Bad Astronomy | Asteroid 2020 VT4 traveled 400 km from Earth on 13 November 2020

Okay, yikes: On Friday (13 November 2020), a small asteroid passed so close to Earth that was barely above our atmosphere: it came about 400 kilometers (240 miles) above the Earth’s surface!

It is shorter than most satellites, even in low-Earth orbit. Yegads!

The good news is that it is so small that even if it kills us it does not get bad and almost certainly burns in our environment.

The asteroid, initially called A10sHcN and then officially renamed the 2020 VT4, was discovered by the ATLAS (Asteroid Terrestrial-Impact Final Warning System) Observatory in Hawaii. It was first viewed about 15 hours After It passed through the earth, which is common. Many times, it is difficult to see the nearby geometry before reaching the nearest approach.

The asteroid came from the east and traveled an incredible 6,772 km from the Earth Center, over the Pacific Ocean. Accounting for the Earth’s 6,371 km radius, this means that it passed only 400 km above the Earth’s surface.


Amazingly, this is not a record. Several meteors have been observed to pass through the Earth’s upper atmosphere and return to space, such as the 1972 Great Daylight Fireball that rose 57 km above the ground (and which was largely lost in massive amounts) during the day. Leaving behind traces of vapors that are easily seen during). Other such people have also been observed.

But in recent years, with modern equipment, more near-misses are being recorded. The August asteroid 2020 QC traveled 3,000 km above the Earth’s surface and in May 2020 JJ passed 7,000 km away.

So, if you don’t count asteroids that temporarily (or permanently) become meteors – or actually hit the ground – the 2020 VT4 is a record breaker.

Its brightness is about 5-10 meters in size. At the top end, the Chelyabinsk Impactor has about half the diameter since 2013. For a given composition (say, rock), the mass of an asteroid depends on its volume, which itself depends on the cube of radius. Since the 2020 VT4 was at the best half-diameter of Chelyabinsk, it would have had about 1 / 8th mass. At the low end it would have only 1/50 th mass.

The Chelyabinsk effect had an energy yield of half a megaton of TNT. Had the 2020 VT 4 hit it would have been 2–10%. Also easily visible during the day, but still most likely it will burn 50 or more kilometers above the ground. It is large enough that small fragments can hit as meteorites, which is cool. But remember this was not Beat.

The size and geometry of its orbit changed considerably due to the gravity of the Earth. It used to have a duration of 1.5 years, but now its number is less than 0.9 years. The half-axis axis of its orbit (half the diameter of an ellipse, making it look like the average distance from the Sun) changed from 195 million kilometers to 136 million. In comparison, the average distance of the Earth from the Sun is 150 million km.

From within the orbit of the Earth, the orbit of Mars was just outside the orbit. Now, it goes out of Venus’s orbit just outside the Earth’s orbit. This is a wonderful change!

I note, as I always do, that asteroids of this size pass us very often, but only hit us once a decade or so. The smaller ones, across a meter or so, hit us once a month! But of course they disintegrate in the atmosphere. Also, the Earth is large and mostly water, which is why you don’t hear much about them.

So this whole thing is good news for me. It is small to open an asteroid Difficult – They are unconscious, and moving fast in the sky – and every time we see each other it means that we are getting better at finding them. They are there whether we look or not, so I prefer that we look! Soon, as larger and better telescopes are online, we’ll get more warnings, better orbital predictions, and maybe, if we see a big enough one to do real damage, we can actually do something about it. .


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