editorial Spitzer steps aside The Spitzer Space Telescope recently ceased operations, powering down its remaining detector after more than a decade and a half of revealing the infrared Universe. Its legacy will be continued by far more expensive missions that will have big boots to fll. he Spitzer Space Telescope was and Infrared Spectrograph instruments. JWST, with its greater angular resolution launched in 2003 and continued PAHs are excellent tracers of conditions in (<0.5”) and increased sensitivity over a Toperating until it was put into safe astrophysical regions from planet-forming similar wavelength range and field of view, mode by NASA indefinitely earlier this year. disks through to the interstellar media of is a natural successor to Spitzer, and indeed It followed in a great line of predecessors: high-redshift galaxies. The final Review in many of the science cases for JWST are built the Infrared Astronomical Satellite (1983) this issue comes from Mark Lacy and Anna on the previous progress brought about by and the Infrared Space Observatory (1995– Sajina, who select some of the highlights Spitzer and its contemporaries (Herschel, 1998), both helium-cooled telescopes with of Spitzer studies of active galactic nuclei WISE, Akari). JWST spectroscopy will 60 cm diameter mirrors. Spitzer — also (AGNs). Spitzer was able to identify a certainly bring further insight into the helium-cooled for the initial six-year period, population of highly obscured AGNs, and atmospheres of the unique TRAPPIST-1 but with a larger, 85 cm diameter mirror then separate the different dust components exoplanet system that Spitzer was pivotal — was the mid-infrared representative in of these distant galaxies. Forthcoming in characterizing, and at the other end of NASA’s Great Observatories programme. Review Articles in the series will cover the distance ladder will provide detailed The Spitzer mission could have continued exoplanets and brown dwarfs, the inner physical and chemical information on slightly longer than its 16 years, but in and outer Solar System, (ultra-)luminous galaxies close to the era of reionization NASA senior review it was decided to retire infrared galaxies and high-redshift galaxies. that Spitzer revealed to us. Spitzer’s science the mission now to cede resources to what is Spitzer project scientist Michael Werner legacy will provide a foundation for years to to be the next great infrared observatory, the shares his unique view of the mission as come, particularly since the treasure trove of James Webb Space Telescope (JWST), due to it has developed, matured, bore fruit and data in the Infrared Science Archive has only launch next year. concluded over more than 40 years. In a been partially explored. In celebration of the Spitzer mission we candid and touching interview, he takes On an equal footing with the science, the dedicate this issue of Nature Astronomy us through the different manifestations of other outstanding legacy that Spitzer has — and the next — to exploring what the Spitzer concept before it launched, the left us with is in space telescope operations. Spitzer contributed to our understanding nail-biting moments while in development, As pointed out in an upcoming Review, of the infrared Universe. Spitzer leaves a and the lessons that have come from leading operating the Spitzer Space Telescope led substantial scientific legacy across many such a successful and long-lived mission. to significant developments in how to plan fields of astronomy and planetary science Jan Cami, on the other hand, provides his and carry out long-duration observations that is spread throughout more than perspective as a user of Spitzer. His team with minimal spacecraft disturbances and 8,000 peer-reviewed papers. It would be discovered a new extraterrestrial allotrope the mitigation of pointing fluctuations. impossible to make a complete summary of carbon by looking at a Spitzer Infrared Spitzer pioneered the Earth-trailing orbit, of everything that Spitzer has enabled us Spectrograph spectrum of a planetary facilitating the operation of the subsequent to learn about the Universe, but in this nebula, realizing a decade-long personal Kepler Space Observatory, also from an retrospective we are publishing a series quest. He talks through the lead-up to the Earth-trailing orbit. The Spitzer instruments of broad Review Articles covering certain discovery of cosmic buckyballs, the public were carefully characterized both before topics, alongside some shorter articles from and academic response and the sprouting and after launch, making data reduction the architects and users of the Spitzer Space of a new branch of astrochemistry. Spitzer more straightforward. Specialist tools were Telescope. All Spitzer-related articles will be facility scientist Thomas Roellig rounds created to reduce and analyse Spitzer data gathered together in an online collection. up the Spitzer content of this issue with an and novel techniques were implemented In this April issue, we start with three overview of the instrumental payload of the to remove instrumental noise, often with Review Articles covering subjects near and telescope in our Mission Control. much community involvement. So while far. Christine Chen, Kate Su and Siyi Xu While much of this issue is a Spitzer will be quite rightly remembered summarize Spitzer’s contribution to the retrospective, a component of many of the for its monumental scientific discoveries study of debris disks around main sequence Review Articles is forward-looking. It is (many of which are revisited in these pages) and white dwarf stars. Spitzer seems built for clear that Spitzer answered many scientific and beautiful images of optically obscured studying these dusty remnants of planetary questions — some of which we did not even regions (see our Picture Story), future users systems that emit light across the infrared know to ask at the time of launch — but also and operators of the comparatively opulent spectrum, but interestingly only a small that it asks further questions that we still and more expansive JWST and WFIRST will number were known before Spitzer came need to find the answers to. The gauntlet owe a huge debt of gratitude to the humbly along, and only the closest had been well will be picked up by the next generation of persistent telescope with a mirror no larger characterized. Looking at larger scales, infrared space telescopes: SPHEREx, SPICA, than a hula hoop. ❐ Aigen Li reviews the polycyclic aromatic WFIRST and, particularly, JWST. JWST will hydrocarbon (PAH) molecules that emit reinstate our ability to take mid-infrared in distinctive bands across the wavelength spectra from space, which ceased when Published online: 14 April 2020 range of Spitzer’s Infrared Array Camera Spitzer exhausted its helium coolant supply. https://doi.org/10.1038/s41550-020-1089-0 NATURE ASTRONOMY | VOL 4 | APRIL 2020 | 293 | www.nature.com/natureastronomy 293.