First results from the analysis of eight 'hot Jupiter' exoplanets suggest that winds and clouds play an important role in the atmospheric make up of these exotic planets. Catherine Huitson of the University of Exeter will present the results at the National Astronomy Meeting in St Andrews on Friday 5 July.
Hot Jupiters are giant exoplanets, similar in size to Jupiter, that orbit so close to their stars that their atmospheres can reach temperatures of 1000-3000 degrees Celsius. Astronomers can detect which gases are present in their atmospheres by analysing the spectrum of starlight filtered through the planet's atmosphere when the planet passes in front of the star. Last year, a team led by the University of Exeter was awarded nearly 200 hours on the NASA/ESA Hubble Space Telescope to examine eight planets using this technique - the largest survey of its type to date.
"These hot Jupiter planets are expected to have a vastly different composition from planets in our own Solar System like Jupiter, where temperatures at the cloud tops are around -150 degrees Celsius. The first planet we measured is one of the hottest to be observed, with a temperature of over 2000 degrees. The early results of the survey are now in, and they present a diverse range of puzzling properties," said Huitson.
The first, very hot planet observed showed an unexpected absence of titanium oxide. Current 3D models of hot Jupiter atmospheres suggest that grains of this heavy molecule should be circulated by fast winds, allowing gaseous titanium oxide to reach the observable upper atmosphere. The non-detection of the gas suggests that either the winds are not as strong as expected or the molecule is forming much larger grains that are too heavy be lifted.
Huitson explained, "Titanium oxide is a solid on Earth, but we expect it to be present in the atmosphere of the hottest hot Jupiters because of the extreme temperatures. This molecule is important because it could trap atmospheric heat high up forming a stratosphere - the same role ozone plays on Earth. However, our results show that this molecule is not present in the upper atmosphere, meaning that we need to revise our understanding of how wind processes distribute materials."
The team also made a confirmed detection of water vapour in the atmosphere of two planets. Importantly, the water was found in the quantities predicted by theory, contrasting with previously observed planets.
"While our models tell us that water (as steam) should be present in hot Jupiter atmospheres, until now the molecule has only been seen in limited quantities and in fewer planets than expected," said Huitson.
"Seeing steam in two exoplanets is a great confirmation of current theory. Our new findings suggest that previous non-detections were caused by opaque, high-up clouds obscuring the parts of the atmosphere where steam is present."
The results presented at the National Astronomy Meeting represent initial findings and work by the team is still ongoing to analyse all the data from the eight-planet Hubble survey.
"A surprising diversity is emerging from the continuing observations among planets with similar temperatures, and the remaining results are sure to present even more surprises as we try to understand such extreme and unknown objects," said Huitson.
Figure1: An artist's impression of the sort of a hot Jupiter (credit: NASA,
ESA, and G. Bacon (STScI)).
Figure 2: Diagram showing the method used to detect atmospheric components
(credit ESA/David Sing).
University of Exeter
Tel: 01392 725571
From 1-5 July, Catherine Huitson can be contacted through the NAM Press
Ms Anita Heward
Royal Astronomical Society
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Dr Robert Massey
Royal Astronomical Society
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Ms Emma Shea
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University of St Andrews
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Landline numbers in NAM 2013 press room (available from 9 a.m. to 5 p.m. from 1-4 July, 9 a.m. to 3 p.m. 5 July):
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NOTES FOR EDITORS
Bringing together more than 600 astronomers and space scientists, the RAS National Astronomy Meeting (NAM 2013) will take place from 1-5 July 2013 at the University of St Andrews, Scotland. The conference is held in conjunction with the UK Solar Physics (UKSP: http://www.
Meeting arrangements and a full and up to date schedule of the scientific programme can be found on the official website at http://www.
About the University of Exeter
The Sunday Times University of the Year 2012-13, the University of Exeter is a Russell Group university and in the top one percent of institutions globally. It combines world-class research with very high levels of student satisfaction. Exeter has over 18,000 students and is ranked 7th in The Sunday Times University Guide, 10th in The Complete University Guide, 10th in the UK in The Times Good University Guide 2012 and 12th in the Guardian University Guide 2014. In the 2008 Research Assessment Exercise (RAE) 90% of the University's research was rated as being at internationally recognised levels and 16 of its 31 subjects are ranked in the top 10, with 27 subjects ranked in the top 20.
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Founded in the 15th century, St Andrews is Scotland's first university and the third oldest in the English speaking world. Teaching began in the community of St Andrews in 1410 and the University was formally constituted by the issue of Papal Bull in 1413. The University is now one of Europe's most research intensive seats of learning - over a quarter of its turnover comes from research grants and contracts. It is one of the top rated universities in Europe for research, teaching quality and student satisfaction and is consistently ranked among the UK's top five in leading independent league tables produced by The Times, The Guardian and the Sunday Times.
The University is currently celebrating its 600th anniversary and pursuing a £100 million fundraising campaign, launched by Patron and alumnus HRH Prince William Duke of Cambridge, including £4 million to fund the creation of an 'Other Worlds' Think Tank and Observatory. The new think tank and Observatory project will extend the University of St Andrews' flagship work on extra-solar planets, and provide a creative environment for problem-focused research, education and continuing public engagement.