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On August 16, 2020, just after midnight Eastern Time (US), a small asteroid buzzed our planet, passing just 2,950 kilometers above the Earth’s surface!
Sensational. This is close. This is only a quarter of the diameter of the Earth! The good news is that she missed, and even if she had hit, she would not have done more than put on an incredible light show, as she is only 3-6 meters in diameter (so, a car the size of a limousine). In other words, it would have burned in the atmosphere.
But this fact miss, and that makes it the closest near miss to an asteroid.
The asteroid is called 2020 HQ and was only discovered a few hours after its closest approach to Earth (over the Indian Ocean). It is quite common for small rocks like this. It was found in images taken by the Zwicky Transient Facility, a 1.3-meter telescope at the Palomar Observatory in California. This relatively modest telescope is equipped with a huge 600 megapixel camera and takes an image of a large part of the sky at a time (7 ° to the side, so each image covers an area 250 times the size of the full moon) that he can imagine all the northern night sky for three nights.
It is designed to search for exploding stars and other events that come and go in the Universe. But closer to home, he can also see asteroids passing in front of Earth. Computers scan the images for the telltale trail of a nearby asteroid, and if they find anything promising, the sighting is reported to a human. About a thousand of these potential visitors meet up every day. Most turn out to be satellites or others, but sometimes they are space rocks.
In this case, a student in India identified the asteroid, and the ZTF team then reported it to the Small Planets Center of the International Astronomical Union, the official custodians of information about the rocks in the sky, and this was quickly confirmed by other observatories.
Considering its brightness and distance, the size can be estimated, and it turned out to be quite small; a bedroom is approximately 3 to 6 meters wide depending on your domestic situation. For comparison, the Chelyabinsk asteroid that burned over Russia in 2013 was 19 meters, much larger than this one.
2020 HQ is what we call an Apollo asteroid. They are near-Earth asteroids whose orbits are on average larger than Earth’s orbit, but also pass through ours. Not all of them get close enough to Earth to pose a threat of impact, but many do. In its elliptical orbit, it gets a little closer to the Sun than the Earth, but comes out farther than Mars, in the asteroid belt. It takes about 2.7 years to circle the Sun once.
It doesn’t look like 2020 HQ is approaching us for some time, however; the next pass is in 2028 and it will be 50 million kilometers. That’s a pretty wide margin. This time, however, it got so close that Earth’s gravity bent its orbit a bit.
Asteroids of this size pass the Earth around this proximity very about once a year. The last one we know of is in May 2020, when 2020 JJ passed about 7,000 km above Earth. The previous narrowly avoided record holder is 2011 CQ1, which has passed about 5,500 km above us.
I note, as I always do, that impacts large enough to cause real damage are very rare. Chelyabinsk is a much rarer event, occurring on a time scale of decades or a century. Even then, they usually burn over the ocean (it covers 70% or more of the Earth’s surface, so the chances are higher) or on land with few or no people.
Those like 2020 HQ burn high in the atmosphere, at best raining down tiny meteorites after they burst. But finding these asteroids is still important! We don’t have good numbers on how many asteroids are overtaking us in any given time, so the more we spot like this, the better we will understand the population of near-Earth (and potentially dangerous) asteroids. I am all for it.
In addition, it shows that we already have observatories, such as the Zwicky Transient Facility, which can find them. And we’ll have some more once the Vera Rubin Telescope is full-time, along with others like space-based NEOCAM, which will not only find them but also give us a much better idea of their size.
Astronomers take these rocks seriously, which is why we are building better observatories to spot them. We want to learn as much as possible about the solar system, but we are human, and we have a personal interest in keeping Earth from being affected too.
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