Why NASA's James Webb Space Telescope Matters So Much - Quanta Magazine
Dec 03, 2021 14 mins, 37 secs

The James Webb Space Telescope promises to revolutionize our understanding of distant planets and deep time.

To look back in time at the cosmos’s infancy and witness the first stars flicker on, you must first grind a mirror as big as a house.

The very faintest, farthest galaxies we would see still in the process of being born, when mysterious forces conspired in the dark and the first crops of stars started to shine. .

But to read that early chapter in the universe’s history — to learn the nature of those first, probably gargantuan stars, to learn about the invisible matter whose gravity coaxed them into being, and about the roles of magnetism and turbulence, and how enormous black holes grew and worked their way into galaxies’ centers — an exceptional mirror is not nearly enough.

Ultraviolet and visible light spewed by the farthest stars in the sky stretched to around 20-times-longer wavelengths during the journey here, becoming infrared radiation.

The ability to see faint infrared sources doesn’t just grant you access to the universe’s formative chapter — roughly the period from 50 million to 500 million years after the Big Bang — it would reveal other, arguably just as significant aspects of the cosmos as well, from properties of Earth-size planets orbiting other stars to the much-contested rate at which space is expanding.

(The whole observatory, for that matter, including its mirrors, cameras and other instruments, its transmitters and its power sources, must have only about 2% of the typical mass of a large ground-based telescope.) Nothing about building a giant yet lightweight infrared-sensing spacecraft is easy, but the unavoidable use of fabric makes it an inherently risky affair.

The rocket is scheduled for liftoff from Kourou, French Guiana, on December 22, more than 30 years after its payload, the James Webb Space Telescope (JWST), was first envisioned and sketched.

Now, he said, “we’re going to put our zillion-dollar telescope on top of a stack of explosive material” and turn things over to fate.

Video: The James Webb Space Telescope is like nothing ever launched into space.

With the Hubble Space Telescope, we’ve learned that stars, galaxies and supermassive black holes existed far earlier in cosmic history than anyone expected, and that they have since undergone radical change.

We’ve learned that dark matter and dark energy sculpt the cosmos.

With the Kepler telescope and others, we’ve seen that all manner of planets decorate galaxies like baubles on Christmas trees, including billions of potentially habitable worlds in our Milky Way alone.

These discoveries have raised questions that the James Webb Space Telescope can address.

“Every time we build new equipment,” Mather said, “we get a surprise.” .

The launch will begin what the astronomer Natalie Batalha called “six months of pins and needles,” as the staggeringly complex telescope will attempt to unfold and focus itself in hundreds of steps.

“It will be our own ‘dare mighty things’ moment,” said Grant Tremblay, an astrophysicist at Harvard University who served on the telescope’s time allocation committee.

We’ll be in The New York Times talking about how this is witnessing the birth of stars at the edge of time, this is one of the earliest galaxies, this is the story of other Earths.” .

The last time NASA launched an observatory of such significance — the Hubble Space Telescope, in 1990 — it was a disaster.

Fixing it was possible because, as an optical telescope that’s sensitive to the colors of the rainbow rather than to infrared light, Hubble can get a clear view from low-Earth orbit, only 340 miles up, instead of having to travel a million miles away.

Images of the galaxy M100 taken by the Hubble Space Telescope before and after astronauts installed a corrective lens on the telescope’s primary mirror in December 1993.

“The puzzle is we see a very lumpy universe today,” said Faber, who was a graduate student studying galaxies in the late ’60s.

Cosmologists knew atoms must have gradually clumped together because of gravity, eventually fracturing into structures like stars and galaxies.

Enter dark matter.

This evidence for substantial missing matter in and around galaxies, dubbed dark matter, matched Fritz Zwicky’s 1930s observations that galaxies seem to attract each other more than they should based on their luminous matter alone.

