A margin for error this large could become problematic for a space probe that is currently flying through interplanetary space at 10 miles per second (36,000 miles per hour), so it needs to make fine adjustments as it gets closer to its target.
To provide a more precise view on Pluto's location ahead of a scheduled New Horizons course correction in July, mission scientists have enlisted the help of the Atacama Large Millimeter/submillimeter Array (ALMA), located in Chile.
ANALYSIS: Hubble Survey Spots Two New Objects Beyond Pluto
To measure distances throughout the Cosmos, astronomers traditionally use the method of astrometry to track the motions of the planets, for example, relative to the "fixed" stars many light-years beyond. But when we're talking about threading an interplanetary needle 40 AU away, a more precise form of astrometry is needed as even stars drift regardless of their distance from us.
Using quasars - ancient active galaxies that can be spied over 10 billion light-years away by the most sensitive radio observatories on the planet - ALMA can provide this mindblowing precision (as these objects are truly fixed in the Universal landscape), adding a new dimension of positioning data to back up decades of optical observations of the distant world.