The Next Great Space Telescope
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The James Web Space Telescope
Astronomers around the world are anticipating another giant leap in the understanding the universe as they await the launch of the next great space telescope this month, the James Webb Space Telescope (JWST). In the past, the introduction of a new technology to look at the sky increased our understanding manyfold. Ever since Galileo turned a telescope to the heavens in 1610, every application of bigger and better telescopes has changed the way we understand the cosmos.
The JWST is a joint NASA–European Space Agency–Canadian Space Agency project. When launched on December 22, it will be the largest telescope ever sent into space. The telescope is named after James Webb, who was the NASA administrator during the early American crewed spacecraft program from 1961 to 1968.
NASA has been sending telescopes into space for decades. The largest to date is the Hubble Space Telescope, launched in 1990. Hubble observes primarily in the visible light spectrum and has made many discoveries. The JWST will observe in the infrared spectrum. Infrared light is really just thermal energy, or heat. Astronomers like to observe distant objects in various frequencies of light, not just the visible. The more light frequencies they study, the more they can learn about the object they are studying. Much of the radiation from these far away objects, such as ultraviolet, infrared, X-ray, and gamma ray, does not make it to Earth’s surface because the atmosphere absorbs it. To observe in these frequencies, astronomers need to place their telescopes in space, above the atmosphere.
The JWST will be 100 times more powerful than Hubble. It has a 6.5-metre-diameter mirror, compared to 2.4 metres for Hubble. The JWST mirror is made up of 18 separate hexagonal mirrors, each 1.3 metres wide. To fit on top of the rocket, the entire telescope is folded up for launch. Then once in space, the assembly opens up like a flower. The mirrors are coated with gold, because gold is excellent at reflecting infrared radiation.
With a larger mirror, the JWST can see objects fainter and farther away than Hubble can. When we use a telescope to see distant objects in the universe, we are seeing them not as they are, but as they were when the light we see left them. The JWST will be able to detect the light from galaxies that are billions of light-years away. It will search for light from the very first stars and galaxies that formed after the Big Bang. The telescope will observe the formation of stars, planetary systems, and galaxies and look for exoplanets (planets orbiting other stars) that may be able to support life.
Unlike Hubble, which is orbiting Earth, the JWST will be positioned 1.5 million kilometres away from Earth, at a gravitationally stable point called Lagrange point 2 (L2). Since the telescope is detecting very faint heat radiation, it needs to be kept very cold, –225 degrees Celsius. The telescope carries a large Sun shield, about the size of a tennis court, to deflect the heat from the Sun. If the telescope were placed in orbit around Earth, it would get too hot. Situated at the L2 point, the telescope will follow Earth around the Sun, making radio communication with the telescope possible.
After it is launched into space, it will take two weeks to slowly unfold all of its various pieces. It will be a tense two weeks since the telescope is on its own. Unlike the five times when space shuttle astronauts visited Hubble to make repairs, astronauts will not be able to reach the JWST because it will be too far away.
Canada has provided two components to the JWST: a scientific instrument and a guidance sensor: the NEar-Infrared Imager and Slitless Spectrograph (NIRISS) and the Fine Guidance Sensor, respectively.
NIRISS will examine the light coming from distant exoplanets and galaxies and determine their composition. A spectrograph spreads the incoming light out into various frequencies. By examining the strength of the light at each frequency, astronomers can figure out the composition of the object. How will this be used? By examining the atmosphere of an exoplanet, astronomers will be able to determine if it is capable of supporting life as we know it.
Canada's Fine Guidance Sensor (FGS) and the Near-Infrared Imager and Slitless Spectrograph (NIRISS) at NASA's Goddard Space Flight Center. (Credit: NASA)
The Fine Guidance Sensor will be used to accurately point the telescope at the star or galaxy the telescope will be examining.
In exchange for supplying these instruments, Canadian astronomers will be given time on the telescope. Over the first few years, teams of astronomers from various Canadian universities will be given over 400 hours of telescope time to carry out a program of study: to look at the atmospheres of exoplanets and to study galaxy clusters that formed not long after the Big Bang.
The JWST has had a troubled development. It is over 10 years behind schedule and billions of dollars over budget. Problems managing the program, technical delays, and the COVID pandemic have all contributed to the delay.
It can be said that astronomers have put all of their eggs in one basket with the launch of the JWST. If something goes wrong with the launch or the deployment of the various pieces over the two-week period after the launch, there is no way to recover. A loss of the launch vehicle would be an instant disaster. If for some reason there is a problem deploying all the various mirrors and sunshields, the telescope may be unusable. A loss of JWST would cripple astronomy for decades.
Meanwhile, there is a new, interesting twist to the JWST story. This summer, NASA is studying evidence that James Webb discriminated against LGBTQ government employees during the late 1940s and 1950s. There was some talk that the telescope would be renamed. That is unlikely now.
JWST watchers are patiently waiting for the December 22 launch.
