By looking at the shifting of stars in photos from the New Horizons probe, astronomers have calculated its position in the galaxy – a technique that could be useful for interstellar missions
Artist’s illustration of NASA’s New Horizons spacecraft in the outer solar system Joe Olmsted/STScI
As it hurtles out of our solar system, NASA’s New Horizons spacecraft is so far from Earth that the stars in the Milky Way appear in markedly different positions compared with our own view. Astronomers have now used this change in perspective to work out the probe’s position in the galaxy, in the first ever example of interstellar navigation.
New Horizons was launched in 2006, initially to study Pluto, but it has since travelled way beyond this point, ploughing on through the Kuiper belt, a vast, wide band of rocks and dust billions of miles from the sun. It is now speeding at tens of thousands of kilometres per hour.
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When gazing at the night sky from Earth, the stars are so far away that they don’t appear to change positions when viewed from different locations, unless you have a powerful telescope. But from New Horizons’ viewpoint, there is a significant change in star positions due to the parallax effect. This was demonstrated in 2020 when the probe beamed back pictures of two nearby stars, Proxima Centauri and Wolf 359, to Earth.
Now, Tod Lauer at the US National Optical-Infrared Astronomy Research Laboratory in Arizona and his colleagues have used this effect to work out the position of New Horizons. They did it by comparing the probe’s photos of Proxima Centauri and Wolf 359 with measurements from the Gaia space telescope, which has produced the most detailed map of stars in our Milky Way.
“We have a good enough three-dimensional map of the galaxy around us that you can find out where you are,” says Lauer. “It’s a remarkable accuracy, with your own camera [on board a spacecraft].”
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To calculate the spacecraft’s position, he and his team looked at the position of the stars as they appeared from New Horizons’ on-board camera, drawing a line of sight back from both stars and working out where the two lines were closest. Then, they used the precise position of both stars from Gaia’s star map to work out where this point was in relation to the solar system.
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