NASA’s New Horizons probe has measured the distance to nearby stars using a technique that’s as old as the ancient mariners, but from a vantage point those mariners could only dream of.
The experiment, conducted on April 22-23 as the spacecraft zoomed 4.3 billion miles out from Earth, produced the farthest-out parallax observations ever made.
“It’s fair to say that New Horizons is looking at an alien sky, unlike what we see from Earth,” principal investigator Alan Stern, a planetary scientist at the Southwest Research Institute, said today in a news release. “And that has allowed us to do something that had never been accomplished before — to see the nearest stars visibly displaced on the sky from the positions we see them on Earth.”
The parallax effect is akin to the method that mariners use to determine their position by triangulation with a sextant. You can determine the distance to an object if you sight it from different locations separated by a known distance, or baseline, and take note of the shift in angular position.
Scientists have long used parallax to determine the distance to other stars, by carefully measuring the ever-so-slight shift in the star’s position against the stellar background when viewed from different spots in Earth’s orbit.
For the April experiment, New Horizons’ camera captured images of two of the closest stars beyond our solar system, Proxima Centauri and Wolf 359. Those images were then compared with views of the same stars as seen from observatories in Australia and Arizona.
The stellar parallax effect would be too subtle to be seen by the human eye from different locations in Earth’s orbit, where the maximum baseline is 186 million miles. But the differences were obvious in the pictures taken by New Horizons.
New Horizons science team member Tod Lauer, an astronomer at the National Science Foundation’s National Optical-Infrared Astronomy Research Laboratory, coordinated the parallax demonstration. “The New Horizons experiment provides the largest parallax baseline ever made — over 4 billion miles — and is the first demonstration of an easily observable stellar parallax,” he said.
Brian May, who’s an astrophysicist and stereo-imagery specialist on the New Horizons team as well as the lead guitarist on the legendary rock band Queen, created stereo versions of the parallax images.
“These photographs of Proxima Centauri and Wolf 359 — stars that are well-known to amateur astronomers and science-fiction aficionados alike — employ the largest distance between viewpoints ever achieved in 180 years of stereoscopy,” May said.
Stern said the experiment provided a novel confirmation of the distances to the two stars. “We’re not actually getting better information,” he told GeekWire. “We’re just doing it the old-fashioned way.”
The parallax experiment also served as a warmup for the fifth anniversary of New Horizons’ flyby of Pluto on July 14. Stern said he expects to get an early start to the celebration, so as not to conflict with the buildup for the launch of NASA’s Perseverance rover to Mars later next month.
After the Pluto flyby in 2015, New Horizons went on to get close-up observations of Arrokoth, a snowman-shaped icy object farther out on the edge of the solar system. Stern and his colleagues are still sifting through the data that’s being sent back in the wake of the Arrokoth encounter on New Year’s Day of 2019 — and considering still more targets for observation.
The New Horizons science team will answer questions about the mission, imaging and deep-space exploration during an AskScience AMA session on Reddit, starting at 1 p.m. ET (10 a.m. PT) Friday.