MOA-2009-BLG-387Lb is an exoplanet in the orbit of the red dwarf MOA-2009-BLG-387L. Its discovery was announced on February 21, 2011, making it the eleventh planet discovered using gravitational microlensing. The planet is thought to be over twice the mass of Jupiter and to have an orbit 80 percent larger than that of Earth's, lasting approximately 1,970 days. However, its exact characteristics are difficult to constrain because the characteristics of the host star are not well known.
Characteristics
Mass and orbit
MOA-2009-BLG-387Lb is a gas giant, with an estimated mass 2.6 times that of Jupiter's and a radius of 1.75 times that of Jupiter and an estimated mean distance of 1.8 AU from its host star. It has an orbital period of approximately 1970 days.[2] Although the mass and mean distance of MOA-2009-BLG-387Lb is estimated, the confidence intervals are very large, indicating that there is a large uncertainty present. These uncertainties are largely due to how the exact parameters of the host star are not known.[1]
On June 7, 2010, long after the microlensing event had subsided, the science teams studying the star used the NACOadaptive optics facility at the Very Large Telescope in Chile to determine the actual apparent magnitude of the star that microlensed its background star, hoping to compare it to the magnitude of the star measured during the microlensing event. A discrepancy was found, a discrepancy that may have been a result of either error or of a planetary body. Interpretation of follow-up observations led to the planet's confirmation. The ratio between the planet's mass and its host star's mass is well-constrained, but a large interval of uncertainty exists because the host star's mass is known within a large confidence interval that spans the mass of all red dwarf stars.[1]
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