NASA’s New Horizons spacecraft carried out an unprecedented deep-space star navigation test while 438 million miles from Earth. Using its long-range camera in April 2020, it captured images of Proxima Centauri and Wolf 359, which appeared slightly shifted in the sky compared to Earth’s view – a striking demonstration of stellar parallax. It was the first-ever demonstration of deep-space stellar navigation. By comparing these images to Earth-based observations and a 3D star chart, scientists calculated New Horizons’ position to within about 4.1 million miles, only about 26 inches across the United States.

Stellar Parallax Test

According to the paper describing the results, accepted for publication in The Astronomical Journal, New Horizons’ camera imaged Proxima Centauri (4.2 light-years away) and Wolf 359 (7.86 light-years) on April 23, 2020. From the spacecraft’s distant vantage point, the two stars appear in different positions than seen from Earth – the essence of stellar parallax. By comparing those images with Earth-based data and a three-dimensional map of nearby stars, the team worked out the probe’s location to within about 4.1 million miles.

As lead author Tod Lauer explained, “Taking simultaneous Earth/Spacecraft images we hoped would make the concept of stellar parallaxes instantly and vividly clear”. He added, “It’s one thing to know something, but another to say ‘Hey, look! This really works!’”.

New Horizons and Future Missions

New Horizons, the fifth spacecraft to leave Earth and reach interstellar space, flew past Pluto and its moon Charon in 2015, sending home the first close-up images of those distant icy worlds. Now on an extended mission, the probe is studying the heliosphere.

New Horizons’ principal investigator Alan Stern called the parallax test “a pioneering interstellar navigation demonstration” that shows a spacecraft can use onboard cameras “to find its way among the stars”, in a statement. He also noted it “could be highly useful for future deep space missions in the far reaches of the Solar System and in interstellar space”