“Is there an asteroid in our sky?”

By Shala Howell, June 2, 2011

All kinds of fun stuff popped up when we asked the iPhone this question–much of it on websites that use a distressing amount of purple and black.

As my daughter would put it, Paul Sutherland has been writing about space for 30-10 years.

These are tough to read on the iPhone’s small screen, so I was pleased to find Skymania, a calm, well-written and interesting site by Paul Sutherland, a man who has been a journalist for nearly as many years as he’s been a member of the British Astronomical Association.

That answer prompted my daughter to ask “Mommyo, why is Daddyo so much smarter than you?”

After reading his site for a while, I now know that my answer of “Probably” <shrug> was as woefully inadequate as my daughter accused it of being at the time.

So here’s the scoop, as I understand it.

Is there an asteroid in our sky?

Asteroids are the left over bits that weren’t wrapped up into planets when our solar system was formed. Most reside peacefully in the asteroid belt between Mars and Jupiter, but there are some whose orbits take them near/across Earth’s orbit. The most important of these Earth-crossing asteroids–at least in my daughter’s opinion–is the one that is thought to have taken out the dinosaurs after it crashed into the Yucatan peninsula in Mexico 65 million years ago. But there are lots of others out there, including a 10m wide rock known as 2009 BD that, according to SpaceWeather.com, will be coasting for the next several months just 215,000 miles away from us.

2009 BD is probably too small to be visible with our family’s little Celestron telescope (although you can bet we’ll be out there looking for it), but never fear, there’s another much larger one, known as 2005 YU55, on track to pass between the Earth and the moon on November 8-9, 2011 at 11:28 p.m. I’ve set my calendar for a little late-night asteroid hunting with the family, even if the odds are slim that my daughter will remember this question by then.

Will either asteroid crash into Earth?

A responsible blogger would probably point out at this juncture that neither asteroid is expected to crash into the Earth. According to Sutherland of Skymania.com, the closer (and larger) of the two, 2005 YU55, will miss us by some 201,700 miles–not even coming close enough to affect our tides. Its 14-month orbit around the Sun is considered to be a fairly stable one, so we’re good for another 100 years or so–giving another giant asteroid, Apophis, plenty of time to take us out when it comes around on Friday, April 13, 2029. (The responsible fear-mongerer in me feels compelled to point out that Apophis isn’t expected to hit us on April 13, 2029 either, just come close enough to change its orbit, making it conceivable that it could crash into us in 2036.)

How often do large space objects come so close to Earth?

Would it comfort you to know that NASA estimates that similarly substantial space objects threaten Earth about once every 25 years? Yeah. Me neither. So let’s stop thinking about it before I feel compelled to mention what might happen in 2182.

Of course, most of the space debris that comes our way is much smaller–meteorites, meteor showers, comets, and such. I hear the Perseids will be visible on August 13 this year. I love it when stuff like this falls on the weekend.

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