Earth Record's Nearest Miss With An 87 XF Falcon-Sized Meteor.

November 24, 2020

Our planet had the closest shave with an asteroid, named 2020 VT4, at just 370km above our crust, destroying the previous record of 2950km.

That altitude is within our atmosphere (80-700km) in what's known as the thermosphere. All at a breakneck speed of 48,303 km/h.

For a bit of tension, that's closer than the International Space Station.

And the new record is an eighth of the former.

AND we didn't even see it coming.

On Saturday, November 14, the space rock skimmed by undetected until some 15 hours later. The "Asteroid Terrestrial-impact Last Alert System" (ATLAS) at Hawaii's Mauna Loa Observatory caught the tail end of the asteroid, but it was already too late.

The ultimate asterisk to these records is they aren't asteroids that become meteors. Meaning, they weren't so close they clipped our atmosphere and hit Earth.

Most don't, a lot do and they're usually quite small. Some have hit the upper limit of our atmosphere and bounced off back into space.
So if you don't count asteroids that temporarily (or permanently) become meteors — or actually hit the ground, 2020 VT4 is a record-breaker.

If the 80-112km altitude barrier was breached we'd have seen one heck of a light show, even in broad daylight.

"The asteroid approached undetected from the direction of the sun. "We didn't see it coming," said." Paul Chodas, director of Nasa's Center for Near-Earth Object Studies.

While it might sound like we dodged a space bullet, the size of the asteroid - relative to a staple in Australian bogan culture - would have barely been noticed.

Estimates put the stone around 5 and 10m wide, and would have burned up before reaching the ground. Fun fact: we can tell the asteroid's size from its brightness.

At that speed and with our air resistance, 2020 VT4's bulk would have vaporised, with some small chunks possibly hitting Earth's surface. Probably over our massive expanse of ocean.

The asteroid appears to be an Apollo-type, meaning it completes a revolution of our Sun every one-and-a-half years.

Only, now that it's met Earth and had a taste of our atmosphere, it's trajectory will make it an "Aten-type" asteroid, with a new orbit of around 10 months.

The semimajor axis of its orbit (half the long diameter of an orbit like the average distance from the Sun) changed from 195 million kilometres to 136 million. For comparison, the Earth's average distance from the Sun is 150 million km.

2020 VT4's orbit used to stretch from just inside Earth's orbit out to just past Mars. Now, it goes from the orbit of Venus to just outside Earth's orbit.

Newly-discovered asteroid A10sHcN approached Earth yesterday, passing only a few hundred miles above the South Pacific Ocean. This encounter shortened its orbit, ensuring that this Earth-crosser will make more frequent close approaches.https://t.co/TmkzojIzPf pic.twitter.com/XrnKiiGTyJ
— Tony Dunn (@tony873004) November 14, 2020

Asteroids the size of 2020 VT4 reach us about once every ten years. Smaller ones - around 1m in diameter - "hit" us around once a month. But because Earth is large and mostly water we never hear about them.

To be fair to the ATLAS team, spotting an asteroid this small is hard. They're tiny compared to how fast they're travelling.

Look at how the naked eye tracks one here.

Plus, it's not very significant.
We aren't in any danger, and the only real plus is to see a light show when asteroids pass us.

As we progress our understanding and technology, we get closer to having a system of more warnings, better orbital predictions. And in future, we can have a system that allows us to do something if an asteroid worth doing some damage wants to visit us.