English: How do researchers spot a distant planet? By observing the changes in light as it orbits its star.

A light curve from NASA’s James Webb Space Telescope’s Near-Infrared Spectrograph (NIRSpec) shows the change in brightness from the LHS 475 star system over time as the planet transited the star on August 31, 2022. This observation was made using NIRSpec’s bright object time-series mode, which uses a grating to spread out light from a single bright object (like the star LHS 475) and measure the brightness of each wavelength of light at set intervals of time. The data show that LHS 475 b is 99% the diameter of Earth and therefore rocky.

To capture these data, Webb stared at the LHS 475 star system for almost 3 hours, beginning about 1.5 hours before the transit and ending about 30 minutes after the transit. The transit itself lasted about 40 minutes. The curve shown here includes a total of 1,158 individual brightness measurements – about one every nine seconds.

LHS 475 b is a rocky, Earth-sized exoplanet that orbits a red dwarf star roughly 41 light-years away in the constellation Octans. The planet is extremely close to its star, completing one orbit in two Earth-days. The planet’s confirmation was made possible by Webb’s data.

The background illustration of LHS 475 b and its star is based on our current understanding of the planet from Webb spectroscopy. Webb has not captured a direct image of the planet or its atmosphere.

NIRSpec was built for the European Space Agency (ESA) by a consortium of European companies led by Airbus Defence and Space (ADS) with NASA’s Goddard Space Flight Center providing its detector and micro-shutter subsystems.