Planet Hunters is a

citizen science Citizen science (CS) (similar to community science, crowd science, crowd-sourced science, civic science, participatory monitoring, or volunteer monitoring) is scientific research conducted with participation from the public (who are sometimes re ...

project to find

exoplanet An exoplanet or extrasolar planet is a planet outside the Solar System. The first possible evidence of an exoplanet was noted in 1917 but was not recognized as such. The first confirmation of detection occurred in 1992. A different planet, init ...

s using human eyes. It does this by having users analyze data from the NASA

Kepler space telescope The Kepler space telescope is a disused space telescope launched by NASA in 2009 to discover Earth-sized planets orbiting other stars. Named after astronomer Johannes Kepler, the spacecraft was launched into an Earth-trailing heliocentric o ...

and the NASA

Transiting Exoplanet Survey Satellite Transiting Exoplanet Survey Satellite (TESS, Explorer 95 or MIDEX-7) is a space telescope for NASA's Explorer program, designed to search for exoplanets using the transit method in an area 400 times larger than that covered by the ''Keple ...

. It was launched by a team led by

Debra Fischer Debra Ann Fischer is a professor of astronomy at Yale University researching detection and characterization of exoplanets. She was part of the team to discover the first known multiple-planet system. Education Fischer received her degree from ...

at Yale University, as part of the

Zooniverse Zooniverse is a citizen science web portal owned and operated by the Citizen Science Alliance. It is home to some of the Internet's largest, most popular and most successful citizen science projects. The organization grew from the original Ga ...

project.

History

Planet Hunters and Planet Hunters 2.0

The project was launched on December 16, 2010, after the first Data Release of

Kepler Johannes Kepler (; ; 27 December 1571 – 15 November 1630) was a German astronomer, mathematician, astrologer, natural philosopher and writer on music. He is a key figure in the 17th-century Scientific Revolution, best known for his laws o ...

data as the Planet Hunters Project. 300,000 volunteers participated in the project and the project team published 8 scientific papers. On December 14, 2014, the project was re-launched as Planet Hunters 2.0, with an improved website and considering that the volunteers will look at K2 data. As of November 2018 Planet Hunters identified 50% of the known planets with an orbital period larger than two years.

Non-Planet Hunters project: Exoplanet Explorers

In 2017 the project Exoplanet Explorers was launched. It was another planet hunting project at Zooniverse and discovered the system

K2-138 K2-138, also designated EPIC 245950175 or EE-1, is a large early K-type main sequence star with a system of up to 6 planets discovered by citizen scientists. Four were found in the first two days of the Exoplanet Explorers project on Zoo ...

and the exoplanet

K2-288Bb K2-288Bb (previously designated EPIC 210693462 b) is a super-Earth or mini-Neptune exoplanet orbiting in the habitable zone of K2-288B, a low-mass M-dwarf star in a binary star system in the constellation of Taurus about 226 light-years from Ea ...

. This project was launched during the television program

Stargazing Live ''Stargazing Live'' is a British live television programme on astronomy that was broadcast yearly on BBC Two over three nights every winter from 2011 to 2017. The series was primarily presented by scientist Brian Cox and comedian and amateur a ...

and the discovery of the K2-138 system was announced during the program.

Planet Hunters: TESS

On December 6, 2018, the project Planet Hunters: TESS was launched. This project uses data from the

(TESS) and is currently active (as of February 2020). This project discovered the Saturn-sized exoplanet TOI-813b.

Planet Hunters: NGTS

On October 19, 2021, the project Planet Hunters: NGTS was launched. It uses a dataset from the Next Generation Transit Survey to find transiting planets. It is the first Planet Hunters project that uses data from a ground-based telescope. The project looks at candidates that were already automatically filtered, similar to the Exoplanet Explorers project. The project found four candidate planets so far.

Planet hunting

The Planet Hunters project exploits the fact that humans are better at recognising visual patterns than computers. The website displays an image of data collected by the NASA Kepler Space Mission and asks human users (referred to as "Citizen Scientists") to look at the data and see how the brightness of a star changes over time. This brightness data is represented as a graph and referred to as a star's ''light curve''. Such curves are helpful in discovering

extrasolar planets An exoplanet or extrasolar planet is a planet outside the Solar System. The first possible evidence of an exoplanet was noted in 1917 but was not recognized as such. The first confirmation of detection occurred in 1992. A different planet, in ...

due to the brightness of a star decreasing when a planet passes in front of it, as seen from Earth. Periods of reduced brightness can thus provide evidence of planetary transits, but may also be caused by errors in recording, projection, or other phenomena.

Special occurrence

Eclipsing binary stars

From time to time, the project will observe

eclipsing binary A binary star is a system of two stars that are gravitationally bound to and in orbit around each other. Binary stars in the night sky that are seen as a single object to the naked eye are often resolved using a telescope as separate stars, in ...

stars. Essentially these are stars that orbit each other. Much as a planet can interrupt the brightness of a star, another star can too. There is a noticeable difference on the light curves. It will appear as a large transit (a large dip) and a smaller transit (a smaller dip).

