Astronomy:List of objects at Lagrangian points

Short description: Wikipedia list article

This is a list of known objects which occupy, have occupied, or are planned to occupy any of the five Lagrangian points of two-body systems in space.

A diagram showing the five Lagrangian points in a two-body system

Sun–Earth Lagrangian points

L1

L₁ is the Lagrangian point located approximately 1.5 million km from Earth towards the Sun.

Past probes

• International Cometary Explorer, formerly the International Sun–Earth Explorer 3 (ISEE-3), diverted out of L₁ in 1983 for a comet rendezvous mission. Currently in heliocentric orbit.
• NASA's Genesis probe collected solar wind samples at L₁ from December 3, 2001 to April 1, 2004, when it returned the sample capsule to Earth. It returned briefly in late 2004 before being pushed into heliocentric orbit in early 2005.
• LISA Pathfinder

Present probes

Animation of Deep Space Climate Observatory's trajectory from 11 February 2015 to 3 January 2017
  DSCOVR ·   Earth ·   Moon

• The Solar and Heliospheric Observatory (SOHO)
• The Advanced Composition Explorer (ACE)
• WIND (spacecraft) (At L₁ since 2004)
• The Deep Space Climate Observatory (DSCOVR), designed to image the sunlit earth in 10 wavelengths (EPIC) and monitor total reflected radiation (NISTAR)

Planned probes

• Aditya-L1
• Kuafu
• Lagrange mission (ESA). One spacecraft in L1 and one in L5.

L2

L₂ is the Lagrangian point located approximately 1.5 million km from Earth in the direction opposite the Sun.

Past probes

Animation of Wilkinson Microwave Anisotropy Probe's trajectory from 1 July 2001 to 7 April 2009
  WMAP ·   Earth

• NASA's Wilkinson Microwave Anisotropy Probe (WMAP) observed the cosmic microwave background from 2001 until 2010. It was moved to a heliocentric orbit to avoid posing a hazard to future missions.
• NASA's WIND from November 2003 to April 2004. The spacecraft then went to Earth orbit, before heading to L₁.
• The ESA Herschel Space Observatory exhausted its supply of liquid helium and was moved from the Lagrangian point in June 2013.
• At the end of its mission ESA's Planck spacecraft was put into a heliocentric orbit and passivated to prevent it from endangering any future missions.
• CNSA's Chang'e 2 from August 2011 to April 2012. Chang'e 2 was then placed onto a heliocentric orbit that took it past the near-Earth asteroid 4179 Toutatis.

Present probes

• The ESA Gaia probe
• The joint Russian-German high-energy astrophysics observatory Spektr-RG

Planned probes

• The ESA Euclid mission, to better understand dark energy and dark matter by accurately measuring the acceleration of the universe.
• The joint NASA, ESA and CSA James Webb Space Telescope (JWST), formerly known as the Next Generation Space Telescope (NGST)
• The ESA PLATO mission, which will find and characterize rocky exoplanets.
• The JAXA LiteBIRD mission.
• The NASA Nancy Grace Roman Space Telescope (WFIRST)
• The ESA ARIEL mission, which will observe the atmospheres of exoplanets.
• The ESA Advanced Telescope for High ENergy Astrophysics (ATHENA)
• The NASA Advanced Technology Large-Aperture Space Telescope, which would replace the Hubble Space Telescope and possibly the JWST.

Cancelled probes

• The ESA Eddington mission
• The NASA Terrestrial Planet Finder mission (may be placed in an Earth-trailing orbit instead)

L3

L₃ is the Sun–Earth Lagrangian point located on the side of the Sun opposite Earth, slightly outside the Earth's orbit.

• There are no known objects in this orbital location.

L4

L₄ is the Sun–Earth Lagrangian point located close to the Earth's orbit 60° ahead of Earth.

