The study of the upper region of an atmosphere.


Operating in two directions simultaneously.


Of, relating to, or resulting from the influence of human beings on nature.


A mission comprised of two spacecraft that are stationed in Earth-Moon libration point orbits. ARTEMIS will provide the first three-dimensional perspective of how energetic particle acceleration occurs near the Moon, in the magnetosphere, and in the solar wind. This will provide scientists with a better understanding of how the solar wind shapes Earth's magnetosphere.

ballistic hop

A term to describe the movement of a particle or ion in an arc-shaped trajectory along a surface.

bow shock

The boundary at which the speed of the solar wind drops when nearing the magnetopause.

CME, coronal mass ejection

A massive burst of solar wind, other light isotope plasma, and magnetic fields rising above the solar corona or being released into space.

crustal magnetic anomaly

A local variation in a planet's magnetic field due to variations in local chemistry or magnetism of the crust.


When a substance is released from or through a surface.

desorption, photon-stimulated

Desorption stimulated by light.

desorption, thermal

Desorption stimulated by heat.

dust lofting

When dust is moved from the lunar surface into the exosphere.

electrons, secondary

Electrons generated by the process of ionization.


Derived or originating internally.

ESD, electrostatic discharge

Electrostatic discharge (ESD) is the sudden and momentary electric current that flows between two objects at different electrical potentials caused by direct contact or induced by an electrostatic field.[1] The term is usually used in the electronics and other industries to describe momentary unwanted currents that may cause damage to electronic equipment.

EVA, extravehicular activity

Work done by an astronaut away from their spacecraft or habitat.


A layer of photoionized atoms from the exosphere that encompasses the lunar dayside.


The uppermost layer of an atmosphere. Its density is so low that the atoms that compose it do not collide.

impact vaporization

A phase transition from a solid to a gas stimulated by the heat and pressure resulting from an impact.

ion refilling

Refilling of the lunar wake by ions or plasma from the solar wind.


Ionization is the physical process of converting an atom or molecule into an ion by adding or removing charged particles such as electrons or other ions.


A portion of the upper atmosphere, containing electrons and electrically charged atoms and molecules, ionized by solar radiation.

Jeans escape

Atmospheric escape is the loss of planetary atmospheric gases to space. There are several processes that can lead to it. In some cases, this can be a very important process; for example, both Venus and Mars have probably lost much of their water due to atmospheric escape since they have a weaker gravitational field strength than Earth.


The Lunar Atmosphere and Dust Environment Explorer (LADEE) is a space exploration mission scheduled for launch on 1 May 2012. To carry out the mission NASA will send a robotic spacecraft into orbit around the Moon, and use instruments aboard the spacecraft to study the Moon's atmosphere and dust in the Moon's vicinity. Instruments will include a dust counter, a neutral mass spectrometer, an ultraviolet-visible spectrometer, and recently announced, a laser communications (lasercomm) terminal.


The Lunar Crater Observation and Sensing Satellite (LCROSS) was a robotic spacecraft operated by NASA. The main LCROSS mission objective was to explore the presence of water ice in a permanently shadowed crater near a lunar polar region. It was successful in discovering water in the southern lunar crater Cabeus.


The Lunar Reconnaissance Orbiter (LRO) is a NASA robotic spacecraft currently orbiting the Moon on a low 50 km polar mapping orbit.The LRO mission is a precursor to future manned missions to the moon by NASA. To this end a detailed mapping program will identify safe landing sites, locate potential resources on the moon, characterize the radiation environment, and demonstrate new technology.


An oscillation in the apparent aspect of a secondary body (such as a satellite like the Moon) as seen from the primary object around which it resolves. Lunar libration allows us to see approximately 59% of the Moon's surface from Earth.

magnetic anomalies

A local variation in a planetary body's global magnetic field or a localized magnetic field on a planetary body without a global magnetic field.


The outer limit of a magnetosphere.


The magnetosheath is the region of space between the magnetopause and the bow shock of a planet's magnetosphere. The regularly organized magnetic field generated by the planet becomes weak and irregular in the magnetosheath due to interaction with the incoming solar wind, and is incapable of fully deflecting the highly charged particles.


The region surrounding the Earth or another astronomical body in which its magnetic field is the predominant effective magnetic field.


The broad elongated extension of a planet's magnetosphere on the side away from the Sun.


A small piece of rock from space, usually dust-sized or smaller, that impacts the Earth or another planetary body.

Monte Carlo simulation

Monte Carlo methods (or Monte Carlo experiments) are a class of computational algorithms that rely on repeated random sampling to compute their results. Monte Carlo methods are often used in simulating physical and mathematical systems. Because of their reliance on repeated computation of random or pseudo-random numbers, these methods are most suited to calculation by a computer and tend to be used when it is unfeasible or impossible to compute an exact result with a deterministic algorithm.

