Exoplanet Explorer: WASP 12b

September 28, 2017

Imagine you’re a poor, helpless planet orbiting a normal yellow dwarf star, a star not so dissimilar to our own Sun. But that star keeps drawing you closer and closer… and closer. You know this could end badly for you, but you cannot resist. Soon, it’s too late. Like the monster from Stephen King’s It, the star is going to eat you alive.

Such is the fate of WASP 12b, an exoplanet discovered in 2008 by the SuperWASP planetary transit survey. Wasp 12b is a carbon rich planet, with an atmosphere of mostly methane and carbon monoxide, and astronomers suspect the planet’s core might be made of graphite and diamond.

You could describe WASP 12b as a hot Jupiter, a gas giant that’s strayed perilously close to its parent star. WASP 12b is also sometimes referred to as a chthonian planet, though in my opinion that seems a bit premature. The planet appears to be in its final death throes, so to speak, but it’s not quite dead yet.

In 2010, observations by the Hubble Space Telescope revealed that the planet’s atmosphere is being stripped away, with streams of matter falling toward the star to be “consumed.” Eventually all that will remain of WASP 12b is its core. At that point, I think the term chthonian planet will be appropriate.

That is assuming, of course, that anything will remain at all. Given how violently WASP 12b is being destroyed, it’s possible even that diamond core will be ripped apart and devoured. According to current estimates, we’ll have to wait about 10 million years to find out—a surprisingly short period of time in the cosmic scheme of things.

P.S.: To my surprise, WASP 12b has started making headlines just in the last few days. Astronomers recently determined the planet is incredibly dark in color, almost pitch black. That seemed strange to me at first, but I guess if you’re going to have a planet with that much carbon, the dark coloration kind of makes sense.


Exoplanet Explorer: COROT 7b

September 26, 2017

In 2009, the French-built COROT space telescope made an astonishing discovery: a planet. A planet that was, at least at the time, the most Earth-like exoplanet ever discovered. Except as we’ve discussed previously, “Earth-like” exoplanets are not necessarily much like Earth. In this case, the term chthonian planet may be a better fit.

Exoplanets are often named after the telescope used to discover them; therefore, this planet has been officially designated COROT 7b (the T, by the way, is silent… it’s a French thing). A press release announcing COROT 7b’s discovery said it has a surface you can walk on. That’s true enough, but I don’t recommend going for a stroll there. The weather forecast sounds terrible.

It’s believed that COROT 7b started out as a gas giant, like Jupiter or Saturn, but it was drawn into an orbit way too close to its parent star. Due to the star’s intense heat and radiation, COROT 7b’s entire atmosphere would have boiled away, leaving only the shrunken, shriveled core of the planet behind.

That shrunken core, which is still orbiting way too close to its parent star, is predicted to be tidally locked, meaning one side of the planet is always facing the sun and the other side is always turned away. That creates an enormous temperature discrepancy similar to, but more extreme than, the temperature discrepancy on Mercury.

And according to this paper from the Royal Astronomy Society, the temperature on the daylight side is high enough to vaporize rock. Allow me to emphasize that point. It’s not just hot enough to melt rock; oh no, that would be too normal. It’s hot enough to vaporize rock. So while COROT 7b seems to have lost its original atmosphere, it may have developed a new atmosphere composed of gaseous sodium and silicon and iron, along with other things we’re not accustomed to thinking of as atmospheric gases.

Then on the night side, where the temperature is much colder, all that vaporized rock would condense to form “mineral clouds,” and pebbles would fall like rain. Or perhaps hail is a more apt analogy. Anyway, if you’re going to go for a walk on COROT 7b, you’ll need more than an umbrella to deal with the weather.


Sciency Words: Chthonian Planet

September 22, 2017

Today’s post is part of a special series here on Planet Pailly called Sciency Words. Each week, we take a closer look at an interesting science or science-related term to help us expand our scientific vocabularies together. Today’s term is:

CHTHONIAN PLANET

In ancient Greece, there were two ways to pray: with your arms raised up to the gods of Olympus or with your arms lowered in deference to the gods of the underworld, also known as the chthonic or chthonian deities.

Regarding spelling and pronunciation, the “chth” thing makes more sense if you’re familiar with how the Greek alphabet works. Much like the “p” in psychology or the “h” in rhinoceros, the “ch” in chthonian becomes silent in English.

