An exoplanet supposedly orbiting a star in the constellation Eridanus is associated with the fictional homeland of Vulcan. “Star wars”, in the spectrum of the star – the spectral spectrum – it can only be a fiction. Analysis of data on the discovery of several exoplanets throughout the galaxy showed that many of the detections were in fact false: merely fluctuations in the light emitted by the star, rather than interaction with an orbiting exoplanet.

Hopes for planet Vulcan have thus been dashed – at least for now – but it’s a conclusion that needs to be made for more reliable exoplanets in the future. The discovery of an exoplanet was announced in 2018: a world named 40 Eridani b orbiting the star 40 Eridani A, a rocky super-Earth that orbits the star approximately every 42 Earth days.

This was discovered based on a property known as radial velocity, which is caused by fluctuations in the wavelength of light from the star. A star with planets around it is not affected by the gravitational effects of planetary orbits. Objects do not rotate around each other, they both revolve around a common center of gravity. This means that the star wobbles slightly in place as the exoplanet moves around; detectable in light.

Any light emitted by a star or part of a star moving toward us is slightly compressed and shifted to the blue end of the spectrum. Light emitted from something moving away from us gets slightly longer and shifts red.

When caused by an exoplanet, it can be detected as the entire star spectrum moves back and forth slightly on normal time scales.

But extracting an exoplanet from this apparent oscillation isn’t always easy. If there is any activity on the surface of the star – bright spots or starspots – these will also cause fluctuations in the spectrum with a periodicity that matches the rotation of the star as it enters and exits the field of view.

The orbital period of the suspected exoplanet was very close to the predicted rotation period of the star, ranging from 37 to 43 days. At the time, the researchers said what they interpreted as an exoplanet signal could be a spin signal, but they were unable to get the star’s full spin period.