NASA’s New Horizons mission begins again at the edge of the solar system

Disclaimer: The author worked with the New Horizons team as a student researcher while she was an undergraduate.

On New Year’s Day three years ago, a small spacecraft zoomed by a chunk of ice billions of miles away, and scientists on Earth cheered. That was the second time the New Horizons probe got up close and personal with an object in the far-away Kuiper Belt—after capturing images of Pluto, its first target, in unprecedented detail.

Now, New Horizons has a third chance to revolutionize how astronomers see the distant parts of our solar system. On October 1, the spacecraft began the third phase of its life: the 2nd Kuiper Belt Extended Mission, or KEM2 for short.

Every few years, each NASA mission—yes, even the 45-year-old Voyager—undergoes a formal review in which administrators decide whether the project should continue. SOFIA, NASA’s observatory-on-an-airplane, was just a victim of this process, shutting down operations on September 30, the end of the administration’s fiscal year. New Horizons, on the other hand, was successfully renewed this summer for a two-year extension to its operations as it continues flying farther out of the solar system.

In KEM2, because the probe is traveling through a uniquely far-out place in space, New Horizons is going to expand its scope beyond the planetary science of its earlier phases. “New Horizons has become this interdisciplinary observatory in the Kuiper Belt,” says Alan Stern, principal investigator of New Horizons. 

The mission is branching out into two more disciplines: astrophysics and heliophysics. New Horizons is going to measure the solar wind, particles streaming out from the sun, and the probe will eventually reach the termination shock and heliopause, two places that can be considered outer boundaries of our solar system. Although Voyagers 1 & 2 reached the heliopause and made similar measurements, they did so with far less sophisticated tech. 

[Related: NASA’s New Horizons is so far away, it’s seeing stars from new angles]

New Horizons will help heliophysicists better understand the shape of our solar system’s edges and explore the limits of our sun’s influence on space. It’s also the “ultimate dark-sky site” for astrophysicists, allowing them to measure the amount of background light in the universe, a key constraint on the history of galaxies.

Although those aims are departures from its previous goals, it will continue to explore far-off bodies of rock and ice, too. New Horizons has been incredibly successful at exploring the outer solar system, providing the first detailed images of both the dwarf planet Pluto and a smaller Kuiper Belt object (KBO) called 2014 MU69. The Kuiper Belt contains a huge number of these icy objects, which are some of the best-preserved relics of our solar system’s early days—a window for astronomers to look into the past of how our planets formed. 

The spacecraft is currently moving a whopping 32,000 miles per hour, faster than even a rocket launching off Earth. It’s about 54 astronomical units (AU) from the sun, and will move 3 AU further away each year, rapidly approaching the edges of our solar system. It’s in unexplored territory—only four other probes, from the Voyager and Pioneer missions, have made it that far out). And those craft took different paths than New Horizons, carrying the now-outdated technology of the 1970s.

“I am excited about how far out we will be going into the distant parts of the solar system,” says Kelsi Singer, project scientist on New Horizons. In two years, she adds, the probe will be at 60 AU–at an edge of the belt that’s nearly impossible for scientists to explore using Earth-based tools. 

Because Kuiper Belt objects are so extraordinarily far away, even our largest telescopes on Earth have trouble spotting the tiny, faint specks. New Horizons, however, will have a much closer view, embedded within the Kuiper Belt itself. In the first extended mission, the team spotted 36 KBOs using the spacecraft’s onboard cameras, the closest from only 0.1 AU away, and they expect similar observations in KEM2. The team also has the opportunity to use New Horizons for unique images of the ice giants, Uranus and Neptune, from an angle we can’t see here on Earth.

[Related: The New Horizons spacecraft just revealed secrets of the most distant object we’ve ever visited]

Plus, New Horizons has an instrument, the Student Dust Counter, to measure how much space dust it encounters, tracing the distribution of dust near the edges of the solar system. Although we usually think of outer space as totally empty, there’s a good amount of dust floating around there, left over from when planets were formed—again, giving astronomers key insight into the history of the solar system. 

For now, the spacecraft is still in hibernation until it awakens in March 2023. Until then, the team is preparing for the exciting science to come, working tirelessly to hunt for new KBO targets with ground-based observations. And if they’re lucky, KEM2 may be the second of many more extended missions to come.
“The spacecraft is in perfect health, and it has the fuel and the power to run through sometime in the 2040s,” Stern says. “This is not the last hurrah of New Horizons by a long shot.”