Hot, steamy ‘waterworld’ exoplanet observed by Hubble

Artist's conception of GJ1214b orbiting its red dwarf star. Credit: NASA, ESA, and D. Aguilar (Harvard-Smithsonian Center for Astrophysics)

The Hubble Space Telescope has made new observations of a “waterworld” exoplanet which has a thick, steamy atmosphere.

The planet, GJ1214b, orbits a red-dwarf star and is about 40 light-years from Earth. It is about 2.7 times larger than Earth, with an estimated temperature of 232 ºC (450 ºF). While it orbits too close to its star to be in the habitable zone, and thus unlikely to have liquid water on its surface, it still apparently does have water in its atmosphere, and a lot of it.

It was initially discovered in 2009 by the MEarth Project using ground-based telescopes. Follow-up observations were made by Hubble in 2010, providing a more detailed look at the composition of its atmosphere.

It wasn’t clear however whether GJ1214b had a thick atmosphere of water vapour or if there was just a planet-wide haze in its atmosphere.

The new studies indicated that it is most likely the former – a hot, steamy atmosphere surrounding the planet. The science team used Hubble’s Wide Field Camera 3 (WFC3) to examine the atmosphere during a transit, when the planet crossed in front of its star. When the star’s light is filtered through the planet’s atmosphere, it can be analyzed to determine its composition. The spectrum turned out to be featureless, consistent with a dense atmosphere composed primarily of water vapour.

According to Zachory Berta of the Harvard-Smithsonian Center for Astrophysics (CfA), “The Hubble measurements really tip the balance in favor of a steamy atmosphere.”

The results also suggest that GJ1214b has more water and less rock than Earth; internally it may be quite different from our planet.

“The high temperatures and high pressures would form exotic materials like ‘hot ice’ or ‘superfluid water,’ substances that are completely alien to our everyday experience,” Berta said.

It could be said that GJ1214b is something like a wetter version of Venus – with a very hot, thick atmosphere but an atmosphere that is humid and saturated with water, instead of one that is bone dry, acidic and composed mostly of carbon dioxide.

The discovery is also another step closer to finding an alien world that is similar to our own. Water, in its various forms, is already known to be abundant in the universe. It may just be a matter of time before we find another waterworld that is actually like Earth – not just a planet with subsurface oceans like on some icy moons in our solar system, but another Earth with oceans, lakes and rivers on its surface. It is also thought possible that there are planets which are covered completely with water, with no continents or islands anywhere.

In the meantime, GJ1214b has shown once again that, like snowflakes, no two planets are exactly the same, with an almost limitless variety out there waiting to be discovered.

The paper is available here.

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