The NASA Spitzer Space Telescope has teamed up with the Polish Optical Gravitational Lensing Experiment (OGLE)'s Warsaw Telescope at the Las Campanas Observatory in Chile to observe a distant gas giant located some 13,000 light-years away. The discovery will help improve our understanding of the distribution of planets throughout the Milky Way galaxy.
The initial discovery of the planet, known as OGLE-2014-BLG-0124L, was made possible thanks to a detection method known as microlensing. When one star passes directly in front of another, the gravity of the closer object acts as a lens, brightening and magnifying the light from the secondary star. If the closer of the two stars has a planet orbiting it, a small blip will be visible in the observed magnification.
The technique allows astronomers to identify and characterize distant objects, and has so far been responsible for the discovery of 30 planets. However, while microlensing is a useful planet-hunting technique, the dim light of the foreground star can make it difficult to pinpoint the distance to the observed planets. Around half of the planets detected through microlensing events have failed to have their locations confirmed by the method.
The planet in question was first discovered by the ground-based Warsaw Telescope, but the team had to call upon the Spitzer Space Telescope – which circles the Sun, currently some 128 million miles (207 million km) from Earth – to work out exactly where the planet resides.
Spitzer was tasked with watching the microlensing event, simultaneously with the ground-based telescope on Earth. Thanks to the huge distance between the installations, the space telescope observed the telltale blip in the magnification some 20 days before its ground-based counterpart, with the difference in time being used to make the distance calculation – a technique known as a parallax measurement. Knowing the distance to the star and its orbiting planet – some 13,000 light-years – also allowed the team to calculate that the planet has a mass around half that of Jupiter.
"We don't know if planets are more common in our galaxy's central bulge or the disk of the galaxy, which is why these observations are so important," said Jennifer Yee of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts.
Spitzer has previously watched 22 other microlensing events in conjunction with the Warsaw Telescope, but this latest observation is the first to confirm the existence of a planet. Looking forward, the space telescope will be used to observe 120 such events this summer (Northern Hemisphere), gathering data that's essential to our understanding of star and planet distribution throughout our home galaxy.
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