​LHS 475 b is the name for an exoplanet, meaning a planet orbiting a star other than our Sun with a diameter almost identical to that of Earth, the first exoplanet discovered by the James Webb Space Telescope. It is 41 light-years away from Earth in the constellation Octantas (visible in the sky only from the southern hemisphere).

The James Webb Space Telescope captured the light coming from the star LHS 475 and measured its intensity over a long period of time with an onboard instrument called NIRSpec (Near Infrared Spectrograph). When the planet LHS 475 b came between the star and the space telescope, the intensity of light from this star decreased, which allowed researchers to learn not only the period of rotation of the planet around the star, but also its diameter.

This method is also used by other telescopes, space or ground, to identify exoplanets. Initially, when this method began to be used, only giant planets, the size of Jupiter or even larger, were detected, because their effect on reducing the intensity of the light captured from the star in this planetary system was much more pronounced.

As telescopes became more powerful and observational techniques improved, smaller and smaller planets could be identified, such as LHS 475 b, which is 99% the diameter of Earth.

LHS 475 b, an uninhabitable planet

However, LHS 475 b is much closer to its star (LHS 475) than Earth is to the Sun, and the exoplanet’s orbital period is only 2 days. This means that the planet LHS 475 b is several hundreds of degrees larger than Earth, and researchers are not yet sure whether the planet has an atmosphere or not, because the data from James Webb is inconclusive: if the star LHS 475 were the size of the Sun, it would be impossible for a planet this close to have an atmosphere, but LHS 475 is a red dwarf, which means that its temperature is about half that of the Sun, which does not necessarily mean that LHS 475 b cannot have an atmosphere.

While exoplanets were only hypotheses a few decades ago, the first such planet orbiting a star other than the Sun was discovered in 1992. Since then, more than 5,000 exoplanets have been discovered, and several thousand more await confirmation, although their number may be several billion in our galaxy alone.

Not all are habitable: some are gas giants, others are too close or too far from the central star of their planetary system, and some orbit much friendlier stars. Most of them were discovered by the Kepler and TESS space telescopes, and the upcoming US space telescope Nancy Grace Roman (scheduled for launch in 2027) will use more methods to detect other exoplanets.

The James Webb Space Telescope is currently the only one that can probe the atmospheres of these distant planets, and data sent back last year revealed exoplanets with water vapor in their atmospheres.

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