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Covered skies in Leo and in Ophiuchus


The unusually flat spectrum detected by Hubble’s for two extrasolar planets of the most common type, both with a mass similar to that of Neptune, leads scientists to hypothesize the presence of clouds at high altitude in their atmospheres. The two studies can be read in Nature.

GJ 436b and GJ 1214b

 The size of GJ 436b and GJ 1214b compared to those of Earth and Neptune.

Credit: NASA & ESA, STScI-PRC14-06b

The keyword this time is featureless: uniform, featureless, flat, monotonous, in fact. So are the measured spectra from the Hubble Space Telescope during hours and hours of observation of two extrasolar planets on behalf of two separate research groups. A monotony revealing: it is thanks to the absence of emission lines – so characteristic signatures of specific molecules – which scientists have been able to cross out, one by one, substances such as water vapor, methane, nitrogen, carbon monoxide, carbon or carbon dioxide from the list of ingredients constituent of the atmosphere of the two planets. And come to infer the presence at high altitude (around a millibar pressure), both in the atmospheres of these distant worlds, on a cloudy enveloping cloak that prevents us from seeing what’s underneath.

Do not imagine, however, the skies flecked with pretty puffy clouds, cirrus clouds or rain. Although it is still too early to speculate on the content of those clouds, the current models on the atmospheres of super-Earths damage to winning not just cute compounds, such as zinc sulfide or potassium chloride. Not exactly breathable air, whereas the first is the salt that gives life to the fluorescent images in picture tubes, and the second is part of the cocktail injected into the death sentences. Not to mention the temperature of the clouds: over two hundred degrees, say the weathermen.

In short, if you know avoid them. Let’s see what we’re talking about these worlds. One is Gliese 436b: every 63 hours in orbit around GJ 436, a star about 30 light-years away in the constellation of Leo, that has a mass equal to 22 times that of the Earth (thus similar to that of Neptune) and a temperature is around 500 degrees. To analyze the spectrum with Hubble’s Wide Field Camera 3, in the course of four observing campaigns from October of 2012 to January of 2013, a team led by Heather Knutson, a professor of planetary science at Caltech.

The other is Gliese 1214b: about 7 times Earth masses, is located 40 light-years from Earth, in the constellation of Ophiuchus, and orbits the parent star in 38 hours. The first author of the study is Laura Kreidberg, a PhD student at the University of Chicago. Together with her supervisor, Jacob Bean, decided to analyze the spectrum of GJ 1214b that conducted what is, to date, the longest ever observing program dedicated to the study of a single Hubble extrasolar planet: something like 96 hours spread of a period of 11 months.

Ultimately, two discoveries with a lot in common, were just posted on the pages of Nature, on two planets highly similar. Two planets from physics still largely unknown, since there are no analogues in our Solar System, but ubiquitous – and this is perhaps the most important aspect of this result – elsewhere: according to the latest research, in fact, super-Earths like these, represent the most common type among all the worlds that populate the Milky Way.

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