Free Astronomy Magazine July-August 2020

12 JULY-AUGUST 2020 EXOPLANETS presence of that can- didate. Meanwhile, the few observations carried out thus far with the new spectrograph have made it possible to exclude the pres- ence of additional planets with masses greater than 0.6 Earth masses and periods of revolution fewer than 50 days. If other plan- ets exist in very nar- row orbits, they are small enough to rep- resent a challenge for ESPRESSO as well. This challenge seems to have already been taken up by this excel- lent instrument, as the Suarez Mascareño’s team has found faint traces of a second sig- nal in the variations of the radial velocity of the red dwarf with a period of 5.15 days that could be produced by a planet with a minimum mass equal to 30% that of Earth’s. If this third potential planet is confirmed, we will have identified the smallest planet ever measured by the radial velocity method. a star with an accuracy of about 1 m/s, ESPRESSO reaches an accuracy of 30 cm/s and it is expected that the next upgrades will push it up to the astonishing accuracy of 10 cm/s. What HARPS showed barely be- fore is now clearly observed with ESPRESSO. The Suarez Mascareño’s team was able to quickly confirm the period of revolution and the mass of Proxima b, but the researchers went even further. Combining all the obser- vations available to them (63 by ESPRESSO + 274 by HARPS and UVES) that were regis- tered in a span of 15 years, the team was able to get a more precise value for the min- imum mass of Proxima b: 1.173 ± 0.086 Earth masses. Having entered full operation just over two years ago, ESPRESSO has not yet been able to provide useful indications of the exis- tence of Proxima c, as the two-year observa- tion period is too short compared to the calculated revolution of the hypothetical planet. ESPRESSO will have to observe the Proxima Centauri system for at least another three years before being able to confirm the C omposite image of the region around Proxima Centauri, taken by the SPHERE instru- ment in five peri- ods between April 2018 and April 2020. The yellow circles in- dicate the best candidates of the planet Proxima c at the respective observation peri- ods. In this case, the identification of the planet also remains uncer- tain. [R. Gratton et al.] A lejandro Suarez Mas- careño, the team leader who, using the ESPRESSO spectrograph, has definitively con- firmed the exis- tence of Proxima b and detected traces of another candidate planet, smaller and in a closer orbit than Proxima c.