English often retains these silent letters as a way to remind us of a word’s origin and history. Also, we have to do something to keep our spelling bees interesting.

Chthonian became an astronomy term in 2003 thanks to this paper: “Evaporation rate of hot Jupiters and formation of Chthonian planets.” The paper describes a scenario in which a hot Jupiter—a gas giant orbiting waaaaay to close to its parent star—has its entire atmosphere stripped away by solar radiation. Only the planet’s rocky and/or metallic core remains. It would probably look something like this:

This is actually a pretty clever play on the original meaning of chthonian, which could refer to the underworld and all things death-related OR could just mean the earth and everything beneath its surface.

In one sense, chthonian planets are dead. Very, very dead. Also, because a chthonian planet is still located dangerously near to its parent star, conditions there would be truly hellish. But in another sense, these chthonian planets would look like any other Earth-like exoplanets, meaning they are rocky, terrestrial worlds, as opposed to Jupiter or Saturn-like gas giants.

For the time being, the idea of chthonian planets is still more or less theoretical. We have not yet proven definitively that such worlds exist. However, several candidate chthonian planets have been identified. I’ll introduce you to two of them next week.


In Memory of Cassini

September 20, 2017

Last week, NASA’s Cassini Mission came to an end when the spacecraft crashed into the planet Saturn. This was, of course, a planned event: a way for the mission to end in a blaze of glory, collect a little extra data about Saturn’s atmosphere, and also protect Saturn’s potentially habitable moons (Titan, Enceladus, and possibly also Dione) from microorganisms that may have hitched a ride from Earth aboard the spacecraft.

Cassini’s last few days were an oddly emotional time, at least for me. Somehow knowing that the end was coming, that everything was proceeding according to schedule, made it a little harder to bear. When the words “data downlink ended” started appearing in my Twitter feed, I got a little misty eyes and had to walk away from the computer for a while.

This despite the fact that I never got to know Cassini all that well. I never really followed the Cassini Mission closely (especially compared the way I follow Juno). Looking back through my old posts, it seems Cassini only ever appeared on this blog twice. Once for that time it spotted sunlight glinting off the surface of Titan’s methane lakes…

… and once more for the time it used precise measurements of Enceladus’s librations to determine that Enceladus does indeed have an ocean of water beneath its crust.

So today I thought I’d turn the floor over to several of the moons of Saturn and also Saturn herself. They’re the ones who got to know Cassini well. Not me. It’s right that they get the chance to give Cassini’s eulogy.


Molecular Monday: The Four Elements

September 18, 2017

For some reason, I’ve been thinking a lot lately about the original elements, the four elements Aristotle wrote about many millennia ago: fire, water, wind, and earth. Of course we no longer think of these as elements in the chemical sense. Instead we have the periodic table of elements, with well over a hundred elements identified so far.

But just for fun, I thought I’d try to find a way to connect the old Aristotelian elements to the first four modern chemical elements: hydrogen, helium, lithium, and beryllium. Here’s what I came up with:

  • Hydrogen: Let’s start by associating hydrogen with “water.” The word hydrogen actually means “water maker.” It got its name because in 1783, Antoine Lavoisier demonstrated that the oxidation of hydrogen gas produced water (this experiment also proved that water is not elemental).
  • Helium: Helium was first detected in the solar spectrum in 1868 and was thus named after the Greek word for “sun.” The Sun is pretty fiery, so my first instinct was to make helium represent “fire.” But I’m going to go with “air” instead, because of helium’s use in balloons and airships.
  • Lithium: As I’ve written about previously, lithium was first discovered using a method called a flame test. When a chemical substance is burned, the color of the flame can be used to determine the chemical’s identity. Lithium burns with a characteristic bright crimson flame. Therefore, I’m choosing to associate lithium with “fire.”
  • Beryllium: Beryllium was first identified in 1798 as a component of the mineral beryl, specifically a form of green beryl we all know as an emerald. So I think I can safely wrap this little game up by connecting beryllium with “earth.”

So how did I do? Do you agree with the connections I came up with? Are there other connections we could think up that might work better?

