NASA Explains Why James Webb Space Telescope Uses 'Salty' Lenses

As NASA completes all major deployments of the James Webb Space Telescope and the observatory enters a “cooling” period, the agency is sharing some interesting facts about the $10-billion (roughly Rs. 74,100 core) observatory. These include some lenses which are made out of salt. But why does this infrared telescope need a “salty” lens? In a new video, scientists working on the telescope shared why salt is vital to the deep space observatory. And the James Webb telescope uses not just one but three kinds of salt lenses.

There are various kinds of lenses. Mirrors are reflective lens, which bend the light, but there are some that allow the light to pass through them. These second types of lenses are called transmissive lenses. For James Webb, infrared light, which behaves differently than visible light, plays a vital role. The key here is: glass absorbs infrared light but salt does not.

The narrator in NASA's video says, “Salts are more than something you sprinkle on your food.” A salt is a combination of a positively charged element and a negatively charged halide. They get their charge from either losing or gaining a negatively charged electron. The salt we usually eat is sodium chloride, but that's not the only type of salt. Some other kinds are: lithium fluoride, Barium fluoride, and zinc selenide.

However in the long run, these lenses are threatened by space debris including micrometeoroids.

NASA Goddard Space Flight Center scientist Michelle Thaller said during a livestream that small impacts from micrometeorites are bound to happen. However, NASA scientists say they took this factor into account as the telescope is meant to last for 10 years. They said they have contingency plans in place to deal with this inevitability.

The five layers of the sunshield not only protect the telescope from the heat but also from dust and debris. But a micrometeoroid can come from any side and damage any part of the telescope. If a mirror is damaged, it can be accounted for.

NASA launched James Webb Space Telescope on December 25 and for the past two weeks, it has been working to unfold it in space. It has completed major deployments like the primary and secondary mirror.