More than 1,000 exoplanets have been spotted by scientists using the Kepler telescope. And, finding them is a chore. Scientists keep a close eye on nearby stars for planets to cross in front of them. This is also known as a transit. By monitoring the tiny changes in a star’s brightness, we can figure out how big an exoplanet and how far it orbits away from its sun. But, what about a super-Earth’s atmosphere? Those details have eluded astronomers, until now.
Their target was 55 Cancri e. An exoplanet with a mass of eight Earth-masses. This exoplanet is part of a class dubbed ‘super-Earths.’ They are big, but not as big as the gas giants in our solar system.
55 Cancri e is part of a planetary system located about 40 light-years away. The super-Earth orbits incredibly close to its parent star, 55 Cancri. A year on 55 Cancri e lasts just 18 hours. You can see where this is going. This super-Earth’ is hot. Temperatures on the surface are believed to be around 2,000 degrees Celsius.
What does that mean for its atmosphere? Water vapour is a no go. But, astronomers did find hydrogen and helium.
“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,” says Angelos Tsiaras, a PhD student at UCL. Tsiaras developed the new analysis technique along with Ingo Waldmann and Marco Rocchetto.
Tsiaras added, “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.”
How 55 Cancri e made the discovery possible
This super-Earth played a part in making the atmosphere analysis possible. 55 Cancri e’s short orbit time meant astronomers could use the Wide Field Camera 3 (WFC 3) on board the Hubble to gather a bunch of observations.
Wide Field Camera 3 inside its enclosure. Credit: NASA
These observations were used to create several spectra. Toss these observations through analytic software, and boom, researchers could see the spectrum of 55 Cancri e.
The spectrum revealed hints of something else besides hydrogen and helium. Hydrogen cyanide. Olivia Venot explains what this means. “Such an amount of hydrogen cyanide would indicate an atmosphere with a very high ratio of carbon to oxygen.”
The next era of telescopes, including the James Webb Space Telescope, should be able to confirm the presence of hydrogen cyanide. That would mean the planet “is indeed carbon rich and a very exotic place,” says Jonathan Tennyson.
Let’s recap. 55 Cancri e orbits its star every 18 hours with temperatures reaching a scorching 2,000 degrees Celsius on the surface. There’s no water vapour, but hydrogen and helium were detected. And there are hints of hydrogen cyanide in its atmosphere. The 2,000 degrees Celsius pretty much means 55 Cancri e is a no go for a colony. Oh, and hydrogen cyanide is extremely poisonous. Definitely a no go.
Can the Hubble study more super-Earths?
Maybe. 55 Cancri e wasn’t Hubble’s first target. In 2014, it studied GJ1214b and HD07658b but couldn’t find any spectral features. Why? It could be because their atmosphere is covered in thick clouds by molecules heavier than hydrogen.
Future infrared telescopes will tell us much more about the planets far outside our solar system. Hopefully, conditions are a bit more friendly to life than 55 Cancri e.