Monte Carlo simulation methods are especially useful in studying systems with a large number of coupled degrees of freedom, such as fluids, disordered materials, strongly coupled solids, and cellular structures (see cellular Potts model). More broadly, Monte Carlo methods are useful for modeling phenomena with significant uncertainty in inputs, such as the calculation of risk in business. These methods are also widely used in mathematics: a classic use is for the evaluation of definite integrals, particularly multidimensional integrals with complicated boundary conditions. It is a widely successful method in risk analysis when compared with alternative methods or human intuition. When Monte Carlo simulations have been applied in space exploration and oil exploration, actual observations of failures, cost overruns and schedule overruns are routinely better predicted by the simulations than by human intuition or alternative "soft" methods.


Outgassing (sometimes called offgassing, particularly when in reference to indoor air quality) is the release of a gas that was dissolved, trapped, frozen, absorbed or adsorbed in some material. It can include sublimation and evaporation which are phase transitions of a substance into a gas, as well as desorption, seepage from cracks or internal volumes and gaseous products of slow chemical reactions. Boiling is generally thought of as a separate phenomenon from outgassing because it consists of a phase transition of a liquid into a vapor made of the same substance


A disturbance of motion, course, arrangement, or state of equilibrium.


Electrons emitted during photoionization.


The ionization of an atom or molecule by the absorption of a high-energy photon.


An ionized gas consisting of positive ions and free electrons in proportions resulting in more or less no overall electric charge, typically at low pressures (as in the upper atmosphere and in fluorescent lamps) or at very high temperatures (as in stars and nuclear fusion reactors).

plasma sheath

The boundary layer of charged particles between a plasma and its surrounding walls, electrodes, or other plasmas. The sheath is generated by the interaction of the plasma with the boundary material. Current flow may be in only one direction across the sheath (single sheath), in both directions across the sheath (double sheath), or when the plasma is immersed in a magnetic field, it may flow along the sheath surface at right angles to the magnetic field (magnetic current sheath).

plasma sheet

A sheet of plasma that extends down the magnetotail dividing the two lobes of the Earth's magnetic field.

plasma void, or wake

A wake, or plasma void, is the low-density cavity left behind a planetary obstacle in the solar wind. For example, solar wind plasma impacts the lunar surface, leading to the formation of a wake, or plasma void, behind the Moon.

polar cold trap

Areas near the Moon's poles, typically in permanently shadowed regions within craters, where the temperatures are cold enough to preserve volatile deposits, such as water ice.

PSR, permanently shadowed regions

Regions in deep polar craters that are never illuminated by sunlight because the Moon is tilted very little relative to the Sun.

radiation pressure

The pressure exerted upon any surface exposed to electromagnetic radiation.


The reduction of a medium's density, or the opposite of compression. Rarefaction can be easily observed by compressing a spring and releasing. Rarefaction waves expand with time; for most gases the rarefaction wave keeps the same overall profile at all times (it is a 'self-similar expansion'). Each part of the wave travels at the local speed of sound, in the local medium. This expansion behavior is in contrast to the behavior of pressure increases, which get narrower with time, until they steepen into shock waves. Rarefaction can refer to an area of low relative pressure following a shock wave.


The act or process of absorbing again.


A term used to describe materials that are chemically and physically stable at high temperatures. Ca, Al, and Ti, among others, are examples of refractory elements.


Regolith is a layer of loose, heterogeneous material covering solid rock. It includes dust, soil, broken rock, and other related materials and is present on Earth, the Moon, some asteroids, and other planets.


The Solar Dynamics Observatory (SDO) is a NASA mission which will observe the Sun for over five years. Launched on February 11, 2010, the observatory is part of the Living With a Star (LWS) program. The goal of the LWS program is to develop the scientific understanding necessary to effectively address those aspects of the connected Sun–Earth system that directly affect life and society. SDO's goal is to understand the Sun's influence on Earth and near-Earth space by studying the solar atmosphere on small scales of space and time and in many wavelengths simultaneously. SDO will investigate how the Sun's magnetic field is generated and structured, how this stored magnetic energy is converted and released into the heliosphere and geospace in the form of solar wind, energetic particles, and variations in the solar irradiance.

SEP, solar energetic particles

High-energy particles coming from the Sun which had been first observed in the early 1940s. They consist of protons, electrons and heavy ions with energy ranging from a few tens of keV to GeV (the fastest particles can reach speed up to 80% of the speed of light). They are of particular interest and importance because they can endanger life in outer space (especially particles above 40 MeV). Solar Energetic Particles (SEPs) can originate from two processes: energetization at a solar flare site or by shock waves associated with Coronal Mass Ejection (CMEs). However, only about 1% of the CMEs produce strong SEP events.


