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Guest : Out of THEMIS, ARTEMIS: Earth's loss is moon's gain
October 27, 2010

By Robert Sanders


An artist's concept of one of the twin ARTEMIS probes in orbit around the moon. Formerly part of the THEMIS suite of five probes in Earth orbit, these two micro-satellites will now observe the solar wind's impact on the Earth's magnetic field at a much greater distance from Earth, and the wake left by the moon as it travels through the magnetosphere. Credit: NASA Goddard Space Flight Center

( -- Two micro-satellites originally launched into Earth's orbit in 2007 by NASA have been redirected by University of California, Berkeley, scientists toward new orbits around the moon, extending study of the earth and moon's interaction with the solar wind.

The second of the two probes settled into a temporary "Lagrange-point" orbit on Friday, Oct. 22, inaugurating science operations for a new mission dubbed ARTEMIS – Acceleration, Reconnection, Turbulence, and Electrodynamics of the Moon's Interaction with the Sun.

Lagrange points are places where the gravity of Earth and the moon balance, creating a sort of gravitational parking lot for spacecraft. The two probes will remain there for six months before transitioning to their final, lunar orbits.

Over the next several years, ARTEMIS will help space scientists understand how the earth's magnetosphere is shaped by the strong solar wind at the distance of the moon and also how the moon's own tiny magnetic field interacts with the solar wind. Using simultaneous measurements of particles and electric and magnetic fields from two locations, ARTEMIS will provide the first three-dimensional perspective of how energetic particle acceleration occurs near the moon's orbit, in the distant magnetosphere, and in the solar wind.

"We currently know very little regarding the space environment of the moon, despite a number of existing and planned observatories there," said Vassilis Angelopoulos, principle investigator for the ARTEMIS mission and a professor of space physics at UCLA. "ARTEMIS is on stable orbits and can provide valuable information regarding the space environment, especially during the approaching solar maximum, as well as fully explore the earth's environment at lunar distances for the first time."

The two probes were originally part of NASA's five-probe THEMIS (Time History of Events and Macroscale Interactions during Substorms) mission, built and operated by UC Berkeley to orbit Earth and determine how storms in the earth's magnetic field disturb the colorful auroras in the Northern and Southern hemispheres.

THEMIS completed is primary mission in 2008 when Angelopoulos announced, "We discovered what makes the Northern Lights dance." The THEMIS team then proposed that the two outermost of the five probes use their extra fuel to propel themselves, via complex maneuvers around the moon and Earth, into lunar orbits – the first two-satellite mission to the moon. The maneuvers would also save the solar-powered spacecraft, which were spending more and more time in the earth's shadow and, for lack of power, in danger of freezing to death.

The two ARTEMIS probes will orbit for about six months around the Lagrange points near the moon before descending to final orbits around the moon. The Lagrange points are places where the gravity of the Earth and moon cancel one another, creating a sort of parking lot for satellites or debris. (Image: NASA Goddard Space Flight Center)
... : NASA - Themis mission site

Wiki : THEMIS mission

NASAexplorer | October 27, 2010

Launched in 2007, NASA's five THEMIS spacecraft have now successfully completed their 2 year mission to determine the cause of geomagnetic substorms. Because they are continuing to work perfectly, NASA is re-directing the outermost two spacecraft to special orbits at and around the Moon. This new mission, which is called ARTEMIS, uses some very complex maneuvers over two years (2009-2010) to get both spacecraft into position.

As the Moon orbits the Earth, it passes in and out of the Earth's magnetic field and the million-mile per hour stream of particles emitted by the Sun known as the solar wind. While in these regions, the two ARTEMIS spacecraft will seek evidence for turbulence, particle acceleration, and magnetic reconnection, three fundamental phenomena that control the nature of the solar wind's interaction with the Earth's magnetosphere. Employing their full complement of instruments and unique two-point vantage points, the spacecraft will study the vacuum the Moon carves out in the solar wind, and the processes that eventually fill this lunar wake. Nearer the Moon, they will observe the effects of surface electric fields, ions sputtered off the lunar surface, and determine the internal structure of the Moon from transient variations in its magnetic field induced by external changes.
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