Exoplanet aurora is out of this world
Earth’s aurorae, or northern and southern lights, provide a dazzling light show to people living in polar regions. Shimmering curtains of green and red undulate across the sky. New research shows that aurorae on distant “hot Jupiters” could be 100-1000 times brighter than earthly aurorae. They also would ripple from equator to poles — due to the planet’s proximity to stellar eruptions — treating the entire planet to an otherworldly spectacle.
Ofer Cohen, a postdoctoral fellow at the Harvard-Smithsonian Center for Astrophysics (CfA), said:
I’d love to get a reservation on a tour to see these aurorae!
Cohen and his team have published a paper about exoplanet aurorae in the May 5, 2011 issue of The Astrophysical Journal.
Earth’s aurorae are created when energetic particles from the sun slam into our planet’s magnetic field. The field guides solar particles toward the poles, where they smash into Earth’s atmosphere, causing air molecules to glow like a neon sign. The same process can occur on planets orbiting distant stars. These are known as exoplanets.
Particularly strong aurorae result when Earth is hit by a coronal mass ejection (CME) — a gigantic blast that sends billions of tons of solar plasma (electrically charged, hot gas) into the solar system. A CME can disrupt Earth’s magnetosphere — the bubble of space protected by Earth’s magnetic field — causing a geomagnetic storm. In 1989, a CME hit Earth with such force that the resulting geomagnetic storm blacked out huge regions of Quebec.
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 eruption. They wanted to learn the effect on the exoplanet’s atmosphere and surrounding magnetosphere.
The gas giant would be subjected to extreme forces. In our solar system, a CME spreads out as it travels through space, so it’s more diffuse once it reaches us. A “hot Jupiter” would feel a stronger and more focused blast, like the difference between being 100 miles from an erupting volcano or one mile away.
Co-author Vinay Kashyap said:
The impact to the exoplanet would be completely different than what we see in our solar system, and much more violent.
In the model, a CME hits the “hot Jupiter” and weakens its magnetic shield. Then CME particles reach the gas giant’s atmosphere. Its aurora lights up in a ring around the equator, 100-1000 times more energetic than earthly aurorae. Over the course of about 6 hours, the aurora then ripples up and down toward the planet’s north and south poles before gradually fading away.
The authors’ future work will examine whether rocky worlds orbiting close to red dwarf stars — a focus in the search for Earthlike planets — could shield themselves from stellar eruptions. Since a red dwarf is cooler than our sun, a rocky planet would have to orbit very close to the star to be warm enough for liquid water. There, it would be subjected to the sort of violent stellar eruptions Cohen and his colleagues studied.
Bottom line: Ofer Cohen, Harvard-Smithsonian Center for Astrophysics, and his team of researchers have published a paper in the May 5, 2011 issue of Astrophysical Journal, detailing their study on exoplanet aurorae of “hot Jupiter” worlds.