NASA’s New Horizons spacecraft captured this image of Pluto (lower right) and its moon Charon (upper left) during the 2015 pass.Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwestern Research Institute
At the edge of the solar system, more than 8 billion kilometers from Earth, NASA’s New Horizons spacecraft is at the center of a dispute over its future.
Pluto’s geology is unparalleled
The rover, which took stunning images during humanity’s first visit to Pluto in 2015, is years away from emerging from the Kuiper Belt, the realm of icy objects orbiting the sun beyond Neptune. In addition to Pluto, it flew by another Kuiper belt object called Arrokoth, but did not find a third to visit before departing. So now NASA plans to reuse the spacecraft primarily as a heliophysics mission, to study space weather and other phenomena that can be measured from its unique location in the solar system.
But some are unhappy with the decision and fear planetary studies will be cut short too soon. “Scientifically, I don’t feel like we’re in diminishing returns yet,” says Kelsey Singer, mission project scientist at the Southwest Research Institute in Boulder, Colorado.
Transforming New Horizons from a planetary explorer into an interstellar envoy mirrors what the agency did with sister spacecraft Voyager after visiting the outer planets in the 1980s, says Nicola Fox, senior science mission manager at NASA in Washington, D.C. The agency wants to make “the best use” of it, she said, in addition to “opening it up to the largest number of interested scientists from various disciplines.”
task resume?
Nobody argues that New Horizons has made some amazing discoveries in the Kuiper Belt, which contains debris left over from the early history of the solar system. The spacecraft has unlocked the secrets of Pluto’s icy surface and revealed more about how the planet’s building blocks come together. Its 2019 flyby of Arrokoth, a 35-kilometer-wide object in the Kuiper Belt made up of two pieces of space rock stuck together, Michel says, “taught us a lot about the fundamental properties of planet formation — that they can completely morph.” Researcher at the University of Canterbury in Christchurch, New Zealand.
New Horizons visited the Arrokoth region of the Kuiper Belt in 2019.Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwestern Research Institute/Roman Tkachenko
Some say that without another Kuiper Belt object flying close by, it becomes difficult to prove planetary science for New Horizons. Tensions surfaced last year after NASA’s planetary science division conducted a “major review” of its operational missions, as it does every few years. A panel of scientists has evaluated eight missions, including New Horizons, for their recent science performance and future promise.
This review rated the current science of New Horizons as “excellent/very good” if planetary science, astrophysics, and heliophysics are included. The rating rose to “very good/good” for planetary science alone, in part because the science team’s proposed studies of Kuiper belt objects are “unlikely to significantly improve the state of knowledge,” according to the review. (The mission science team disputes this conclusion.)
NASA used the review in its decision to operate the spacecraft as a heliophysics mission, said Lori Glaze, the agency’s chief of planetary sciences. “Because that’s where the strength is – in the science that can be done from now on,” she says.
The focus is on the distant solar system snowman
NASA will fund the mission from its planetary science budget through Sept. 30, 2024. After that, management could be taken over by a much smaller Heliophysics Division, potentially involving a new group of scientists. In March, NASA asked US researchers for ideas about what New Horizons science could do across disciplines, “to gauge the level of interest from the broader scientific community in pursuing the next phase of science leadership for the mission, and to estimate appropriate annual costs.” “
For the mission’s current science team, this amounts to an obsession. “There will be an indoor party on October 1st next year,” says Alan Stern, the mission’s principal investigator, who is also at the Southwest Research Institute. Fox replies that the New Horizons team was asked to submit a proposal to lead spacecraft science in the Heliophysics Division starting in October 2024, and the researchers declined.
Full replacement of a mission’s science team is relatively rare, says Amanda Hendricks, a researcher at the Planetary Science Institute in Boulder, Colorado. “We’re entering kind of new territory.”
in a “unique position”
Now the question is what can science do with New Horizons and how. Although its plutonium energy source dwindles over time, it has enough for probably another quarter century.
The craft is currently in the outer part of the Kuiper belt (see ‘Up there’), and little is known about it because it can’t be observed well from Earth. “New Horizons is in a very unique location, and there is almost no other way to get this information,” says Singer.
Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwestern Research Institute
Among other studies, New Horizons has taken repeated images of distant Kuiper Belt objects, gathering information about their shapes and surface properties. The spacecraft is also analyzing dust in the Kuiper Belt – data that can shed light on how often space rocks collide with each other.
In recent years, the spacecraft has begun to expand its range. In astrophysics, New Horizons’ location allows it to study several types of background light that permeate the solar system. And in solar physics, ongoing and future studies are exploring the streams of charged particles emitted by the sun. “They are very valuable in conjunction with Voyagers,” says Stamatios Krimigis, an astrophysicist and the only scientist to have participated in missions to every planet in the solar system and Pluto.
New Horizons, which cost $780 million to build, launch and fly over Pluto, costs NASA about $10 million annually. Fox and Glaze said nature that the decision to move the mission away from planetary science was not motivated by budget issues, such as those that delayed the Venus mission and raised concerns about the cost of returning samples from Mars.
Both also said that if a Kuiper belt object is discovered that New Horizons can reach, NASA would be open to discussing it, even if the mission has already been moved to heliophysics. Stern and his team continue to search for an overhead target by the time they left.
