An element spotted in an exoplanet is the heaviest element yet to be identified in a world beyond our solar system. Elements like this are expected to be both relatively rare and difficult to spot, but finding them is key to understanding how planets form and evolve over time.
at the National Astronomical Observatories of China and his colleagues found this heavy element, samarium, in a planet called MASCARA-4b, which is about 557 light years from Earth.聽MASCARA-4b is an ultra-hot Jupiter, which is to say that the planet鈥檚 outer layers are gaseous and it has surface temperatures of up to 2000掳C on account of orbiting incredibly close to its star.
The researchers observed MASCARA-4b using the Very Large Telescope in Chile, analysing a spectrum of starlight filtering through the top of the planet鈥檚 atmosphere. They found a variety of heavy elements. One of them was barium, which was previously the heaviest element ever spotted in an exoplanet atmosphere with an atomic number of 56. Another was the heavier element, samarium, whose atom contains six more protons than barium and has an atomic number of 62.
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鈥淓very star and planet should contain these elements from birth. The question is why they are so abundant to be detected,鈥� says Wang. 鈥淕iven their large atomic number, they should usually reside in high-pressure low-altitude regions and not be easy to detect.鈥�
The fact that the researchers were able to detect samarium on MASCARA-4b means that the element hasn鈥檛 sunk to the bottom of the atmosphere, as we might expect. The discovery also suggests that ultra-hot Jupiters might have fewer lighter elements in their atmospheres compared with other exoplanets. Because samarium tends to react with water vapour and oxygen, its presence on MASCARA-4b indicates that the planet has very little of those two substances.
Finding heavy elements like this is getting easier thanks to improved instrumentation, and continuing to hunt for more will elucidate the compositions of these strange worlds, a crucial clue in determining how they form. 鈥淐omparisons with those of their host stars and other planets will help us better understand the formation and evolution of planets and their atmospheres,鈥� says Wang.
arXiv
