Size matters in the detection of exoplanet atmospheres
September 19, 2017

Size matters in the detection of exoplanet atmospheres

A group-analysis of 30 exoplanets orbiting distant stars suggests that size, not mass, is a key factor in whether a planet’s atmosphere can be detected. The largest population-study of exoplanets to date successfully detected atmospheres around 16 ‘hot Jupiters’, and found that water vapour was present in every case.

The work by a UCL-led team of European researchers has important implications for the comparison and classification of diverse exoplanets. The results will be presented by Angelos Tsiaras at the European Planetary Science Congress (EPSC) 2017 in Riga on Tuesday 19th September.

“More than 3,000 exoplanets have been discovered but, so far, we’ve studied their atmospheres largely on an individual, case-by-case basis. Here, we’ve developed tools to assess the significance of atmospheric detections in catalogues of exoplanets,” said Angelos Tsiaras, the lead author of the study. “This kind of consistent study is essential for understanding the global population and potential classifications of these foreign worlds.”

The researchers used archive data from the ESA/NASA Hubble Space Telescope’s Wide Field Camera 3 (WFC3) to retrieve spectral profiles of 30 exoplanets and analyse them for the characteristic fingerprints of gases that might be present. About half had strongly detectable atmospheres.

Results suggest that while atmospheres are most likely to be detected around planets with a large radius, the planet’s mass does not appear to be an important factor. This indicates that a planet’s gravitational pull only has a minor effect on its atmospheric evolution.

Most of the atmospheres detected show evidence for clouds. However, the two hottest planets, where temperatures exceed 1,700 degrees Celsius, appear to have clear skies, at least at high altitudes. Results for these two planets indicate that titanium oxide and vanadium oxide are present in addition to the water vapour features found in all 16 of the atmospheres analysed successfully.

“To understand planets and planet formation we need to look at many planets: at UCL we are implementing statistical tools and models to handle the analysis and interpretation of large sample of planetary atmospheres. 30 planets is just the start,” said Ingo Waldmann, a co-author of the study.

“30 exoplanet atmospheres is a great step forward compared to the handful of planets observed years ago, but not yet big-data. We are working at launching dedicated space missions in the next decade to bring this number up to hundreds or even thousands,” commented Giovanna Tinetti, also UCL.

Further information

EPSC 2017 abstract:

The research at UCL has been funded by the Science and Technology Facilities Council (STFC) and the ERC projects ExoLights (617119) and ExoMol.

Results are summarized by Tsiaras et al. in the paper “A population study of hot Jupiter atmospheres,” which has been submitted to the Astrophysical Journal.

The team of astronomers in this study consists of A. Tsiaras (UCL, UK), I. P. Waldmann (UCL, UK), T. Zingales (UCL, UK/INAF Osservatorio Astronomico di Palermo, Italy), M. Rocchetto (UCL, UK), G. Morello (UCL, UK), M. Damiano (UCL, UK/INAF Osservatorio Astronomico di Palermo, Italy), K. Karpouzas (Aristotle University of Thessaloniki, Greece), G. Tinetti (UCL, UK), L. K. McKemmish (UCL, UK), S. N. Yurchenko (UCL, UK), J. Tennyson (UCL, UK)


Montage of artist’s impressions of exoplanetary systems. Credit: Alexaldo
Artist’s impressions of exoplanetary system. Credit: Alexaldo
Artist’s impressions of exoplanetary system. Credit: Alexaldo
Artist’s impressions of exoplanetary system. Credit: Alexaldo
Artist’s impressions of exoplanetary system. Credit: Alexaldo

Science Contacts

Angelos Tsiaras
University College London
+44 (0)7477 834386

Prof Giovanna Tinetti
University College London
+44 (0) 7912 509617

Media Contacts

Anita Heward
Europlanet Media Centre
+44 7756 034243

Dr Rebecca Caygill
UCL Communications & Marketing
+44 (0)77 3330 7596

Notes for Editors

About the NASA/ESA Hubble Space Telescope

The Hubble Space Telescope is a project of international cooperation between ESA and NASA.

About UCL (University College London)

UCL was founded in 1826. We were the first English university established after Oxford and Cambridge, the first to open up university education to those previously excluded from it, and the first to provide systematic teaching of law, architecture and medicine. We are among the world’s top universities, as reflected by performance in a range of international rankings and tables. UCL currently has over 39,000 students from 150 countries and over 12,500 staff. Our annual income is more than £1 billion. | Follow us on Twitter @uclnews | Watch our YouTube channel | Follow us on Twitter @uclnews | Watch our YouTube channel

EPSC 2017

The European Planetary Science Congress (EPSC) 2017 ( is taking place at the Radisson Blu Latvija in Riga, from Sunday 17 to Friday 22 September 2017.  EPSC is the major European annual meeting on planetary science and in 2017 is hosted for the first time in the Baltic States. Around 800 scientists from Europe and around the world will attend the meeting and will give around 1,000 oral and poster presentations about the latest results on our own Solar System and planets orbiting other stars.

EPSC 2017 is organised by Europlanet and Copernicus Meetings. The Local Organising Committee is led by Baltics in Space, a not-for-profit organisation that is supporting 25 members centred around nine Baltic space facilities for the conference. The meeting is sponsored by Investment and Development Agency of Latvia, the Latvian Ministry of Education and Science, Latvijas Mobilais Telefons, Finnish Meteorological Institute, The Estonia-Latvia programme, The Representation of the European Commission in Latvia, the Planetary Science Institute, Latvijas Universitate and The Division for Planetary Sciences of the AAS.

Details of the Congress and a full schedule of EPSC 2017 scientific sessions and events can be found at the official website:


Since 2005, the Europlanet project has provided European’s planetary science community with a platform to exchange ideas and personnel, share research tools, data and facilities, define key science goals for the future and engage stakeholders, policy makers and European Citizens with planetary science. Europlanet is the parent organisation of the European Planetary Science Congress (EPSC), and the EPSC Executive Committee is drawn from its membership.

The Europlanet 2020 Research Infrastructure (RI) is a €9.95 million project to address key scientific and technological challenges facing modern planetary science by providing open access to state-of-the-art data, models and facilities across the European Research Area. The project was launched on 1st September 2015 and has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 654208. Europlanet 2020 RI is led by the Open University, UK, and has 33 beneficiary institutions from 19 European countries.

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Baltics in Space

The philosophy of the nonprofit organization, Baltics in Space, is to “Inventory, Identify, and Integrate” with a sprinkling of Inspiration to build a space product greater than the sum of its parts. The best resource in the space business is people. With an eye to strengthening the triple helix links (Industry, Education, Research), its planned outcomes are integrating Baltic-wide space events, compiling catalogs of skill-sets for prospective users and Baltic space project development with distributed teams and Baltic space education.