Why are James Webb’s mirrors gold?

The James Webb Large Primary Mirror is usually the largest star in space telescope photographs. After all, its 6.5 meters in diameter makes it almost invisible, and much more if you add an impressive golden color that automatically captures our eyes. But, Did you know that NASA used one of the most valuable materials to create this mirror? on the ground? That’s right, we are talking about gold, and it was not just a whim.

Although the images of James Webb are quite a spectacle, the engineering of this machine is no less amazing. In fact, it is thanks to this incredible technology that Webb is able to capture more detailed images than its smaller brother Hubble.

But exactly how much gold does the 18 mirrors that make up James Webb’s primary mirror cover? According to the website Webb telescopeto cover these tools, NASA used about 48 grams of the precious metal.. “The mass equivalent of a golf ball that would fill a volume the size of a marble,” says the aforementioned source.

The Science Behind James Webb’s Primary Mirror

No, NASA didn’t use gold to show the world how many millions of dollars it cost to build the James Webb Space Telescope. The artifact’s 18 hexagonal mirrors have a fairly bright gold plating, but it’s clear that the space agency chose to use this metal for other than aesthetic reasons.

In fact, this was such a popular question that NASA decided to answer it. Paul Geithner, Deputy Project Manager for the James Webb Space Telescope, mentioned that There are two reasons why the agency decided to use this material in the manufacture of the telescope..

• The first refers to the ultraviolet and visible light emitted by the first luminous celestial object that existed in the universe. After 13,000,000,000,000,000 years and an ever-accelerating expansion of the universe, this light went through a redshift process. What does it mean? Well, visible light has been stretched in such a way that its waves have moved to the infrared level.
• The second reason has to do with clouds of gas and dust. Geithner explains that because planets and stars form inside these clouds, they are very difficult to see in visible light alone. That’s why they rely on infrared waves.which can really penetrate these gaseous formations and allow us to see what is inside and outside.

For both reasons, James Webb mirrors were designed with a specific task in mind: reflect as much infrared light as possible. And this is where gold comes into play.

Reflectivity of materials: why NASA chose gold

In a series of videos released by NASA during James Webb’s construction, he delves into a very important part of the process: the gold selection criteria. So we know that The agency studied several other metals in developing the primary mirror. telescope.

Also, it is at this point that they comment on the reflectivity of certain materials. and its efficiency in reflecting infrared light.

According to the narrator in the video, “There are a number of reflective materials that are excellent at reflecting infrared light.” The first of these is aluminum, which can reflect up to 85% of light at this frequency. This is followed by silver, which can raise your bet to 95%. Gold takes the crown, with 99% infrared light reflectivity emitted by celestial objects.

While silver is still a great candidate, there is a problem: it tarnishes too easily. Meanwhile, gold not only offers the best reflectivity. It is also one of the least reactive metals with other chemicals.and it is so durable that it can stay in space without rusting or deteriorating.

How much gold was used in James Webb?

The best thing is that the amount of material itself was quite minimal. Although the process of coating the hexagons is difficult and probably expensive, the amount of gold used is truly amazing considering the size of James Webb’s primary mirror.

Gold plating on James Webb mirrors it’s 100 nanometers thick. If you need context to get the picture, consider that the average mirror is 3,000,000 nm (3 mm) thick.

How did they manage to apply such a thin layer of gold? This process is known as vacuum vapor deposition.. As the name suggests, a small amount of gold is then evaporated in a vacuum chamber. The material then condenses on the surface, creating a film on the mirror. This process takes at least an hour and is performed separately in each of the hexes. In fact, there is a video to prove it.