At this point, we have discovered a number of exoplanets that fall under the general label of ‘Earth-like’. They are rocky and many orbit far from their host stars, which can result in moderate temperatures. But “Like” has a lot of work there. In many cases, we don’t even know if the Earth has an atmosphere. The greenhouse effect means that the atmosphere can have a large impact on the temperature of the earth. Thus, the Earth-like category includes dry, scorching hellscapes with massive atmospheres like Venus, and dry, frozen tundras with tenuous atmospheres like Mars.
However, the opportunity to image the atmospheres of rocky exoplanets is increasingly available. And today, researchers are releasing results that point the Webb Space Telescope at a rocky planet orbiting a nearby star, and the new hardware is so sensitive that it can detect stars blocking light from the planet. It shows that it can be detected. This result suggests that the planet has little atmosphere and radiates most of the heat burned by nearby stars.
Ultracold dwarfs and their seven planets
TRAPPIST-1 is a small, reddish star about 40 light-years from Earth, an “ultracold dwarf” in astronomical parlance. Although the star itself is fairly unremarkable, it is notable for its many planets, seven in total have been identified so far. A celestial body that looks like a small rock. Stars give off little light, but the planets are all packed closer together than Mercury is to the Sun.
This leaves many stars in what is known as the habitable zone. The habitable zone is the region where the heat emitted by the star allows liquid water to exist on the surface of the planet. But it also depends on the properties of the planet’s atmosphere. There is also reason to think that planets very close to dwarf stars may have no atmosphere. During the first billion years or so of dwarf existence, they are prone to violent explosions that can burn up atmospheres unprotected by strong magnetic fields.
It’s still possible that geological processes create secondary atmospheres after the star settles.
TRAPPIST-1 therefore provides an excellent opportunity (seven opportunities, in fact) to test some of our ideas about exoplanet atmospheres. Both the Hubble Space Telescope and the Spitzer Space Telescope also imaged starlight passing near several planets as they passed between Earth and TRAPPIST-1. These observations set limits on the thickness of the gas above these planets and provided no indication of the atmosphere.
However, these measurements have many uncertainties. Also, with its huge mirror and advanced imaging hardware, the Webb Telescope will provide new opportunities to see some of the TRAPPIST planets again.
