Encyclopedia/1. The Cosmos & The Natural World/3. Astronomy & Planetary Science • Curated by Admin Timeline.sg
The discovery and atmospheric characterization of exoplanets have evolved from ancient philosophical speculations to a modern scientific revolution, with milestones including the first confirmed exoplanets around a pulsar in 1992, the detection of the first exoplanet around a Sun-like star in 1995, and the advent of space telescopes like Kepler and JWST enabling detailed atmospheric studies.
Chronological Storyline (44 Milestones)
400 BCE
Democritus Proposes Infinite Worlds
Greek philosopher Democritus speculates on the existence of countless other worlds, laying early conceptual foundations for exoplanets. #astronomy #philosophy
Democritus Proposes Infinite Worlds By user:shakko - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=5535206
1584 CE
Giordano Bruno's Infinite Universe
Italian philosopher Giordano Bruno argues for an infinite universe with many solar systems, presaging exoplanet concepts. #astronomy #history
Giordano Bruno's Infinite Universe By Unknown author - https://wellcomeimages.org/indexplus/obf_images/bc/3d/265d1be073eb34224006d0d35b02.jpg Gallery: https://wellcomeimages.org/indexplus/image/L0015152.html Wellcome Collection gallery (2018-04-01): https://wellcomecollection.org/works/qgt4dt8k CC-BY-4.0, CC BY 4.0, https://commons.wikimedia.org/w/index.php?curid=133537203
1755 CE
Kant's Nebular Hypothesis
Immanuel Kant proposes the nebular hypothesis for solar system formation, implying that other stars might have planets. #astronomy #science
Kant's Nebular Hypothesis By NASA, ESA, and the Hubble Heritage Team (STScI/AURA)-ESA/Hubble Collaboration - HubbleSite: gallery, NewsCenter, Public domain, https://commons.wikimedia.org/w/index.php?curid=1489643
1855 CE
First Claim of an Exoplanet
Captain W.S. Jacob claims detection of a planetary companion around 70 Ophiuchi based on orbital anomalies, later disproved. #astronomy
First Claim of an Exoplanet By Ophiuchus_constellation_map.png: Torsten Bronger derivative work: Kxx (talk) - Ophiuchus_constellation_map.png, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=10850776
1916 CE
Barnard's Star Planetary Claim
E. E. Barnard discovers a star with high proper motion; later claims of planets around Barnard's Star arise but are refuted. #astronomy
Barnard's Star Planetary Claim By Steve Quirk - https://web.archive.org/web/20080721013827/http://my.hwy.com.au/~sjquirk/images/film/barnard.html, Public domain, https://commons.wikimedia.org/w/index.php?curid=3160016
1952 CE
Otto Struve Proposes Radial Velocity Method
Otto Struve suggests that exoplanets could be detected by their gravitational influence on host stars, laying groundwork for radial velocity searches. #astronomy
Otto Struve Proposes Radial Velocity Method By NRAO/AUI/NSF - https://public.nrao.edu/gallery/otto-struve/, CC BY 4.0, https://commons.wikimedia.org/w/index.php?curid=169657223
1961 CE
Drake Equation Formulated
Frank Drake presents the Drake equation, estimating the number of communicative civilizations and spurring interest in exoplanet detection. #astronomy #seti
Drake Equation Formulated By NRAO/AUI/NSF - https://public.nrao.edu/gallery/frank-drake/, CC BY 4.0, https://commons.wikimedia.org/w/index.php?curid=169654646
1988 CE
Gamma Cephei Ab Claimed
First exoplanet candidate around a Sun-like star, gamma Cephei Ab, is proposed but not confirmed until 2002. #astronomy
Gamma Cephei Ab Claimed By User:21.Andromedae - Own work, CC BY 4.0, https://commons.wikimedia.org/w/index.php?curid=157281461
Jan 9, 1992 CE
First Confirmed Exoplanets Discovered
Aleksander Wolszczan and Dale Frail announce the discovery of two planets orbiting pulsar PSR B1257+12, the first confirmed exoplanets. #astronomy
1994 CE
First Exoplanet Candidate Around a White Dwarf
Planet candidates around pulsar PSR B1620-26 are reported, but later reinterpreted. #astronomy
