Icarus Planets Lose Their Atmospheres

Planets: Don’t Fly Too Close to Your Star

In the old legend of Icarus, the man-god flew too close to the Sun against his father’s warnings. The heat from our star melted his waxy wings and Icarus plummeted to his death. It’s a cautionary tale as old as humanity.

There’s a new variation on that myth, and it has to do with a subset of super-Earth exoplanets recently studied by astronomers. These are rocky worlds with atmospheres and they make tight orbits around their stars. Intense radiation from their parent stars simply blows away their atmospheres, leaving behind a barren wilderness of a planet.

This doesn’t happen to every massive planet and its star, but it may be something that happens as young stars and their newly formed planets evolve over time. The most likely candidates for this atmospheric stripping are worlds that received 650 times MORE radiation than Earth receives from the Sun. The planetary atmospheres don’t have a chance. They just get blown away — gone with the stellar wind.

Asteroseismology Tells the Tale

The astronomers who found these airless worlds used data from the Kepler mission to study  the stars where these worlds orbit.  The data helped researchers perform asterseismology to characterize the host stars, and to figure out the sizes of their super-Earth planets. The worlds without atmospheres turn out to be a new category of exoplanets, and occupy a niche in planetary formation and evolution that astronomers are still working to understand.

Asteroseismology is a technique that reveals the inner structure of a star. Astronomers use it to measure a star’s pulsations. Different rates of oscillations give clues to activity at several depths and the star’s surface. It’s not unlike studying seismic waves on Earth during earthquakes. In that case, geologists use the waves to understand the structure beneath of the surface of our planet.

A star’s oscillations are reflected in its brightness variations. Even the most subtle pulsations can tell something about the star, and finding planets barren of atmospheres orbiting distant stars gives a clue about past and current stellar activity. Asteroseismology helps complete that picture.

I’m constantly amazed at the things we learn about the cosmos using such tools as the Kepler telescope. What started out as a planet search is yielding amazing peeks into the interiors of stars, too.

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