Space probes designed to study the sun are the last place you’d expect to experience humidity issues. However, a recent study found that aluminum filters on two different moons deteriorated as the water eroded their surface. Filters help detect excessive ultraviolet (EUV) radiation, so any turbidity will definitely affect their effectiveness. Although the problem has been open for a while, scientists finally know what’s causing it.

NASA’s Solar Dynamics Observatory (SDO, launched in 2010) and NASA and the European Space Agency’s Solar Heliospheric Observatory (SOHO, launched in 1995) share the same problem. SOHO’s solar EUV monitor dropped by about 35 percent in the first six months; It got 60 percent worse over the next five years.

Solar probes aren’t exactly cheap, and it’s also not worth starting annual recalibration missions to send new sensors into space. Understanding why the filters dim could make future solar probe missions more reliable.

In 2021, a team of scientists led by physicist Charles Tarrio from the National Institute of Standards and Technology (NIST) experimentally discovered that this is not the smog-causing carbon buildup long thought to be. guilty.

Now they’ve discovered what it is, and it’s incredible: the oxidation of aluminum from the presence of water and ultraviolet radiation. As layers of oxidized metal build up, the filter fogs up, blocking the light waves the sensor is designed to monitor.

The surface of aluminum is usually naturally covered with an oxide surface layer that results when the oxygen atoms bond with the atoms on the aluminum surface. UV light increases the oxidation rate, causing additional oxide layers to form.

Normally, there isn’t much oxygen in space to bond with aluminum, but the presence of water containing oxygen atoms can make a difference. To test the water hypothesis, the researchers created EUV radiation using NIST’s Synchrotron Ultraviolet Radiation Facility (SURF) by blasting it into an aluminum filter in a vacuum chamber where water vapor was introduced.