English: Researchers used NASA’s James Webb Space Telescope’s Near-Infrared Spectrograph (NIRSpec) to observe exoplanet LHS 475 b during August 31, 2022, using the NIRSpec bright object time-series mode; a grating to spread out light from an object and measure the brightness of each wavelength at set intervals of time.

A transmission spectrum is made by comparing starlight as it filters through a planet’s atmosphere while it moves in front of a star to the unfiltered starlight detected when the planet and star do not coincide. Each of the 56 data points (white dots) on this graph represents the amount of light that the planet blocks from the star at a different wavelength of light, molecules in the planet’s atmosphere show by increasing the apparent size of the planet at specific wavelengths. Although additional data are required before a conclusion can be made, the data shown here is consistent with a featureless spectrum representative of a planet that has no atmosphere (The yellow line represents the best-fit model for a featureless spectrum that contains no evidence of the planet’s atmosphere). The researchers studying LHS 475 b suggest that an additional, upcoming observation may act as a “tie breaker,” allowing them to identify any presence of carbon dioxide – or any other molecule – or rule everything out and conclude the planet has no atmosphere.

The purple line represents a pure carbon dioxide atmosphere and is indistinguishable from a flat line at the current level of precision. An atmosphere made up of pure carbon dioxide is far more difficult to detect, even for Webb’s advanced instruments. “We require very, very precise data to be able to distinguish a pure carbon dioxide atmosphere from no atmosphere at all,” explained Jacob Lustig-Yaeger of the Johns Hopkins University Applied Physics Laboratory. “A pure carbon dioxide atmosphere may be thin like the one on Mars, making it difficult to detect.” The green line represents a pure methane atmosphere, which is not favored since if methane were present, it would be expected to block more starlight at 3.3 microns.The gray lines extending above and below each data point are error bars that show the uncertainty of each measurement, or the reasonable range of actual possible values. For a single observation, the error on these measurements is extremely small (30 to 50 parts per million).

LHS 475 b is a rocky exoplanet approximately that same size as Earth. It orbits a constellation Octans red dwarf star at approximately 40.7 light-years distance from Earth, extremely close to its star with a one orbital period of approximately 48 hours. The planet’s discovery was confirmed with data from the Webb Telescope.

The background illustration is based on current understanding of the planet from Webb spectroscopy only. 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.