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Flying Space Toasters: Electrified Exoplanets Really Feel the Heat

Posted on June 5, 2013

Overheated and overinflated, hot Jupiters are some of the strangest extrasolar planets to be discovered by the Kepler mission… and they may be even more exotic than anyone ever thought. A new model proposed by Florida Gulf Coast University astronomer Dr. Derek Buzasi suggests that these worlds are intensely affected by electric currents that link them to their host stars. In Dr. Buzasi’s model, electric currents arising from interactions between the planet’s magnetic field and their star’s stellar wind flow through the interior of the planet, puffing it up and heating it like an electric toaster.

In effect, hot Jupiters are behaving like giant resistors within exoplanetary systems.

Artist’s concept of “hot Jupiter” exoplanet HD 149026b (NASA/JPL-Caltech)

Artist’s concept of “hot Jupiter” exoplanet HD 149026b (NASA/JPL-Caltech)

Many of the planets found by the Kepler mission are of a type known as “hot Jupiters.” While about the same size as Jupiter in our own solar system, these exoplanets are located much closer to their host stars than Mercury is to the Sun — meaning that their atmospheres are heated to several thousands of degrees.

One problem scientists have had in understanding hot Jupiters is that many are inflated to sizes larger than expected for planets so close to their stars. Explanations for the “puffiness” of these exoplanets have generally involved some kind of extra heating process — but no model successfully explains the observation that more magnetically active stars tend to have puffier hot Jupiters orbiting around them.

“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 Dr. 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.”

More magnetically active stars have more energetic winds, and would provide larger currents — and thus more heat — to their planets.

The currents start in the magnetosphere, the area where the stellar wind meets the planetary magnetic field, and enter the planet near its north and south poles. This so-called “global electric circuit” (GEC) exists on Earth as well, but the currents involved are only a few thousand amps at 100,000 volts or less.

On the hot Jupiters, though, currents can amount to billions of amps at voltages of millions of volts — a “significant current,” according to Dr. Buzasi.

A Spitzer-generated exoplanet weather map showing temperatures on a hot Jupiter HAT-P-2b.

A Spitzer-generated exoplanet weather map showing temperatures on hot Jupiter HAT-P-2b.

“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,” Dr. Buzasi says. “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.”

Other electrical heating processes have previously been suggested by other researchers as well, once hints of magnetic fields in exoplanets were discovered in 2003 and models of atmospheric wind drag — generating frictional heating — as a result of moving through these fields were made in 2010.

(And before anyone attempts to suggest this process supports the alternative “electric universe” (EU) theory… um, no.)

“No, nothing EU-like at all in my model,” Dr. Buzasi told Universe Today in an email. “I just look at how the field aligned currents that we see in the terrestrial magnetosphere/ionosphere act in a hot Jupiter environment, and it turns out that a significant fraction of the resulting circuit closes inside the planet (in the outer 10% of the radius, mostly) where it deposits a meaningful amount of heat.”

Source: Universe Today, story by Jason Major

   
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