by Mario Damasso

One of the goals of the ESPRESSO Guaranteed Time Observations (GTO) consortium is the precise characterisation of a selected sample of planetary systems discovered in transit by the space telescope TESS. One such a target is the main sequence star HIP 29442 (TOI-469), already known to host a validated sub-Neptune companion TOI-469.01. A team lead by Mario Damasso (INAF-OATo), also including Alessandro Sozzetti from our Institute, has followed-up the star with ESPRESSO to verify the planetary nature of TOI-469.01 by precisely measuring the mass thanks to high-precision radial velocities. The measurements not only confirmed the planetary nature of TOI-469.01, but also they allowed the team to discover two additional close-in planetary companions, nearly five times more massive than the Earth. Through an in-depth reanalysis of the TESS light curve, the team could also detect their low signal-to-noise transit signals, measuring radii close to 1.5 times the radius of the Earth. The study revealed that HIP 29442 is a compact multi-planet system. A preliminary composition analysis revealed that the outermost planet HIP 29442 b appears as a typical sub-Neptune, likely surrounded by a gas layer of pure H-He. For the innermost companions HIP 29442 c and HIP 29442 d, the analysis supports an Earth-like composition.

The planetary system orbiting HIP 29442 offers the opportunity to study in one shot time planets straddling the gap in the observed radius distribution of close-in, small-size exoplanets (the so-called ‘Fulton gap’). High-precision photometric follow-up is required to get more accurate and precise radius measurements, especially for planets c and d. This, together with our determined high-precision masses, will provide accurate and precise planets’ bulk structure, and enable an accurate investigation of the system’s evolution.

The paper describing the results about HIP 29442 A compact multi-planet system transiting HIP 29442 (TOI-469) discovered by TESS and ESPRESSO. Radial velocities lead to the detection of transits with low signal-to-noise ratiohas been accepted for publication on Astronomy & Astrophysics.

Sketch of the compact three-planet system detected around the star HIP 29442 (AU=astronomical unit)

Sketch of the compact three-planet system detected around the star HIP 29442 (AU=astronomical unit).