First Detection of Super-Earth Atmosphere

This video shows an artist's impression of the super-Earth 55 Cancri e moving in front of its parent star. During these transits astronomers were able to gather information about the atmosphere of the exoplanet. The Scientists were able to retrieve the spectrum of 55 Cancri e embedded in the light of its parent star. The analysis showed that the atmosphere of 55 Cancri e consists mainly of helium and hydrogen with hints of hydrogen cyanide.Credit: ESA/Hubble, M. Kornmesser

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Artist’s impression of 55 Cancri e

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Artist’s impression of 55 Cancri e (close-up)

For the first time astronomers were able to analyse the atmosphere of an exoplanet in the class known as super-Earths. Using data gathered with the NASA/ESA Hubble Space Telescope and new analysis techniques, the exoplanet 55 Cancri e is revealed to have a dry atmosphere without any indications of water vapour. The results, to be published in the Astrophysical Journal, indicate that the atmosphere consists mainly of hydrogen and helium.

The international team, led by scientists from University College London (UCL) in the UK, took observations of the nearby exoplanet 55 Cancri e, a super-Earth with a mass of eight Earth-masses [1]. It is located in the planetary system of 55 Cancri, a star about 40 light-years from Earth.

Using observations made with the Wide Field Camera 3 (WFC3) on board the NASA/ESA Hubble Space Telescope, the scientists were able to analyse the atmosphere of this exoplanet. This makes it the first detection of gases in the atmosphere of a super-Earth. The results allowed the team to examine the atmosphere of 55 Cancri e in detail and revealed the presence of hydrogen and helium, but no water vapour. 

These results were only made possible by exploiting a newly-developed processing technique.

“This is a very exciting result because it’s the first time that we have been able to find the spectral fingerprints that show the gases present in the atmosphere of a super-Earth,” explains Angelos Tsiaras, a PhD student at UCL, who developed the analysis technique along with his colleagues Ingo Waldmann and Marco Rocchetto. “The observations of 55 Cancri e’s atmosphere suggest that the planet has managed to cling on to a significant amount of hydrogen and helium from the nebula from which it originally formed.”

Super-Earths like 55 Cancri e are thought to be the most common type of planet in our galaxy. They acquired the name ‘super-Earth’ because they have a mass larger than that of the Earth but are still much smaller than the gas giants in the Solar System. The WFC3 instrument on Hubble has already been used to probe the atmospheres of two other super-Earths, but no spectral features were found in those previous studies [2].

55 Cancri e, however, is an unusual super-Earth as it orbits very close to its parent star. A year on the exoplanet lasts for only 18 hours and temperatures on the surface are thought to reach around 2000 degrees Celsius. Because the exoplanet is orbiting its bright parent star at such a small distance, the team was able to use new analysis techniques to extract information about the planet, during its transits in front of the host star.

Observations were made by scanning the WFC3 very quickly across the star to create a number of spectra. 

By combining these observations and processing them through analytic software, the researchers were able to retrieve the spectrum of 55 Cancri e embedded in the light of its parent star.

“This result gives a first insight into the atmosphere of a super-Earth. We now have clues as to what the planet is currently like and how it might have formed and evolved, and this has important implications for 55 Cancri e and other super-Earths,” said Giovanna Tinetti, also from UCL, UK.

Intriguingly, the data also contain hints of the presence of hydrogen cyanide, a marker for carbon-rich atmospheres.

“Such an amount of hydrogen cyanide would indicate an atmosphere with a very high ratio of carbon to oxygen,” said Olivia Venot, KU Leuven, who developed an atmospheric chemical model of 55 Cancri e that supported the analysis of the observations.

“If the presence of hydrogen cyanide and other molecules is confirmed in a few years time by the next generation of infrared telescopes, it would support the theory that this planet is indeed carbon rich and a very exotic place,” concludes Jonathan Tennyson, UCL. “Although hydrogen cyanide, or prussic acid, is highly poisonous, so it is perhaps not a planet I would like to live on!”

Notes

[1] 55 Cancri e has previously been dubbed the “diamond planet” because models based on its mass and radius have led to the idea that its interior is carbon-rich.

 

[2] Hubble observed the super-Earths GJ1214b and HD97658b in 2014, using the transit method. The observations did not show any spectral features, indicating an atmosphere covered by thick clouds made of molecular species much heavier than hydrogen.

More Information

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

The results were summarized by Tsiaras et al. in the paper “Detection of an atmosphere around the super-Earth 55 Cancri e” which is going to be published in the Astrophysical Journal.

The team of astronomers in this study consists of A. Tsiaras (UCL, UK), M. Rocchetto (UCL, UK), I. P. Waldmann (UCL, UK), O. Venot (Katholieke Universiteit Leuven, Belgium), R. Varley (UCL, UK), G. Morello (UCL, UK), G. Tinetti (UCL, UK), E. J. Barton (UCL, UK), S. N. Yurchenko (UCL, UK), J. Tennyson (UCL, UK).

