The Euclid telescope operated by the European Space Agency (ESA) has been steadily losing eyesight due to layers of water molecules freezing onto its mirrors. This is unfortunate for a project whose goal is to use extremely sensitive sensors to observe the dark universe, but the telescope’s developers have devised a way to keep Euclid warm in the icy depths of space.
With the use of a visible light camera (VIS), a near-infrared camera, and a spectrometer, Euclid began in July 2023 with the goal of studying the dark universe—the regions of our universe that are composed of dark energy and dark matter (NISP). The science crew of the expedition started calibrating the telescope’s instruments not long after it was launched. Team members saw a progressive decrease in the amount of light measured from stars that VIS was continuously observing during this procedure.
“Some stars in the Universe vary in their luminosity, but the majority are stable for many millions of years,” Mischa Schirmer, calibration scientist for Euclid, said in a statement. “So, when our instruments detected a faint, gradual decline in photons coming in, we knew it wasn’t them—it was us.”
The team now thinks, after months of research, that many layers of water molecules have probably frozen onto Euclid’s optical sensors’ mirrors. Even while the water ice layer was only a few tens of nanometers thick—roughly the same width as a strand of DNA—it was sufficient to impair Euclid’s extremely acute vision.
According to ESA, the telescope is progressively releasing the water from various components of the spaceship after having most likely absorbed it from the atmosphere during its assembly on Earth. Those released molecules of water will adhere to the first surface they come into contact with in the frigid temperatures of space.
Euclid is currently 1.5 million kilometers (or one million miles) from Earth, where the temperature can drop as low as -455 degrees Fahrenheit. At this distance, frozen water molecules are a typical issue for spacecraft, but Euclid needs to keep its optical system clear of ice in order to study the black universe.
The crew devised a plan to use a pre-launch decontamination operation to heat the spacecraft in order to help offset the freezing water issue with the telescope. Turning on the telescope’s onboard heaters, however, can have an impact on its mechanical structure and cause expansion that might prevent the spacecraft from shrinking back to its initial size.
Rather, ESA reports that mission control will issue commands to warm low-risk optical components of the spacecraft, beginning with two of Euclid’s independently tunable mirrors. Should it fail to resolve the issue, the researchers will proceed with heating other sets of mirrors on Euclid.
“De-icing should restore and preserve Euclid’s ability to collect light from these ancient galaxies, but it’s the first time we’re doing this procedure,” Reiko Nakajima, VIS instrument scientist, said in a statement. “We have very good guesses about which surface the ice is sticking to, but we won’t be sure until we do it.”
It’s an experimental process, but the risk is justified because Euclid may be unable to survey a third of the sky with previously unheard-of sensitivity—enough to see even the tiniest galaxies.
Euclid has previously bounced back from a concerning problem. The telescope’s exact pointing at specific areas of the universe was made possible by its precision guiding sensors, which were periodically losing sight of guide stars shortly after launch. Euclid’s software was patched by the local team, enabling a complete recovery.