Also in the ’70s, Jim Peebles and Jerry Ostriker of Princeton University calculated that rotating galactic disks consisting only of stars, gas and dust should become unstable and swell into spheres; they posited that invisible matter must be creating a stronger gravitational well within which the visible disk rotates.

In 1979, Faber and Gallagher wrote an influential paper compiling all the evidence for dark matter, which they pegged at about 90% of the matter in the universe.

These researchers realized that dark matter, with its substantial gravity and imperviousness to light’s pressure, could have bunched up relatively quickly in the early universe.

Peebles, who won half of the 2019 Nobel Prize in Physics for his contributions to cosmology, developed a qualitative picture in which dark matter particles would have glommed together into clumps (known as halos) that then combined into bigger and bigger clumps.

Though visible matter was at that time too complicated to simulate, researchers surmised that the conglomerating dark matter would have brought luminous matter along for the ride: Corralled within dark matter halos, atoms would have bumped together, heated up, sunk toward the center and eventually gravitationally collapsed into stars and disk-shaped galaxies.

One of the Hubble telescope’s most impactful discoveries, and a major impetus for building its successor, the Webb, occurred in 1995, two years after its corrective lens was installed.

Bob Williams, then the director of the Space Telescope Science Institute in Baltimore, the operations center for Hubble as it will be for Webb, decided at the suggestion of some postdocs to devote all 100 hours of his “director’s discretionary time,” with which he could point Hubble wherever he wanted, to pointing it at nothing — a dark, featureless little patch of sky narrower than a thumbnail moon.

Bahcall and his wife, Neta Bahcall, well-known astrophysicists, were typical in thinking that structures like stars and galaxies arose relatively late in cosmic history.

But during the 100-hour exposure, the lid of a treasure chest opened: The small rectangle of space glittered with thousands of galaxies of all shapes, sizes and hues.

Taken over 10 days in December 1995, the Hubble Deep Field photo revealed about 3,000 galaxies within a patch of sky about one-twelfth the width of the moon.

Farther-away galaxies in the Hubble Deep Field photo appear redder, since their light has traveled longer through expanding space to get here and therefore has been stretched, or “redshifted,” to longer wavelengths.

Galaxies appear at all ages and stages of development — proof that the universe has changed radically over time.

“That was a great intellectual breakthrough, that you could take one picture with a telescope, you could look back in time, and you could see that the universe was a different beast back then.” .

This bolstered the theory that they didn’t form on the strength of their gravity alone, but were carried on the backs of merging dark matter halos. .

“The beautiful universe with the beautiful [spiral and elliptical galaxies] of today is really kind of a late development,” Faber said, “and that too was visible in the picture.” Some of the duckling galaxies were colliding and merging, supporting the hierarchical clustering theory of cosmic structure growth.

And clumps of stars in the long-ago galaxies were surprisingly bright, indicating that the stars were far more massive and luminous than modern, sun-type stars. .

Astronomers observed that most galaxies reached peak luminosity, forming stars most quickly, around “redshift 2” — the distance from which light has stretched to twice its emitted wavelength by the time it gets here, corresponding to about 2 billion years after the Big Bang.

But galaxies in the process of forming, their matter somehow fragmenting into stars for the first time, are both too far and too faint for Hubble to detect, and too redshifted: The light from these galaxies has stretched straight out of the visible part of the electromagnetic spectrum and into the infrared.

“What Hubble succeeded in doing with the Hubble Deep Field is finding that there were galaxies at redshifts much higher than we thought,” Neta Bahcall told me.

In October 1995, two months before Hubble stared at nothing and glimpsed the history of time, the Swiss astronomer Michel Mayor announced another major discovery at a conference in Florence, Italy: He and his graduate student, Didier Queloz, had spotted a planet orbiting another star.

“It’s funny how these things happen, because in retrospect it was a pivotal moment,” Batalha said recently, framed by three planets orbiting a star in her virtual background.

Growing up in California’s East Bay, Batalha (then Natalie Stout) hardly thought about science, though she was thrilled, at age 17, by Sally Ride’s trip to space in 1983.

