NASA’s Spitzer Space Telescope: the legacy of a Universe in infrared

Ahead of the retirement of the Spitzer Space Telescope in 2020, we spoke to Dr Michael Werner, Project Scientist of the mission since 1984, to discuss its greatest achievements.

An artist's concept showing NASA's Spitzer Space Telescope in front of an infrared image of the Milky Way. Credit: NASA/JPL-Caltech

NASA’s Spitzer Space Telescope is due to be permanently switched off in January 2020, ending a phenomenal 16-year mission that has brought the secrets of the Universe to astronomers – in infrared. Spitzer was launched on 25 August 2003 from Cape Canaveral Air Force Base in Florida and orbits the Sun on a path similar to the Earth’s orbit, but trailing about 250 million kilometres behind our planet.

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Its infrared view enables astronomers to see objects that would be normally unseen in visible light, and the mission has provided unprecedented views of our cosmos, from discovering a new ring around Saturn to unlocking the secrets of stellar formation, beautiful cosmic clouds called nebulae and planets orbiting stars beyond our Solar System – known as exoplanets.

It has even carried out observations of some of the most distant galaxies in the known Universe.

Read more about the Spitzer Space Telescope:

Dr Michael Werner has been lead scientist on the Spitzer Space Telescope mission since 1984 and his new book, More Things In The Heavens, reveals how important infrared astronomy has been to increasing our understanding of the cosmos.

BBC Sky at Night Magazine spoke to Dr Werner to discuss the values of infrared astronomy and the legacy of the Spitzer Space Telescope.

Michael Werner, project scientist of the Spitzer Space Telescope
Michael Werner, Project Scientist of the Spitzer Space Telescope

When did astronomers first realise the benefits of infrared astronomy?

The technical difficulties of detecting infrared radiation caused infrared astronomy to lag behind studies of the Universe at visible wavelengths.

Infrared work began in earnest in the 1960s using instruments on large ground-based telescopes, such as the famed 200-inch telescope at Mount Palomar.

Others sent telescopes into the upper atmosphere on balloons or high-flying aircraft.

Although there had been very substantial previous work, I think it was the IRAS all sky survey in 1983 that really showed to the entire community the power of the infrared for astronomical investigation.

IRAS achieved over-the-entire-sky sensitivity levels in the infrared that previously had been accomplished only on a few very limited areas, cataloging hundreds of thousands of sources in the infrared.

These included forming stars, galaxies, post-main sequence objects and on and on.

IRAS’s discovery of dust discs around main sequence stars, now known to be a signal of exoplanetary systems around these stars, presaged the tremendous explosion of the study of exoplanets that has becomes Spitzer’s forté.

This all-sky map in the infrared was composed using six months of data from the Infrared Astronomical Satellite. The bright horizontal line is the plane of the Milky Way, and the centre of the Milky Way is in the centre of the image. Copyright: NASA/JPL-Caltech
This all-sky map in the infrared was composed using six months of data from the Infrared Astronomical Satellite. The bright horizontal line is the plane of the Milky Way and the centre of the Galaxy is in the centre of the image. Copyright: NASA/JPL-Caltech

What does infrared reveal about the Universe that optical light does not?

We used to summarise infrared astronomy as “the old, the cold and the dirty”.

The “old” because the cosmic expansion redshifts light from distant objects into the infrared. This is some of the oldest light in the Universe because it has been travelling towards us for billions and billions of years.

The “cold” because in the infrared we can see objects that are too cool to radiate much visible light.

In practice this means cooler than ~2000K or so and includes brown dwarf stars, interstellar or circumstellar matter, planets and exoplanets.

The “dirty” because much of the infrared light that we see is radiated by particles of interstellar and circumstellar dust, and also because dust clouds that are opaque at visible wavelengths may be quite transparent in the infrared.

How did Spitzer come to be? Was it a difficult project to get off the ground?

Spitzer began life in the early 1970s as a proposed attached payload to operate from the bay of the Space Shuttle and to return to Earth after a few weeks for replenishment and installation of new instruments.

Its evolution from this concept into the elegant, compact system that has operated from solar orbit for over 15 years was indeed tortuous and often difficult.

What kept us going and made it all worthwhile was the huge gain in capability we envisioned [and realised] from putting infrared detector arrays into space on a cold telescope.

A major milestone along the way was the designation of Spitzer as the highest priority new space mission by the 1990 decadal review of priorities for US astronomy and astrophysics.

An artist's illustration of the TRAPPIST-1 system that was discovered by the Spitzer Space Telescope and the ground-based TRAPPIST telescope. Credit: NASA/JPL-Caltech
An artist’s illustration of the TRAPPIST-1 system that was discovered by the Spitzer Space Telescope and the ground-based TRAPPIST telescope. Credit: NASA/JPL-Caltech

 What do you think have been Spitzer’s highlights?

First there was the identification of seven Earth-sized exoplanets – planets around stars beyond our Solar System – orbiting the same faint red star now known as TRAPPIST-1.

Three of these exoplanets are in the ‘habitable zone’, the region around this star where water would be liquid on the surface of a rocky planet, which is thought to be a prerequisite for the formation of life as we know it on Earth.

Second has been the identification and characterisation (often jointly with the Hubble Space Telescope) of very distant galaxies, which we see when the evolving Universe was only 3 per cent of its current age and about 8 per cent of its present size.

I think that most Spitzer scientists would agree on the above; beyond which personal choice is at play.

I personally like the discovery of a giant new ring around Saturn; the identification of the C60 molecule or ‘buckyball’ in space; the measurements of winds and the studies of energy transport processes in the atmospheres of exoplanets; the determination that planet formation is well under way within a few million years of the initial collapse of a forming star; and showing the many similarities – in composition, architecture, and dynamic processes – between our Solar System and exoplanetary systems.

This allows insights from our own Solar System to be used in the study of exoplanetary systems, and vice versa.

Spitzer has enabled the study of the cosmic history of star formation from the earliest observable epochs to the current day.

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Dr. Michael Werner is Spitzer Space Telescope Project Scientist and Chief Scientist for Astronomy and Physics at the Jet Propulsion Laboratory, California Institute of Technology.