Tuesday, January 1, 2019

Astronomers Discover an Ultra-dense Sub-Neptune Alien World Orbiting a Sun-like Star

Phase-folded K2 light curve to the orbital period of HD 119130 b and residuals. Credit: Luque et al., 2018.

Using NASA's prolonged Kepler exoplanet-hunting mission, known as K2, an international team of astronomers has detected an ultra-dense sub-Neptune alien world, which orbits a sun-like star. The finding is reported in a paper published December 21 on arXiv.org.

Kepler is so far the most prolific planet-hunting telescope. The spacecraft has discovered more than 2,600 exoplanets to date. After the failure of its two reaction wheels in 2013, the mission was repurposed as K2 to perform high-precision photometry of selected fields in the ecliptic. The mission was retired in November 2018.

A group of researchers, led by Rafael Luque of University of La Laguna, Spain, has analyzed data provided by K2’s Campaign 17 lasting from March 1 to May 8, 2017, what resulted in finding transit signal from a sun-like star known as HD 119130 (other designation EPIC 212628254). Planetary nature of this signal was confirmed by follow-up observations using the WIYN 3.5-m telescope at Kitt Peak Observatory in Arizona, the Subaru 8.2-m telescope in Hawaii, and the 3.5-m telescope at the Calar Alto Observatory in Spain.

The newly found exoplanet, designated HD 119130 b, is a warm sub-Neptune with a radius of about 2.63 Earth radii and approximately 24.5 times more massive than our planet. In general, the so-called sub-Neptunes are worlds that transition from rocky planets to gas giants.

With a mean density of around 7.4 g/cm^3, HD 119130 b is one of the densest sub-Neptune planets known to date. 

“HD 119130 b becomes one of the densest sub-Neptune planet known to date, joining a rare population with only K2-66 b (Sinukoff et al. 2017) as a comparable case,” the astronomers wrote in the paper.

According to the study, HD 119130 b has an equilibrium temperature of 795 K, and orbits its host approximately every 17 days at a distance of 0.13 AU from it. With spectral type G3 V, effective temperature of about 5,725 K, the nearly 7-billion-year-old parent star has a mass similar to our sun but is around 9 percent larger. The planetary system is located some 373 light years away from the Earth.

What still puzzles the researchers is how such a dense planet like HD 119130 b, located relatively close from its host, may have formed. The authors of the paper assume that it could be due inward migration via dynamical interactions with another body. They suppose that there could be another planet in this system still undetected, with a minimum mass of about 33 Earth masses. However, more observations of HD 119130 are required to confirm this hypothesis.