A planet’s slim-fast plan

A planet orbiting very close to its sun can quickly lose weight.

If you sit in a parked car on a hot summer’s day, you may feel like you’re melting. But that’s nothing compared to what some planets go through.

Scientists have been studying a planet called HD209458b, which orbits precariously close to its star. The star itself is about 150 light-years from Earth. HD209458b is one-eighth the distance from its sun as Mercury is from ours.

 

Artist’s depiction of a cometlike wind of hydrogen gas (blue) escaping from the outer atmosphere of the planet HD209458b, which tightly orbits its parent star (yellow).

 

European Space Agency

New observations of HD209458b suggest that brutal gusts of heat and radiation along with strong tugs of gravity from its star may be too much for the planet to bear. Every second, in fact, 10,000 tons of hydrogen gas get blasted off of HD209458b, Alfred Vidal-Madfar of the Astrophysics Institute of Paris and his colleagues report.

At that rate, the planet will probably still be okay. Weighing in at 70 percent the mass of Jupiter, HD209458b has lost only 0.1 percent of its mass since its birth 5 billion years ago.

But the findings suggest that other planets which orbit even closer to their stars might evaporate completely. That could help explain why scientists have found so few planets with super-tight orbits outside the solar system.

As scientists continue to learn more about the atmosphere of HD209458b, one question lingers: When will they come up with a name for the planet that’s easier to remember?

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