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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Is Kepler getting close to finding another Earth?

Size comparisons of Kepler planetary candidates. Credit: NASA Ames/Wendy Stenzel

The longer the Kepler mission keeps searching for exoplanets, the more amazing discoveries it makes. The Kepler mission team just released their third catalogue of new planetary candidates – 1,091 to be exact. This bring the total number of planetary candidates found by Kepler so far to 2,321, which orbit 1,790 stars. Confirmed planets so far now number 760, from Kepler and other telescopes.

These are the same candidates which had been previously discussed at the Kepler Science Conference last December, but now the official catalogue is available to the public.

A primary goal of Kepler is to find out how many planets among the stars being studied are Earth-sized and how many orbit within a star’s “habitable zone” where it would be possible for liquid water to exist. Ideally, planets which fit both criteria would be the “holy grail” of the mission.

Over 200 Earth-sized planets have now been added to the catalogue, and over 900 planets that are less than twice the size of Earth. There are also 46 planets in the habitable zone, and of these, ten are Earth-sized.

With the latest results, the number of planets found that are less than twice the size of Earth increased by 197%. Planets larger than twice the size of Earth, however, increased by 52%. This confirms the earlier trends seen that smaller rocky planets outnumber larger gas or ice giants.

There are also more multi-planet systems being discovered; 20% of the stars studied compared to 17% last year.

One of the Earth-sized planetary candidates found would seem to be of particular interest – KOI-494.01. It is still awaiting final confirmation, but the data so far support it being a real planet. It is estimated to have a mass 15% greater than Earth and a radius only 5% greater. The mean surface temperature is now estimated to be only about 1 ºC (33.8 ºF) cooler than on Earth. The estimated mean surface temperature (Ts) of KOI-494.01 is listed at 287 K (14 ºC / 56.93 ºF). Not bad!

According to the Earth Similarity Index (ESI), an estimated measure of how similar a planet is to Earth, KOI-494.01 now has an ESI rating of 99%. In the previous catalogue, it was listed at 97%. The confirmed planet with the highest rating so far is Gliese 667Cc, at 85%.

There is also a growing list of other Earth-sized candidates with ESI ratings close to that of KOI-494.01. See the summary lists here, updated March 3, 2012.

According to Natalie Batalha, Kepler deputy science team leader at San Jose State University in California, “With each new catalog release a clear progression toward smaller planets at longer orbital periods is emerging. This suggests that Earth-size planets in the habitable zone are forthcoming if, indeed, such planets are abundant.”

The updated findings continue the trend of exoplanets which are smaller like Earth, some of which orbit in their stars’ habitable zones. While these are likely to be of a wide variety, depending on other factors like composition, star type, etc., the discovery of planets like KOI-494.01 is an encouraging sign that there may indeed be other worlds out there similar to our own.

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Scientists find new clues about the interiors of ‘Super-Earth’ exoplanets

Artist's conception of "Super-Earth" exoplanet Kepler-22b, which is about 2.4 times larger than Earth. Credit: NASA

As we learned in science class in school, the Earth has a molten interior (the outer core) deep beneath its mantle and crust. The temperatures and pressures are increasingly extreme, the farther down you go. The liquid magmas can “melt” into different types, a process referred to as pressure-induced liquid-liquid phase separation. Graphite can turn into diamond under similar extreme pressures. Now, new research is showing that a similar process could take place inside “Super-Earth” exoplanets, rocky worlds larger than Earth, where a molten magnesium silicate interior would likely be transformed into a denser state as well…

See Universe Today for the full article.

Tidal heating on some exoplanets may leave them waterless

Venus as photographed by the Pioneer Venus Orbiter spacecraft in 1978. Some exoplanets may suffer a similar fate as this scorched world. Credit: NASA/JPL/Caltech

As the number of exoplanets being discovered continues to increase dramatically, a growing number are now being found which orbit within their stars’ habitable zones. For smaller, rocky worlds, this makes it more likely that some of them could harbour life of some kind, as this is the region where temperatures (albeit depending on other factors as well) can allow liquid water to exist on their surfaces. But there is another factor which may prevent some of them from being habitable after all – tidal heating, caused by the gravitational pull of one star, planet or moon on another; this effect which creates tides on Earth’s oceans can also create heat inside a planet or moon…

See Universe Today for the full article.

When stars play planetary pinball

Artist's conception of a binary star sunset as seen from the exoplanet Kepler-16b. For some planets, such views may be only temporary. Credit: NASA/Ames Research Center/Kepler Mission

Many of us remember playing pinball at the local arcade while growing up; it turns out that some stars like it as well. Binary stars can play tug-of-war with an unfortunate planet, flinging it into a wide orbit that allows it to be captured by first one star and then the other, in effect “bouncing” it between them before it is eventually flung out into deep space…

See Universe Today for the full article.