Excerpt from  thespacereporter.com

According to a NASA statement, the agency’s Spitzer Space Telescope has taken part in the discovery of one of the most distant exoplanets yet found. Spitzer observations were combined with data from the Polish Optical Gravitational Lensing Experiment’s Warsaw Telescope, part of the Las Campanas Observatory in Chile. The newly found exoplanet is approximately 13,000 light-years from Earth, and could yield new clues as to the distribution of planets throughout the Milky Way.

The Warsaw Telescope gathers data through the phenomenon known as microlensing, which occurs when a star passes in front of another, more distant star as seen from Earth’s vantage point. The gravity of the nearer star magnifies and intensifies the distant star’s light; any planets orbiting the distant star appear as small disruptions in the magnification. So far, the microlensing methods has identified around 30 exoplanets, the most distant of which is around 25,000 light-years away.

However, the microlensing method cannot always show how far away are the more distant stars and their planets; the distances to about half of the exoplanets found with microlensing cannot be ascertained. Fortunately, Spitzer is able to help. Located 128 million miles from Earth, Spitzer is able to observe a microlensing event at a different time from the Warsaw Telescope, a method called parallax. In the case of the newly discovered exoplanet, the microlensing event was longer than norman, lasting 150 days. 
Spitzer observed the event 20 days earlier than Warsaw. This time delay allowed the distance to the newly found planet to be calculated. With the distance, the planet’s mass, approximately half that of Jupiter, also was determined.

“We’ve mainly explored our own solar neighborhood so far,” said Sebastiano Calchi Novati of NASA’s Exoplanet Science Institute at the California Institute of Technology. “Now we can use these single lenses to do statistics on planets as a whole and learn about their distribution in the galaxy.”