First Exoplanet Candidate Around a White Dwarf By Unknown author, Public domain, https://commons.wikimedia.org/w/index.php?curid=1998685
Oct 6, 1995 CE
51 Pegasi b: First Exoplanet Around a Sun-Like Star
Michel Mayor and Didier Queloz announce the discovery of 51 Pegasi b, a hot Jupiter orbiting a Sun-like star, revolutionizing exoplanet science. #astronomy
51 Pegasi b: First Exoplanet Around a Sun-Like Star By ESO/M. Kornmesser/Nick Risinger (skysurvey.org) - ESO website, CC BY 4.0, https://commons.wikimedia.org/w/index.php?curid=39719418
Oct 12, 1999 CE
First Transiting Exoplanet Detected
HD 209458b becomes the first exoplanet observed transiting its star, enabling measurement of size and density. #astronomy
First Transiting Exoplanet Detected By Aldaron, a.k.a. Aldaron - Own work, incorporating public domain images for reference planets (see below), inspired by Thingg's size comparison, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=8903868
2000 CE
First Exoplanet Atmosphere Detected
Sodium absorption is detected in the atmosphere of HD 209458b, marking the first detection of an exoplanet atmosphere. #astronomy #atmospheres
Mar 8, 2001 CE
Hubble Detects Exoplanet Atmosphere Composition
Hubble Space Telescope detects hydrogen, oxygen, and carbon in the atmosphere of HD 209458b. #astronomy #atmospheres
Sep 24, 2002 CE
First Exoplanet Discovered by Transit (from ground)
The first transiting exoplanet from a ground-based survey, TrES-1, is announced. #astronomy
First Exoplanet Discovered by Transit (from ground) By Aldaron, a.k.a. Aldaron - Own work, incorporating public domain images for reference planets (see below), inspired by Thingg's size comparison, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=8927390
2003 CE
First Exoplanet Found by Microlensing
OGLE 2003-BLG-235/MOA 2003-BLG-53 is the first exoplanet discovered via gravitational microlensing. #astronomy
2004 CE
First Direct Image of an Exoplanet
The brown dwarf 2M1207b is imaged directly around a brown dwarf, representing the first direct image of an exoplanet candidate. #astronomy
First Direct Image of an Exoplanet By Aldaron, a.k.a. Aldaron - Own work, incorporating public domain images for reference planets (see below), inspired by Thingg's size comparison, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=8902848
2005 CE
Spitzer Detects Exoplanet Infrared Light
NASA's Spitzer Space Telescope detects infrared light from exoplanets HD 209458b and TrES-1, revealing their temperatures. #astronomy
Spitzer Detects Exoplanet Infrared Light By NASA/JPL-Caltech - http://www.spitzer.caltech.edu/images/3072-SIRTF-Spitzer-Rendered-against-an-Infrared-100-Micron-Sky, Public domain, https://commons.wikimedia.org/w/index.php?curid=85585
2006 CE
First Exoplanet with Measured Orbital Motion
HR 8799's planets are directly imaged and their orbital motion confirmed, a milestone for direct imaging. #astronomy
First Exoplanet with Measured Orbital Motion By Image: NASA, ESA, CSA, STScI, Laurent Pueyo (STScI), William Balmer (JHU), Marshall Perrin (STScI) - HR 8799 (NIRCam Image), Public domain, https://commons.wikimedia.org/w/index.php?curid=162292518
Mar 1, 2007 CE
Water Vapor Detected in Exoplanet Atmosphere
Spitzer detects water vapor in the atmosphere of HD 189733b, a hot Jupiter. #astronomy #atmospheres
Water Vapor Detected in Exoplanet Atmosphere By SevenSpheres - Own work, CC BY 4.0, https://commons.wikimedia.org/w/index.php?curid=99268874
Jun 30, 2008 CE
First Exoplanet System with Multiple Transiting Planets
The Kepler mission's early data reveal a transiting exoplanet system with multiple planets. #astronomy
Nov 13, 2008 CE
Direct Imaging of Multiple Exoplanets
The HR 8799 system's three planets are directly imaged, the first multiple-planet direct imaging discovery. #astronomy
Mar 6, 2009 CE
Kepler Space Telescope Launches
NASA's Kepler mission launches to discover Earth-sized exoplanets in the habitable zone via transit photometry. #astronomy
