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HD20794 is a G6V-type star known for hosting a multi-planetary system. It is bright (V-mag = 4.27) and close (d = 6.04 pc), and the extraordinary stability of the star during tens of years of HARPS observing campaigns made it a preferential target of RV surveys. Several works on the system found different planets with different properties. We revisited the planetary system of HD 20794, taking advantage of a larger and revised dataset collected with both HARPS and ESPRESSO. We can recover signals from three super-Earths at orbital periods of 18, 89, and 647 days. The corresponding masses are all below 10 Earth masses. While the two inner planets have been claimed in previous works on the system, the outer planet corroborates a candidate proposed by Cretignier et al. 2023.
The outer planet, HD 20794 d, crosses the habitable zone of the star. Its eccentric orbit spans a range of distances from 0.75 AU to 1.96 AU, corresponding to a factor of 7 in stellar irradiation. Due to this, the blackbody temperature of the planet goes between 178K maximum and 288 K. The planet is now the best candidate for atmospheric characterization with Habitable Worlds Observatory (HWO). The separation of the outer planet from the star goes from 124 to 322 mas between periastron and apoastron, suitable for HWO. HWO is sensitive enough to investigate the planet. The potential habitability of such a planet is a matter of debate, and direct imaging can help to solve the riddle.
