STEREO Probes Near Lagrangian Points
Two
identical NASA spacecraft are preparing to enter a point in the
universe that may eventually answer the question of how our moon
was born.
The spacecraft duet, called Solar Terrestrial Relations
Observatory, or STEREO, are nearing a zone known as the Lagrangian
points. At these points, the gravity of the sun and Earth combine
to form gravitational wells where asteroids and space dust tend to
gather. The 18th-century mathematician Joseph-Louis Lagrange
realized there were five such wells in the sun-Earth system. The
twin probes are about to pass through two of them, named L4 and
L5.
During their journey, the spacecraft will use a
wide-field-of-view telescope to look for asteroids orbiting the
region. Scientists will be able to identify if a dot of light is an
asteroid because it will shift its position against stars in the
background as it moves in its orbit.
"These points may hold small asteroids, which could be leftovers
from a Mars-sized planet that formed billions of years ago," said
Michael Kaiser, STEREO project scientist at NASA's Goddard Space
Flight Center in Greenbelt, MD. "According to Edward Belbruno and
Richard Gott at Princeton University, about 4.5 billion years ago
when the planets were still growing, a hypothetical world called
Theia may have been nudged out of L4 or L5 by the increasing
gravity of other developing planets like Venus, sending it on a
collision course with Earth. The resulting impact blasted the outer
layers of Theia and Earth into orbit, which eventually coalesced
under their own gravity to form the moon."
This concept is a modification of a scientific "giant impact"
theory of the moon's origin. The theory explains puzzling
properties of the moon, such as its relatively small iron core. At
the time of the giant impact, Theia and Earth would have been large
enough to be molten, enabling heavier elements, like iron, to sink
to the center to form their cores. An impact would have stripped
away the outer layers of the two worlds, containing mostly lighter
elements like silicon. The moon eventually formed from this
material.
Launched in October 2006, STEREO'S primary
mission is to give three-dimensional views of space weather by
observing the sun from the two points where the spacecraft are
located. Images and other data are then combined for study and
analysis.
Space weather produces disturbances in electromagnetic fields on
Earth that can induce extreme currents in wires, disrupting power
lines and causing wide-spread blackouts. It also can affect
communications and navigation systems. Space weather has been
recognized as causing problems with new technology since the
invention of the telegraph in the 19th century.