Although astronomers have now discovered more than 5,000 exoplanets, or planets outside the Solar System, most of these planets are much larger than Earth. This is partly because it is easier to see larger planets from great distances in space. So it’s exciting when an Earth-sized planet is discovered – and the Hubble Space Telescope recently confirmed that a nearby planet, small by exoplanet standards, is 1.07 times the size of Earth.
The planet LTT 1445Ac was first discovered by NASA’s Transiting Exoplanet Survey Satellite (TESS) in 2022, but its exact size was difficult to determine due to the plane of its orbit around its star as seen from Earth. “There was a possibility that this system has inhomogeneous geometry and if so, we would not be able to measure the true shape. But with Hubble’s capabilities we captured its diameter,” lead researcher Emily Paas of the Harvard-Smithsonian Center for Astrophysics said in a statement.
The new observations show that the planet is 1.07 times the diameter of Earth, so it is a rocky planet like Earth, with similar gravity on the surface. However, it is not a habitable place as its surface temperature is 260 degrees Celsius. It is part of a triple star system located only 22 light years away, making it one of the closest exoplanets to transit a star.
“Planetary transits are exciting because we can characterize their atmospheres spectroscopically, not only with Hubble but also with the James Webb Space Telescope,” Pass said. “Our measurement is important because it tells us that this is likely a very close-to-terrestrial planet. We look forward to follow-up observations that will allow us to better understand the diversity of planets around other stars.
One of the most important capabilities of the James Webb Space Telescope is the ability to study the atmospheres of exoplanets, which is the next step in understanding these planets and the search for Earth-like planets. But this research shows that the venerable Hubble telescope, now more than 30 years old, remains important for exoplanet research as well.
“Hubble remains a major player in our characterization of exoplanets,” said Laura Kreidberg of the Max Planck Institute for Astronomy, who was not involved in the research. “There are precious few terrestrial planets that are close enough for us to learn about their atmospheres – at just 22 light years away, LTT 1445ac is right next door in galactic sight, so it’s one of the best planets in the sky to follow. Can be done and learn about its atmospheric properties.
This research has been published in The Astronomical Journal.