Discovery and Mass Measurements of a Cold, 10-Earth Mass Planet and Its Host Star

TL;DR

This paper reports the discovery and mass measurement of a cold, 10-Earth mass planet orbiting a low-mass star using gravitational microlensing, demonstrating the method's capability to characterize exoplanets and test planet formation theories.

Contribution

It introduces a new microlensing measurement of a low-mass, cold exoplanet and shows the potential of space-based parallax measurements for detailed characterization.

Findings

The planet has a mass of approximately 10.4 Earth masses.

The host star has a mass of about 0.56 Solar masses.

The orbital period is roughly 7.6 years.

Abstract

We present the discovery and mass measurement of the cold, low-mass planet MOA-2009-BLG-266Lb, made with the gravitational microlensing method. This planet has a mass of m_p = 10.4 +- 1.7 Earth masses and orbits a star of mass M_* = 0.56 +- 0.09 Solar masses at a semi-major axis of a = 3.2 (+1.9 -0.5) AU and an orbital period of P = 7.6 (+7.7 -1.5} yrs. The planet and host star mass measurements are enabled by the measurement of the microlensing parallax effect, which is seen primarily in the light curve distortion due to the orbital motion of the Earth. But, the analysis also demonstrates the capability to measure microlensing parallax with the Deep Impact (or EPOXI) spacecraft in a Heliocentric orbit. The planet mass and orbital distance are similar to predictions for the critical core mass needed to accrete a substantial gaseous envelope, and thus may indicate that this planet is a "failed" gas giant. This and future microlensing detections will test planet formation theory predictions regarding the prevalence and masses of such planets.