Anecdotal reports of 10 antihelium nuclei striking the International Space Station have inspired theoretical physicists to speculate beyond our current models in search of an explanation. While a small handful of cosmic particles may seem insignificant, the signature of an antihelium rain is peculiar enough for researchers to think of the event as a downpour in the desert.

Scientists from the Perimeter Institute for Theoretical Physics in Canada and Johns Hopkins University in the US suggest in their newly published analysis that physics should be looked at outside the currently accepted Standard Model and suggest that it could be dark matter. The Alpha Magnetic Spectrometer (AMS-02) has been on the International Space Station since 2011 and has secretly recorded more than 200 billion cosmic ray events.

Although most of these were ordinary particles traveling at high speeds across long distances in space, unpublished reports suggested that ten of them were quite unusual, consisting of pairs of antiprotons bonded to one or two antineutrons.

Theoretically, antiparticles such as positrons, antineutrinos, and antiquarks should have emerged from the Big Bang furnace in about the same numbers as electrons, neutrinos, and quarks, and they should have quickly extinguished each other in the gamma-ray stream. The fact that the universe is made up of much more than the expanding glow of electromagnetic radiation suggests that we don’t fully understand something about the balance of primordial matter and antimatter.

Just as a fine mist of antimatter can be compressed on Earth using particle colliders, nature continues to release antiprotons and antineutrons during high-energy cataclysms. Some will even escape destruction and occasionally encounter detectors here on Earth.

AMS-02’s intended detections involved antiprotons and antineutrons in the form of antihelium nuclei, a rare combination that requires the antiparticles to be slow-moving and tightly packed to give them a chance to bind to subatomic particles.

Interestingly, for every antihelium nucleus containing two antineutrons, an isotope called antihelium-4, there were two antihelium nuclei containing one antihelium-3. Based on established physics alone, the top researchers found a measured isotope ratio of 10,000 to one. Whatever created the two varieties of antimatter isotope and sent them to us wasn’t as discriminating as the known processes that sized the antihelium, suggesting that the initial conditions required the subatomic building blocks to move incredibly slowly before being ejected.

One possibility is the decay of a currently unknown particle that could even be classified as dark matter. Even if such a particle exists, the question of how it flies through space at a speed that is infinitesimally small compared to the speed of light still remains.

Working backwards, the researchers theorize that an incredibly hot, rapidly growing plasma concentration of known particles could provide both the acceleration and the right ratio of antihelium nuclei. While such “fireballs” have never been observed, they could occur in collisions between dark matter blobs containing enough antiquarks.

The second possible scenario involves so-called “dark dwarfs.” These hypothetical balls of dark photons, dark electrons, and dark neutrons could also collide with each other, creating conditions that would spew out antihelium at measured rates.

No model is fully developed, and it consists of complex dynamics whose potential details are hotly debated. And that’s just the physics we know; dark matter itself has yet to be confirmed as a material phenomenon, let alone understood.

But even in the mathematics of highly speculative models like this one, there may lie the seeds of discovery that could turn other unexpected measurements into fireballs of colliding darkness.

After another six years of operation, AMS-02 could continue to collect data that could provide another look at the origin of this strange antihelium rain. Or it could confirm that something unexpected is creating antimatter atoms in the far reaches of space and taunting us from the shadows. The study was published on: Physical Examination.