Water hidden in hot Jupiters

Illustration of a hot Jupiter planet with its clouds (Image NASA/JPL-Caltech)
Illustration of a hot Jupiter planet with its clouds (Image NASA/JPL-Caltech)

An article published in “The Astrophysical Journal” describes a research about the possible presence of water in the planets of the type called hot Jupiter. Those are gas giants just like Jupiter but orbit very close to their stars and consequently have very high surface temperatures. A team of scientists at NASA’s JPL led by Aishwarya Iyer tried to understand why the atmosphere of some hot Jupiters doesn’t seem to contain water.

Observations of 19 exoplanets hot Jupiters made in the past with the Hubble Space Telescope were analyzed to understand the composition of their atmosphere. The Wide Field Camera 3 instrument detected water in its vapor state because of the high temperatures in the atmosphere of 10 of those exoplanets. They were studied separately in different research with different methods of analysis so the JPL team decided to establish certain standards to conduct a consistent research.

The data of the 19 hot Jupiters were put together to create an overall average light spectrum for the whole group. The data were then compared with models of clear and cloudless atmospheres and with those of various cloud thicknesses. The result was that on almost all exoplanets they studied haze or clouds were blocking an average of half the atmosphere.

In some of these planets, it was possible to detect water above the clouds or haze. According to the researchers, this suggests that there may be more of it under them undetectable because blocked by clouds and haze. The doubt is given in part by the fact that it’s unclear what those clouds and haze are made of but research carried out in the past show that they can block the water below.

This research confirms the results of a study published in the journal “Nature” in December 2015 that used data from the Spitzer Space Telescope as well. This time the scientists used a single instrument to have uniform data on the examined exoplanets. In this way they could estimate the amount of water blocked by the atmosphere.

It’s important that different studies confirm a theory, in this case because determining the amount of water and other molecules present in hot Jupiters may help better understand their formation. One of the questions is whether these planets formed close to their stars or they moved from an original position that was farther away. Gas giant planets in general influence the evolution of their solar systems so their study may also provide information on other planets’ evolution.

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