William Atkins
Friday, 10 April 2009 20:35
Science -
Space
Page 2 of 4
And, they answer:
“We propose that the giant impactor could have formed in a stable orbit among debris at the Earth's Lagrange point $L_4$ (or $L_5$). We show such a configuration is stable, even for a Mars-sized impactor. It could grow gradually by accretion at $L_4$ (or $L_5$), but eventually gravitational interactions with other growing planetesimals could kick it out into a chaotic creeping orbit which we show would likely cause it to hit the Earth on a zero-energy parabolic trajectory. This paper argues that this scenario is possible and should be further studied.”
So, the
STEREO (Solar TErrestrial REelations Observatory) mission takes on the Belbruneo and Gott suggestion.
The twin probes of STEREO are now beginning a hunt for Theia at the Sun-Earth Lagrange point, the fairly large regions in space where the gravitational pull from the Sun and the gravitational pull from the Earth are equal. Thus, an object theoretically would remain stable at any of these points. (Added for clarification [4-15-09]: An object at one of the Lagrange points has an orbit equal to the Earth's orbit so it maintains its position in relation to the Earth-Sun pair.)
Five (L1, L2, L3, L4, and L5) such Lagrangian (L) points exist in the Sun-Earth system. L-points are about 50 million kilometers wide.
Go to the NASA media release “
STEREO Hunts for Remains of an Ancient Planet near Earth” to see an illustration of these five L-points, along with other illustrations of the "Big Splash."
Within the NASA article, Mike Kaiser, STEREO project scientist at the Goddard Space Flight Center (Maryland), stated,
“The name of the planet is Theia. It's a hypothetical world. We've never actually seen it, but some researchers believe it existed 4.5 billion years ago—and that it collided with Earth to form the Moon."
The two Princeton theorists believe that Theia, along with other planetesimals (small bodies that sometimes form into planets) was positioned at either the L4 or L5 point when it was forming millions of years ago, the only two Lagrange points that lie on the orbit of the Earth about the Sun.
Page three continues.
