The search for Earthlike worlds

In July 2022, just six days after NASA declared that the James Webb Space Telescope was ready for full science operations, the observatory aimed its gold-plated mirrors at a star named TRAPPIST-1.

Located 40 light-years away from Earth, TRAPPIST-1 has seven known planets. At least three are in the star’s habitable zone, the not-too-hot, not-too-cold region where liquid water can exist on a body’s surface. This makes them prime targets in the search for Earthlike worlds.

TRAPPIST-1 is a red dwarf, a type of star that is small, dim, and cool (by stellar standards). Roughly three-fourths of the stars in the Milky Way are red dwarfs. If TRAPPIST-1 swapped places with our Sun, its habitable zone would fit entirely within the orbit of Mercury. Although planets there would be at the right temperature for liquid water, they could also be bathed in radiation harmful to life as we know it.

“The missing piece is whether the habitable zone of a red dwarf is truly habitable because it’s so close to the star,” said Jessie Christiansen, a research scientist at the NASA Exoplanet Science Institute.

That’s where JWST comes in. The space telescope can scan the atmospheres of certain exoplanets as they transit in front of their stars, looking for chemical compounds linked to the presence of life.

JWST could not initially determine whether TRAPPIST-1b, the planet closest to the star, has an atmosphere. Scientists saw intense magnetic activity and solar flares during their observations, which contaminated their data and raised questions on whether life could survive on any worlds near the star.

TRAPPIST-1c sits near the inner edge of the habitable zone and has been theorized to be Venuslike. But JWST observations found little evidence for a thick carbon dioxide atmosphere, leading scientists to hypothesize that the planet formed with very little water. Results are still pending for TRAPPIST-1d, e, and f, the three planets inside the habitable zone, said Christiansen.

“So as of yet, JWST has not unlocked this mystery of whether rocky exoplanets around red dwarf stars can have atmospheres,” she said. “I expect this year we will come one step closer to that answer.”

JWST is just one instrument in a broad toolkit scientists use to search for and characterize Earthlike exoplanets. New, powerful ground-based observatories are set to come online soon while the scientific community eyes the development of the Habitable Worlds Observatory, a “super Hubble” designed to directly image dozens of Earthlike worlds in their stars’ habitable zones.