Youngest Hot Jupiter Provides Clues To Formation Of These Exoplanets

How do hot Jupiters form? The youngest hot Jupiter to be discovered is providing clues that may unravel the mystery behind these exoplanets' formation.

Hot Jupiters are Jupiter-sized gas giant planets that orbit unusually close to their stars. In some cases, hot Jupiters tend to be so close to their parent stars that they circle around them in as few as 18 hours.

No such planet exists in our own solar system since those closer to the Sun are rocky, not gassy, and orbit farther away than hot Jupiters do.

Given hot Jupiters' unique characteristics, the question of how they formed remains a mystery. Did they really form close to their parent star, or did they form farther away, and then migrated closer?

A new study published in the Astronomical Journal, wherein researchers reported the discovery of possibly the youngest hot Jupiter ever found, may just provide a clue to answer these questions.

In the study, researchers reported the discovery of exoplanet HIP 67522 b, which is just about 490 lightyears away from the Earth. HIP 67522 b is 10 times the size of the Earth, suggesting that it is a gas-dominated planet, and is only a few million years younger than its 17-million-year-old star. By comparison, most known hot Jupiters are over a billion years old, making this the youngest to be discovered so far.

It was identified by NASA's Transiting Exoplanet Survey Satellite via the transit method and confirmed by the Spitzer Space Telescope.

Because of HIP 67522 b's very young age, astronomers can use it to possibly understand how hot Jupiters form. So far, there are three main hypotheses for hot Jupiter formation, the first being that they simply formed close to their parent stars and remained in that position. However, young stars often erupt in massive explosions and would therefore disrupt any potential planet trying to form nearby.

The other two hypotheses suggest hot Jupiters form farther away from their parent stars then eventually move closer. However, the difference between the two lies in why the hot Jupiters moved closer.

In the second hypothesis, hot Jupiters move closer to their stars early on in the formation of the planetary system because their orbits are disrupted by the gravity of the disk of gas and dust that formed both the star and the planet. In the third hypothesis, the hot Jupiters migrate closer to the star later on in their lives, when it is the gravity of other planets in the system that cause the migration.

Given that HIP 67522 b is already close to its parent star at such a young age, the third hypothesis is likely not applicable anymore, at least in this case.

Naturally, studying one hot Jupiter is not enough to create a clear picture of how they all form. However, it does provide a significant clue to their formation.

"In the community right now there is no clear consensus about which formation hypothesis is most important for reproducing the population we have observed," astrophysicist Yashuhiro Hasegawa said, according to a news release from NASA. Hasegawa was not involved in the study. "The discovery of this young hot Jupiter is exciting, but it's only a hint at the answer. To solve the mystery, we will need more."