Space Observatories: Eyes Above the Atmosphere

Launched on 18 November 1989 and operating until 1993, this NASA satellite made the first detailed map of the cosmic microwave background from a Sun-synchronous orbit at 900 km. Its principal investigators John Mather and George Smoot shared the 2006 Nobel Prize in Physics.

Operating since 1990 in low Earth orbit, Hubble observes in the ultraviolet, visible and near-infrared. A flaw in its main mirror was corrected by a Space Shuttle servicing mission in 1993, after which it produced some of the most detailed images of distant galaxies ever taken.

Launched in 1999 and named for Subrahmanyan Chandrasekhar, Chandra sees X-rays, which Earth's atmosphere absorbs, so no ground instrument can. It studies hot, energetic places such as supernova remnants, galaxy clusters and the surroundings of black holes.

Launched on 25 August 2003, Spitzer observed in infrared light until 2020 from an Earth-trailing solar orbit, with its instruments cooled to 5.5 K. It revealed cool, dust-hidden objects and in 2016 helped find five of the seven known TRAPPIST-1 planets.

Formerly called the Gamma-ray Large Area Space Telescope, Fermi has watched the sky in gamma rays from low Earth orbit since 2008. It studies pulsars, active galactic nuclei and gamma-ray bursts, and in 2010 announced two gamma-ray emitting bubbles around the Milky Way.

Launched in 2009, Kepler orbited the Sun to avoid Earth occultations and stray light, and its photometer continually watched the brightness of about 150,000 stars for the small dip made by a passing planet. It confirmed thousands of exoplanets before running out of fuel in 2018.

Launched by Ariane 5 on 14 May 2009, this European Space Agency observatory worked from the second Sun-Earth Lagrange point, 1.5 million km from Earth, until 2013. It measured anisotropies in the cosmic microwave background, returning to the afterglow that COBE first mapped, with far greater precision.

Launched by the European Space Agency in 2013, Gaia measured the positions, distances and motions of nearly two billion stars from near the Sun-Earth L2 point, building the most detailed three-dimensional map of the Milky Way yet made. Its science observations ended in January 2025.

Launched in 2021 and operating since 2022 near the Sun-Earth L2 point, Webb has a mirror of 18 hexagonal segments and observes from long-wavelength visible light through the mid-infrared, 0.6 to 28.5 micrometres. That reach lets it see galaxies closer to the early universe than any earlier telescope.

Launched on 1 July 2023 from Cape Canaveral, this wide-angle European telescope orbits Sun-Earth L2 with a 600-megapixel visible-light camera and a near-infrared spectrometer and photometer. It aims to probe dark matter and dark energy by surveying the shapes and redshifts of galaxies.