New Neighbors

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Astronomers using NASA’s Transiting Exoplanets Survey Satellite (TESS) have discovered a compact three-planet system around the star HR 858. The newly-discovered planets orbit HR 858, a slightly-evolved F-type star, which is also a member of a visual binary system. The star lies in the constellation of Fornax, approximately 104.4 light-years from Earth. It has a radius 30% larger than the Sun, and a temperature of about 10,700 degrees Fahrenheit (5,928 degrees Celsius).

Named HR 858b, c and d, the new planets are all about twice the size of Earth and have periods of 3.6, 6 and 11.2 days, respectively. This compact and near-resonant architecture harkens back to the systems of tightly packed inner planets discovered by Kepler, but HR 858 is hundreds to thousands of times brighter than the hosts of those Kepler systems.

According to the team, HR 858 is one of the brightest stars known to host transiting exoplanets, trailing only HD 219134, pi Mensae, and 55 Cancri.

Pre-launch estimates of the TESS planet yield predicted a handful of planet discoveries around naked-eye stars, and so far only HR 858 and pi Mensae have fit this description. HR 858 will likely retain its privileged position as one of the brightest transit hosts in the sky and most favorable systems for detailed study.

paper detailing the discovery will be published in a journal of the American Astronomical Society (AAS).

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