That everyday happenings could be explained with mathematical equations “gave meaning to my life,” Batalha said.

Next time, NASA greenlit Borucki’s proposal, and Batalha became a project scientist.

The Kepler Space Telescope — designed by Borucki and his team to continually monitor the brightness of approximately 150,000 stars in search of the dips of transiting planets — lifted off in March 2009.

“Kepler 10b was identified in the first 10 days of data we got back from the spacecraft,” Batalha said.

Happily, the Webb telescope will be powerful enough to probe the atmospheres and climates of other Earths — or even, if we’re very lucky, find evidence of an actual alien biosphere.

“Infrared is fantastic for exoplanets,” Batalha said.

One morning in 1987, the astrophysicist Riccardo Giacconi, who was then the director of the Space Telescope Science Institute (STScI) and of the yet-to-launch Hubble, asked deputy director Garth Illingworth to start thinking about Hubble’s successor.

“He said, ‘Trust me, you’ve got to start early because I know it takes ages to do this.’” Hubble had been under development since around 1970, spearheaded in its early years by the NASA astronomer Nancy Roman following decades of campaigning by Princeton’s Lyman Spitzer; they are known as the mother and father of Hubble.

to brainstorm about the next-generation space telescope.

“We started thinking about what would be good to go beyond Hubble and to complement whatever it did and explore new areas,” Illingworth said, “and the IR was one clear area.” Infrared light is prohibitively difficult to observe from the ground.

The trio figured that in space, where the infrared background is more than 1 million times lower, there would be plenty to see.

For an IR telescope to be as sensitive as Hubble, which has a 2.4-meter-wide primary mirror, Illingworth, Bely and Stockman realized that it would need to be significantly bigger, since it detects bigger wavelengths.

Rather than actively cool the telescope, they thought to exploit the extreme frigidity of outer space by blocking the heat of the Earth, moon and sun.

Their vague conception of a large, passively cooled infrared telescope, greatly elaborated upon, would become the cargo now awaiting launch in Kourou.

Leading astronomers convened at STScI in 1989 to discuss the science that an infrared space telescope might be good for.

John Mather, an astrophysicist at NASA’s Goddard Space Flight Center, has been the senior project scientist for the Webb telescope for a quarter century.

“Shaping and polishing telescope mirrors is a dark art that goes back hundreds of years,” said Sarah Kendrew, a Belgian-British astronomer who works on MIRI, one of Webb’s instruments.

NASA administrator Sean O’Keefe broke a tradition of naming telescopes for scientists — the Hubble telescope, for instance, refers to the American astronomer Edwin Hubble — and instead honored an earlier administrator, James Webb, who was head of the space agency during the Apollo era.

Various institutions, from the University of Arizona to the European Space Agency, signed up to build the cameras, spectrographs and coronagraphs that will swivel into place at the focal point of the optics, slicing and dicing different chunks of the pooled infrared light.

Michael Menzel of NASA’s Goddard Space Flight Center is the lead mission systems engineer for the Webb telescope — the chief engineer for the project.

The Webb telescope emerged from a vacuum chamber at NASA’s Johnson Space Center in Houston on December 1, 2017, after about 100 days of cryogenic testing.

“A delay causes its own cascade of issues,” Tremblay said — and more expense: “It costs $10 million a month just to keep James Webb on the clean room floor.” As the investment rose, so did the need for the mission to succeed.

An engineer examines test mirror segments in the clean room of NASA’s Goddard Space Flight Center in Maryland; a technician helps to pack up the sunshield for the final time in February 2021.

Once the Hubble got working, humanity soaked up the sight of the cosmos like near-sighted kids wearing glasses for the first time.

In 1998, two rival teams of astronomers used the Hubble along with other telescopes to observe supernovas in distant galaxies and ascertain that the expansion of the universe is accelerating.