• Asteroid 2010 TK7 is the first discovered "tadpole" orbit companion to Earth, orbiting L₄ with a mean distance of about one astronomical unit.
• STEREO A (Solar TErrestrial RElations Observatory – Ahead) made its closest pass to L₄ in September 2009, on its orbit around the Sun, slightly faster than Earth.
• OSIRIS-REx passed near the L4 point and performed a survey for asteroids between 9 and 20 February 2017.

L5

L₅ is the Sun–Earth Lagrangian point located close to the Earth's orbit 60° behind Earth.

• Asteroid (419624) 2010 SO16, in a horseshoe companion orbit with Earth, is currently proximal to L₅ but at a high inclination.
• STEREO B (Solar TErrestrial RElations Observatory – Behind) made its closest pass to L₅ in October 2009, on its orbit around the Sun, slightly slower than Earth.
• The Spitzer Space Telescope is in an Earth-trailing heliocentric orbit drifting away c. 0.1 AU per year. In c. 2013–15 it has passed L₅ in its orbit.
• Hayabusa2 passed near L₅ during the spring of 2017, and imaged the surrounding area to search for Earth trojans in 18 April 2018.

Proposed

• Lagrange mission (ESA). One spacecraft in L5 and one in L1.

Earth–Moon Lagrangian points

L2

• ARTEMIS
• Chang'e 5-T1
• Queqiao relay satellite

L4 and L5

• Kordylewski clouds
• future location of TDRS-style communication satellites to support L₂ satellite

Past probes

• Hiten was the first spacecraft to demonstrate a low energy trajectory, passing by L₄ and L₅ to achieve lunar orbit at a very low fuel expense, compared to usual orbital techniques. Hiten did not find any conclusive increase in dust density at Lagrange points.

Proposed objects

• Exploration Gateway Platform
• In his 1976 book The High Frontier: Human Colonies in Space Dr. Gerard O'Neill proposed the establishment of gigantic Space Islands in L₅. The inhabitants of the L5 Society should convert lunar material to huge solar power satellites. Many works of fiction, most notably the Gundam series, involve colonies at these locations.

Sun–Venus Lagrangian points

L4

• 2013 ND15

Sun–Mars Lagrangian points

Asteroids in the L₄ and L₅ Sun–Mars Lagrangian points are sometimes called Mars trojans, with a lower-case t, as "Trojan asteroid" was originally defined as a term for Lagrangian asteroids of Jupiter. They may also be called Mars Lagrangian asteroids.

L4

• (121514) 1999 UJ7

L5

• 5261 Eureka
• (101429) 1998 VF31
• (311999) 2007 NS2
• (385250) 2001 DH47, 2001 FG24, 2001 FR127 (not confirmed as true Lagrangian asteroids)

Source: Minor Planet Center [1]

Sun–Jupiter Lagrangian points

Asteroids in the L₄ and L₅ Sun–Jupiter Lagrangian points are known as Jupiter Trojan asteroids or simply Trojan asteroids.

L4

• Trojan asteroids, Greek camp

L5

• Trojan asteroids, Trojan camp

Saturn–Tethys Lagrangian points

L4

• Telesto

L5

• Calypso

Saturn–Dione Lagrangian points

L4

• Helene

L5

• Polydeuces, follows a "tadpole" orbit around L₅

Sun–Uranus Lagrangian points

L3

• 83982 Crantor, follows a "horseshoe" orbit around L₃

L4

• 2011 QF99
• 2014 YX49

Sun–Neptune Lagrangian points

Minor planets in the L₄ and L₅ Sun–Neptune Lagrangian points are called Neptune trojans, with a lower-case t, as "Trojan asteroid" was originally defined as a term for Lagrangian asteroids of Jupiter.

L4

• 385571 Otrera
• 385695 Clete
• 2001 QR322
• 2005 TN53
• 2006 RJ103
• 2007 VL305

L5

• 2008 LC18
• 2004 KV18
• 2011 HM102

Source: Minor Planet Center [2]

See also

• Lagrangian point (especially section on spacecraft and missions)
• Trojan points
  • Trojan asteroid
  • Trojan moon
  • Trojan planet