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Jan 12, 2023 - Science

JWST confirms its first alien planet, and it's the size of Earth

Miriam Kramer
Artist's illustration of a planet rising with its bright, red star in the background

Artist's illustration of the planet LHS 475 b. Source: NASA/ESA/CSA/Leah Hustak (STScI)

The James Webb Space Telescope has confirmed its first planet orbiting a distant star, and it's a rocky world just about the same size as Earth.

Why it matters: Part of the scientific value of the JWST is its ability to characterize alien planets. This finding opens the door to learning more about what the atmosphere of this planet could be.

What they found: Researchers turned the JWST's powerful eye on a star system suspected to have a planet about 41 light-years away.

  • NASA's TESS spacecraft first hinted at the world's existence, but the JWST's new observations confirmed the planet — named LHS 475 b.
  • The planet orbits its star — which is smaller and cooler than the Sun — every two days, and the data suggests the world is hundreds of degrees warmer than the Earth.
  • While the planet has an incredibly close orbit, because the star is smaller and cooler, the planet could still have an atmosphere, according to NASA.

The intrigue: Figuring what — if any — atmosphere envelopes LHS 475 b is going to take a bit longer for scientists to piece together.

  • "The telescope is so sensitive that it can easily detect a range of molecules, but we can’t yet make any definitive conclusions about the planet’s atmosphere," Erin May, of the Johns Hopkins University Applied Physics Laboratory, who worked on these results, said in a statement.
  • The research team has been able to rule out a few different atmospheric compositions. They think LHS 475 b doesn't have an atmosphere that's thick and methane-rich, like Saturn's moon Titan, but it's possible the planet has an atmosphere that is entirely made of carbon dioxide.
  • The team should get more information with followup observations this summer.

How it works: The JWST found the planet by watching the change in its star's light created when the world passed in front of its star from the telescope's perspective.

  • Those dips in starlight can tell scientists about the orbit, size and other characteristics of a faraway planet.
  • Transits like these can also help scientists piece together a world's atmosphere by seeing how light scatters when it passes through that atmosphere, giving them a sense for what molecules might be present within it.
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