Super-earth has super-fast orbit
“Researchers first spotted TOI-1685 b in observations made by TESS”
We keep getting reminders that the Milky Way’s planetary diversity dwarfs what we see in our own Solar System. The newfound exoplanet TOI-1685 b is yet another case in point. Astronomers found it circling a dim red dwarf star about 122 light years from Earth. ‘Circling’ is much too ordinary a word for TOI-1685 b’s motion, however, as the alien world whips around its parent star once every 0.67 Earth days. Red dwarfs, also known as M dwarfs, are much smaller and dimmer than Earth’s Sun, but TOI-1685 b’s extreme proximity to its host star, called TOI-1685, makes it a very toasty world nonetheless. The discovery team estimates its surface temperature to be around 796 degrees Celsius. Researchers first spotted TOI-1685 b in observations made by NASA’S Transiting Exoplanet Survey Satellite (TESS). As its name suggests, TESS looks for transits – the tiny dips in brightness caused by planets crossing their host stars’ faces from the Earth-orbiting spacecraft’s perspective. TESS noted such a dip around the red dwarf TOI-1685. A team of astronomers then confirmed the planet’s existence using data gathered by the CARMENES spectrograph instrument, which is installed on the 3.5-metre telescope at the Calar Alto Observatory in Spain. CARMENES is short for Calar Alto high-resolution search for M dwarfs with Exoearths with Near-infrared and optical Echelle Spectrographs. This instrument hunts for planets using the radial velocity, or Doppler method, looking for little wobbles in a star’s motion caused by the gravitational tug of an orbiting planet. The combined data allowed researchers to determine that TOI-1685 b is a super-earth about 1.7 times bigger and 3.8 times more massive than our home planet. The resulting bulk density, about 4.2 grams per cubic centimetre, makes TOI-1685 b the least dense ultra-short-period planet around an M dwarf discovered to date. For some perspective, Earth’s bulk density is about 5.5 grams per cubic centimetre. The fact that TOI-1685 b transits and is quite warm makes it a good candidate for follow-up studies by other instruments. In that regard, TOI-1685 b is similar to another recent exoplanet find made using TESS and CARMENES data, Gliese 486 b.