spaceSpace and Physics

An Asteroid The Size Of A Skyscraper Will Swing Past Earth Next Month


Jonathan O'Callaghan

Senior Staff Writer

I. Pilon/Shutterstock

A medium-sized asteroid is going to fly past Earth next month, which as usual has sparked all sort of alarming headlines – but there’s nothing to worry about.

The asteroid is called 2002 AJ129 and, as its name suggests, it was discovered in 2002. On February 4, it’s scheduled to fly past our planet at a distance of 4.2 million kilometers (2.6 million miles) which, you know, is fine. That’s about 11 times further than the Moon.


AJ129 is estimated to be between 548 and 1,225 meters (1,798 to 4,019 feet) across, which is the size of a pretty tall skyscraper. This would probably cause a lot of damage if it hit us. Fortunately, it’s not going to.

It takes 1.61 years for the asteroid to orbit the Sun, during which time it moves from within the orbit of Mercury to about the orbit of Ceres in the asteroid belt. This means it crosses the orbits of Mercury, Venus, Earth, and Mars.

That’s actually pretty cool, and as a result the asteroid makes regular close passes to all four terrestrial planets. Earth gets a few more close flybys up to 2032, then Venus gets one, and then later in the century Mars and Mercury.

Its closest approach to any of these bodies will be Earth, when it comes about 680,000 kilometers (424,000 miles) from our planet, about twice the distance of the Moon. Fortunately, that’s not going to happen until February 2172, so you shouldn’t have too much to worry about.


AJ129 belongs to a group of asteroids known as the Apollo asteroids. These cross Earth’s orbit regularly, with more than 8,000 asteroids in this group – the largest of near-Earth objects. About 1,500 of these, including AJ129, are classified as being “potentially hazardous”.

NASA defines an asteroid as potentially hazardous if its orbit takes it within about 7.5 million kilometers (4.6 million miles) of our planet, and its bigger than 140 meters (500 feet) in size. AJ129 fits both of those bills, as do many other asteroids.

There’s a running list kept of the asteroids that pose the most threat to us, with each given a rating from zero to 10 on the Torino scale to determine how dangerous they are. No asteroid currently ranks above zero, so we’re doing okay at the moment.

But there is always the chance an asteroid could pose a danger to us in the future. When that happens, it’d be good if we were prepared to spot it and push it out the way. Maybe practicing by observing objects like AJ129 isn’t such a bad idea.


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