BAN #258: Slow Trololo, Mind the super-Earth gap

[Spiral Galaxy M81 image credit: Adam Block/Mount Lemmon SkyCenter/University of Arizona]

Apropos of nothing

Not everything needs to be themed

If you’re familiar with the Trololo Guy meme, then this is going to be a surreal Inception-like dip into Internet bizarreness.

And if you’re not, then it’ll just be confusing.

Either way, here’s the next 14 minutes of your life.

It’s bizarrely magnificent, and my life is better knowing this exists and having listened to it.

P.S. There are a TON of videos of music made slower this way, and some of them are oddly compelling. Search YouTube for “slower music” or “slower theme” and you’ll find them. This one from Jurassic Park is particularly cool.

Astro Tidbit

A brief synopsis of some interesting astronomy/science news

Mind the super-Earth gap!

HD 15337 is a star about 150 light years away. In some ways it’s similar to the Sun: About 5 billion years old, with a mass about 90% the Sun’s (making it a K star, if you know your stellar classifications), and a tad cooler.

[HD 15337 (arrowed), a star with two unusual exoplanets. Credit: Aladin]

But in one way it’s very different: It hosts two exoplanets in between the masses of Earth and Neptune, something our solar system doesn’t have. Neptune is about 17 times the mass of Earth, and as far as we know there’s no planet in that gap in our system (unless Planet Nine is, but who knows).

It turns out planets in that gap are the most common kind in the galaxy! We call them super-Earths when they’re up to about twice the diameter of Earth, and mini-Neptune’s when they’re bigger than that. It’s thought that once a planet gets to a certain size, it can retain more atmosphere, so you wind up not seeing too many planets right around that twice-Earth’s-diameter size. Once you get that big, you tend to get a lot bigger.

[Earth (left) and Neptune, to size scale. Credit: NASA / jcpag2012 at wikimedia]

HD 15337 is bright enough to be observed by TESS, the Transiting Exoplanet Survey Satellite, which looks at brighter (and therefore, generally, closer to us) stars. If a planet orbits the star in such a way that it passes directly in front of the star, we see a mini-eclipse called a transit, and the star gets a bit dimmer. The amount it dims tells us the size of the planet. TESS found the two planets, called HD 15337b and c, and was able to get their diameters: b is about 1.64 times wider than Earth, and c is 2.39.

Where this gets interesting is that very high-resolution spectroscopy was used to get their masses (as they orbit the star in bigger circles the star makes smaller circles, and that can be measured by looking at the Doppler shift in its light; this is called the reflex or radial velocity method). The planet b has a mass about 7.5 times Earth’s, and c is 8.1. That means they’re about the same mass! Cool.

But because c is bigger, it has a lower density (same amount of stuff in a bigger volume = lower density). Its density is about 3 grams per cc, while b’s is a whopping 9.3. That’s nearly twice Earth’s density! That means planet b likely has a lot of iron in it, more than Earth does. Planet c is lower density than Earth (we’re at about 5.5 grams per cc), and so is likely a rocky planet with a thick atmosphere.

Both planets are close to the star, with periods (years) of 5 and 17 days, which means they’re hot. That too is interesting: Planet b may have once had a thicker atmosphere, but it so close to the star that it lost a lot of it — when you heat up a gas it expands, and that means the atmosphere puffs up, and the gravity of the planet may not be enough to hold on to it. The atmosphere it has now may be what’s called a secondary atmosphere, one that leaked out of heated rocks after the first atmosphere was lost. How peculiar! At least to us.

The other planet, c, may have a hydrogen-rich atmosphere. Its density implies it has a lot of water in it, but it’s hot enough that water would not just be in the form of steam, but also the molecules could break apart into hydrogen and oxygen. The hydrogen would tend to move up in the atmosphere since it’s lighter, making the upper layers (the ones we’d see if we could look at it more closely) dominated by hydrogen.

Here’s something I didn’t know: Other stars have been found with planets like this, straddling the “radius gap” of twice Earth’s size. And, like those others, the denser one is closer to the star. That may be due to what I said above, the inner planet losing its first atmosphere and replenishing it with outgassing. This may be a universal truth of sorts, something that very commonly happens with exoplanet systems.

That’s pretty amazing. We see enough planets, and in enough detail, to be able to determine things like that! Not only that, but the atmospheres of these planets have changed over time, which means we cam learn something about planetary evolution over time as well.

Remember, these planets were not seen directly! No blip of light next to the star, nothing like that. Instead we see their effects on their host star’s light (blocking it when the transit, or very subtly changing the color as they orbit and tug on the star). That’s incredible, that we can know so much about objects we really can’t even see!

I’ve been doing astronomy and long time, folks. One of the things I love about it very dearly is that it can still surprise me.

Et alia

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