Episode for October 3rd, 2023 Download

Meet TOI-1853 b, one of the weirdest exoplanets ever discovered! It’s about the size of Neptune, but four times more massive. It orbits its star so closely that it completes a full orbit in just 1.24 days. This makes it very hot, and it’s located in a region of space known as the “hot Neptune desert,” where astronomers have been looking for Hot Neptunes but unable to find any.

So on the one hand, this is great: we have a Neptune sized planet close to its star where we haven’t seen many. On the other hand, this is a really strange world. It’s the size of Neptune sure, but four times more massive than Neptune and about 73 times more massive than Earth.

Astronomers infer the mass by looking at the wobble of the host star as the planet orbits it. They get the size by looking at how much the host star’s light dimmed as it passed in front of it, they can also get the orbital period by looking at the dips several times.

So here we have a huge and massive planet close to its star. How did it get there?

Scientists are baffled by TOI-1853 b. They’re not sure how it formed, or why it’s so massive. One possibility is that it started out as a gas giant, but lost its atmosphere due to the intense radiation from its star. Another possibility is that it formed in a much cooler region of space, and then migrated closer to its star later on.

There are planets this size all over the place, but not this massive. One way astronomers infer whether a planet is rocky or not is by it size. It’s assumed that larger planets are gas giants and one reason we don’t see Hot Neptunes that much is their atmospheres get stripped away. So if that happened in this case, what could account for the mass involved here?

The planet’s mass is too large to have formed from the accumulation of small dust particles from the planet-forming disk. It is also unlikely that the planet formed in its current location, as solids have difficulty condensing there.

So astronomers tell us we are left with two rather strange possibilities: either TOI-1853 b is a rocky planet with a thin atmosphere: This is the most likely scenario, as it is consistent with the planet’s density. The atmosphere would be so thin that it would account for only one percent of the planet’s mass.

The other is its got a rocky core with a thick layer of water: This is less likely, but possible. The water would be in a supercritical state, meaning that it would be both a liquid and a gas. The pressure near the rocky core would force the water to form high-pressure solids.

Whatever its origins, TOI-1853 b is a fascinating planet and probably not a very habitable one. Life here would be bone-crushingly hot. Imagine weighing 73 times more than you do now and living right next door to the star.

The study of exoplanets is a journey of discovery, and we are only just beginning to scratch the surface of what is possible. Every new planet we find challenges our understanding of how planets form, where they came from, and what they are like. We have already learned so much about exoplanets in a short period of time. We have discovered planets of all sizes and shapes, orbiting stars of all types. We have found planets made of gas, rock, and even water. We have even found planets that could potentially be habitable.

Even with this progress, we are still surprised by what we find. There is so much more to learn.