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T

he telescope Galileo Galilei first

pointed at the heavens in 1609 had

a lens no wider than a slice of cu-

cumber. Yet with that modest tool,

he saw the rings of Saturn, the

moons of Jupiter—and sparked a

scientific revolution that toppled

Earth as the center of the cosmos.

Astronomy has come a long way

since then. But when the James Webb Space

Telescope launches in December, with a

6.5-meter mirror that would tower over

Galileo himself, it will open views of the

universe’s first stars and galaxies, probe the

atmospheres of planets around

other stars—and launch another

revolution. “James Webb will

blow the lid off everything,” says

exoplanet hunter Sasha Hinkley

of the University of Exeter.

Webb’s mirror has more than

five times the light-gathering

power of the 31-year-old Hubble

Space Telescope. Unlike Hubble,

Webb will work in the infrared,

allowing it to see the heavily “redshifted”

light of distant objects and peer through

clouds of obscuring dust. It will also be

able to sift exoplanet atmospheres for gases

whose infrared fingerprints are mostly off-

limits to ground-based observatories. “We’ve

never looked at the universe at these wave-

lengths and these depths and resolution,”

says Steve Finkelstein of the University of

Texas, Austin, who will lead several projects

looking at distant galaxies in Webb’s first

year. “I think we’ll be in for some surprises.”

More than 1000 teams of astronomers

from across the globe applied for time

on Webb in its first year, and

286 got lucky. They will task

the telescope with a range of in-

quiries: looking for ice-covered

oceans on Uranus’s 27 moons,

searching for elusive medium-

size black holes, and resolving

conflicting measurements of

the expansion rate of the uni-

verse. But broadly speaking,

they will use Webb to pursue

two overriding themes, at opposite ex-

tremes of time and distance: the early uni-

verse and nearby planetary systems.

Researchers want to glimpse the uni-

verse’s gargantuan first stars and study

how messy clumps of them evolved into

orderly, spiral galaxies. They want to wit-

ness the evolution of the giant black holes

at the centers of many galaxies and chart

their role in clearing a fog of neutral hy-

drogen gas that filled the early universe.

In the nearby universe, Webb is expected

to transform our knowledge of how gas

and dust around young stars coalesce into

planets, what conditions on those worlds

are like, and whether they provide a wel-

coming habitat for life.

It is a dream telescope, and one that has

been many years—and $10 billion—in the

making. Early on, Webb was expected to

launch in 2011 for less than $2 billion. But

the complexity of new technologies such as

the segmented mirror and the cryocoolers

that keep instruments cold enough to see

far-infrared wavelengths led to delays and

Just 40 light-years

away, the seven

known planets of the

TRAPPIST-1 system

(artist’s concept)

are Earth-size.

The James Webb Space

Telescope will probe

the composition

of their atmospheres.

At long last, the James Webb Space Telescope is set to launch. It will capture

cosmic dawn and bring alien worlds into view By Daniel Clery

MACHINE

12 NOVEMBER 2021 • VOL 374 ISSUE 6569 807