Destination L2: JWST's Journey in 2018
by Sophia Nasr
Okay, I gotta geek out a bit: the James Webb Space Telescope IS COMPLETE!!! I've been waiting for this space telescope to become a reality forever!
The JWST, *named after former NASA administrator James Webb, is a next generation space telescope, with 7 times the collecting area of the Hubble, and 18 hexagonal mirrors making for a 6.5 meter mirror. It is also sensitive to infrared light, unlike the Hubble. This will allow the JWST to probe the formation of galaxies and stars in the early Universe, as well as planet formation. The reason infrared light is useful for early stars and galaxies is due to the expansion of the Universe—as the Universe expands at an accelerated rate, the farther we look into the Universe, the more redshifted objects become because they are moving away from us more rapidly. This causes light emitted at visible wavelengths to become redshifted, hence infrared will be useful to probe these objects. For planet and star formation, because they occur within clouds of dust, infrared light is optimal as it is able to get through, as the longer wavelengths don't get scattered off the dust particles like the shorter wavelengths of visible light do. And since planets emit in the infrared, the JWST will be able to study planets around other stars as well.
The JWST will be placed at the Lagrange 2 (L2) point some 1.5 million kilometers from Earth, which is behind Earth such that the Earth will shield it from the Sun. This means that humans cannot repair this telescope like the Hubble (which was only 560 km from Earth)—the JWST needs to work before launching! This is why testing will be done during this period to ensure the JWST goes into space without issues. It is set to launch in 2018. With an eye that can see deeper into space, the JWST will reveal much about the Universe that yet remains hidden to us.
Because the JWST will be placed at L2, here's a bit of an explanation about Lagrange points. **These points are named after mathematician and astronomer Joseph-Louis Lagrange (actually, the mathematician and physicist Leonhard Euler had a hand in the discovery of some of these points too, but Lagrange's analysis of the points, as well as the discovery of the remaining points, earned him the naming of the points; you can find out more about this, as well as the mathematical formalisms, linked below). There are 5 Lagrange points around Earth's orbit (in fact, this is true for any two-body system, where the two-body system in this case is the Earth-Sun system; Jupiter has them as well, and L4 and L5 are where its Trojan asteroids lie; more on why this is the case this later). L1 lies the same distance from Earth as L2 (1.5 million kilometers), but instead of the Earth being between that point and the Sun as is the case for L2, it lies between the Earth and Sun. This makes it a great place for missions studying the Sun, like the Solar and Heliospheric Observatory. L2, although farther from the Sun, won't have a longer orbital period as you'd expect, thanks to Earth's gravitational pull—it'll have the same orbital period as Earth, keeping it shielded from sunlight throughout the mission. This is where the WMAP and Planck, satellites that studied the CMB, are located. It is worth noting the same is the case for L1—you would expect a shorter orbital period because it's closer to the Sun, but because of Earth's gravitational pull, its orbital period is the same as that of Earth. L3 lies opposite Earth's orbit behind the Sun (no satellites have been placed at this point). L4 and L5 lie at 60 degree angles ahead and behind Earth along its orbit.
Now, let's talk about the stability of these points. L1, L2, and L3 are unstable points, whereas L4 and L5 are stable. The reason L1, L2, and L3 are unstable is because the gravitational potential contour sort of places them atop a hill (think of a ball sitting on top of a curved surface), where a tiny nudge in either direction would cause an object to fall out of equilibrium—these are called "metastable" points. Because they're metastable, objects here tend to drift out of equilibrium, and a slight nudge in any direction could cause a satellite to drift off. Because of this, satellites at these points require adjustments to ensure they remain in place, which the JWST will get, just as WMAP and Planck have. L4 and L5, on the other hand, are stable, sitting atop a potential hill where you could think of it as a hill with a surface curved inward at the top to keep objects in place, so that any nudges in any directions push them right back down to equilibrium. This is why there's a bunch of dust and some Trojan asteroids at L4 and L5 near Earth, and why Jupiter has some 6000 Trojan asteroids at these points! L2, as you may have guessed, is a great place to put a satellite studying the Universe, because the Earth blocks sunlight from interfering with data. This makes it a great point for the JWST. ***But it won't be completely shielded from the Sun by the Earth because it'll orbit about the L2 point; this is where its sun shield comes in (which also has solar panels, one of its power sources; you can learn more about this and its instruments at JWST's official website, linked below). The difficulty, however, is that we cannot send humans to make repairs because of how far it is; this is why the testing previously mentioned is so important: the JWST must reach its destination at L2 without problems that require human hands to fix!
As we await in anticipation for the launch of the JWST, one thing is for sure: this next generation space telescope will reveal the early Universe to us in ways we've never seen before.
More on the JWST: World's Largest Telescope is Complete, Expected to Launch in 2018
About James Webb: Who is James Webb
More on Lagrange points: Lagrange Points
Mathematical formalism and history/discovery of Lagrange points: The Lagrange Points
*Added info and link to who James Webb is.
**Added the origin of the naming of the Lagrange points.
***Added a bit more info on how the JWST will move about L2 so as not to confuse the reader into thinking the satellite will always be shielded by the Earth (it needs a sun shield), as well as noting that solar panels are one source of its power.