Kepler Space Telescope Launches By NASA - https://science.nasa.gov/toolkits/spacecraft-icons (image link), Public domain, https://commons.wikimedia.org/w/index.php?curid=76268556
Aug 24, 2010 CE
First Multi-Planet Transiting System from Kepler
Kepler discovers the first multi-planet transiting system, Kepler-9, with two Saturn-mass planets. #astronomy
First Multi-Planet Transiting System from Kepler By NASA/Ames/JPL-Caltech - https://www.nasa.gov/mission_pages/kepler/news/two_planet_orbit.html, Public domain, https://commons.wikimedia.org/w/index.php?curid=129058825
Dec 20, 2010 CE
Kepler-22b: First Kepler Planet in Habitable Zone
Kepler-22b is confirmed as the first Kepler planet within its star's habitable zone. #astronomy
Kepler-22b: First Kepler Planet in Habitable Zone By NASA/Ames/JPL-Caltech - http://kepler.nasa.gov/news/nasakeplernews/index.cfm?FuseAction=ShowNews&NewsID=165, Public domain, https://commons.wikimedia.org/w/index.php?curid=24187911
Jan 10, 2011 CE
First Rocky Exoplanet Confirmed
Kepler-10b becomes the first confirmed rocky exoplanet, with a density consistent with an iron-rich composition. #astronomy
First Rocky Exoplanet Confirmed By Aldaron, a.k.a. Aldaron - Own work, incorporating public domain images for reference planets (see below), inspired by Thingg's size comparison, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=12657193
Feb 21, 2012 CE
Carbon Dioxide Detected in Exoplanet Atmosphere
Hubble detects carbon dioxide and carbon monoxide in the atmosphere of the hot Jupiter HD 189733b. #astronomy #atmospheres
Apr 18, 2013 CE
Kepler-62f: Habitable Zone Super-Earth
Kepler discovers Kepler-62f, a super-Earth in the habitable zone of its star. #astronomy
Kepler-62f: Habitable Zone Super-Earth By NASA Ames/JPL-Caltech - http://www.nasa.gov/mission_pages/kepler/news/kepler-62-kepler-69.html, Public domain, https://commons.wikimedia.org/w/index.php?curid=25666606
Apr 17, 2014 CE
First Earth-Sized Planet in Habitable Zone
Kepler-186f is announced as the first Earth-sized planet orbiting within the habitable zone of another star. #astronomy
First Earth-Sized Planet in Habitable Zone By NASA Ames/SETI Institute/JPL-Caltech - [1], [2], Public domain, https://commons.wikimedia.org/w/index.php?curid=32229517
Jan 6, 2015 CE
Transit Spectroscopy of Exoplanet Atmosphere
A study using Hubble's WFC3 reveals a featureless transmission spectrum for GJ 1214b, indicating a high-altitude haze. #astronomy #atmospheres
Transit Spectroscopy of Exoplanet Atmosphere By Aldaron, a.k.a. Aldaron - Own work, incorporating public domain images for reference planets (see below), inspired by Thingg's size comparison, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=8854174
Jul 23, 2015 CE
Kepler-452b: Another Habitable Zone Earth-Sized Planet
Kepler-452b is announced as a near-Earth-sized planet in the habitable zone of a Sun-like star. #astronomy
Kepler-452b: Another Habitable Zone Earth-Sized Planet By NASA Ames/JPL-Caltech/T. Pyle - http://www.nasa.gov/image-feature/soaking-up-the-rays-of-a-sun-like-star-artistic-concept, Public domain, https://commons.wikimedia.org/w/index.php?curid=41807518
Aug 24, 2016 CE
Proxima Centauri b Discovered
An Earth-mass planet is found orbiting Proxima Centauri, the closest star to the Sun, in its habitable zone. #astronomy
Proxima Centauri b Discovered By ESO/M. Kornmesser - https://www.eso.org/public/images/ann16056a/, CC BY 4.0, https://commons.wikimedia.org/w/index.php?curid=50869082
Feb 22, 2017 CE
TRAPPIST-1 System Announced
NASA announces the TRAPPIST-1 system with seven Earth-sized planets, three in the habitable zone, a record. #astronomy
TRAPPIST-1 System Announced By Processing and color compositing by Nrco0e; original images by Sloan Digital Sky Survey - Own work; processed from images acquired from the SDSS DR17 archive, CC BY 4.0, https://commons.wikimedia.org/w/index.php?curid=191888700
