Popular exo-atmospheres

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A handful of exoplanets are gathering most of the attention on this website, the hot Jupiters HD 189733, HD 209458 and WASP-12b, the super-Earth GJ 1214b, and the young giant planets in the HR 8799 system.

Is this merely a reflection of the interest of our team, or are these exoplanets really the most popular and best studied? Below is a tally of the publications making reference to a selection of exoplanets in NASA’s ADS abstract service.

Reference to eight exoplanets in peer-reviewed scientific papers since 1999.

Reference to eight exoplanets in peer-reviewed scientific papers since 1999.

This publication data confirms that, indeed, a handful of objects that get frequent mention on exoclimes.com do receive most of the attention in the scientific literature.

The plot also reveals a few other features:

Interest in the two closest transiting hot Jupiter, HD 189733b and HD 209458b, shows no sign of abating – unlike TrES-1 for instance, which was a popular target as the first detection from transit surveys amenable to atmosphere measurements, but then trailed off as numerous other transiting planets were detected, including easier targets.

The HR 8799 system, ‘189 and ‘209 are well established as the most-studied exo-atmospheres.

We also see the two closest transiting hot Neptunes, GJ 436b and HAT-P-11b, getting a fair amount of mentions, comparable to super-Earth GJ 1214b.

With all these publications, and the large associated amounts of models, what do we know about the atmosphere of these planets?

For ‘189, ‘209 and the HR 8799b system, a substantial amount, enough to be able to sketch, in broad terms, the main characteristics of these alien atmospheres.

The hot Neptunes GJ 436b and HAT-P-11b are tougher nuts to crack, because of their small size and cooler atmospheres.

As for the super-Earth GJ 1214b, after a huge investment in observation facilities including a large amount of space telescopes time, we know a single thing: we do not see any signal from the atmosphere in transmission. Which implies the presence of high-altitude clouds in its atmosphere, according to current models (see previous post).

There is another intriguing feature in the histogram of publications: rather than an exponential growth over time, the total number seems to grow by steps – in 2000 with the first transiting planet, in 2005 with the first secondary-eclipse data, in 2010 with the first direct-imaging detection – each followed by plateaus of relatively constant interest.

With the rhythm of discovery for exoclimes at one key object every 5 years or so, we are due to the next landmark soon. It could be an Earth-class planet transiting a nearby star, or a directly imaged system with planets smaller than those of HR 8799.

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About Author

I am a professor of planetary science at the University of Exeter. My specialty is the study of exoplanets, in particular the observation and modelling of exoplanet atmospheres. I have done my PhD a the University of Geneva and worked in Chile, France and Switzerland.