Thread by @BadAstronomer

1/n Sometimes astronomy is hard to relate to. I get that. But on my blog today I wrote about a planet around a nearby star that grew to *enormous* size in a very short time, and I’m still reeling from this knowledge.

syfy.com/syfywire/wait-…

The planet orbiting the star AS209 isn’t seen directly, but is eating up the dusty disk around the star from which it formed, and from that astronomers estimate it has about 70 times Earth’s mass, or about 3/4 the mass of Saturn. That’s a big planet.

3/n But — and this is the important bit — measurements of the star indicate it’s only about a million years old. That’s brand spankin’ new.

So this planet grew to a mass 70 times Earth’s in less than a million years.

That’s FAST. Like holy crap fast. How fast is it?

Earth’s mass is about 6 x 10^21 tons. So this planet has a mass of 4 x 10^23 tons. (Hey, that’s almost a mole of tons! Cool!)

Dividing by a million, that means it grew, on average, at a rate of 400 quadrillion tons per year.

That’s too big to grasp! So let’s see…

5/n Divide by 365 to get that it grew by about a quadrillion tons per *day*.

Nope. Still too big. OK, let’s divide by 86,400, the number of seconds in a day to find…

It gained mass by 13 billion tons per second.

PER SECOND.

6/n Let's put that in perspective. A cubic kilometer of water has a mass of billion tons. So this is equivalent to 13 cubic km of water. Rock is about 3 times the density of water, so this mass gain is equivalent to roughly 4 cubic km of rock.

Per second.

7/n The dinosaur-killer asteroid was about 10 km wide. That's a volume of about 500 cu. km. Keep in mind this impact killed off 75% of all species on Earth.

The planet orbiting AS 209 gains mass at the equivalent rate of one dinosaur-killer EVERY TWO MINUTES.

8/n That's... beyond terrifying. The amount of energy slamming into this planet is incomprehensible. I could translate that into a yield in megatons but then we're back to the ridiculously big number problem again.

9/n But I think you can see why we know that very young planets are very very hot. They are under constant bombardment that deposits so much energy they can't get a chance to cool off. At least not until they run out of material to eat.

10/n And remember, there but for the grace of time goes us. The Earth once grew this way too. Maybe it took us a bit longer, maybe not. We have less mass, too, but still, the rate of growth is mind-crushing. The Earth's interior is still hot from this after 4.5 billion years!

11/11 I think I'll leave you with that. The next time you read an article with big numbers that seem out of your grasp, remember you can divide them down to make it something understandable. Even if terrifying.

And here's the article again:

syfy.com/syfywire/wait-…

12/11 … and hey, if you like this sort of thing, I just saw that my book “Death from the Skies!” is only $9.99 for Kindle right now. It’s chock full o’ sweaty apocalyptic science.

amazon.com/gp/product/014…