Awaiting its official commissioning in a few weeks, the James Webb Telescope will try its hand at exoplanetary science with the observation of two strange rocky worlds in unprecedented detail. These two super-Earths are located about fifty light years from our planet.
Rocky planets are notoriously more difficult to observe than gas giants with our current technical means. This is mainly due to the relative luminosity of these small worlds bathed in that of their star. However, the mighty mirror of the James Webb Telescope and its location in deep space should allow astronomers to see things a little more clearly.
Soon, the observatory will will concentrate on two planets slightly larger than Earth, called “super-Earths”. They are called 55 Cancers and et LHS 3844 b.
None of these worlds are habitable for life as we know it. However, studying them could still be a testing ground for future in-depth studies of planets comparable to our own.
55 Cancer: An Infernal Planet
55 Cancri e orbits its parent star just 2.4 million kilometers (about 4% of the relative distance between Mercury and the Sun) and goes around it every six p.m. Such closeness is obviously not without consequences. The planet is indeed locked by the tides. In other words, like the Moon with the Earth, it shows only one side to its star. On the day side, the temperature is around 2 500 °Cwhile on the night side it is approx. 1100°C.
However, some observations made with the Spitzer telescope (the former infrared specialist) suggest that some of the daytime heat moves to the night side. This could be due to the presence of a thick atmosphere capable of moving heat around the planet.
Two teams will be in charge of studying this infernal planet. One, led by Renyu Hu of NASA’s Jet Propulsion Laboratory, will examine the planet’s thermal emission for signs of an atmosphere. A second team led by Alexis Brandeker from Stockholm University will measure the emittance heat on the illuminated side.
LHS 3844 b : un hot world without atmosphere
LHS 3844 b is also very close to its star, completing one revolution every eleven hours. The star is however smaller and cooler than that of 55 Cancri e. It’s around 770°C on the day side, but that heat doesn’t seem to disperse to the night side. It would thus seem that this planet does not have a substantial atmosphere.
For its study, a team led by astronomer Laura Kreidberg, from the Max Planck Institute for Astronomy, will use the spectroscopy (study of the spectra of electromagnetic radiation emitted or absorbed by a substance). Thermal emission spectra from the daylight side of the planet will be compared to known rocks like basalt and granite to see if they can deduce a surface composition.
These two surveys will thus give us new insights into rocky planets in general, helping us to understand what the early Earth looked like.