December 14, 2010

Exoplanetary Bow Shocks

Exoplanetary Bow Shock
We've heard of stellar bow shocks before. But I bet no one has heard of bow shocks of planets just yet! Exoplanetary Bow Shocks would be an amazing sight to see. I am surprised by the lack of pictures that I can find on the web on how it would look like. So I made one of my own.

Now here's an unusual trivia about exoplanetary bow shocks which caught my attention: Exoplanetary Bow Shocks can also appear from behind the planet! Astrophysicists call them "behind-shocks".

Another case, is when the shock trails the planet. In the “behind-shock” case, the planet orbits the star beyond the Keplerian co-rotation radius, so that the coronal plasma lags behind the planetary motion. In order to develop a behind-shock, the planet must be in a prograde orbit.

Now, of course I wanted to imagine how a bow shock would look like when viewed from the surface of the planet. A question brewed in my mind: Would an exoplanetary bow shock look like the Aurora? Yes. But you would not be around long enough to see much of it, for the bow shocks described in the paper are stellar plasma emanating from the star that interacts with the magnetic fields of both the planet and star itself. Imagine yourself being burnt to a crisp while watching a beautiful 'Aurora' show.

The planetary magnetic field is believed to be responsible for shielding the planet against the erosion of the planetary atmosphere by the host star’s wind or the impact of energetic cosmic particles. Such effects could harm creation and development of life in the planet.
Furthermore, the presence of a planetary magnetic field may induce star-planet interactions, e.g., through reconnection between stellar and planetary magnetic field lines.

But of course, planets farther away from the star would have a more gentler bow shock, and a milder shower of stellar material. I would assume different kinds of beauty and variety that one would see if one were to look up from the surface of an exoplanet with a faint bow shock. And it hit me! We have those here on earth! We know them as Aurora Borealis and Aurora Australis!

And that whole visual imagining is the whole reason why the arxiv paper inspired me to write a story, entitled “Worlds Hopper”. The ArXiV paper is rich with information. It contains lists and data tables of exoplanets which may possibly have bow shocks. Some of them are WASP-12b, OGLE-TR-56b, WASP-19b, SWEEPS-11,WASP-4b,WASP-18b, CoRoT-7b, CoRoT-14b, HAT-P-7b, OGLE-TR-132b, CoRoT-1b, TrES-3, and WASP-5b.

Well, these bow shocked exoplanets are quite a handful, eh? Go check out the paper and tell me what you think.

Prospects for Detection of Exoplanet Magnetic Fields Through Bow-Shock Observations During Transits
Transit Variability in Bow Shock-Hosting Exoplanets (PDF)
Short Story: Worlds Hopper