Astronauts Andrew Morgan of NASA and Luca Parmitano of the European Space Agency are outside of the International Space Station (ISS) as we speak. The duo are taking a space walk to fix a key dark matter experiment. You can watch (and rewatch) the progress here.
Spacewalks happen regularly (there was a historic one just last month), but Friday’s is the most complex servicing mission since the Hubble repair mission, according to the NASA. The last Hubble repair took place a decade ago. The astronauts are working to fix an exciting experiment on the hunt for dark matter, the stuff that makes up most of the universe’s mass but has only been observed indirectly. After a decade of development, the Alpha Magnetic Spectrometer (AMS) was brought to the ISS on the second-to-last space shuttle flight in 2011.
The AMS is a controversial particle detector onboard the ISS that measures the high-energy particles beaming through space called cosmic rays. Most famously, it’s one of several experiments that have spotted an excess in the antimatter partner to the electron, called the positron. To this day, it’s not completely clear where these extra positrons in cosmic rays come from—maybe they originated in a nearby neutron star, or maybe they’re the sign of something more exotic, like dark matter. Research using AMS data will also hopefully verify a strange drop-off in high-energy antimatter observed by China’s DAMPE satellite.
AMS is also on the hunt for antimatter, most importantly antimatter counterparts to the helium nuclei. Cosmic rays can’t produce these nuclei, which means they would have been born somewhere else in the universe, perhaps in a mostly-antimatter galaxy. Many are skeptical that these areas in the universe exist, Science reports.
For all the work AMS has done, it’s also in rough shape. Three of its four coolant pumps have failed. Friday’s space walk is part of a series (there might be four or five of them) to replace the pumps and replenish the coolant. If those repairs fail, at least the experiment will have expanded scientists’ knowledge of cosmic rays and how they work.