Recent research suggests that a rocky, Earth-size planet located in our Milky Way galaxy may possess an atmosphere, opening up the exciting possibility of liquid water on its surface and the potential to support life. This breakthrough is based on two separate studies published in the Astrophysical Journal Letters that focus on the TRAPPIST-1 system, which is home to seven rocky planets orbiting a single star.
Both studies detail initial findings from observations made by NASA’s James Webb Space Telescope, indicating that one specific planet, known as TRAPPIST-1e, may have an atmosphere rich in nitrogen, similar to Earth's. However, further studies are required to confirm these findings. These results mark a significant advancement in the ongoing quest for extraterrestrial life within our solar system and beyond.
In conjunction with these findings, NASA recently announced that a rock sample collected on Mars may hold evidence of ancient microbial life. Present-day Mars has a thin atmosphere primarily composed of carbon dioxide, nitrogen, and argon. Yet, scientists believe that billions of years ago, Mars had a thicker atmosphere that allowed liquid water to flow on its surface. The presence of liquid water is widely regarded as a crucial ingredient for life, emphasizing the importance of studying planetary atmospheres.
To maintain liquid water, a planet or moon must have an atmosphere to prevent water from evaporating into space. This necessity makes the search for exoplanet atmospheres one of the most compelling areas of research in astronomy. “Ultimately, we want to find a planet where we can identify a molecule that can only be produced by life,” explained Ryan MacDonald, an exoplanet astronomer at the University of St Andrews in Scotland and a co-author of both studies. “But first, we need to identify planets that possess atmospheres.”
The TRAPPIST-1 system, located approximately 40 light-years away from Earth, has garnered significant attention since its discovery in 2016 due to its potential to host planets with conditions suitable for extraterrestrial life. Each light-year is roughly 6 trillion miles, making this a relatively close system in astronomical terms. TRAPPIST-1e, in particular, is situated in the theoretical “habitable zone,” where temperatures may be just right for liquid water to exist on its surface.
For the new studies, astronomers utilized the James Webb Space Telescope to observe four transits of TRAPPIST-1e, moments when the planet passed in front of its star. The telescope did not directly detect an atmosphere surrounding TRAPPIST-1e but instead measured how the exoplanet absorbed light, providing insight into what, if anything, envelops the planet. By analyzing light similar to a prism, researchers can discern which colors are absorbed, indicating the presence of specific atoms or molecules of gas.
During the four transits observed, the researchers did not find evidence of a hydrogen-rich atmosphere or significant concentrations of carbon dioxide. However, the observations suggest that TRAPPIST-1e may have an atmosphere abundant in nitrogen, which is an exciting indication of potential habitability. “This is an exciting step and helps us narrow down the possibilities of an atmosphere that is perhaps more Earth-like,” stated Caroline Piaulet-Ghorayeb, a postdoctoral fellow at the University of Chicago who was not involved in the studies.
Earth’s atmosphere contains high concentrations of nitrogen gas, and similar conditions are found on Titan, one of Saturn’s moons, which also has a nitrogen-rich atmosphere and is believed to harbor a vast underground ocean. However, the methane-filled environment on Titan would mean that any life forms there would differ significantly from those on Earth.
Investigating these celestial bodies presents numerous challenges. The TRAPPIST-1 star is small yet extremely active, creating substantial background noise that researchers must analyze. Ryan MacDonald and his colleagues spent over a year dissecting data from the James Webb Telescope to distinguish the chemical signatures of TRAPPIST-1e from its star. To confirm the presence of an atmosphere, they plan to study TRAPPIST-1e during 15 additional transits in the coming years.
Further studies are anticipated for three other planets in the TRAPPIST-1 system—TRAPPIST-1f, TRAPPIST-1g, and TRAPPIST-1h. This ongoing research will bring scientists closer to answering some of the most profound questions about exoplanets and the possibility of life beyond Earth. “We haven’t yet convincingly found an atmosphere on any rocky planet outside of the solar system, which makes searching for atmospheres on temperate planets extremely exciting,” Piaulet-Ghorayeb remarked. “But there’s a lot of work to do.”
