Hubble Space Telescope sees a ‘terrestrial’ planet, similar to Earth but ‘super-hot’

It is rocky, has measurements close to ours but the temperature of its surface is 260 degrees Celsius: there cannot be life as we know it

Framed by Hubble Space Telescope an exoplanet – a planet outside our solar system – with dimension similar to Earth. The space telescope of NASA And Hex measured the size of the closest exoplanet of the size of the Earth transiting in front of the surface of a nearby star. ESA explains that this alignment, called a transit, opens the door to subsequent studies to see what kind of atmosphere, if any, the ‘rocky world’ observed by Hubble might have.

The tiny planet, LTT 1445Ac, was discovered for the first time by NASA’s Transiting Exoplanet Survey Satellite (TESS) in 2022 but, ESA points out, the geometry of the planet’s orbital plane compared to its star, seen from Earth, was uncertain because Tess does not have the right optical resolution for these circumstances. This means that the detection could have been a so-called ‘grazing transit’ in which a planet grazes only a small portion of the disk of the parent star and such a situation would produce an imprecise lower limit of the planet’s diameter. “There was the possibility that this system had an ‘unfortunate’ geometry and, if so, we would not measure the right size. But with Hubble’s capabilities we were able to center its diameter” assures Emily Pass of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts (USA).

Hubble observations show that the planet makes a normal transit through the disk of the star, so scientists were able to obtain the actual size of only 1.07 times the diameter of Earth. For scientists, this means that the planet is a rocky world, just like Earth, and with approximately the same surface gravity. Unfortunately, scholars have also verified that the surface temperature of the exoplanet is around 260 degrees Celsius: too hot to imagine the presence of life as we know it.

ESA also reports that the planet orbits the star LTT 1445A, which is part of a triple system of three red dwarf stars located 22 light-years away in the constellation Eridanus. The star has two other reported planets that are larger than LTT 1445Ac. A pair of two other dwarf stars, LTT 1445B and C, are located about 4.8 billion kilometers from LTT 1445A, also observed by Hubble. Scientists explain that the alignment of the three stars and the cutting-off orbit of the BC pair suggest that everything in the system is coplanar, including the known planets.

“Transit planets – Emily Pass continues – are exciting because we can characterize their atmospheres with spectroscopy, not only with Hubble but also with the James Webb Space Telescope. Our measurement is important because it tells us that it is probably a very close terrestrial planet”. “We look forward to continuing observations that will allow us to better understand the diversity of planets around other stars,” the scientist further states.

“Hubble remains a key player in our characterization of exoplanets,” comments Professor Laura Kreidberg of the Max Planck Institute for Astronomy in Heidelberg, Germany, who however did not take part in this study. “There are precious few terrestrial planets that are close enough for us to know their atmospheres: at just 22 light-years away, LTT 1445Ac is right next door in galactic terms, so it’s one of the best planets in the sky to track and learn about its atmospheric properties” finally observes astronomer Laura Kreidberg.