18 ASTRONOMY • JUNE 2020
Warm and
not so fuzzy
ON JANUARY 30, NASA TURNED
OUT THE LIGHTS ON THE SPITZER
SPACE TELESCOPE. The infrared-sensitive
observatory had far exceeded initial expectations.
When the spacecraft blasted off from Florida in
August 2003, scientists hoped the mission would
last at least two and a half years and, with any
luck, live to see its fifth birthday. But Spitzer sur-
vived, and even thrived, until a few months after
it turned sweet 16.
Spitzer was the fourth and final component
of NASA’s Great Observatories program, which
also included the Hubble Space Telescope, the
Chandra X-ray Observatory, and the Compton
Gamma Ray Observatory. This quartet was
designed to deliver super-sharp views of the heav-
ens across a broad span of wavelengths. Originally
christened the Space Infrared Telescope Facility
(SIRTF), Spitzer was renamed for American
physicist Lyman Spitzer Jr., an early and vocal
advocate for space-based telescopes, once the
observatory opened its eye to the universe.
Spitzer’s primary mirror measured 33 inches
(0.85 meter) across, and its three science instru-
ments recorded infrared radiation, or heat, with
wavelengths between 3 and 180 micrometers.
Needless to say, heat from nearby objects would
have swamped the telescope’s sensitive detectors.
The biggest source of heat in near-Earth space is
Earth itself, so NASA launched Spitzer into an
orbit around the Sun that trails our planet and
drifts slowly away.
Yet spacecraft generate their own heat. To
combat this source of infrared radiation, Spitzer
carried a tank of liquid helium that kept its
instruments chilled to –449 degrees Fahrenheit
(–267 degrees Celsius). When the helium ran outin May 2009, the spacecraft warmed to a toasty
–408 F (–244 C). Although two of Spitzer’s instru-
ments could no longer operate, the two shortest-
wavelength channels on its infrared camera
continued to function with little change in sensi-
tivity for another decade.
Spitzer’s window on the universe allowed
astronomers to study regions largely hidden from
optical telescopes. Because infrared radiation pen-
etrates dust, the observatory could peer inside
stellar nurseries to watch stars being born. It also
looked through the thick dust lanes that clog the
Milky Way’s disk and confirmed that our galaxy
is a barred spiral.
The observatory’s ability to detect heat signa-
tures exposed the inner workings of giant molecu-
lar clouds, revealed failed stars known as brown
dwarfs, and discovered a slew of exoplanets as well
as the constituents in the atmospheres of many of
these worlds. Notably, Spitzer discovered four of
the seven known planets in the TRAPPIST-
system, at least three of which appear to lie in the
star’s habitable zone where liquid water could exist
on a rocky planet’s surface.
Although Spitzer is now gone, its impact will
be felt for years to come. That impact will endure
in part because NASA’s 6.5-meter James Webb
Space Telescope, currently scheduled for launch
in March 2021, will also probe the universe at
infrared wavelengths and follow up on many
of Spitzer’s discoveries. Not a bad legacy for an
observatory astronomers once hoped would last
two and a half years.Senior Editor Richard Talcott has covered the Great
Observatories since the launch of Hubble in 1990. His
latest book is Space Junk (Ziga Media, 2019).