June 4, 2013
Exoplanets Electrified By Stellar Winds
John P. Millis, Ph.D. for redOrbit.com — Your Universe Online
When scientists began seeking out planets outside of our solar system, they anticipated seeing systems much like our own. Small, rocky worlds orbiting a couple of astronomical units from the host star, with the gas giant planets orbiting farther out. After all, much effort had been given to explaining how a solar system such as ours would form.
Only, this is not what has been found. Many solar systems are constructed with planets much larger than Jupiter orbiting at a fraction of Mercury´s orbit. This defies what we believed we knew about solar systems, how they form and how they evolve. One of the leading issues is that many of these “hot Jupiters” are very puffy — even larger than expected, given their mass.
This means that these gas giants must be generating heat beyond what would be expected from solar radiation. Now researchers at Florida Gulf Coast University (FGCU) believe they may have the answer. They noticed that these puffy stars arise in systems with more magnetodynamic stars, so they concluded that the heating could come from interactions of stellar magnetic fields with planetary magnetospheres, driving current formation on the surface of the worlds. This added electric energy would penetrate through the planet, providing the extra heat scientists calculate should exist.
“This kind of electric heating doesn´t happen very effectively on planets in our solar system because their outer atmospheres are cold and don´t conduct electricity very well,” says FGCU astronomer Derek Buzasi. “But heat up the atmosphere by moving the planet closer to its star and now very large currents can flow, which delivers extra heat to the deep interior of the planet -- just where we need it.”
Problems still exist, however. This still does not explain how the gas giant formed so close to its star. With such a powerful stellar wind, the light gases needed to form the atmospheric structure would have become unbounded to the core, preventing the planet from properly forming.
“It is believed that these hot Jupiter planets formed farther out and migrated inwards later, but we don´t yet fully understand the details of the migration mechanism. The better we can model how these planets are built, the better we can understand how solar systems form. That in turn, would help astronomers understand why our solar system is different from most, and how it got that way.”