Exoplanet Aurora… Light ‘Em Up!

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One of the most beautiful and mysterious apparitions – be it north or south – here on Earth is an auroral display. We know it’s caused by the Sun-Earth connection, so could it happen around exoplanets as well? New research shows that aurorae on distant “hot Jupiters” could be 100-1000 times brighter than Earthly aurorae, creating a show that would be… otherworldly!

“I’d love to get a reservation on a tour to see these aurorae!” said lead author Ofer Cohen, a SHINE-NSF postdoctoral fellow at the Harvard-Smithsonian Center for Astrophysics (CfA).

As we are now aware, aurorae occur here on Earth when the Sun’s energetic particles encounter our magnetosphere and are shifted towards the poles. This in turn excites the atmosphere, ionizing the particles. Much like turning on your electric stove, this causes the “element” to glow in visible light. It happens here… and it happens on Jupiter and Saturn as well. If other suns behave like our own and other planets have similar properties to those in our solar system, then the answer is clear.

Exoplanets have aurorae, too.

Cohen and his colleagues used computer models to study what would happen if a gas giant in a close orbit, just a few million miles from its star, were hit by a stellar blast. He wanted to learn the effect on the exoplanet’s atmosphere and surrounding magnetosphere. In this scenario, the solar storm is much more focused and far more concentrated when it impacts a “hot Jupiter”. In our solar system, a coronal mass ejection spreads out before it reaches us, but what would happen if it collided with a nearer planet?

“The impact to the exoplanet would be completely different than what we see in our solar system, and much more violent,” said co-author Vinay Kashyap of CfA.

Using modeling, the team took a look at the scenario. The solar blast would slice into the exoplanet’s atmosphere and weaken its magnetic shield. The auroral activity would then form a ring around the equator, 100-1000 times more energetic than seen here on Earth. It would then travel up and down the planet’s surface from pole to pole for hours, gradually weakening – yet the planet’s magnetosphere would save it from erosion. This type of study is important for understating habitable properties of Earth-like worlds.

“Our calculations show how well the planet’s protective mechanism works,” explained Cohen. “Even a planet with a magnetic field much weaker than Jupiter’s would stay relatively safe.”

Original News Source: Harvard-Smithsonian Center for Astrophysics News.