The Hubble Space Telescope might be getting on in years, but it's still making important observations. Astronomers have turned the iconic space telescope toward one of our nearest neighbors, a star system called LTT 1445 that's home to the nearest transiting exoplanet. Hubble has confirmed previous findings that this is a small, rocky world. More than that, Hubble determined that it's almost exactly the size of Earth and is just 22 light-years away. Don't pack your bags yet, though.
The exoplanet, cataloged as LTT 1445Ac, was first detected by NASA's Transiting Exoplanet Survey Satellite (TESS) in 2022. TESS is not designed to zero in on specific star systems—it observes large parts of the sky in search of stars that decrease in brightness at regular intervals, which can indicate an exoplanet is transiting in front of them. It spotted a potential rocky exoplanet around one of three red dwarf stars in LTT 1445, but the detection was unclear.
The TESS data looked Earth-like, but there was a chance it could be a so-called "grazing transit," where the exoplanet's orbit just barely clips the edge of the star from our perspective. This can produce an inaccurate lower limit for its size. TESS lacks the optical resolution to confirm one way or the other, so astronomers led by Emily Pass of the Harvard-Smithsonian Center for Astrophysics turned to Hubble for the new study.
Hubble confirms that LTT 1445Ac transits normally across the star and has a radius of 1.07 Earth diameters. That means we're looking at a rocky planet similar in size to Earth. A separate measurement of radial velocity in the system by the European Southern Observatory’s Very Large Telescope showed the world to have a mass 1.37 times that of Earth. The team used this value to calculate the density of LTT 1445Ac at 5.9 grams per cubic centimeter, just above Earth's density of 5.51 grams per cubic centimeter.
So, LTT 1445Ac is almost exactly the same size as Earth with one-third more gravity. That wouldn't be pleasant for humans, but it doesn't rule out life. The temperature is a bigger issue. While the stars in LTT 1445 are smaller and cooler than the sun, the Earth-like world orbits a mere 2.47 million miles from the star. That's about 2.6% of Earth's orbital distance. Astronomers have estimated the exoplanet's surface temperature at a scorching 500 degrees Fahrenheit (around 260 degrees Celsius). That means no liquid water and, therefore, no life as we know it.
So, it might not be a good vacation spot, but it's a compelling subject of study. It's close in astronomical terms, and the frequent transits (every 3.12 Earth days) make it feasible to analyze its potential atmosphere with instruments like the James Webb Space Telescope.