A sink consumes or absorbs something, converse to a source which produces something.

solar flare

A brief eruption of intense high-energy radiation from the sun's surface, associated with sunspots and causing electromagnetic disturbances on the earth, as with radio frequency communications and power line transmissions.

solar storm

A solar storm (a.k.a. geomagnetic storm) is a temporary disturbance of the Earth's magnetosphere caused by a disturbance in space weather. Associated with solar flares and resultant solar coronal mass ejections (CME), a geomagnetic storm is caused by a solar wind shock wave and/or cloud of magnetic field which typically strikes the Earth's magnetic field 3 days after the event. The solar wind pressure on the magnetosphere and the solar wind magnetic field will increase or decrease depending on the Sun's activity. The solar wind pressure changes modify the electric currents in the ionosphere, and the solar wind's magnetic field interacts with the Earth's magnetic field causing the entire structure to evolve. Magnetic storms usually last 24 to 48 hours, but some may last for many days In 1989, an electromagnetic storm disrupted power throughout most of Quebec[and caused aurorae as far south as Texas.

solar wind

The continuous flow of charged particles from the Sun that permeates the Solar System. It mostly consists of electrons and protons with energies usually between 10 and 100 keV. The stream of particles varies in temperature and speed over time. These particles can escape the Sun's gravity because of their high kinetic energy and the high temperature of the corona.


A process in which fragments of material (spall) are ejected from a body due to impact or stress. In the context of impact mechanics it describes ejection or vaporization of material from a target during impact by a projectile. In planetary physics, spallation describes meteoritic impacts on a planetary surface and the effects of a stellar wind on a planetary atmosphere. In the context of mining or geology, spallation can refer to pieces of rock breaking off a rock face due to the internal stresses in the rock; it commonly occurs on mine shaft walls. In the context of anthropology, spallation is a process used to make stone tools such as arrowheads by knapping. In nuclear physics, spallation is the process in which a heavy nucleus emits a large number of nucleons as a result of being hit by a high-energy particle, thus greatly reducing its atomic weight.


A process whereby atoms are ejected from a solid target material due to bombardment of the target by energetic particles. Sputtering is one of the forms of space weathering, a process that changes the physical and chemical properties of airless bodies, such as asteroids and our Moon. It is also one of the possible ways that Mars has lost most of its atmosphere and that Mercury continually replenishes its tenuous surface-bounded exosphere.


STEREO (Solar TErrestrial RElations Observatory) is a solar observation mission.Two nearly identical spacecraft were launched into orbits that cause them to respectively pull further ahead of and fall gradually behind the Earth. This will enable stereoscopic imaging of the Sun and solar phenomena, such as coronal mass ejections.


The location on the surface of a planet or moon where the Sun is directly overhead.


A spot or patch appearing from time to time on the sun's surface, appearing dark by contrast with its surroundings. Sunspots are regions of lower surface temperature and are believed to form where loops in the sun's magnetic field intersect the surface; an individual spot may persist for several weeks. The number of sunspots on the solar surface fluctuates according to a regular cycle, with times of maximum sunspot activity recurring every eleven years.

surface-sputtered ions

Ions released by a surface, such as that of the Moon, by sputtering.

terminator region

Region between the sun lit side of a planet or moon and the night side. Shadows can be very long in the region emphasizing geographic features. Unique phenomena can occur in this region which will have large temperature differences between areas that are close together.


The process of particles reaching thermal equilibrium through interaction.


Also called triboelectric charging or the triboelectric effect. Tribocharging involves the transfer of electrons between materials. When the materials are placed in contact and then separated, such as by rubbing them together, negatively charged electrons are transferred from the surface of one material to the surface of the other material. The material that loses electrons becomes positively charged, while the material that gains electrons is negatively charged.


A group of chemical elements and chemical compounds with low boiling points that are associated with a planet's or moon's crust and/or atmosphere. Examples include nitrogen, water, carbon dioxide, ammonia, hydrogen, and methane, all compounds of C, H, O and/or N, as well as sulfur dioxide. In astrogeology, these compounds, in their solid state, often comprise large proportions of the crusts of moons and dwarf planets. In terrestrial geology, the term more specifically refers to components of magma (mostly water vapor and carbon dioxide) that affect the appearance and strength of volcanoes. Volatiles in a magma with a high viscosity, generally felsic with a higher silica (SiO2) content, tend to produce eruptions that are explosive. Volatiles in a magma with a low viscosity, generally mafic with a lower silica content, tend to vent and can give rise to a lava fountain.

wake, or plasma void

A wake, or plasma void, is the low-density cavity left behind a planetary obstacle in the solar wind. For example, solar wind plasma impacts the lunar surface, leading to the formation of a wake, or plasma void, behind the Moon.