New Technique Estimates the Magnetic Field of a Distant Exoplanet

Understanding the magnetic fields of planets is important for understanding how they interact with the rest of the cosmic bodies around them. Now, scientists have developed a new method that allows them to estimate the magnetic field of a distant exoplanet, telling them a bit more about the planet outside of the solar system.

On Earth, the magnetic field protects living creatures from cosmic rays. It also helps animals navigate, such as during yearly migrations. This means that determining the magnetic field of an exoplanet could potentially tell scientists whether or not it's a candidate for harboring life.

In this case, the exoplanet is called HD 209458b. Also known as Osiris, this exoplanet is a hot Jupiter, which means that it's a hot, gaseous giant. It orbits very close to its host star and completes one revolution around the star every 3.5 Earth days.

In order to learn a bit more about the planet, the researchers used observations from the Hubble Space Telescope in the hydrogen Lyman-alpha line at the time of the exoplanet's transit. At first, the researchers examined the absorption of the star radiation by the atmosphere of the planet. After, they estimated the shape of the gas cloud surrounding the hot Jupiter, and the size and configuration of the magnetosphere.

"We modeled the formation of the cloud of hot hydrogen around the planet and showed that only one configuration, which corresponds to specific values of the magnetic moment and the parameters of the stellar wind, allowed us to reproduce the observations," said Kristina Kislyakova, one of the researchers, in a news release.

The researchers believe that the size of the atomic hydrogen envelope is defined by the interaction between the gas outflows form the planet and the incoming stellar wind protons. By knowing the parameters of the atomic hydrogen cloud, the researchers could estimate the size of the magnetosphere with a model.

In this case, the researchers found that the exoplanet's magnetosphere was just 2.9 planetary radii, relatively small. This, however, is consistent with estimates of the effectiveness of the planetary dynamo for this planet.

The new method could also be used for other planets, including Earth-like planets. This, in particular, might allow scientists to pinpoint which planets are most likely to harbor life.

The findings are published in the journal Science.