No, Comet ATLAS is NOT going to hit Earth. (And the coronavirus has nothing to do with it either.) Yvette Cendes Follow Apr 6 · 5 min read

Comet ATLAS on March 14, 2020. Image credit: Martin Gembec

Astronomer here! I wanted to write a quick post on something a few people have privately messaged me about because it’s circulating on social media, which made me realize others may be wondering about it too (or if not, wishing they had something to say to Uncle Ed on FB going on about it). The gist is this- there is a newly discovered comet about to hit us, which some versions of this story attribute a giant size to like “half the size of the sun,” and it’s going to hit Earth in a few weeks so coronavirus was unleashed to keep us at home/ from noticing.

So I am here to tell you no, this is not going to happen, and here are the actual facts! First, Comet ATLAS is real. It was discovered late last year by a survey legit designed to discover asteroids and comets that might hit Earth, called ATLAS, and comets are named after their discoverer (its full name is actually C/2019 Y4 ATLAS). And the cool thing is, it’s actually getting bright really fast! As in, already bright enough to be seen with a good pair of binoculars, and it’s still coming in to the sun. This means at the current rate of brightening, it may become visible to the naked eye under dark skies in just two or three weeks, and maybe bright enough to be seen in cities (like, as bright as a planet), with a large tail, a few weeks after that in early May. This would mean it would be a “Great Comet,” which we haven’t had one of in many years- not since Hale-Bopp in 1997 if you’re in the northern hemisphere. (This comet’s orbit is almost exclusively a northern hemisphere one, so yes, this means if you are in North America or Europe you’ll be able to see it if it gets bright enough.)

Now the first thing to emphasize is estimating comet brightness in the future is HARD. Comets are basically balls of icy dirt that are just a few miles wide, and spend most of their orbits (typically thousands of years or longer) far from the sun. When they come in close (like, closer than Jupiter), which usually lasts for a few months, the heat from the sun starts releasing gasses from the comet, which creates a visible halo of gas called a coma and sometimes a tail. Comet tails btw are not behind the comet as it travels, but instead usually pointed away from the sun.

What this means in actuality though for comet brightness is there is no reason to assume comet brightness will continue as it has been once they start getting brighter, because it all depends on the comet composition, and when it’s a thousands of year orbit it’s not like we have studied it before. (Halley’s Comet is famous because of its short orbit for a comet at 76 years, so we know it’s usually a bright and memorable comet as it’s so well studied.) The comet may still turn out to be a dud, or even completely break up as it gets warmer- we really don’t know. But you know astronomy, just because we don’t know how bright it will get doesn’t mean it’s not fun to speculate about!

That said, here’s what we do know. We know the comet’s orbit really well- this is basic physics any undergrad physics major can do these days, and after a few careful observations we can calculate its orbit. There’s even dedicated charts where you can look up where to find it, based on that calculated orbit. Its closest approach to Earth is going to be on May 23, at which point it will be about 72 million miles (~115 million km) from us- for scale, the moon is about 240,000 miles (~500,000 km) from us in its orbit. This thing is not getting close enough to hurt us in any way, and the only way it will affect us is with this potentially getting a pretty comet to admire while we’re all bored at home. Finally, it looks like it is on a 6,000 year orbit, so be sure to get a good look because you won’t get another one!

“But, Yvette,” I hear you inquire, “I read this thing is huge! Maybe five times the size of Jupiter, or half the size of the sun!” So, this appears to be floating around in the tabloids (sorry but I refuse to link them), and I had a depressing time tracking it down. The origin of these statements appears to be this report where amateur astronomers try to estimate the size of the coma (or gas) surrounding the comet, and based on those observations extrapolated the size of the gas, and got about 450,000 miles (720,000 km). This really isn’t that weird for a comet- the coma density is far less than Earth’s atmosphere, so tough to equate the two. In fact, if you want an example, in 1910 there was a conspiracy theory that everyone was going to die one night because Earth passed through Halley’s Comet’s tail. Obviously, that didn’t happen. But yes, the conclusion here is it’s really disingenuous to say the comet is half the size of the sun based on one amateur reporting, when the comet itself as most people think of it is only a few miles in size.

Finally, speculation that this has to do with coronavirus. I mean, we know throughout history that people always thought comets are a sign for something, so perhaps it’s not unusual that some people are saying the same now about this comet. But, guys, firstly coronavirus is very real and serious, and you should all follow social distancing guidelines in your area and stay at home. Second, the timing if you believe the conspiracy theory is terrible- as I said, this thing was discovered in late December, and the first coronavirus case was in November. I know people are really good by nature in trying to find patterns in things… but a comet on a 6,000 year orbit was going to come this way at this time with or without a pandemic on Earth.

Anyway, I hope this post is helpful for some folks! Please let me know if you have any further questions!

TL;DR- Comet ATLAS won’t hit us, has nothing to do with coronavirus