June 5, 2024
This spring NASA will launch what could become one of this decade’s most transformative missions in astrophysics. But you’ve almost certainly never heard of it—and it’s not even going to space. Dubbed the High-Energy Light Isotope eXperiment (HELIX), the mission seeks to solve a long-standing mystery about just how much antimatter there is in the universe and where it comes from—all from a lofty perch in Earth’s stratosphere, slung beneath a giant balloon set for long-duration flights above each of our planet’s desolate poles.
Led by Scott Wakely, an astrophysicist at the University of Chicago, HELIX is designed to study cosmic rays—subatomic particles that pelt our planet from the depths of interstellar and even intergalactic space. These particles include those of ordinary matter’s opposite-charge version, called antimatter. Scientists suspect the sources for the antimatter showering Earth from space could be almost anything, ranging from emissions by conventional astrophysical objects to the esoteric behavior of dark matter, the invisible stuff that seems to govern the large-scale behavior of galaxies. Figuring out which explanation is right may depend on a deceptively simple measurement: gauging how much time each of two specific particles spent hurtling through the galaxy. It’s like carbon-dating cosmic rays. “The models are all over the place. A measurement of this ratio is what everybody wants,” says Nahee Park, an astrophysicist at Queen’s University in Ontario and a member of the HELIX team.