Since finding all the planets in our Solar System, the search was on for planets around other stars (extrasolar planets). As methods and technology improve, more extrasolar planets are found. Below are some highlights in the history of these discoveries.
1781 – Planet Uranus discovered
Sir William Herschel discovers Uranus, the 7th planet out from our Sun.
1846 – Neptune discovered
Johann Galle first observes Neptune, which had been predicted by John Adams and Le Verrier.
1930 – Pluto discovered
Clyde Tombaugh observes Pluto, which had been predicted by Percival Lowell. Pluto has since been renamed as a dwarf planet.
1988 – Possible extrasolar planet found
Observations of the star Gamma Cephei suggest a planet, but results are not accurate enough (later confirmed in 2003).
1992 – First clear evidence for extrasolar planet
Aleksander Wolszcza and Dale Frail find the first extrasolar planet around an old, ‘dead’ collapsed star called a pulsar.
1995 – First extrasolar planet around ordinary star
Michel Mayor and Didier Queloz detect first extrasolar planet orbiting 51 Pegasi, a star like our Sun.
1999 – First multiple-planet system
The star Upsilon Andromedae is found to have several planets in orbit around it.
1999 – First use of transit method
HD209458b becomes first extrasolar planet to be confirmed by the transit method. Professor Denis Sullivan of Victoria University of Wellington makes the transit observations.
2001 – Atmosphere found on extrasolar planet
The Hubble Space Telescope detects an atmosphere around HD209458b.
2004 – Launch of Rosetta
In March 2004, an European Space Agency probe called Rosetta was launched from Kourou, French Guiana, to rendezvous with a comet traveling at 24,600 mph. It will take at least 7 years until it is the right position.
2004 – First direct image of extrasolar planet
2M1207b becomes the first extrasolar planet to have a direct image taken, in infrared wavelengths. Until this time, all extrasolar planets had been found by indirect methods.
2005 – Extrasolar planet found by microlensing method
OGLE-2005-BLG-390Lb is found by the gravitational microlensing method.
2007 – Possible water found on extrasolar planet
Spitzer infrared space telescope detects water on HD189733b.
2007 – Largest extrasolar planet found
XO-3b is found, the most massive extrasolar planet so far, 4 times the diameter of Jupiter.
November 2007 – Most planets around one star
5 planets are found around star 55 Cancri, making it the star with the most known planets in orbit around it.
December 2007 – Orbiting telescope joins hunt
The European COROT optical telescope is launched into orbit. It searches for extrasolar planets using the transit method.
2008 – Extrasolar planet imaged in visible light
Formalhaut b becomes the first extrasolar planet to be directly imaged by an optical telescope.
June 2008 – Smallest extrasolar planet found
MOA-2007-BLG-192Lb becomes the smallest planet found orbiting a normal star. It is found by gravitational microlensing using a telescope at Mt John, New Zealand.
December 2008 – 300 and counting
Advances in technology have led to over 300 extrasolar planets being found, with 20 stars having more than one planet.
Check out the latest on probable extrasolar planets from NASA here.
February 2009 – Extrasolar planet found only twice size of Earth
CoRoT-Exo-7b, found using the transit method, becomes the smallest extrasolar planet found to this date.
March 2009 – Another orbiting telescope joins hunt
NASA launches the Kepler orbiting telescope to be used in the search for small extrasolar planets, mainly using the transit method.
November 2014 – Rosetta first spacecraft to land on a comet
On 12 November 2014 the European Space Agency's Rosetta lands on comet Churyumov-Gerasimenkot (comet 67P). To achieve this, experts from over 20 countries worked together for decades and for 10 years Rosetta travelled 6.4 billion kilometres through the solar system.
September 2016 – End of Rosetta
On 30 September 2016 there was a controlled crash landing into the comet that brought an end to the Rosetta mission. See the European Space Agency website for further information.
April 2019 – Transiting Exoplanet Survey Satellite (TESS) launched
In April 2018, NASA launched Transiting Exoplanet Survey Satellite (TESS) – the next step in the search for planets outside of our solar system, including those that could support life. TESS will survey 200,000 of the brightest stars near the sun to search for transiting exoplanets.
Read the case study Planet hunting with Year 7 to 8 students about teacher Matt Boucher’s unit on light that incorporated the citizen science projects Agent Exoplanet and Planet Hunters. The unit plan is here.
November 2018 – End of the Kepler Space Telescope
After 9 years in space, far long than originally anticpated, NASA's Kepler space telescope finally runs out of fuel and is retired.
Not only did it show us how many planets could be out there, it sparked an entirely new and robust field of research that has taken the science community by storm. Its discoveries have shed a new light on our place in the universe, and illuminated the tantalizing mysteries and possibilities among the stars.
Thomas Zurbuchen, NASA
