Launch Date February 17, 2007
Launch Site Cape Canaveral, Florida, USA
Destination Earth’s Moon
Type Orbiter
Status Successful - Extended Mission in Progress
Nation United States
Alternate Names Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon's Interaction with the Sun


ARTEMIS (Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon's Interaction with the Sun) is made up of two probes P1 and P2. They were originally members of the successful mission THEMIS in Earth orbit studying Earth's aurora, but were redirected to the moon in an effort to save the two probes from losing power in Earth's shade. Through this new mission scientists look to learn more about the Earth-moon Lagrange points, the solar wind, the Moon's plasma wake and how the Earth's magnetotail and the moon's own weak magnetism interact with the solar wind.


Both spacecraft arrived in lunar orbit in 2011. ARTEMIS is the first mission ever to orbit the moon's Lagrangian points - points on either side of the moon where the moon and Earth's gravity balance perfectly. It is also was the first to move from the Lagrangian to lunar orbit. Since arrival, the twin orbiters have contributed to lunar and Earth science as well as helping study the solar wind.

Key Dates

Feb. 17, 2007: Launch

Jan. 1, 2009: THEMIS-P1 and P2 are Reassigned, Renamed and Redirected to the Moon

Aug. 25, 2010: ARTEMIS-P1 Arrives at the L2 Lagrange Point

Oct. 22, 2010: ARTEMIS-P2 Arrives at the L1 Lagrange Point

In Depth

ARTEMIS stands for "Acceleration, Reconnection, Turbulence and Electrodynamics of the moon's Interaction with the Sun" and is a reassignment mission made up of two probes that were previously members of the completed and successful THEMIS mission to study Earth's aurora.

Since THEMIS's two probes P1 and P2 were found to be spending as much as 8 hours in the shadow of the Earth, and therefore running out of power the mission team came up with a plan to save the two probes. P1 and P2 still had ample fuel and so they were redirected and renamed ARTEMIS-P1 and P2, forming a new mission about the moon in order to study the Earth-moon Legrange points, the solar wind, and how the Earth's magnetotail and the moon's weak magnetism interact with the solar wind by using simultaneous measurements of particles and electric and magnetic fields from two locations. "Using two repurposed satellites for the ARTEMIS mission highlights NASA's efficient use of the nation's space assets," said Dick Fisher, director of the Heliophysics Division in NASA's Science Mission Directorate at the agency's headquarters in Washington.

ARTEMIS will also study the moon's plasma wake. The moon's plasma wake is so called because it is a turbulent cavity carved out of the solar wind by the moon itself, similar to the wake created by a speedboat. "This is a giant natural laboratory filled with a whole zoo of plasma waves waiting to be discovered and studied," says David Sibeck, ARTEMIS project scientist at the Goddard Space Flight Center.

Both probes have arrived at their initial destination: On 25 August 2010 ARTEMIS-P1 arrived at about-moon orbit (called an Earth-moon libration orbit) at the L2 Lagrange point, and ARTEMIS-P2 arrived at the L1 Lagrange point in an about-moon orbit on 22 October that same year. Lagrange points are places where the gravity of Earth and moon balance, creating a sort of gravitational parking spot for spacecraft. Because they lie just outside Earth's magnetosphere, Lagrange points are excellent places to study the solar wind. Sensors onboard the ARTEMIS probes will have in situ access to solar wind streams and storm clouds as they approach our planet -- a possible boon to space weather forecasters. After making magnetospheric observations from opposite sides of the Moon for three months ARTEMIS-P1 will be maneuvered from its position at the far side of the Moon and will join its sister spacecraft ARTEMIS-P2 at the L1 Lagrange point.

After six months at the Lagrange points, ARTEMIS will move in closer to the moon -- at first only 100 km from the surface and eventually even less than that. From this range the spacecraft will look to see what the solar wind does to a rocky world where there are only areas of magnetism to protect it. Studying how the solar wind electrifies, alters and erodes the moon's surface could reveal valuable information for future explorers and give planetary scientists a hint of what's happening on other unmagnetized worlds around the solar system.


Launch Vehicle: Delta II

Spacecraft Instruments:

  1. Data Processing Unit
  2. Electric Fields Instrument (EFI)
  3. Flux Gate Magnetometer (FGM)
  4. Search Coil Magnetometers (SCM)
  5. Electrostatic Analyzer (ESA)
  6. Solid State Telescope (SST)

Additional Resources

National Space Science Data Center Master Catalog: THEMIS-B (ARTEMIS-P1)

National Space Science Data Center Master Catalog: THEMIS-C (ARTEMIS-P2)

Out of THEMIS, ARTEMIS: Earth's loss is Moon's gain

Two NASA Spacecraft Begin New Exploration Assignments

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