An update on the ARTEMIS twins

Following three years in lunar orbit ARTEMIS P1 and P2 are in excellent condition. Originally in Earth orbit, both spacecraft have been in lunar orbit since the summer of 2011 and in space since February 2007  [UC Berkeley].

Jasper Halekas
Acting Deputy Principal Investigator ARTEMIS
Space Physics Research Group
Space Sciences Lab
University of California at Berkeley

For those of you who aren't familiar with ARTEMIS, (the Acceleration, Reconnection, Turbulence, and Electrodynamics of the Moon's Interaction with the Sun mission) is an on-going "mission of opportunity," utilizing two of the original five-spacecraft heliophysics constellation THEMIS mission, "re-tasked" to study the interaction of the Moon and it's space plasma environment. 

The two ARTEMIS spacecraft have now been in elliptical equatorial orbits around the Moon since 2011 and continue to operate flawlessly. Both probes are in very stable orbits, and the health of the spacecrafts and all instruments remains very good.

A sample of the elaborate year-long transfer of the two "re-tasked" THEMIS probes from Earth orbit to lunar orbit. ARTEMIS P1 was the first spacecraft navigated to, and performing station-keeping operations around, the Earth-Moon L1 and L2 Lagrangian points [UC Berkeley].

Current ARTEMIS lunar investigations are focusing on measuring pickup ions from the exosphere, the electrostatic charging of the surface, the plasma wake, and the interaction of the solar wind with remanent crustal magnetic anomalies. ARTEMIS also uses lunar orbit as a platform to observe the solar wind and (around full Moon) the distant terrestrial magnetotail.

More details on recent studies can be found HERE.

With the LADEE mission about to enter its nominal science orbit, and LRO placing new emphasis on its own measurements of the lunar exosphere, ARTEMIS plays a key role by providing complementary measurements of the solar and terrestrial plasma that acts as both a source and sink for the lunar exosphere, affecting dust released from the lunar surface. Together, these three missions team together to measure the inputs, dynamics, and outputs of the coupled system formed by the Moon's surface, its dusty exosphere and the space environment.

All ARTEMIS data is publicly available on a few-day time scale, and we welcome participation from the community. More information on the mission, instrumentation, data (including summary plots), software, etc. is available from http://artemis.ssl.berkeley.edu, or by contacting the team directly.

Related Posts:

Several NASA spacecraft track energy through space (September 26, 2013)

Electric Moon jolts the solar wind (June 2, 2012)

Can we re-purpose space assets? (March 19, 2012)

NASA still studies advantage of lunar resources (February 15, 2012)

Then there were five... in lunar orbit (January 5, 2012)

Twin ARTEMIS probes to study Moon in 3D (July 15, 2011)

ARTEMIS P1 successfully enters lunar orbit (July 1, 2011)

"Dead spacecraft walking" (October 28, 2010)

YouTube demonstration of the re-routing of the two retired THEMIS orbiters to their new bonus mission in lunar orbit.

Electric Moon Jolts the Solar Wind

ARTEMIS P1 is seen in relation with the orbit of its twin P2 and the GRAIL twins Ebb and Flow below them in low lunar orbit. Together with with the Lunar Reconnaissance Orbiter NASA presently has five vehicles in lunar orbit. The schematic animation can be explored in startling depth using NASA's online Eyes on the Solar System application [NASA/Science].

With the Moon as the most prominent object in the night sky and a major source of an invisible pull that creates ocean tides, many ancient cultures thought it could also affect our health or state of mind -- the word “lunacy” has its origin in this belief. Now, a powerful combination of spacecraft and computer simulations is revealing that the Moon does indeed have a far-reaching, invisible influence -- not on us, but on the Sun, or more specifically, the solar wind.

The solar wind is a thin stream of electrically conducting gas called plasma that’s constantly blown off the surface of the Sun in all directions at around a million miles per hour. When a particularly fast, dense or turbulent solar wind strikes Earth’s magnetic field, it can generate magnetic and radiation storms that are capable of disrupting satellites, power grids, and communication systems. The magnetic “bubble” surrounding Earth also pushes back on the solar wind, creating a bow shock tens of thousands of miles across over the day side of Earth where the solar wind slams into the magnetic field and abruptly slows from supersonic to subsonic speed.

Unlike Earth, the Moon is not surrounded by a global magnetic field. “It was thought that the solar wind crashes into the lunar surface without any warning or ‘push back’ on the solar wind,” says Dr. Andrew Poppe of the University of California, Berkeley. Recently, however, an international fleet of lunar-orbiting spacecraft has detected signs of the Moon’s presence “upstream” in the solar wind. “We’ve seen electron beams and ion fountains over the Moon’s day side,” says Dr. Jasper Halekas, also of the University of California, Berkeley.

These phenomena have been seen as far as 10,000 kilometers above the Moon and generate a kind of turbulence in the solar wind ahead of the Moon, causing subtle changes in the solar wind’s direction and density. The electron beams were first seen by NASA’s Lunar Prospector (1998-1999), while the Japanese Kaguya (2007-2009) mission, the Chinese Chang’e-1 mission, and the Indian Chandrayaan-1 mission all saw ion plumes at low altitudes. 

NASA’s ARTEMIS mission has now also seen both the electron beams and the ion plumes, plus newly identified electromagnetic and electrostatic waves in the plasma ahead of the Moon, at much greater distances from the Moon. “With ARTEMIS, we can see the plasma ring and wiggle a bit, surprisingly far away from the Moon,” says Halekas. ARTEMIS stands for “Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon’s Interaction with the Sun”.

“An upstream turbulent region called the ‘foreshock’ has long been known to exist ahead of the Earth’s bow shock, but the discovery of a similar turbulent layer at the Moon is a surprise,” said Dr. William Farrell of NASA’s Goddard Space Flight Center in Greenbelt, Maryland. Farrell is lead of the NASA Lunar Science Institute’s Dynamic Response of the Environment At the Moon (DREAM) lunar science center, which contributed to the research.

Computer simulations help explain these observations by showing that a complex electric field near the lunar surface is generated by sunlight and the flow of the solar wind. The simulation reveals this electric field can generate electron beams by accelerating electrons blasted from surface material by solar ultraviolet light. Also, related simulations show that when ions in the solar wind collide with ancient, “fossil” magnetic fields in certain areas on the lunar surface, they are reflected back into space in a diffuse, fountain-shaped pattern. These ions are mostly the positively charged ions (protons) of hydrogen atoms, the most common element in the solar wind.

“It’s remarkable that electric and magnetic fields within just a few meters (yards) of the lunar surface can cause the turbulence we see thousands of kilometers away,” says Poppe. When exposed to solar winds, other moons and asteroids in the solar system should have this turbulent layer over their day sides as well, according to the team.

“Discovering more about this layer will enhance our understanding of the Moon and potentially other bodies because it allows information about conditions very near the surface to propagate to great distances, so a spacecraft will gain the ability to virtually explore close to these objects when it’s actually far away,” said Halekas.