atmospheric escape

All posts tagged atmospheric escape

Tidal Evolution and Mass Loss for Close-in Exoplanets

Posted by admin on December 17, 2025
Posted in: Research. Tagged: , , .
An artist's conception of CoRoT-7 b.
An artist’s conception of CoRoT-7 b.

CoRoT-7 b was the first confirmed rocky exoplanet and was discovered by the CoRoT mission, but, with an orbital from its host star of only 0.0172 AU (100 times closer than the Earth is to the Sun), its origins may be unlike any rocky planet in our Solar system. In Jackson+ (2010), my colleagues and I considered the roles of tidal evolution and atmospheric mass loss in CoRoT-7 b’s history, which together have modified the planet’s mass and orbit. If CoRoT-7 b has always been a rocky body, evaporation may have driven off almost half its original mass, but the mass loss may depend sensitively on the extent of tidal decay of its orbit. As tides caused CoRoT-7 b’s orbit to decay, they brought the planet closer to its host star, thereby enhancing the mass loss rate. Such a large mass loss also suggests the possibility that CoRoT-7 b began as a gas giant planet and had its original atmosphere completely evaporated. In this case, we found that CoRoT-7 b’s original mass probably did not exceed 200 Earth masses (about two-third of a Jupiter mass). Tides raised on the host star by the planet may have significantly reduced the orbital semimajor axis, perhaps causing the planet to migrate through mean-motion resonances with the other planet in the system, CoRoT-7 c. The coupling between tidal evolution and mass loss may be important not only for CoRoT-7 b but also for other close-in exoplanets, and future studies of mass loss and orbital evolution may provide insight into the origin and fate of close-in planets, both rocky and gaseous.

Related Press:

Related Scientific Publications:

  • Jackson+ (2010). “The roles of tidal evolution and evaporative mass loss in the origin of CoRoT-7 b.” MNRAS 407, 910.
  • Jackson+ (2010). “Is CoRoT-7 B the Remnant Core of an Evaporated Gas Giant?” BAAS 42, 444.

Helium in the eroding atmosphere of an exoplanet

Posted by admin on February 22, 2019
Posted in: BSU Journal Club. Tagged: , , , .

Artist’s conception of a hot Jupiter shedding mass.

The very first exoplanet discovered around a Sun-like star, 51 Peg b, was a shocker – it’s a giant planet like Jupiter made mostly of hydrogen and helium but 100 times closer to its sun than Jupiter is to ours and whizzes around its orbit every 4 days.

Indeed, when its discoverers Michel Mayor and Didier Queloz first spotted the telltale spectral wobble of a planet in a 4-day orbit, they didn’t believe their discovery. At the time, everyone knew (or thought they knew) that planets like Jupiter could only form very far away from their host star.

Worse, so close to its star, 51 Peg b’s was being super-heated, and Mayor and Queloz worried that such a hot gas giant might quickly lose its hot, bloated atmosphere. And in their discovery paper, they suggested that the giant planet we see today as 51 Peg b might have started out as a brown dwarfthat shed trillions and trillions of lbs.

Later studies showed those early concerns about atmospheric blow-off were overblown and planets as massive as 51 Peg b, even if they are as scorched, probably can’t lose more than a fraction of their original mass. Since then, hot Jupiters like 51 Peg b, while cosmically rare, have become a fairly common type of exoplanet discovery.

But that doesn’t mean these planets aren’t losing a lot of mass, and a recent study from David Sing and colleagues looks at one of the mass-losing-est planets we know of, WASP-107b

Artist’s conception of WASP-107b transiting its host star.
From https://en.wikipedia.org/wiki/WASP-107b.

Sing and colleagues collected transit observations in infrared wavelengths of the WASP-107 system using the venerable Hubble Space Telescope. By looking in the infrared, they could search for the spectral signals of different gases in WASP-107b’s atmosphere.

WASP-107b is an especially good target for atmospheric characterization because its host star is very bright (compared to other planet hosts) and the planet itself is very low density – it has a mass a tenth that of Jupiter’s but a radius almost as big, giving the planet a density comparable to wind-packed snow.

With such a low density, WASP-107b’s atmosphere is puffy and distended, which means that its atmospheric gases can easily imprint their spectral signatures on the light observed by Hubble, making them easy to detect.

And for the first time in any exoplanet, Sing and colleagues saw signs of helium gas in WASP-107b’s atmospheric spectrum. In fact, the helium signal they saw was so whopping big that it suggests WASP-107b’s atmosphere is actively escaping, at a rate of about 10,000 tons per second.

Escape of WASP-107b’s atmosphere. The planet is the small grey circle near bottom, the star is the yellow circle, and the escaping atmosphere is shown in blue. The black line is the planet’s orbit. From Sing et al. (2018).

Even with such a high escape rate, WASP-107b won’t fall apart anytime soon – Sing and colleagues estimate it would only lose about 4% of its mass in a billion years.

But as we continue to find more exoplanets, we should probably expect to find more even closer to their host stars with even puffier atmospheres, perhaps some on the verge of being gravitationally ripped apart. So as with 51 Peg b’s discovery, exoplanets are likely to keep challenging our preconceived notions about where planets can and cannot be.