Lagrangian point

Definition

A Lagrangian point is a point of interplanetary gravitational stability in a two body orbital configuration. Devised by the Italian/French mathematician and astronomer, Joseph Louis Lagrange (1736-1813), Lagrangian points are currently used to describe the influence of the planets over local space, provides a location for Trojan asteroids and may possibly be used by future space missions as a "stepping stone" to Mars and the Moon.

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Current missions using the Lagrangian points of the Earth-Sun system

• $L_{1}$

• The Solar and Heliospheric Observatory (SoHO) - A multi-instrument observatory contantly observing the Sun.
• Advanced Composition Explorer (ACE) - An in-situ observatory measuring the properties of the solar wind and solar radiation.

• $L_{2}$

• Wilkinson Microwave Anisotropy Probe (WMAP) - Surveying the sky, observing the microwave radiation left over by the Big Bang.

Objects observed in the Mars-Sun $L_{4}$ and $L_{5}$ points

Asteroids in the $L_{4}$ and $L_{5}$ Mars-Sun Lagrangian points are often called Mars Trojan asteroids. A handful of asteroids are in stable solar orbits, leading ($L_{4}$) and following ($L_{5}$) the path of Mars including an asteroid named "1999 UJ7" (at $L_{4}$) and "5261 Eureka" (at $L_{5}$).

Uses of the Mars $L_{1}$ and $L_{2}$ points

• An "early warning system" to notify settlers about the onset of solar storms.
• Communications satellites inserted in stable orbits around the Lagrangian points - long-term nodes of communication between Earth and Mars. Could be extended to include the $L_{4}$ and $L_{5}$ points to allow communication even when Mars is in conjunction.
• A manned space station acting as a "staging post" for missions to asteroids or refuge before making the final plunge into Mars' gravitational well.

See also

• 5261 Eureka on Wikipedia
• List of objects at Lagrangian points