Major Space Telescopes and Missions for Exoplanet Research

Exoplanets are planets located outside our solar system that orbit other stars, brown dwarfs, or stellar remnants. The systematic search for these planetary systems transformed modern astrophysics from theoretical predictions to direct observation. Space telescopes overcome the atmospheric distortion, light absorption, and weather limitations of ground-based observatories. Space agencies including NASA, the European Space Agency (ESA), and the Canadian Space Agency (CSA) deploy specialized space-borne observatories to discover, count, and analyze exoplanets. These space missions rely on precise detection techniques to calculate planetary mass, radius, orbital dynamics, atmospheric composition, and potential habitability.

Detection Methods Used by Space Telescopes

Astronomers use several indirect and direct observational methods to identify extrasolar planets from space platforms.

• Transit Photometry: Measures the periodic dimming of a host star’s light as an orbiting planet passes directly between the star and the telescope. This method determines the planet’s radius and orbital period.
• Transit Spectroscopy: Analyzes starlight passing through an exoplanet’s atmosphere during a transit. Chemical elements in the atmosphere absorb specific wavelengths, revealing gases like water vapor, carbon dioxide, and methane.
• Astrometry: Measures tiny, precise shifts in a star’s position in the sky caused by the gravitational tug of an orbiting planet.
• Gravitational Microlensing: Uses the gravitational field of a foreground star and its planet to act as a natural lens, magnifying the light of a background star.
• Direct Imaging: Takes actual photographs of exoplanets by blocking the host star’s bright light using internal coronagraphs or external starshades.

Major Historic and Decommissioned Missions

Early space missions established that planetary systems are common across the Milky Way galaxy.

CoRoT (Convection, Rotation and Planetary Transits)

CoRoT was a French Space Agency (CNES) mission in partnership with ESA, operational from 2006 to 2013. It was the first space telescope dedicated to exoplanet search using transit photometry. CoRoT discovered the first rocky exoplanet with a confirmed radius and density, CoRoT-7b.

Kepler Space Telescope and K2 Mission

NASA launched Kepler in March 2009 as its first dedicated exoplanet-hunting space telescope. Kepler stared continuously at a fixed patch of 150,000 stars in the Cygnus-Lyra region. After reaction wheel mechanical failures in 2013, NASA repurposed the spacecraft into the “K2” mission to survey fields along the ecliptic plane. Kepler operated until October 2018 and discovered over 2,600 confirmed exoplanets, proving that planets outnumber stars in the galaxy.

Spitzer Space Telescope

Spitzer was one of NASA’s Great Observatories, operating in the infrared spectrum from 2003 to 2020. Spitzer was the first telescope to directly capture light from an exoplanet (a “hot Jupiter”) and created the first thermal weather map of an exoplanet atmosphere. It also revealed five of the seven Earth-sized planets in the famous TRAPPIST-1 system.

Active Space Observatories

Modern active space observatories conduct all-sky surveys and detailed atmospheric characterization.

Transiting Exoplanet Survey Satellite (TESS)

NASA launched TESS in April 2018 as a successor to Kepler. Unlike Kepler’s deep narrow field view, TESS conducts an all-sky survey covering nearly 85% of the sky using a high-eccentricity lunar resonant orbit (P/2). TESS focuses on bright, nearby stars to identify target exoplanets for detailed follow-up study.

CHaracterising ExOPlanet Satellite (CHEOPS)

ESA launched CHEOPS in December 2019 as a Small-class (S-class) mission. CHEOPS does not search for new planets randomly; instead, it targets bright stars known to host exoplanets. It measures ultra-precise planet sizes in the super-Earth to Neptune range to calculate exact bulk densities.

James Webb Space Telescope (JWST)

Launched in December 2021 as a joint effort by NASA, ESA, and CSA, JWST operates at the Sun-Earth Lagrange Point 2 (L2). Featuring a 6.5-meter primary mirror, JWST uses high-resolution infrared spectroscopy to analyze exoplanet atmospheres. It made the first definitive detection of carbon dioxide and sulfur dioxide in an exoplanet atmosphere.

Gaia Mission

ESA launched the Gaia space observatory in December 2013. Gaia’s primary goal is creating a 3D astrometric map of over one billion stars. By measuring tiny star wobbles, Gaia detects giant exoplanets in wide orbits via astrometry.

Comparison of Primary Exoplanet Space Missions

Upcoming and Future Exoplanet Missions

Next-generation space missions focus on searching for Earth-analogs in habitable zones and performing chemical surveys of planetary atmospheres.

• PLATO (PLAnetary Transits and Oscillations of stars): Scheduled for launch by ESA, PLATO uses 26 small telescopes mounted on a single platform. It will search for terrestrial planets in the habitable zone around Sun-like stars and combine transit data with stellar oscillations (asteroseismology) to determine accurate planet and star ages.
• Ariel (Atmospheric Remote-sensing Infrared Exoplanet Large-survey): ESA’s Ariel mission will perform a large-scale chemical survey of over 1,000 known exoplanets. It will analyze atmospheric chemistry, thermal structures, and clouds across hot and warm gas giants, Neptunes, and super-Earths.
• Nancy Grace Roman Space Telescope: NASA’s wide-field infrared observatory will perform an extensive gravitational microlensing survey of the inner Milky Way. It carries a technology demonstration Coronagraph Instrument to directly image nearby gas giant exoplanets.
• Habitable Worlds Observatory (HWO): A conceptual NASA strategic mission designed specifically to directly image and take spectra of at least 25 habitable-zone Earth-like planets around other stars to search for atmospheric biosignatures.

Core Facts on Exoplanets and Space Missions

• First Confirmed Exoplanet Discovery: Discovered in 1992 around the pulsar PSR B1257+12 by Aleksander Wolszczan and Dale Frail.
• First Exoplanet Around Main-Sequence Star: Discovered in 1995 (51 Pegasi b) by Michel Mayor and Didier Queloz, who won the 2019 Nobel Prize in Physics.
• Total Confirmed Exoplanets: Astronomers have confirmed over 6,000 exoplanets across the Milky Way.
• Habitable Zone Concept: Also called the “Goldilocks Zone,” it is the range of distances around a host star where liquid water can exist on a planet’s surface.
• TRAPPIST-1 System: A system of seven Earth-sized terrestrial planets orbiting an ultra-cool red dwarf star 40 light-years away.
• Hot Jupiters: A class of gas giant exoplanets that are physically similar to Jupiter but orbit extremely close to their parent stars with short orbital periods.
• Super-Earths: Exoplanets with a mass higher than Earth’s but substantially below those of the Solar System’s ice giants, Uranus and Neptune.
• Biosignatures: Chemical indicators in an exoplanet atmosphere, such as simultaneous presence of oxygen, ozone, methane, and water vapor, that suggest biological processes.