Astronomers using NASA’s Spitzer Space Telescope and the Polish Optical Gravitational Lensing Experiment (OGLE) telescope at the Las Campanas Observatory in Chile have discovered one of the most distant exoplanets known – a gas giant planet approximately 13,000 light-years away, called OGLE-2014-BLG-0124Lb.
This artist’s conception shows OGLE-2014-BLG-0124Lb. Image credit: Christine Pulliam / CfA.
OGLE-2014-BLG-0124Lb was detected using a technique called microlensing.
Microlensing is a form of gravitational lensing in which the light from a background source is bent by the gravitational field of a foreground lens to create distorted images.
The technique as a whole has yielded about three dozens planet discoveries so far, with the farthest residing 25,000 light-years away, OGLE-2008-BLG-092LAb. However, roughly half of these exoplanets cannot be pinned down to a precise location.
That’s where the Spitzer telescope can help astronomers, thanks to its remote Earth-trailing orbit. The telescope circles our Sun, and is currently about 128 million miles (207 million km) away from Earth.
When Spitzer watches a microlensing event simultaneously with a telescope on Earth, it sees the star brighten at a different time, due to the large distance between the two telescopes and their unique vantage points. This technique is generally referred to as parallax.
This map of our Milky Way Galaxy shows the location of the gas giant OGLE-2014-BLG-0124Lb and other exoplanets discovered with microlensing. Image credit: NASA / JPL-Caltech.
“Spitzer is the first space telescope to make a microlens parallax measurement for a planet. Traditional parallax techniques that employ ground-based telescopes are not as effective at such great distances,” said Jennifer Yee of the Harvard-Smithsonian Center for Astrophysics, a co-author on the study published in the Astrophysical Journal (arXiv.org version).
In the case of OGLE-2014-BLG-0124Lb, the duration of the microlensing event happened to be 150 days long. Both Spitzer and OGLE’s telescopes detected the telltale planetary blip in the magnification, with Spitzer seeing it 20 days earlier. This time delay between viewing of the event by the telescopes was used to calculate the distance to the star and its planet.
Knowing the distance allowed the scientists also to determine the mass of OGLE-2014-BLG-0124Lb, which is about half that of Jupiter.
According to the astronomers, the planet orbits a star with a mass of 0.7 solar masses at a distance of 3.1 AU.
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A. Udalski et al. 2015. Spitzer as a Microlens Parallax Satellite: Mass Measurement for the OGLE-2014-BLG-0124L Planet and its Host Star. ApJ 799, 237; doi: 10.1088/0004-637X/799/2/237
