D-15: Large Adjective Astronomy

The following is another guest post originally written by Murmeldjuret on the Stellaris forums. Reproduced here with permission. Thanks, Murmedjuret.

 

As much as we all love Hubble Space Telescope and its images, it is getting rather old. 26 years old as a matter of fact. There has been talk about sending up a newer and larger space telescope, but the cost would be well, astronomical. Why space telescopes then? Well because they do not have a pesky atmosphere between them and space. The atmosphere is turbulent, varying in heat, pressure, and humidity. The atmosphere also heavily absorbs in some wavelengths, effectively making them dark to anyone on the ground. Notably ozone in ultraviolet and water in infrared. Seeing in infrared is very important as dustclouds and nebula more easily block shorter wavelengths. Many stars and galaxies are invisible behind dustclouds unless you look at them infrared.

The successor to Hubble Space Telescope (the James Webb Space Telescope or JWST) is planned to be launched in 2018, and it is primarily a near infrared (NIR) telescope, capable of seeing from 600nm (visible orange) to 28000nm.
It will be better than anything we now have at imaging brown dwarfs, planets, kuiper belt, comets, galactic cores, and anything else cold or hidden behind a dustveil. It won’t be in the same RGB colours we see, but it will still generate detailed images in false colour.

Problem with infrared is that anything cold will also be seen by it, namely the interplanetary dust in the solar system. The sun and dust could also warm it so much it takes pictures of its own lens, welcome to infrared optics. It has to be launched to L2 lagrange point, 1.5 million kilometers behind earth, so the dust around earth is far away. It has a massive sunshield to block the sunlight and cool it down so it doesn’t see its own optics.

Its mirror’s effective diameter is 6.5m, which compared to Hubble’s 2.4m is quite a bit larger. It is actually too large to fit on any launch system and has to be folded up to fit inside. It will be in a elliptic orbit at L2 lagrange point, following earth but orbiting the sun and not earth. It will use a few m/s delta-v per year to maintain the orbit, so the L2 orbit is not exactly cheap.

Spoiler: James Webb Space Telescope

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Now, what is the alternative to massively expensive space telescopes? Well that is ground based telescopes, currently the highest resolution is 0.001 arcesconds from the Very Large Telescope Array, with its four 8.2m telescopes. With the advent of high energy lasers, ground based telescopes have gotten a lot better. 0.001 arcseconds resolution is about 1 pixel being 2x2m on the surface of the moon. The only way before to counteract the turbulent atmosphere was to find a stationary star and using the stars distorted movement to compensate with adaptive optics. This is all fine and well, but most of space does not have a stationary star. The modern solution is to use a high energy laser at a specific wavelength that makes sodium fluoresce, or glow.
In the upper atmosphere there is a sodium layer, and this high energy laser creates an artificial guidestar in that layer. We can use this artificial guidestar to compensate for the turbulence.

Though a 8.2 meter telescopes on earth don’t even come close to the resolution you get from 6.5m in space. What does? 39 meter telescopes. The greenlighted 39m European Extremely Large Telescope, yes that is the name, is planned to be finished in 2024, and it will have a resolution more than 10x what Hubble has. NASA also has a 30m telescope under construction, but it looks like it might get cancelled from budget, religious, and a 39m telescope already being underway. Like JWST, ELT will take images of distant solar systems and galaxies, meaning we can resolve planets, not just infer them from looking at the star.

Spoiler: VLT with guidestar laser

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Spoiler: ELT Dome with car for scale

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So JSWT will be able to take the best images we have ever seen before of space, and it will launch in two years, and a few years after that we will get a telescope we don’t even know how good it will be. JWST will be able to see things we have never seen before from its high resolution infrared system, and then we will get even higher resolution images from ELT. If you want to compare cost, the JWST lands at 8.8 $billion, and E-ELT at 1.5 $billion.

Spoiler: Comparison between mirrors

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Here is comparison of the different space imaging systems, with a human, tenniscourt, basketball court, and a Radio Telescope for comparison. JWST and Hubble are down in the bottom left, E-ELT is on the right. There is a human just below E-ELT for scale. The big grey ring in the background? That is the other proposal that was discarded in favour of ELT. The European Overwhelmingly Large Telescope with a 120m mirror. Yes, that was the planned name. It was cancelled because we don’t even know if it is possible to build a dome to hold it. The ELT is already a composite mirror of nearly 800 panels, and it would only be a fraction of the requirement for OLT.

So what can we expect?
Well the first mission of JWST is to look at KIC 8462852, which we have been unable to rule out contains intelligent life. High resolution infrared images would tell us a lot about the system.
This is an image of Formalhaut b, a massive planet around an A-sequence star we saw two episodes ago. We can already resolve it to several pixels. This is what we might see of it with JWST and ELT:

Spoiler: Disclaimer: I photshoped the right image, mostly based on guesswork

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The above image might not seem like it but we see both a moon and rings surrounding the planet, scattered dustcloud and noise (it is scaled up from 60×60).

As wondrous as Hubble’s images have been, they are about to look very outdated.

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