Magnetic Fields on Distant Exoplanets?

Twenty Years of exoplanet research has seen incredible advances in detecting planets orbiting distant stars, as well as their size, orbit period, orbit distance, and even atmospheric composition.  But the next step in understanding exoplanets is to learn about their magnetic fields.

We know that many exoplanets should have magnetic fields.  It makes sense, since nearly every world in our own solar system has some sort of magnetism.  But for the first time, an international team of Astronomers, led by Kristina Kislyakova of the Space Research Institute of the Austrian Academy of Sciences, have discovered a way to detect magnetic fields on an exoplanet.

They looked at H-Alpha images of the planet HD 209458b as it passed in front of its star.  Looking at the planet’s absorption of stellar radiation, they were able to model the size and shape of the surrounding gas cloud, which allowed them to model the planet’s magnetosphere.  When only one such model would reproduce the observed distribution of hydrogen in the atmosphere, the team realized they were successful.

Credit: NASA/ESA/CNRS/Alfred Vidal-Madjar

The planet HD 209458b is about 150 light years from Earth in the constellation Pegasus.  It is known as a ‘hot-Jupiter,’ meaning it is a planet comparable to the size and mass of Jupiter, with an orbit distance even closer than Mercury.  Hot Jupiters were the first exoplanets to be detected due to their size and strong gravitational effect on their home star.  This particular planet is the first to have it’s atmospheric composition determined, and its relative ease of study is why astronomers use it as a baseline to test new methods in exoplanet research.

To increase the accuracy of their model, the Astronomers accounted for some of the parameters that alter the interactions between the planet’s atmosphere and the stellar wind, such as gravitational effects, pressure, radiation acceleration, and spectral line broadening.

According to Kislyakova, “The planet’s magnetosphere was relatively small beeing only 2.9 planetary radii corresponding to a magnetic moment of only 10% of the magnetic moment of Jupiter.”

Astronomers study magnetic fields due to their influence on the evolution of a planet.  They shield the planet from Solar Wind particles and can protect against the erosion of the planet’s atmosphere.

On Earth, the magnetic field protects life on Earth from harmful Solar radiation, producing the gorgeous Aurorae near the poles.  On Mars, where there is no magnetic field, solar wind particles batter the planet, blasting away any atmosphere Mars may have had in the past.

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