Sky & Telescope - USA (2020-01)

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THE INFRARED SKY by Michael Werner & Thomas Soifer

tVANISHING CONTINENT The North America Nebula familiar to visual

observers (top) disappears when viewed at infrared wavelengths with

Spitzer (bottom). Dark clouds become transparent, and the glow of

dusty cocoons enveloping baby stars appears more prominent.

18 JANUARY 2020 • SKY & TELESCOPE

Spitzer’s

O

n January 30, 2020, an era in astronomy will end.

On this date, NASA’s Spitzer Space Telescope will

send us its fi nal observations, fi nishing a remarkable,

16-year exploration of the universe at infrared wavelengths.

Spitzer is one of the four Great Observatories, a quartet

of space telescopes launched by NASA in the 1990s and early

2000s to unveil the multiwavelength universe, from infra-

red to gamma ray. Originally known as the Shuttle Infrared

Telescope Facility (SIRTF), the telescope concept came to life

in 1971, when NASA was seeking payloads to fl y on the Space

Shuttle. Converted in 1984 to a free-fl ying observatory orbit-

ing Earth, SIRTF underwent a series of (sometimes drastic)

redefi nitions before being launched as a Great Observatory

into a heliocentric orbit in August 2003.

Although the public often latches onto Hubble (another

Great Observatory) as the pinnacle of scientifi c discov-

ery machines, astronomers already knew while planning

Spitzer that there was at least as much to explore at infrared

wavelengths as at visible ones. Infrared radiation pierces our

galaxy’s giant molecular clouds to reveal the dusty cocoons

of forming stars. It also unveils distant galaxies heavily

enshrouded in cosmic dust. Furthermore, because the uni-

verse’s expansion stretches the light from distant galaxies

to longer wavelengths, it is infrared, not visible light, that

enables us to look back in time to the universe’s fi rst few

billion years.

Still, back when mission planners were fi rst envisioning

what Spitzer would do, no planets were known to orbit stars

other than the Sun, and the most distant objects known lay

10 to 11 billion years in the universe’s past. Now, Spitzer

has not only seen exoplanets crossing in front of their stars

but also directly detected the glow from their heat and the

chemical components of their atmospheres. We thought we

were being bold in developing science programs to look back

NASA’s premier eye on the infrared sky is

shutting down after operating more than

three times longer than designed.