8 and get even closer to the Moon, to a distance of 148,729 miles at 7.13am on November 9.

The asteroid will become bright enough to see in small telescopes over the nights of November 8 and 9, looking like an 11th magnitude star moving fairly rapidly across the night sky.

Robin Scagell, of the UK’s Society for Popular Astronomy, told Skymania News: “It is rare that we get the chance to see an asteroid up close and moving so fast across the sky. Telescopes in back gardens around the world will be trained on it, particularly with the knowledge that it’s missing us by a cosmic hair’s breadth.”

There is absolutely no reason for anyone to be alarmed. The asteroid is in a 14-month orbit around the Sun that will frequently bring it into our neighbourhood. But that orbit has been well enough established to rule out any impact in our lifetimes.

Astronomers have been aware of this Potentially Hazardous Object since it was discovered in December 2005 by Robert McMillan, head of the NASA-funded Spacewatch Program at the University of Arizona.

The giant radio dish at Arecibo in Puerto Rico was used to produce a crude image of it when it passed at a distance of 1.5 million miles in April last year.

NASA reminded us of its existence with a news release headed “Spacecraft Earth to Perform Asteroid ‘Flyby’ This Fall” which created the serene image that we would be visiting it.

By comparing the close approach with unmanned missions to fly past other asteroids, their article rightly pointed out that we would have a great chance to view YU55 close up, while at the same time not scaring the horses.

(This did not prevent some of the usual suspects on the web to raise the old nonsense about conspiracies, cover-ups, 2012, Mayan calendars or whatever.)

NASA asteroid expert Don Yeomans was wheeled out to explain that everything will be fine for at least 100 years, though we have no reason yet to suspect that Earth is in any danger of being a target for a long time after that.

Yeomans, head of the Near-Earth Object Program Office at NASA’s Jet Propulsion Laboratory in California, said: “On November 8, asteroid 2005 YU55 will fly past Earth and at its closest approach point will be about 201,700 miles (325,000 km) away.

“This asteroid is about 400 meters (1,300 ft) wide – the largest space rock we have identified that will come this close until 2028.”

He added: “YU55 poses no threat of an Earth collision over, at the very least, the next 100 years. During its closest approach, its gravitational effect on the Earth will be so miniscule as to be immeasurable. It will not affect the tides or anything else.”

NASA estimates that similar-sized objects threaten us about once every 25 years. Earth is in the sights of another giant asteroid called Apophis which will zip by closer than geostationary satellites on Friday 13th of April, 2029. Uncertainty over the effects of that near miss mean an impact six years later in 2036 cannot be ruled out.

You only have to look at the Moon’s cratered landscape to see the scars left by cosmic collisions. Thankfully the solar system today is a much less violent place today than when those asteroid impacts happened, billions of years ago. But asteroids like 2005 YU55 remind us of the need to monitor the heavens for incoming by nature’s own missiles.

• Discover space for yourself and do fun science with a telescope. Here is Skymania’s advice on how to choose a telescope. We also have a guide to the different types of telescope available. Check out our monthly sky guide too!

©PAUL SUTHERLAND, Skymania.com

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