[Reading Science] First Direct Observation of Earth-like Exoplanet Achieved

Web Telescope Directly Captures Faint Light from Trappist-1 b Planet 40 Light-Years from Earth Using MIRI
Previously, Small Exoplanets Could Only Be Observed Indirectly
Temperature Measured to Determine Presence of Atmosphere

The James Webb Space Telescope (JWST) has, for the first time ever, directly captured the faint light of a small exoplanet located far from Earth, measured its temperature, and confirmed that it has little to no atmosphere.

Virtual image of the TRAPPIST-1 star system. Photo by NASA

The NASA Ames Research Center announced these research results on the 28th (local time) in the international scientific journal Nature. The center reported that it successfully imaged the first planet of the TRAPPIST-1 star system, TRAPPIST-1 b, located about 40 light-years from Earth, using the Mid-Infrared Instrument (MIRI).

This marks the first time humanity has directly observed a small rocky planet outside the solar system, similar in size to Earth. Until now, humans have been unable to directly observe small exoplanets located far beyond the solar system. Stars like the Sun emit their own light, making distant direct observation possible. However, planets orbiting stars, like Earth, do not emit light themselves and are only dark. Observations had to rely on indirect methods such as shadows caused by the planet orbiting the star to infer density, size, and atmospheric components. Occasionally, supergiant planets like Jupiter have been partially observed due to their large size.

In particular, the TRAPPIST-1 b planet observed this time is very close to its host star. The distance between the host star and this planet is only about 1/40th of the distance between the Sun and Mercury. Compared to the Earth-Sun distance, it is about 1/100th, making it extremely close. In general, planets close to the central star of a star system are obscured by the star's light and heat, making distant observation impossible.

However, in this case, the central star of the star system is a low-temperature red dwarf, and the high-sensitivity observation capability of the MIRI instrument equipped on JWST worked together to achieve the first 'direct observation.' NASA explained, "For the first time, we observed all the light emitted from a cold, small exoplanet similar to the rocky planets in our solar system," adding, "This provides a significant clue to determine whether planets orbiting small active stars like TRAPPIST-1 can maintain an atmosphere necessary for sustaining life."

Kang Sung-joo, a curator at the Gwacheon National Science Museum, said, "This observation was considered almost impossible until now, but it succeeded because of JWST's MIRI," and explained, "It is a meaningful discovery as humanity has directly observed an Earth-like small rocky planet for the first time."

Schematic diagram of temperature measurement on Trappist-1 b planet. Photo by NASA website

The research center also succeeded in measuring the temperature of TRAPPIST-1 b and determining the presence of an atmosphere based on the observation results. The atmospheric temperature of this planet was found to be about 500K (450 degrees Fahrenheit, 232.2 degrees Celsius). This is similar to the temperature the research team had predicted if the planet had little to no atmosphere. In other words, it is estimated that TRAPPIST-1 b either lacks an atmosphere or has a very thin one. Curator Kang explained, "If there is an atmosphere, circulation occurs, keeping the planet's temperature relatively low, but if there is no atmosphere, the temperature is observed to be very high due to direct sunlight," adding, "The measured temperature level from this observation closely matched the predicted value assuming no atmosphere, leading to the conclusion that TRAPPIST-1 b likely does not have an atmosphere."

The TRAPPIST-1 star system was first observed in early 2017. Seven rocky planets orbit the red dwarf star, attracting attention for its similarity to the solar system. Especially, TRAPPIST-1 b, the closest planet to the TRAPPIST-1 star, although too close to be in the so-called Goldilocks zone (habitable zone), is a rocky planet similar in size to Earth and has been one of the main targets for scientists searching for the possibility of life.

Scientists evaluate that the successful direct observation of an exoplanet outside Earth once again demonstrates the remarkable capabilities of JWST. Although TRAPPIST-1 is a red dwarf star, TRAPPIST-1 b receives four times more light than Earth does from the Sun due to its proximity. Nevertheless, MIRI equipped on JWST accurately captured the faint mid-infrared light reflected from the planet and even measured its temperature. The Hubble Space Telescope and the retired Spitzer Space Telescope had previously observed the TRAPPIST-1 star system but had never confirmed the presence or absence of an atmosphere.