In space, the James Webb Telescope will look like a giant sunflower sitting on a silver "surfboard" to protect the telescope from the sun. heat and glare from the Sun. The petals of this flower will consist of eighteen gold-plated beryllium hexagons which together will form a mirror more than six meters in diameter. But why gold, precisely?
The result of a collaboration between NASA, the European Space Agency and the Canadian Space Agency, the James Webb Space Telescope should lift off on December 24 at the latest early . Once deployed, it will be the most powerful observatory ever launched into space. The secret to his impressive powers of observation? A huge golden mirror whose objective will be to capture as much light as possible from the most distant objects in the universe.
The primary mirror of the James Webb Telescope spans 6.5m in diameter , which makes it much larger than that of the Hubble Space Telescope (2.4 m in diameter). This mirror consists of eighteen hexagonally shaped segments designed to interlock with each other. This form was obviously not chosen at random.
"If the segments were perfectly circular, there would be spaces between them ", says NASA, adding that a near-circular shape was still desired, because it "allows the light to be concentrated in the most compact region of the detectors ". An oval mirror, for example, would have elongated images in one direction, while a square mirror would have sent much of the light out of the central region.
In addition to its shape which allows it to capture light from very far away, the JWT mirror also works with actuators. There are six at the back of each hexagonal segment. All of these mechanical parts will move each of these mirrors slightly, allowing the mission team to fine-tune the view from the observatory.
Besides its hexagonal shape and huge size, the most notable feature of this mirror is its gold coating. But then, why gold?
In fact, gold is extremely reflective. It offers the highest reflectivity over a very wide band of wavelengths. This metal would therefore be ideal insofar as the telescope will be responsible for capturing a maximum of individual photons. Here, the primary mirror of the JWT will be approximately 98% reflective , which means that it will reflect about 98% of the incoming photons. Technically speaking, it is difficult to do better.
However, note that while the mirror segments of the JWT are indeed covered in gold, they are not solid gold, but constructed from beryllium, a very light metal . For your information, each of these segments weighs about twenty kilos on Earth. Beryllium is also very strong, durable and can also retain its shape once exposed to the extremely cold temperatures that the JWT will need to operate at (down to -220°C).