University College London was founded in 1826. It was 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. UCL is among the world’s top universities, as reflected by performance in a range of international rankings and tables. UCL currently has over 35 000 students from 150 countries and over 11 000 staff.

Links

• Images of Hubble
• Link to science paper
• Release on the Europlanet Media Centre website

Contacts

Angelos Tsiaras
UCL
United Kingdom
Tel: +44 (0)20 3549 5844
Email: atsiaras@star.ucl.ac.uk

Giovanna Tinetti
UCL
United Kingdom
Tel: +44 (0) 7912509617
Email: g.tinetti@ucl.ac.uk

Olivia Venot
KU Leuven
Belgium
Email: olivia.venot@ster.kuleuven.be

Mathias Jäger
ESA/Hubble, Public Information Officer
Garching, Germany
Tel: +49 176 62397500
Email: mjaeger@partner.eso.org

Source: ESA/Hubble - Space Telescope/News

Ground-Based Detection of Super-Earth Transit Paves Way to Remote Sensing of Small Exoplanets

This artist's conception shows the super-Earth 55 Cancri e (right) compared to the Earth (left). Astronomers using a ground-based telescope have measure the transit of 55 Cancri e for the first time. It is the shallowest transit ever detected from the ground. Credit: NASA/JPL. High Resolution (jpg)  -  Low Resolution (jpg)

Astronomers have measured the passing of a super-Earth in front of a bright, nearby Sun-like star using a ground-based telescope for the first time. The transit of the exoplanet 55 Cancri e is the shallowest detected from the ground yet. Since detecting a transit is the first step in analyzing a planet's atmosphere, this success bodes well for characterizing the many small planets that upcoming space missions are expected to discover in the next few years.

The international research team used the 2.5-meter Nordic Optical Telescope on the island of La Palma, Spain, a moderate-sized facility by today's standards but equipped with state-of-the-art instruments, to make the detection. Previous observations of this planet transit had to rely on space-borne telescopes.

The host star, 55 Cancri, is located just 40 light-years away from us and is visible to the naked eye. During its transit, the planet crosses 55 Cancri and blocks a tiny fraction of the starlight, dimming the star by 1/2000th (or 0.05%) for almost two hours. This shows that the planet is about twice the size of Earth, or 16,000 miles in diameter.

"Our observations show that we can detect the transits of small planets around Sun-like stars using ground-based telescopes," says Ernst de Mooij of Queen's University Belfast in the United Kingdom, lead author of the study.

He continues, "This is especially important because upcoming space missions such as TESS and PLATO should find many small planets around bright stars and we will want to follow up the discoveries with ground-based instruments."

TESS is a NASA mission scheduled for launch in 2017, while PLATO is to be launched in 2024 by the European Space Agency; both will search for transiting terrestrial planets around nearby bright stars.

"With this result we are also closing in on the detection of the atmospheres of small planets with ground-based telescopes," says co-author Mercedes Lopez-Morales of the Harvard-Smithsonian Center for Astrophysics (CfA). "We are slowly paving the way toward the detection of bio-signatures in Earth-like planets around nearby stars."

"It's remarkable what we can do by pushing the limits of existing telescopes and instruments, despite the complications posed by the Earth's own turbulent atmosphere," says study co-author Ray Jayawardhana of York Univerity in Canada. "Remote sensing across tens of light-years isn't easy, but it can be done with the right technique and a bit of ingenuity."

The planet 55 Cancri e is about twice as big and eight times as massive as Earth. With a period of 18 hours, it is the innermost of five planets in the system. Because of its proximity to the host star, the planet's dayside temperature reaches over 3100° Fahrenheit (1700° Celsius), hot enough to melt metal, with conditions far from hospitable to life. Initially identified a decade ago through radial velocity measurements, it was later confirmed through transit observations with the MOST and Spitzer space telescopes.

Until now, the transits of only one other super-Earth, GJ 1214b circling a red dwarf, had been observed with ground-based telescopes. The Earth's roiling air makes such observations extremely difficult. But the team's success with 55 Cancri e raises the prospects of characterizing dozens of super-Earths likely to be revealed by upcoming surveys.

"We expect these surveys to find so many nearby, terrestrial worlds that space telescopes simply won't be able to follow up on all of them. Future ground-based instrumentation will be key, and this study shows it can be done," adds Lopez-Morales.

The research team also includes Raine Karjalainen and Marie Hrudkova of the Isaac Newton Group of Telescopes. Their findings appear in a paper to be published in The Astrophysical Journal Letters.

Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.

For more information, contact:

David A. Aguilar 
Director of Public Affairs 
Harvard-Smithsonian Center for Astrophysics 
617-495-7462 
daguilar@cfa.harvard.edu

Christine Pulliam 
Public Affairs Specialist 
Harvard-Smithsonian Center for Astrophysics 
617-495-7463 
cpulliam@cfa.harvard.edu

Source: Harvard-Smithsonian Center for Astrophysics