A Landmark Discovery 41 Light-Years Away
Astronomers have announced the best evidence to date for an atmosphere on a rocky planet outside our solar system. The planet in question is 55 Cancri e, a super-Earth located 41 light-years away in the constellation of Cancer. Using the powerful infrared
capabilities of the JWST, researchers detected atmospheric gases that are likely rich in carbon dioxide or carbon monoxide. This finding is a huge step forward, as previous observations were unable to determine if the planet was a bare rock or if it held a gaseous envelope.
Meet the 'Hell Planet' Super-Earth
To call 55 Cancri e 'rocky' might paint the wrong picture. With a diameter nearly twice that of Earth and a mass about eight times greater, it orbits its sun-like star at a staggering proximity—completing a full year in just 18 hours. This close orbit means the planet is likely tidally locked, with one side perpetually facing its star. The result is a world with a surface so hot, estimated at around 1,540 degrees Celsius, that it is believed to be covered in a bubbling ocean of magma. Finding an atmosphere here is surprising, as the intense heat and radiation were expected to have stripped any gas away long ago.
How Webb Sensed the Atmosphere
The JWST cannot take a direct picture of 55 Cancri e. Instead, it uses a technique called secondary eclipse spectroscopy. As the planet moves behind its star, the telescope measures the total light from the system (star plus planet). When the planet is hidden, it measures the light from the star alone. By subtracting the second measurement from the first, scientists can isolate the infrared light coming just from the planet's dayside. This light contains the chemical fingerprints of any gases present. The data showed the planet was cooler than a bare rock world would be, suggesting a thick atmosphere is distributing heat.
An Atmosphere From a Magma Ocean
The detected atmosphere is not a primordial one that has been there since the planet’s formation. Such an atmosphere would have been blown away by the star's intense radiation. Instead, scientists believe this is a 'secondary' atmosphere, which is being continuously replenished. The theory is that the gases, including carbon dioxide and carbon monoxide, are bubbling up and being released from the vast magma ocean on the planet's surface. This process of outgassing from molten rock could be what sustains the atmosphere despite the harsh conditions.
Why This Discovery Matters
While 55 Cancri e is far too hot to be habitable, this discovery is a monumental proof of concept. It demonstrates that the JWST has the capability to detect and analyse the atmospheres of rocky planets, a key goal in the search for life elsewhere. Understanding how a planet so close to its star can maintain an atmosphere provides crucial insights into planetary evolution. Studying this magma ocean world may even offer a window into the early history of planets like Earth, Venus, and Mars, which are also thought to have gone through magma ocean stages in their distant past.
