Archive for March 9, 2020

03/09/2020 – A NASA mission to the Trojans, strange asteroids in Jupiter’s orbit

March 9, 2020 Comments off

Ephemeris for Monday, March 9th. Today the Sun will be up for 11 hours and 36 minutes, setting at 7:41, and it will rise tomorrow at 8:03. The Moon, at full today, will rise at 7:46 this evening.

Lucy is a NASA mission ( whose name is not some tortured acronym. It is named for a Beatles tune and a hominid fossil found in Africa. It will set off in October next year to study two groups of strange asteroids, Jupiter’s Trojan asteroids. These asteroids lie in two swarms in Jupiter’s orbit averaging 60 degrees ahead and 60 degrees behind Jupiter. They congregate around two gravitational points in the Jupiter-Sun system called Lagrangian points, specifically L4 ahead of Jupiter and L5 behind. The Lucy spacecraft will put itself in such an orbit that it can loop between the Earth’s orbit and each of the two Trojan swarms passing by several of the asteroids. In general the names given to the asteroids are for the characters from Homer’s Iliad.  The L4 group named or the Greeks and the L5 group named for the Trojans. I’ll be visiting this mission and that of Trojan asteroids in the future. The Earth actually has one known Trojan asteroid.

The times given are for the Traverse City/Interlochen area of Michigan. They may be different for your location.


trojan asteroids of Jupiter

The inner solar system with Jupiter’s Trojan asteroids. The Hilda asteroids have orbital periods of 2/3rds Jupiter’s period.  Their elliptical orbits rise from the asteroid belt (white dots) to the L3, L4 and L5 points respectively. Credit: Mdf at English Wikipedia.

Lagrange points

The 5 Lagrange points about two bodies orbiting each other. The Lagrange or Lagrangian points of gravitational equilibrium were discovered by Joseph-Louis Lagrange (1736-1813). Credit Georgia State University.