Two asteroids in brush with Earth

We got a reminder today that the Earth remains something of a cosmic shooting gallery as not one but TWO large asteroids skimmed past us. Both space rocks, which are in entirely different orbits, came closer than the Moon, with one coming to a fifth its distance, within 50,000 miles.

An impression of an asteroid flying by Earth

Both missiles were bright enough to become visible in larger backyard telescopes, looking like faint stars swiftly moving against the heavenly backdrop.

The first asteroid, labelled 2010 RX30, was estimated to be up to 65ft (20m) wide and on a course to fly past us at a distance of 154,000 miles, or 248,000km. The second, called 2010 RF12, is up to 46ft (14m) across and was due to fly by at a distance of 49,088 miles (79,000km) a few hours later.

Astronomers said there was no danger of either colliding with the Earth and if they had, they would have been expected to break up in the atmosphere as dazzling fireballs and a shower of meteorites.

Both asteroids were only detected on Sunday by an automatic routine patrol in Tucson, Arizona, called the Catalina Sky Survey. The same survey regularly detects such debris littering the solar system including a small asteroid that produced a shower of stones over the Sudan in October 2008. Hundreds of fragments of the 80-ton space rock were later recovered from the Nubian Desert.

NASA estimate that an asteroid as big as 10m across from an estimated undiscovered population of about 50 million would be expected to pass within a lunar distance almost on a daily basis and that one might strike Earth’s atmosphere about every 10 years on average.

But the double encounter is a chilling reminder of the threat from much larger asteroids dubbed Potentially Hazardous Objects which do have orbits around the Sun that intersect with our own orbit.

In July, NASA experts reported that an asteroid more than 600 yards wide has a one-in-a-thousand chance of hitting the Earth in 2182. An impact would have around 65,000 times the force of the atomic bomb dropped on Hiroshima and could devastate a city.

Before that, a 25 million-ton space rock called Apophis will skim by three times before then. On Friday 13th of April, 2029, it will come closer than TV and communications satellites. After that it will make two other close encounters, the first in 2036 and then again in 2068. Remember that the odds of a collision with either asteroid are extremely small. Impacts are also beginning to be spotted regularly in the clouds of Jupiter.

• 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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