List of objects at Lagrangian points

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.

Present probes

• WIND (spacecraft) (At L1 since 2004)
• The Solar and Heliospheric Observatory (SOHO)
• The Advanced Composition Explorer (ACE)
• The Deep Space Climate Observatory (DSCOVR), designed to monitor global warming
• LISA Pathfinder

Planned probes

• Kuafu

L₂

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

Past probes

• 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.
• CNSA's Chang'e 2^[1] 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.
• 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.

Present probes

• The ESA Gaia probe

Planned probes

• 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 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.^[2]
• Dust clouds^[3]

L₅

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

• Asteroid 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) makes its closest pass to L₅ in October 2009, on its orbit around the Sun, slightly slower than Earth.^[2]
• The Spitzer Space Telescope is in an Earth-trailing heliocentric orbit drifting away c. 0.1 AU per year. In c. 2013–15 it will pass L₅ in its orbit.
• Dust clouds^[3]

Earth–Moon Lagrangian points

L₂

• ARTEMIS
• Chang'e 5-T1

L₄ and L₅

• possible 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.^[4]

Proposed objects

• Exploration Gateway Platform
• In his book "The High Frontier" 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–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

• 1999 UJ7

L₅

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

Source: Minor Planet Center

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

L₄

• 2011 QF99 ^[5]

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) 2004 UP10
• (385695) 2005 TO74
• 2001 QR322
• 2005 TN53
• 2006 RJ103
• 2007 VL305

L₅

• 2008 LC18
• 2004 KV18
• 2011 HM102

Source: Minor Planet Center

See also

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

Footnotes

1. "China's Moon orbiter Chang'e-2 travels 1.5 km into outer space". The Economic Times. 2011-08-30. Retrieved 2011-08-31.
2. NASA - Join STEREO and Explore Gravitational "Parking Lots" That May Hold Secret of Moon's Origin
3. John Baez' Lagrange Points page
4. Hiten
5. The first known Uranian Trojan and the frequency of temporary giant-planet co-orbitals: Mike Alexandersen, Brett Gladman, Sarah Greenstreet, J.J. Kavelaars, Jean-Marc Petit