Why is the JWST infrared?

The James Webb Space Telescope (JWST) is set to launch into orbit a whopping 930,000 miles (1.5 million kilometers) from Earth in 2018 [source: JWST]. It’s set to observe some pretty spectacular science in the process: The JWST is designed to help us look far into the depths of the universe and help us understand the very early beginnings of galaxies, stars and planets. If you are up-to-date on your supersensitive telescopes, you might be frowning and harrumphing that Hubble already did that. Why the repeat?

First off, life is short — let’s not get all worked up about telescopes that haven’t done us any harm. Second, NASA is quick to point out that JWST isn’t just a replacement for Hubble; it’s designed to look at space a little differently. Despite its similar mission to Hubble, JWST is equipped with some new technology and advancements that are going to let us probe a little deeper into the universe and collect images with more precision.

The biggest change from Hubble? Instead of observing in the visible and ultraviolet spectrum, JWST will be performing almost all of its observations in infrared. Because infrared wavelengths are so obviously superior, right?

Hmm. That doesn’t check out. Why the heck does it matter that the Webb is looking at the infrared spectrum?

There are several reasons that infrared is ideal for JWST, and each one fits nicely into some goals of the telescope’s mission. For one, JWST is going to study nebulae — big, dusty clouds where stars are born. And while nebulae are gorgeous, scientists are not thrilled that they do a great job of obscuring the stars and the space around them. Infrared lets us look into those pretty clouds and get a better look at early star formation [source: Masetti].

Scientists also want JWST to get a good glimpse at some early galaxies. Here’s one problem with “looking” at early galaxies: The farther back we look, the light that was once visible or ultraviolet has now become harder and harder to see by the time it has reached us. The light has now gone through a redshift and is only visible on the infrared spectrum. Got an infrared telescope? You can now see the first bright objects in the universe [source: Masetti].

One more infrared advantage: It can help us determine the atmospheres of exoplanets, our cosmic cousins that orbit other stars. JWST will be doing spectroscopy of those exoplanets by making detailed measurements of certain lights at different wavelengths or energies. Certain elements will give off different energies; by looking at the absorption spectrum, you can see what molecules are present in the atmosphere. Infrared can show a larger number of spectral features than can visible or UV wavelengths [source: Masetti].

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