Using the HARPS-N spectrograph on the Italian Telescopio Nazionale Galileo at the Roque de los Muchachos Observatory (Canary Islands), astronomers have discovered three super-Earths and a gas giant orbiting a nearby star called HD 219134.
This artist’s impression shows the super-Earth exoplanet HD 219134b. Image credit: NASA / JPL-Caltech.
HD 219134, also known as HR 8832, is a 5th magnitude K-dwarf star located approximately 21 light-years away in the constellation Cassiopeia.
The star is slightly colder and less massive than our Sun. It is so bright that it’s visible to the naked eye.
The planetary system HD 219134 hosts an outer giant planet and three inner super-Earths, one of which transits in front of the star.
The transiting super-Earth, named HD 219134b, is approximately 4.5 times more massive than the Earth and 1.6 times larger, and orbits its star once every three days.
The planet has a density similar to the Earth’s. It is by far the closest transiting planet known today.
The astronomers predict that the scorching-hot planet – known to be terrestrial through measurements of its mass and size – would have a rocky, partially molten surface with geological activity, including volcanoes.
“In the inner regions, a planet weighing 2.7 times the Earth orbits HD 219134 in 6.8 days, and a planet of 8.7 times the mass of the Earth resides on a 46.8-day orbit,” the scientists said.
“If, by chance, these two planets would be in a coplanar configuration with their third inner sister, HD 219134b, as often observed for compact systems, the whole family might be transiting.”
This image shows the K-dwarf star HD 219134 (center). Image credit: Centre de Données astronomiques de Strasbourg / SIMBAD.
According to team member Prof Stéphane Udry from the University of Geneva in Switzerland, ESA’s CHEOPS satellite will provide the perfect tool for future observations to capture the potential transits.
“Being able to characterize three transiting super-Earths in a single bright and close system would provide incomparable constraints for planet formation and composition models, in particular for super-Earths,” said Prof Udry, who is a co-author of a paper accepted for publication in the journal Astronomy & Astrophysics (arXiv.org preprint).
The system HD 219134 also includes a planet of small-Saturn type at 2.1 astronomical units, orbiting the star in a bit more than three years.
“This system, reminiscent of our own Solar System with the inner small planets and the outer gaseous one, will without doubt encounter a growing interest from the astronomical community,” the astronomers said.
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F. Motalebi et al. 2015. The HARPS-N Rocky Planet Search I. HD219134b: A transiting rocky planet in a multi-planet system at 6.5 pc from the Sun. A&A, accepted for publication; arXiv: 1507.08532
