But how can ice form on James Webb in space?

It may seem surprising, but ice can form on components of the James Webb Telescope, even in space. How is this possible and what is NASA doing to limit the risks?

Gradually, James Webb Space Telescope (JWST) adjust your “view” of our Universe. Launched into space in late 2021, the observatory is in the process of aligning its mirrors. It should be ready for science in the summer of 2022. This involves cooling the telescope, which is designed to operate in the infrared.

One of its instruments, MIRI (which must observe in the mid-infrared), requires an operating temperature below -266 °C. Therefore, how do you remember NASA on March 30, 2022, is equipped with a refrigerator. ” But it also requires radiators to control its cooling and prevent ice from forming in space. “, adds the agency. One may be surprised that ice can form at the observatory, right in the middle of space.

But where does this water come from?

To understand this, you have to go back a bit, to the time of the launch of the JWST. ” Moist air was trapped between components, such as the sun visor membranes and their many insulating layers. », highlighted the space agency To this must be added the materials of the telescope that were capable of absorbing the value of water, present in the Earth’s atmosphere. ” Most of this air escaped just 200 seconds after liftoff, but some moisture remained. “, completes NASA.

Preparation of the MIRI instrument. //Source: NASA/Chris Gunn; Caption: NASA/Rob Gutro (cropped photo)

In space, water does not behave as it does in our planet. « In a perfect vacuum, water can only exist as a gas, but even space is not a perfect vacuum. », Explain the space agency In this other environment, water degasses (loses its gas) above -113°C (160 Kelvin). ” If water molecules float and come into contact with a surface cooler than 140 Kelvin [ndlr : -133°C], they will stick to it in the form of ice and will never come off. This is extremely important for the Webb telescope to avoid. », it states The NASA

In order not to find itself in this situation, NASA has planned the cooling of James Webb, and this as soon as the deployment of the heat shield. The temperature drop was handled carefully, the order in which the components had to cool down was not chosen randomly. ” This allowed the water to escape into space instead of freezing into sensitive components.. »

As for MIRI, the refrigerator is therefore in charge of transporting the heat to the other side of James Webb’s sun visor, where it is hot. It is essential to remove the water to properly cool MIRI, or store the water in the areas provided for it. Know that you can follow online cooling of this instrument. The objective is to cool the MIRI below 6 Kelvin (-270°C), without “ruining” it by letting the water freeze in this instrument; hence the importance of having an adequate heating technique.

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