Gravitational microlensing has led to the detection of
planets with masses ranging from more than Jupiter to a few times the mass of
Earth. It involves measuring the magnification of light from a distant
background star due to the lensing effect by the gravitational field of a
foreground star. During a microlensing event, a lightcurve of the background
star is produced as the foreground star crosses in front of it. The presence of
planets around the foreground star can produce sharp deviations in the
otherwise smooth and symmetric lightcurve of the background star.
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Figure 1: Artist’s impression of a habitable Earth-like moon
around a gas giant planet.
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Figure 2: An illustration of a microlensing event of a
distant background star by a foreground star with and without a planet.
Using the Keck telescope near the summit of Mauna Kea in
Hawaii, a team of astronomers observed a microlensing event and reported the
discovery of a gas giant planet that is probably within the habitable zone of
its parent star. This planet is identified as MOA-2011-BLG-293Lb. It has a mass
of 4.8 ± 0.3 Jupiter mass and orbits its parent star at a distance of 1.1 ± 0.1
AU, where one AU is the average Earth-Sun separation distance. The planet’s
parent star is a Sun-like star with a mass of 0.86 ± 0.06 solar mass. MOA-2011-BLG-293Lb
and its parent star are located at an estimated distance of 25,000 light years
away, near the centre of the Milky Way galaxy.
MOA-2011-BLG-293Lb is interesting because a hypothetical
terrestrial-size moon in orbit around it can support Earth-like conditions and
may be potentially habitable. Since MOA-2011-BLG-293Lb circles its parent star
near the outer edge of the habitable zone, a terrestrial-size moon around this
giant planet would require some sort of greenhouse warming effect to keep its
surface warm enough to sustain liquid water. MOA-2011-BLG-293Lb is also one of
the furthest planets discovered to date.
Reference:
V. Batista et al. (14 October 2013), “MOA-2011-BLG-293Lb:
First Microlensing Planet possibly in the Habitable Zone”, arXiv:1310.3706
[astro-ph.EP]