A Planetary Companion around a Metal-Poor Star with Extragalactic Origin

TL;DR

This paper reports the discovery of a planet orbiting a metal-poor star with an extragalactic origin, highlighting a unique case that challenges existing planet formation theories and expands the diversity of known planetary systems.

Contribution

It presents the first detection of a planet around a star with extremely low metallicity and an extragalactic origin, using radial velocity measurements.

Findings

Detected a 1.25 MJup planet with a 16.2-day orbit.

First planet found around a star with very low metallicity.

Star belongs to a stellar stream indicating extragalactic origin.

Abstract

We report the detection of a planetary companion around HIP 13044, a metal-poor star on the red Horizontal Branch. The detection is based on radial velocity observations with FEROS, a high-resolution spectrograph at the 2.2-m MPG/ESO telescope, located at ESO La Silla observatory in Chile. The periodic radial velocity variation of P = 16.2 days can be distinguished from the periods of the stellar activity indicators. We computed a minimum planetary mass of 1.25 MJup and an orbital semi-major axis of 0.116 AU for the planet. This discovery is unique in three aspects: First, it is the first planet detection around a star with a metallicity much lower than few percent of the solar value; second, the planet host star resides in a stellar evolutionary stage that is still unexplored in the exoplanet surveys; third, the star HIP 13044 belongs to one of the most significant stellar halo streams in the solar neighborhood, implying an extragalactic origin of the planetary system HIP 13044 in a disrupted former satellite of the Milky Way.