HD 3167d: New Super-Earth Discovered around Nearby Star

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Dr. Jessie Christiansen, a staff scientist at the NASA Exoplanet Science Institute, and colleagues have discovered a ‘super-Earth’ exoplanet orbiting HD 3167, a bright star in the constellation Pisces. The discovery will be published in an upcoming issue of the Astronomical Journal (arXiv.org preprint).

This illustration shows one possible scenario for the super-Earth HD 3167d. Image credit: NASA / JPL-Caltech.

This illustration shows one possible scenario for the super-Earth HD 3167d. Image credit: NASA / JPL-Caltech.

HD 3167 is a K0-type dwarf star, also designated as EPIC 220383386 and 2MASS J00345752+0422531.

The star has a radius and a mass roughly 86% that of the Sun, and is approximately 8 billion years old.

At a distance of just 149 light-years, HD 3167 is one of the closest and brightest stars hosting multiple transiting planets.

In September 2016, Vanderburg et al announced they had spotted two small, short-period planets — HD 3167b with a period of 0.95 days and HD 3167c with a period of 29.8 days — in orbit around the star.

Assisted by several telescopes and instruments, Christiansen et al confirmed the existence of HD 3167b and HD 3167c planets and discovered additional one, increasing the number of known planets in the system to three.

The newfound planet, named HD 3167d, is a super-Earth with a mass 6.9 times that of our home planet.

It whips around its parent star in just 8.5 days (between the orbits of the previously known planets).

The astronomers also precisely measured radii, masses, and densities of HD 3167b and HD 3167c.

With a mass of 5 Earth-masses and a radius approximately 1.7 times that of Earth’s, HD 3167b is a hot super-Earth with a likely rocky composition.

“The measured mass and radius of HD 3167b indicate a bulk density of 5.6 g/cm3; consistent with a predominantly rocky composition, but potentially having a thin envelope of hydrogen/helium or other low-density volatiles,” Dr. Christiansen and co-authors said.

HD 3167c is a warm sub-Neptune planet. It has a mass 9.8 times that of Earth’s and a radius 3 times that of Earth’s.

“The resulting bulk density of HD 3167c is 1.97 g/cm3. The mass and radius can be explained by a wide range of compositions, all of which include low-density volatiles such as water and hydrogen/helium,” the scientists said.

“HD 3167 promises to be a fruitful system for further study and a preview of the many exciting systems expected from the upcoming NASA TESS mission,” they concluded.

In a separate, independent study of the HD 3167 system, Gandolfi et al also reached the conclusion that HD 3167b is a rocky super-Earth and that HD 3167c is a low-density mini-Neptune.

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Jessie L. Christiansen et al. 2017. Three’s Company: An additional non-transiting super-Earth in the bright HD 3167 system, and masses for all three planets. AJ, in press; arXiv: 1706.01892

Davide Gandolfi et al. 2017. The transiting multi-planet system HD3167: a 5.7 MEarth Super-Earth and a 8.3 MEarth mini-Neptune. arXiv: 1706.02532