I guess the Force was with us: In the early morning hours of May 4, a small asteroid 3-6 meters* opposite passed from Earth, passing our world only 7000 kilometers – only for the radius of the Earth itself! It passed so close to us that its orbit was significantly altered by Earth’s gravity.
Before you panicked, at this diameter (for the size of the car) it would not cause real damage, even if I had hit us. But that would be put on hell show, creating an intensely glowing ball of fire easily brighter than the full moon when it burns and disintegrates in our atmosphere, probably a few tens of kilometers above the earth’s surface. It is likely that small pieces reached the ground as meteorites. But we really missed him and now he̵
It was discovered just hours before the closest approach from the automated study of Sky Catalina Sky, an observatory in Arizona. Repeatedly sweeps the sky, looking for moving objects such as asteroids. The asteroid, later named 2020 JJ**, was found in four observations made in the protocol around 06:00 UTC. The astronomers were alerted, checked to see if it was real, and then reported to the Center for Small Planets in Massachusetts. The report was then published at 06:36.
This part is amazing: An automatic signal was sent around the world and minutes later other observatories were heading to the coordinates of the object (which, mind you, was so close that observatories in different parts of the planet would see it in different parts of the sky!) . For less than time (!!) it is observed by other telescopes in Arizona, as well as by observatories in Hawaii and Illinois.
This part made the hairs on the back of my neck stand up: For a short time, before the observations hit his trajectory, there was a 5% chance of a hit! I know that they are not short odds – a 1 in 20 chance is quite small† – but still it is high for impact. Of course, as I said, even so I had hit that would not be dangerous. Just spectacular.
As I already wrote, when an asteroid is first discovered, the orbit calculated for it is quite vague, as we do not have a long enough arc to be able to predict where it will be in the future. Small uncertainties in position add up early to large ones. The analogy I like is if you’re an outfielder in a baseball game and as soon as the dough hits the ball, you close your eyes. Now predict where the ball will be when it lands. Yes / No. But if you keep watching it, you will be able to see its trajectory much better.
Asteroid Video: Crash Course Astronomy # 20
So the projected orbit of 2020 JJ was a fuzzy cone spread enough to include the Earth. But then more observatories saw it, the uncertainty shrank, the cone narrowed, and it was determined that we would miss it. But not by much.
The closest approach was at 12:03 UTC on May 4, when it was about 13,400 km from the center of the Earth. Given that the radius of our planet is just under 6400 km, this means that it missed us by about 7000 km. This is quite close, and in fact the orbit of the asteroid visibly changed after it passed when Earth’s gravity distorted its path.
In fact, it’s amazing that it was visible at all; he is so small that he has fainted quite a bit. He entered from a direction that was quite opposite the Sun in the sky, which was lucky. This means that it is night time and we also see it “full” (if it was closer to the Sun, we see less light than it, so it is a crescent moon like a new moon and therefore much paler). Many times with asteroids of this size we do not see them after they have already passed.
In fact, once observations were included, the trajectory of JJ 2020 was so well defined that its position was known about 5 km perpendicular to its path. If it had actually struck us, the place where it entered our atmosphere would have been precisely determined with this precision. This is damn impressive. Remember that all observations were made during two hoursThis is actually reassuring; astronomers get really good at this kind of thing!
It is in an approximately two-year elliptical and slightly inclined orbit that takes it from just inside Earth’s orbit to go beyond past Mars, and is now heading back into deeper space. But it is still in orbit, bringing it closer to Earth, so it will return. Probably not for long. And if we see it again, that’s fine too. Space is large, and this asteroid is small. This does not threaten us. But there are bigger than them, and it’s good to know that we have so many eyes in the sky watching us and we’re doing such a good job at it.
* Rough size rat, if you will.
†Although significantly higher than 3720 to 1,