TESS found two more rocky super-Earths only 33 light-years away. Let's point the James Webb at them and study their atmospheres.
HD 260655b is closest to the star with an orbital period of 2.7 days. Its radius is 1.2 Earth radii, and its mass is 2.14 Earth masses.
they have formed within the same protoplanetary disk,” the authors write. And since the host star is so small, only about 0.4 solar masses, the super-Earths exhibit more influence on it. This makes measuring the planets’ masses and densities easier. But decisions on which planets are suitable for atmospheric characterization by the JWST come down to specific metrics. The authors computed two values for these rocky exoplanets and compared them to their peers in NASA’s Exoplanet Archive. The values are the Transmission Spectroscopy Metric and Emission Spectroscopy Metric Both planets are in the top quartile of desirable targets for JWST spectroscopy. HD 260655 b is among the top 10 terrestrial planets for atmospheric characterization.
The team measured the wobble exhibited by the star as the orbiting planets tugged on it. Those measurements reveal the planets’ masses. By combining their masses with their sizes, the researchers found their densities. That led to the conclusion that they’re rocky planets. It also means that if the planets do have atmospheres, they’re likely not extended hydrogen atmospheres.
Another interesting fact about these planets concerns what exoplanet scientists call the small planet radius gap. It’s an “… observed scarcity of planets with radii between 1.5 and 2 times Earth’s radius,” as Wikipedia defines it. Scientists think that the gap could be due to photoevaporation. Different researchers have defined the gap differently in terms of planet radii, but both planets in the system are less than 1.5 Earth radii.
Planet b is different. Since it’s so much closer to its star, it’s unlikely to have much of an atmosphere. In both cases, if the planets have atmospheres, they’re highly unlikely to have extended hydrogen atmospheres.