Is an old NASA probe about to redraw the frontier of the solar system?

NASA’s New Horizons spacecraft is hurtling out of the solar system at an incredible speed. It is currently about 8 billion kilometres from the sun, and by the time you finish reading this story, it will have sped thousands of kilometres further into the frigid gloom. It is lonely out there. Even the giant planet Jupiter is but a tiny speck.

New Horizons is mainly known for giving us our first proper look at the dwarf planet Pluto in 2015. Until then, we had only seen it as a blurry smudge. It has also taught us much about the solar system’s outer reaches and the small, frozen worlds that float there. “It’s really been an Alice in Wonderland kind of story,” says Alan Stern, the principal investigator of the mission. “It’s been dreamlike and we’ve discovered wonderful things.”

However, the dream isn’t over yet because New Horizons may be poised for a surprise final act. In early 2024, one of its detectors recorded an unexpected uptick in the amount of dust it was encountering. Since that material could have been created in collisions between rock fragments, astronomers now wonder if there are many objects beyond the rubble-strewn Kuiper belt often considered the edge of the solar system. If so, our system’s boundaries will need to be redrawn and our models of how it formed thrown into doubt.

Stern and his colleagues are obviously keen to take advantage of their probe’s unique position to learn more about this unexplored wilderness while they still can. “It’s an…