Apr 18, 2018 CE
TESS Space Telescope Launches
NASA's Transiting Exoplanet Survey Satellite (TESS) launches to survey nearby stars for transiting exoplanets. #astronomy
TESS Space Telescope Launches By Orbital ATK / NASA - https://svs.gsfc.nasa.gov/vis/a010000/a012700/a012782/TESS_alone_high_res.jpg https://svs.gsfc.nasa.gov/12782, Public domain, https://commons.wikimedia.org/w/index.php?curid=108981705
Jun 1, 2018 CE
First TESS Exoplanet Discovery
TESS discovers its first exoplanet, Pi Mensae c, a super-Earth. #astronomy
First TESS Exoplanet Discovery By Mensa_constellation_map.png: Torsten Bronger derivative work: Kxx (talk) - Mensa_constellation_map.png, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=10850065
Oct 8, 2019 CE
Nobel Prize for Exoplanet Discovery
Michel Mayor and Didier Queloz receive the Nobel Prize in Physics for the discovery of 51 Pegasi b. #astronomy
Nobel Prize for Exoplanet Discovery By Photograph: JonathunderMedal: Erik Lindberg (1873-1966) - Derivative of File:NobelPrize.JPG, PD-US, https://en.wikipedia.org/w/index.php?curid=58432969
Sep 21, 2020 CE
First Exoplanet Atmosphere Detected from Ground
Ground-based telescopes detect molecular absorption in the atmosphere of the hot Jupiter WASP-19b, demonstrating ground capability. #astronomy #atmospheres
First Exoplanet Atmosphere Detected from Ground By ESA/Hubble & NASA - https://www.spacetelescope.org/images/heic1524a/, CC BY 4.0, https://commons.wikimedia.org/w/index.php?curid=153825808
Dec 25, 2021 CE
James Webb Space Telescope Launches
JWST launches, promising unprecedented capabilities for exoplanet atmospheric characterization. #astronomy
James Webb Space Telescope Launches By NASA - https://www.jwst.nasa.gov/content/webbLaunch/whereIsWebb.html, Public domain, https://commons.wikimedia.org/w/index.php?curid=114125719
Jul 12, 2022 CE
First JWST Exoplanet Atmosphere Spectrum
JWST delivers its first exoplanet atmosphere spectrum of WASP-39b, revealing clear evidence of carbon dioxide. #astronomy #atmospheres
First JWST Exoplanet Atmosphere Spectrum By NASA, ESA, CSA, J. Olmsted (STScI) - Illustration (Artist’s Impression) of WASP-39 b and Its Star, CC BY 4.0, https://commons.wikimedia.org/w/index.php?curid=125907007
Jun 24, 2023 CE
JWST Detects Carbon Dioxide on Exoplanet
JWST detects carbon dioxide in the atmosphere of the hot Saturn WASP-39b, confirming earlier findings. #astronomy #atmospheres
Nov 15, 2023 CE
JWST Detects Sulfur Dioxide in Exoplanet Atmosphere
JWST detects sulfur dioxide in the atmosphere of WASP-39b, an indication of photochemistry. #astronomy #atmospheres
Mar 5, 2024 CE
JWST Reveals Atmospheric Composition of TRAPPIST-1 Planet
JWST observations of TRAPPIST-1b suggest a hazy atmosphere, advancing habitable zone studies. #astronomy #atmospheres
JWST Reveals Atmospheric Composition of TRAPPIST-1 Planet By SevenSpheres - Own work, CC BY 4.0, https://commons.wikimedia.org/w/index.php?curid=139371121
May 15, 2024 CE
First Exoplanet Atmosphere Detection by Another Space Telescope
The CHEOPS space telescope contributes to atmospheric characterization of a hot Jupiter, expanding European capabilities. #astronomy
First Exoplanet Atmosphere Detection by Another Space Telescope By European Space Agency - "Browse all missions" page at the European Space Agency science portal (Archived 9 April 2026); originally published with a CC BY-SA IGO 3.0 licence on "Cheops explores mysterious warm mini-Neptunes" at the European Space Agency (Archived 9 April 2026)., CC BY-SA 3.0 igo, https://commons.wikimedia.org/w/index.php?curid=188551993
Feb 1, 2025 CE
PLATO Mission Launch (Projected)
ESA's PLATO mission is planned to launch, aiming to find Earth-like planets around Sun-like stars. #astronomy )
PLATO Mission Launch (Projected) By ESA/ATG Europe - https://www.esa.int/ESA_Multimedia/Images/2023/05/Plato_key_visual, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=175139220