Multiplanet systems

As of December 2017, there are a total of 621 multiplanet systems, or stars that contains at least two confirmed planets. In a multiplanet system plot, there are many different patterns of transit. Due to the different sizes of planets, the transits dip down to different points.

Stellar flares

Stellar flare The asterisk ( ), from Late Latin , from Ancient Greek , ''asteriskos'', "little star", is a typographical symbol. It is so called because it resembles a conventional image of a heraldic star. Computer scientists and mathematicians often v ...

s are observed when there is an explosion on the surface of a star. This will cause the star's brightness to shoot up considerably, with a steep drop off.

Discoveries

So far, over 12 million observations have been analyzed. Out of those, 34 candidate planets had been found as of July 2012. In October 2012 it was announced that two volunteers from the Planet Hunters initiative had discovered a novel Neptune-like planet which is part of a four star double binary system, orbiting one of the pairs of stars while the other pair of stars orbits at a distance of around 1000 AU. This is the first planet discovered to have a stable orbit in such a complex stellar environment. The system is located 7200

light years A light-year, alternatively spelled light year, is a large unit of length used to express astronomical distances and is equivalent to about 9.46 trillion kilometers (), or 5.88 trillion miles ().One trillion here is taken to be 1012 ...

away, and the new planet has been designated PH1b, short for Planet Hunters 1 b. ''Yellow indicates a circumbinary planet. Light green indicates planet orbiting around one star in a multiple star system. Light blue indicates host stars with a planetary system consisting of two or more planets. Values for the host stars are acquired via

SIMBAD SIMBAD (the Set of Identifications, Measurements and Bibliography for Astronomical Data) is an astronomical database of objects beyond the Solar System. It is maintained by the Centre de données astronomiques de Strasbourg (CDS), France. SIM ...

'' ''and otherwise are cited. The apparent magnitude represents the V magnitude.''

Community TESS Object of Interest

Planet Hunters TESS publishes Community TESS Object of Interest (CTOI) at ExoFOP, which can be promoted into a TESS Object of Interest (TOI). Of the 151 CTOIs submitted by Planet Hunters researchers, 81 were promoted to TOIs (as of September 2022). The following exoplanets first submitted as Planet Hunters CTOIs were later researched by other teams: TOI 1759 b, TOI 1899 b, TOI 2180 b and TOI 4562 b.

Variable stars and unusual systems

In September 2013 the project discovered the unusual

cataclysmic variable In astronomy, cataclysmic variable stars (CVs) are stars which irregularly increase in brightness by a large factor, then drop back down to a quiescent state. They were initially called novae (), since ones with an outburst brightness visible to ...

KIC 9406652. In April 2014 the unusually active SU Ursae Majoris-type

dwarf nova A U Geminorum-type variable star, or dwarf nova (pl. novae) is one of several types of cataclysmic variable star, consisting of a close binary star system in which one of the components is a white dwarf that accretes matter from its companion. Dw ...

GALEX J194419.33+491257.0 was discovered. This

was discovered as a background dwarf nova of KIC 11412044. In January 2016 unusual dips in KIC 8462852 were announced. The unusual

light curve In astronomy, a light curve is a graph of light intensity of a celestial object or region as a function of time, typically with the magnitude of light received on the y axis and with time on the x axis. The light is usually in a particular freq ...

of KIC 8462852 (also known as Boyajian's Star) has engendered speculation that an alien civilization's

Dyson sphere A Dyson sphere is a hypothetical megastructure that completely encompasses a star and captures a large percentage of its solar power output. The concept is a thought experiment that attempts to explain how a spacefaring civilization would meet ...

is responsible. In June 2016 the project found 32 likely

eclipsing binaries A binary star is a system of two stars that are gravitationally bound to and in orbit around each other. Binary stars in the night sky that are seen as a single object to the naked eye are often resolved using a telescope as separate stars, in w ...

. The work also announced likely exoplanets. In February 2018 the first transiting exocomets were discovered. The dips were found by one of the authors, a Planet Hunters participant, in a visual search over five months of the complete Q1-Q17 ''Kepler'' light curve archive spanning 201250 target stars. In February 2022 Planet Hunters:TESS announced the discovery of BD+61 2536 (TIC 470710327), a massive hierarchical triple star system. The system is predicted to undergo multiple phases of mass transfer in the future, and likely end up as a double neutron star gravitational wave progenitor or an exotic Thorne-Zytkow object.

References

External links

* {{Official website, http://www.planethunters.org/ Astronomy websites Astronomy projects Human-based computation Citizen science Internet properties established in 2010 Exoplanet search projects