Okay, maybe this was more of an exercise in creativity than science. I’m okay with that. And besides, in the half-hour I spent researching for this post, I learned a few things about the first four elements of the periodic table that I didn’t know before. That’s always a plus.

Anyway, next time on Molecular Monday, we’ll be talking about boron. Now I wonder if I can find some way to associate boron with the girl from The Fifth Element.


Sciency Words: Retropy

September 15, 2017

Today’s post is part of a special series here on Planet Pailly called Sciency Words. Each week, we take a closer look at an interesting science or science-related term to help us expand our scientific vocabularies together. Today’s term is:

RETROPY

In any serious conversation about time travel—and I mean any serious, scientific discussion of time travel, as in the kind of discussion actual real-life physicists might have—there’s a term that is virtually guaranteed to come up: entropy.

I’ve tried to define entropy before for Sciency Words, but I’ve never felt like I’ve done the term justice. It’s a big concept, and kind of a weird concept, and sometimes a depressing concept. It’s also a concept that most of us sort of grasp intuitively, even if we can’t quite put it into words.

The simplest definition is that entropy is the amount of disorder in a system, or perhaps the degree to which a system has decayed. Another good definition is that entropy is the measure of the amount of energy in a system that cannot or can no longer be used for work.

According to the second law of thermodynamics, the total entropy of any closed system will tend to increase over time. You can depend upon that! This makes entropy relevant to time travelers, because it’s one of the very few physical properties that is dependent on which direction time is flowing.

As we move forward in time, entropy will increase. And if entropy is increasing, you (as a time traveler) can be sure that you are traveling forward in time. And if you observe that the entropy of a closed system is decreasing, you can be sure you’re traveling into the past.

In the vocabulary of professional time travelers, there should probably be a special term for when entropy goes into reverse. I don’t know what that word is, but fellow blogger and poet James Ph. Kotsybar (also known as the Bard of Mars) recently proposed a pretty good option: retropy, short for retro-entropy.

He even wrote a haiku about it. It’s worth checking out, along with many of the Martian Bard’s other science-themed poems.


TRAPPIST-1: Come On, How Many Planets Are Enough?

September 12, 2017

Remember TRAPPIST-1? That ultra-cool dwarf star with a miniaturized solar system of seven planets?

Whenever we talk about TRAPPIST-1, we really should specify that it has seven planets that we know about. Astronomers are still searching for more. Specifically, they’re searching for larger, Jupiter-like bodies.

So far, astrometric observations (precise measurements of a star’s gravitational “wobble”) have ruled out some possibilities. There are no planets in the TRAPPIST-1 System with masses greater than 4.6 times the mass of Jupiter with orbital periods of one year or less, and no planets with masses greater than 1.6 times the mass of Jupiter with orbital periods of five years or less.

That still leaves the door open for a lot of other very large planets. Just imagine if we discover a couple of Saturn-mass objects, or half a dozen Neptunes. Heck, there could still be Jupiter-mass planets out there! Or maybe not. It could just be the seven Earth-sized planets we already know about.

As explained in this article from Centauri Dreams, there are currently two competing theories to explain how gas giants form. One of these theories would probably allow gas giants to form around TRAPPIST-1; the other probably would not.

  • Core Accretion: a large, rocky core forms first and then envelops itself in gases from the proto-planetary disk surrounding a newborn star. This would be a very slow formation process.
  • Disk Instability: The proto-planetary disk surrounding a young star “destabilizes,” forming whispy structures like the spiral arms of a galaxy. Knots of gas in these spiral arms would condense into planet shapes, and the rocky cores of these planets would form later (or in some cases perhaps not at all) from asteroids or other debris captured by the gas giant’s gravity. This process would happen quickly.

Given what we know so far about TRAPPIST-1, it’s unlikely gas giants could have formed there by core accretion. TRAPPIST-1’s protoplanetary disk wouldn’t have been around long enough. Therefore if we find gas giants orbiting TRAPPIST-1, that would challenge the core accretion model and give more credence to disk instability.

So now the search is on!

Will we find gas giants around TRAPPIST-1? I kind of hope we do. First off, it would make TRAPPIST-1 even more awesome than it already is. And secondly, it would mean the core accretion model—the traditionally accepted view among astrophysicists—is wrong, or at least incomplete, and when theories turn out to be wrong or incomplete, that’s when the real fun of science begins.