Free Astronomy Magazine May-June 2022

13 MAY-JUNE 2022 ASTRO PUBLISHING Spectroscopic Observations (ESPRESSO). It was during these more recent VLT observations that astronomers spotted the first hints of a signal corresponding to an ob- ject with a five-day orbit. As the sig- nal was so weak, the team had to conduct follow-up observations with ESPRESSO to confirm that it was due to a planet, and not simply a result of changes in the star itself. “After obtaining new observations, we were able to confirm this signal as a new planet candidate,” Faria says. “I was excited by the challenge of detecting such a small signal and, by doing so, discovering an exo- planet so close to Earth.” At just a quarter of the mass of Earth, Proxima d is the lightest exo- planet ever measured using the ra- dial velocity technique, surpassing a planet recently discovered in the L 98-59 planetary system. The tech- nique works by picking up tiny wobbles in the motion of a star cre- ated by an orbiting planet’s gravita- tional pull. The effect of Proxima d’s gravity is so small that it only causes Proxima Centauri to move back and forth at around 40 centimetres per second (1.44 kilometres per hour). “This achievement is extremely im- portant,” says Pedro Figueira, ESPRESSO instrument scientist at ESO in Chile. “It shows that the ra- dial velocity technique has the po- tential to unveil a population of light planets, like our own, that are expected to be the most abundant in our galaxy and that can poten- tially host life as we know it.” “This result clearly shows what ESPRESSO is capable of and makes me wonder about what it will be able to find in the future,” Faria adds. ESPRESSO’s search for other worlds will be complemented by ESO’s Extremely Large Telescope (ELT), currently under construction in the Atacama Desert, which will be crucial to discovering and study- ing many more planets around nearby stars. !