By Jonny Lupsha, Wondrium Staff Writer
NASA’s $10 billion successor to Hubble is fueled up and ready to go. The James Webb Space Telescope uses infrared, rather than visible light, to see the Universe. An astrobiologist explains why it matters.
A space center in French Guiana, a small region along the north coast of South America, is currently hosting the James Webb Space Telescope (JWST) before its launch on the rocket Ariane 5 on December 25. The JWST is a space telescope that will detect infrared light to observe outer space in ways that its predecessor, the famous Hubble Space Telescope, cannot.
So what can JWST do and why is it such a big deal? In an exclusive interview, The Great Courses Daily spoke with Dr. Sarah Rugheimer, Glasstone Research Fellow at Oxford University and professional astrobiologist, for this three-part series looking at this historic launch. Dr. Rugheimer, who also partnered with The Great Courses for the Audible Audiobook Searching for Extraterrestrial Life, earned her M.A. and Ph.D. in astrophysics from Harvard University.
Hubble vs. Webb
Most of us are familiar with the Hubble Space Telescope. Among its many accomplishments, it helped determine the age of the Universe. The JWST sees the world a different way—literally. It will look at the Universe in infrared light, compared to Hubble’s detectors which mainly operate in the wavelength region of visible light.
“Hubble was the first big optical telescope we ever did and James Webb is the first big infrared space telescope,” Dr. Rugheimer said. “You can’t have a telescope that does all of the wavelengths because they just require very different designs and operating conditions. What Hubble did for optical astronomy, James Webb will do for infrared astronomy, and the questions you can answer with different wavelengths are very different.”
For example, the JWST has the ability to look at the first stars and galaxies that formed in the Universe. This is because due to the Universe expanding and those ancient stars moving away from us, the wavelength of those stars gets stretched, like a Slinky®, from the visible spectrum to the infrared spectrum. The JWST can basically look further back in time than ever before, closer to the Big Bang.
Sorry to Keep You Waiting
Before sending back groundbreaking pictures of outer space, Hubble got off to a rocky start. A calibration error in the grinding of one of its mirrors caused Hubble’s initial images to be blurry, until astronauts could launch a second mission to give it corrective lenses. This fiasco occurred in 1991 and was fixed in 1993.
It’s also a part of why the JWST, colloquially known as “James Webb,” spent so much time in testing and was delayed for so long. Far too big to fit into a rocket ordinarily, the James Webb has been folded like origami for its flight.
During its 30-day trip to the second Lagrange point, a million miles from Earth, JWST will unfold. A solar shield that keeps it cool will deploy, as will an array of 18 hexagonal mirrors that deploy into one mirror 21 feet across. A NASA engineer said that in order to achieve the accuracy of a single solid mirror, the 18 hexagonal mirrors must align to 1/10,000 the thickness of a human hair. Everything has to be perfect.
“It’s a $10 billion mission, and we’re not going to be able to go and service it with astronauts like Hubble,” Dr. Rugheimer said. “Hubble is only 340 miles away from Earth; James Webb is one million miles. It’s going to take a month to get there, and you can’t just go up and fix it if something went wrong like with Hubble.”
Why does the JWST need to be so far away? In order for their instruments to work, infrared telescopes need to be far enough into space so that they can escape the heat given off by Earth’s atmosphere. In fact, according to Dr. Rugheimer, the ideal temperature for the telescope’s observational purposes is about 40 Kelvin, or approximately -387° Fahrenheit. One of the main infrared instruments, MIRI, will need to be cooled even further, to only 7 Kelvin. This is close to absolute zero, the lowest temperature theoretically possible, equivalent to -459.67° Fahrenheit.
Keeping its distance from Earth isn’t the only way the JWST keeps cool. In fact, the component most responsible for shading it from the Sun is its enormous solar shield, which also caused at least one delay to the launch in 2018. Back then, seven tears were found in the sun shield and, during test deployments, it snagged. If this happened in space, it could mean critical mission failure.
“The solar shield is five layers of reflective, high-performance plastic, Kapton, which blocks solar light really well,” Dr. Rugheimer said.
In fact, according to the telescope’s official Twitter account, the solar shield is equivalent to wearing sunblock with an SPF rating of one million.
“This solar shield will do the majority of the cooling by just blocking the light that can come to it, and then there will be coolants on the instruments themselves that will allow them to cool them to their proper operating temperature.”
Besides looking further back in time than Hubble and seeing the Universe’s first galaxies and stars, the JWST has another revolutionary feature: It can look at the atmospheric conditions of exoplanets. In the next part of our James Webb Space Telescope series, which publishes tomorrow, Dr. Rugheimer explains how and why.