Planet Vulcan declared a stellar illusion

Astronomers at Dartmouth College in the US have announced that a planet thought to orbit the star 40 Eridani A is actually an illusion caused by the star’s activity. This planet was nicknamed Vulcan after a planet from the Star Trek franchise that was located in the same system. Study published in The Astronomical Journal.

The discovery of planet candidate HD 26965 b was announced in 2018, but five years later scientists began to doubt whether it was real. In the new work, astronomers carried out precise measurements of the radial velocity of the star HD 26965, which characterizes the rate of change in the distance between the object and the observer and is determined based on the Doppler effect. The observations were made using the NEID spectrograph mounted on a telescope at the Kitt Peak National Observatory (Arizona, USA).

When a massive object, such as a planet, orbits a star, it causes the star itself to oscillate, which is visible through shifts in spectral lines due to the Doppler effect. However, the scientists who initially discovered HD 26965’s wobbles warned that they could be caused by activity in the star itself, rather than the planet. If the existence of “Vulcan” were confirmed, it would be a super-Earth at a distance of 16 light years from the Sun, intermediate in size between Earth and Neptune. Its period of rotation around the star was estimated at 42 Earth days.

Scientists analyzed light at different wavelengths emitted by different layers of the outer shell (photosphere) of the star HD 26965. It turned out that their Doppler shifts are very different, which can be explained by convection of the star’s mantle and the presence of dark and bright regions on the surface. Both factors can significantly distort the light signal, creating the illusion of a planet’s presence.