This exposed the existence of an accelerating agent infusing all of space, known as dark energy.

(Another 26% is dark matter, and 4% is luminous atoms and radiation.) .

The astronomer Wendy Freedman used Hubble to observe pulsating stars called cepheids.

Its fast expansion may point to additional unknown ingredients in the cosmos beyond dark matter and dark energy.

She’ll lead a team that will use the Webb telescope to scrutinize cepheids and other stars more closely; they hope to measure the expansion rate precisely enough to tell for sure whether there’s an exotic fundamental ingredient afoot.

She and her team at Arizona are planning to use more than half of their whopping 900 hours of guaranteed telescope time to do a new deep-field survey, one that will peer deeper into the past than ever before.

Whereas Hubble could see the faint smudges of galaxies at redshift 10, corresponding to 500 million years after the Big Bang, Webb should be able to see those smudges very clearly and spot brand-new galaxies germinating farther away, perhaps as far back as 50 or 100 million years after the Big Bang.

After using NIRCam to get an image of their dark patch of the sky, they’ll identify the galaxies in the patch that are farthest away and use NIRSpec, Webb’s near-infrared spectrograph, to take the galaxies’ spectra, from which Rieke and her colleagues can deduce their chemical compositions.

The standard story is that early gas clouds, stars and galaxies mostly consisted of hydrogen, and supernovas and other explosive events gradually forged heavier elements.

“Close to the limit that Hubble can go to, there are quasars” — super-bright centers of galaxies powered by supermassive black holes — “and it looks like they have almost the same elements as the sun.

The Hubble Space Telescope is in low-Earth orbit, close enough for a Space Shuttle visit.

There are as many reasons for wanting to see the first stars and galaxies as there are astronomers, astrophysicists and cosmologists.

She and her colleagues will use the proto-galaxies to deduce the distribution of sizes of dark matter halos that must have existed in the early universe, and when they formed.

This can reveal whether dark matter is “cold,” that is, made of slow-moving particles, or “warm,” since particles that whizz around would have taken longer to huddle into halos.

They don’t know what the distribution of [dark matter] clump sizes will be, so they guess

“The main conclusion from my research,” Behroozi said, “is even if you try to make a reasonable guess, we still have no clue what James Webb will see.”

She found it inspiring to see a team accomplish something so grand, but it was the possibility of discoveries being so close at hand “that was really what flipped on my brain to start thinking about exoplanets as a concept,” said Natasha Batalha, who is serious and precise, like her mother. 

“I didn’t want to saturate their lives with science,” Natalie Batalha said

Not only will the telescope have close to 100 times Hubble’s resolution, but it will see exoplanets far more clearly against the background of their host stars, since planets emit more infrared than optical light, while stars emit less

“Imagine being in a plane and looking down at an insane cloud deck, and you can’t see the surface at all,” Natasha Batalha said

When I video-chatted with Hammel, she screen-shared PowerPoint slides highlighting various exo-worlds of interest that Webb will turn its eye toward on behalf of different observers: Kepler 16b, which orbits two stars; the suspected “lava world” 55 Cancri e; and the seven rocky planets of the nearby Trappist-1 star system

(Hammel, who gets 100 hours of guaranteed observer time as a longtime member of the Webb science team, will browse our own solar system, including Jupiter’s red spot, the mysterious, far-flung objects of the Kuiper belt, and Hammel’s oft-overlooked favorites, Uranus and Neptune, which appeared as a pair of plush toys behind her on her office couch.) 

NASA’s Nancy Grace Roman Space Telescope, slated to launch later this decade, is mostly designed to study dark energy; Earth-like exoplanets are the purview of a future telescope concept provisionally known as LuvEx, an ultraviolet, optical and IR telescope that (if funded by Congress) will launch in the mid-2040s

Assuming that, over the next few months, everything unfolds as it should and the James Webb Space Telescope finds its focus, it will point at 11 of these planets on behalf of Natasha Batalha and her team

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