Martin Connors
Centre for Natural and Human Science, Athabasca University, Athabasca Alberta CANADA
Christian Veillet
Canada-France-Hawaii Telescope, Mauna Kea, Hawaii USA
Paul Wiegert
Dept. of Physics, UWO, London Ontario, N6A 3K7 CANADA
Kimmo Innanen
Dept. of Physics and Astronomy, York University, Toronto Ontario, M3J 1P3 CANADA
Seppo Mikkola
Tuorla Observatory, University of Turku, 21500 Piikkio FINLAND
If you put an asteroid exactly on the same orbit as the Earth, what would happen? Would it stay on the orbit? Drift away? Or crash into our planet? The answer depends on exactly where you place the asteroid. There are five points on or near the Earth's orbit, known as the Lagrange points, where an asteroid will remain stationary with respect to the Earth. The locations of the Lagrange or L-points are shown below.
Asteroids placed anywhere else will drift around in various ways depending on where they have been placed.
If asteroids were placed exactly on the L-points and there were no perturbations (not even the small ones caused by the other planets in the Solar System), they would stay there indefinitely. But because there are these perturbations, asteroids at the L1, L2 and L3 points will wander away over time: only the L4 and L5 points are stable. And thus, there may be asteroids orbiting there. It is the objective of this collaboration to discover them.
| There are in fact a variety of positions near the L4 and L5 points which can also maintain asteroids in a stable fashion, though these asteroids will not remain perfectly stationary with respect to the Earth (some hypothetical members of this asteroid group are shown above). For an MPEG animation of a simulation of these particles' motions, click here (3.1 Mb). A small preview section appears to the left. Note: the red asteroids are not special, they have just been coloured differently to make their motion easier to follow against the group. Also note that the mutual gravitational attraction of the group plays no role here, it is much smaller than any of the other perturbations the group is subjected to. |
All the planets in our Solar System have Lagrange points, just as Earth does. So far, many asteroids have been discovered at Jupiter's L4 and L5 points, and two at Mars'. Jupiter's asteroids are mostly named after heroes of the Trojan Wars, and thus are often called "Trojans" for short. Asteroids at Earth's L4 and L5 points are sometimes referred to as "Earth Trojans".
Flight through the L4 point (3.1 Mb)
Asteroids on Earth's orbit (6.0 Mb)
.
What do our telescope images look like? The animated GIF below
shows three small segments of the Canada-France-Hawaii telescope's
field of view. We track the telescope at the expected speed of
the asteroids, so stars appear as long streaks, main belt asteroids
as short streaks, and Earth Trojans as circular or nearly-circular
dots. A candidate detection is shown below.
other MPEG movies
This animation shows a scene which begins from a vantage point above
the Solar System. The camera matches the Earth's velocity, traveling
along to touch down on the "top" of the Earth, all the while looking
at the L4 point. After a brief stop, the camera flies through the L4
cloud and finishes its journey pointing back towards the Earth, which
can be seen on the right-hand edge of the screen. Note that the size
of the Sun, planets and asteroids has been greatly exaggerated in all
the sims and figures to aid visibility.
In this simulation, 23 asteroids are placed on the Earth's orbit at 15
degree intervals and simulated over 1 million years. All the planets'
influences are accounted for though not all can be seen in the frame.
None of the asteroids collide with the Earth, and none escape. Counter
to intuition, the Earth ends up sitting in a gap as the dynamics of
the situation cause the asteroids to keep their distance. Asteroids
are colour-coded according to their initial position: note that at the
end most remain clustered on their original side, though it is
possible for bodies to pass from the vicinity of one L point to the
other. Also note that, after a million years, most asteroids are no
longer on perfectly circular orbits, gentle "stirring" by the planets
has altered their orbits somewhat.
Telescope images
One
Two
Three
Four
Five
Six
Preprint:
For a technical analysis of the results of our survey, check out the preprint.
Related links
Have a question or comment? Email Paul Wiegert at pwiegert[remove this and put the @ symbol here]uwo.ca
Earth Lagrange and Trojan asteroid main page
© Copyright 2000-2004 by Paul Wiegert
