Webb Telescope Hunting Atmospheres

Updated: Jan 3

On Christmas Day of 2021, the James Webb Telescope, a 25-year old dream machine, finally made it from an engineer's drawing board into physical reality.

Named for the first NASA administrator, it was conceived as a replacement for both the magnificent Hubble Space Telescope that photographed the edge of our universe in glorious color and the incredible Kepler Space Telescope that did the impossible, capture images of planets orbiting stars light years away. It was originally scheduled to launch in 2007 but never had a chance of doing so with budgets too small to build the mirror alone.

And oh that mirror. That mirror alone is a design miracle. The scientists at NASA eschewed the old Cassegrain model of a single reflective device to capture interstellar light for a honeycomb model. The Hubble used the old model. This new model uses a series of hexagonal mirrors connected to each other for greater visibility and precision of measurement over time. The mirrors are manipulated by a computer to ensure their maximum ability to capture light over time.

One major problem with the single mirror design is heat distortion. As cold as deep space is, space telescopes still rely on machinery to work. That machinery has many moving parts and those moving parts generate a lot of heat. Mirrors are made of glass with a gold plating on the back side to reflect the light to where it needs to go to be measured. The problem with glass is that it is actually an amorphous solid -more than a supercooled liquid and less than a solid-meaning that its surface will distort if enough heat is applied to it. This is how glass blown lamps and other items are made. The moving parts mentioned above generate a significant amount of heat in the vacuum of space and that heat ends up distorting the giant mirrors. This actually happened early on with the Hubble and a mechanical device had to be flown up to it to adjust the focus of the light bouncing off that mirror to be able to use the telescope from that point on. The solution to that problem were those interlinked hexagonal mirrors. Any one could still be affected by that internal heat but only that mirror would then have to be adjusted rather than the entire device. In the Webb, that adjustment is accomplished automatically and constantly by computer.

Beyond that amazing achievement is the hexagonal shape itself. A normal circular mirror the size of that used in the Webb would literally be too large to fit into a rocket. Therefore, a completely new design and shape had to be crafted to achieve the size needed for the Webb to do its job and still fit into the rocket framing in order to be launched into space. The revolutionary design of the hexagonal shape solves that problem by enabling the mirror to be folded into the rocket and then unfolded when deployed in space. Normal circular mirrors also often have dead spots on their edge where light is not captured. The hexagonal shape of the mirrors in the Webb avoid that as well by fitting perfectly together eliminating those dead spots. As currently constructed, it is 7x the diameter of the Hubble which will give the Webb nearly 40x the light gathering power of Hubble. That will also enable the Webb to see 7x farther into space than Hubble could. Since Hubble could see 13.7 billion light years, that would imply Webb might see 100 billion years away.

A Webb of Two Telescopes-Hubble and Kepler

The Hubble Space Telescope was built to find and study the most distant objects in the then known universe. It did so with aplomb. The first space-based telescope showed us that the universe was 13.7 billion years 30% older than the previous Earth-based estimate. A second major discovery of this scope was that the universe was expanding not contracting as previously thought. That expansion due to the as-yet discovered 'dark matter' that is apparently flattening more space than gravity is curving. The curving would cause interstellar objects to remain close while the flattening would allow them to escape.

The Kepler Space Telescope had a different mission altogether. Conceived after Hubble on a whim of an idea in 1984, it was finally launched in 2009, 25 years later, to use a completely different method to find possible planets outside our solar system. It would use a transit system to find those planets rather than the mirror-based light gathering system Hubble used. A transit system means it would gather light from a star and wait until that light dimmed briefly. The theory was that the dimming would have to be due to an object, likely an orbiting planet, blocking the star light. The location of the planet and star would then be determined by interferometry. This ingenious concept proved itself worthy of construction almost immediately.

The Webb May find the First Interstellar Atmosphere

That a single telescope can see both near and far with equal precision is an engineering marvel. That it can do so without losing accuracy is a gem of computer science. It is a bi-focalled wonder of engineering that may find our first exoplanet with an atmosphere and therefore the first planet outside our solar system that may be habitable. Then the only question will be how to access that planet?

Go Jimmy Webb, Go!!!

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