Just as drivers scrape ice off car windshields during the winter, say scientists at the European Space Agency (ESA). Euclid The observatory is trying to “defrost” the telescope – from a million miles away.
Layers of ice, roughly the width of one strand of DNA, accumulated on Euclid's mirrors. The agency said in a statement on March 19 (Tuesday) that although the ice is small, it appears to have caused a “small but gradual decrease” in the amount of starlight captured by the telescope. The telescope is continuing its science observations for now while scientists begin heating the low-risk optical parts of the spacecraft to begin the defrosting process. The agency said these low-risk areas correspond to sections of the telescope where released water is unlikely to impair other instruments.
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“The melting ice should restore Euclid's ability to collect and preserve light from these ancient galaxies, but this is the first time we have done this,” said Reiko Nakajima, a Euclid scientist at the University of Bonn in Germany. “We have pretty good guesses about what surface the ice sticks to, but we won't be sure until we do.”
The problem is not entirely common for space telescopes. Scientists know it is nearly impossible to prevent trace amounts of water in the air from reaching the spacecraft during assembly, so “it was always expected that water would gradually accumulate and contaminate Euclid's view,” the European Space Agency said in a statement Tuesday.
After a brief period Euclid launch In July last year, scientists warmed the telescope using on-board heaters to vaporize most of the water molecules that would have entered the spacecraft before liftoff. But “a significant portion” of it appears to have survived, perhaps by being absorbed into the telescope's multiple layers of insulation, which have become loose since arriving in the vacuum of space. In the cold environment of space, these molecules tend to stick to the first surface they land on, one of which appears to be telescope mirrors.
This problem first arose when the mission team observed a gradual decrease in starlight that was measured using one of Euclid's two scientific instruments, called the Visible Instrument (VIS). To help catalog the 1.5 billion galaxies and their star clusters, VIS collects visible light from stars in a similar way to how a smartphone camera works, only with 100 times as many pixels. Therefore, its resolution is equivalent to a 4K screen.
“Some stars in the universe vary in luminosity, but the majority are stable for millions of years,” Mischa Shermer, a Euclid scientist leading the de-icing campaign, said in the statement. “So, when our instruments detected a faint, gradual drop in incoming photons, we knew it wasn't them, it was us.”
The easiest solution is to heat the entire spacecraft, but doing so would also warm the telescope's mechanical structure, whose components will expand but not necessarily return to their original state even after a week, mission scientists say. This would limit Euclid's vision, and thus affect the quality of the data he collected. The telescope is affected by even the smallest temperature changes. So Schirmer and her colleagues plan to first heat Euclid's low-risk optical parts, starting with two mirrors that can be heated independently of each other, and then observing how the change affects the amount of light collected by the VIS.
This icy dilemma marks the spacecraft's second problem in one year. Last September, a sensor intended to find stars for navigation purposes incorrectly flagged cosmic rays as stars, meaning the telescope could not identify the star patterns it relied on to orient itself to specific areas of the sky. It was the case Pinned After a month.
As for the latest release, scientists expect small amounts of water to continue to be released during Euclid's six-year lifetime in orbit. So, if they succeed in the de-icing campaign this time, the same procedure could keep the Euclid systems ice-free for the rest of their mission.
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