Oct 26, 2021 - Science

A possible planet outside of our galaxy

A whirlpool galaxy
The Whirlpool Galaxy seen by the Hubble Space Telescope and Chandra X-ray Observatory. Photo: NASA/CXC/SAO/R. DiStefano, et al./ESA/STScI/Grendler

Scientists may have seen the first planet orbiting a star outside of our galaxy.

Why it matters: The discovery may be a proof of concept for scientists looking for alien worlds far beyond Earth and our solar system.

Details: The possible planet was seen by astronomers in the Whirlpool Galaxy, 28 million light-years away using NASA's Chandra X-ray Observatory, according to a new study in Nature Astronomy.

  • Chandra discovered the potential world by looking for dips in X-rays that would indicate a planet has passed between the telescope and the object or objects its orbiting.
  • The study suggests the planet the team found is about the size of Saturn and orbits in a binary system composed of a star that's about 20 times the mass of the Sun and a neutron star or back hole.
  • "We are trying to open up a whole new arena for finding other worlds by searching for planet candidates at X-ray wavelengths, a strategy that makes it possible to discover them in other galaxies," an author of the study Rosanne Di Stefano of the Harvard-Smithsonian Center for Astrophysics said in a statement.

The big picture: Most of the thousands of worlds outside of our solar system discovered by scientists have been spotted circling relatively nearby stars, almost all of them less than 3,000 light-years away.

  • Missions like TESS are designed to search for these planets and help scientists characterize them.
  • TESS looks for planets that pass between the telescope and its star, causing a dip in the star's light in much the same way that Chandra discovered the planet candidate in the Whirlpool Galaxy.

But, but, but: It's going to be very difficult to confirm the possible planet seen outside of our galaxy is truly there.

  • "Unfortunately to confirm that we’re seeing a planet we would likely have to wait decades to see another transit," co-author of the study Nia Imara of the University of California at Santa Cruz, said in the statement. "And because of the uncertainties about how long it takes to orbit, we wouldn't know exactly when to look."
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