When the International Space Station (ISS) project was planned, there was a lot of talk about how it would serve as a port of call for scientists, engineers, and tourists as it became our best new platform for peace. In the decades that have followed, the ISS has served to bring nations of the world together in space, providing a home-away-from-home for Americans, Russians, Japanese, and other nations’ astronauts and cosmonauts. [Ed. note: Go watch Babylon 5, everyone!] What it hasn’t always done is perform cutting-edge research. All that began to change, however, with the addition of new instruments such as the NICER space telescope and CALET, the CALorimetric Electron Telescope.

The ISS provides a middle ground between “can’t easily be upgraded” self-orbiting spacecraft and the “fly out your grad students at will” easy-to-tinker-with ground telescopes. The Japanese Kibo experiment module on the ISS houses both exposed instruments on an outside terrace and also has a pressurized section. Exposed to space, CALET uses its detectors to look for fast-moving charged particles called cosmic rays. It has the capacity to detect not just the energy of what hits it but also the composition. Since its installation in 2015, CALET has detected teraelectronvolt particle after particle, and it is hoped that one day it might detect dark matter or at least the interactions of regular and dark matter.

While it hasn’t yet seen that dark matter, it has seen some pretty weird stuff. In a new paper appearing in Physical Review Letters, researchers led by O. Adriani looked at the specific behaviors of cosmic rays made of iron as compared to other atoms like carbon, hydrogen, and oxygen. They find that while the three lighter-weight atoms all behave roughly the same, with similar distributions in their energies, iron is very different, and, as co-author Michael Cherry puts it: Something that needs to be emphasized is that the way the elements get from the sources to us is different, but it may be that the sources are different as well.

Cosmic rays interact with magnetic fields on their way from their source to our detectors. This can lead some heavy elements like iron to break down into smaller particles. We think. This means that when we see iron, it has probably – maybe – gotten to us in its primary state, while the other atoms may be origins of the cosmic ray formation or child particles. While we really don’t know the details on what’s going on, this research from CALET on the ISS tells us something is going on, and here is to hoping that with more years of data, we’ll not only figure out what that something is but also – maybe – detect dark matter.

More Information

UMBC press release

Japanese, Italian, US physicists reveal new measurements of high-energy cosmic rays (EurekAlert)

“Measurement of the Iron Spectrum in Cosmic Rays from 10 GeV/n to 2.0 TeV/n with the Calorimetric Electron Telescope on the International Space Station,” O. Adriani et al., 2021 June 14, Physical Review Letters