The Cluster mission has been watching the movements of ions in the Earth’s magnetosphere. The ions studied were O+, ionised oxygen atoms, which exist in high relative abundances in the upper atmosphere. The magnetosphere is the region in space where Earth’s magnetic field dominates over other magnetic fields, most notably that carried by the plasma of the solar wind, which determines where the charged particles in the solar wind go. O+ ions in our own atmosphere are generated by ionising radiation from the Sun. When a geomagnetic substorm is occurring and auroral particles start to ionise particles in our own atmosphere, then the number of O+ ions escaping increases. These gather in the magnetotail (the magnetosphere is pulled out into a windsock shape by the pressure of the solar wind from the Sun on one side and the wake on the other) before being forced back toward Earth by the tail pulsing in and out during the substorm. Then the ions form a ring around the Earth called the ring current. This current generates its own magnetic field, as all currents do, which has the effect of weakening the Earth’s own field, letting more stuff in. In a further experiment from Cluster, it was seen that radio waves created by particles being pushed out of the magnetotail, which accelerate some auroral particles into our atmosphere also disrupt this ring current by pushing its particles into the atmosphere as well. This leads to enhancement of the ionosphere, which can have an effect on radio communications and satellites.
Meanwhile, the THEMIS mission, which sees five satellites positioned around the magnetosphere/solar wind boundary in order to watch how it changes with time, is to see two of its satellites peel off and orbit the Moon in the ARTEMIS mission. Having long exceeded their expected two year mission, the three year old probes have already been allowed to drift to the point where the Moon’s gravity will overwhelm the Earth’s gravity and pull them into a new orbit. From this point, should the funding be available to ground control, they will be positioned in front of and behind the Moon to view the shockfront and wake of the solar wind as it hits an object with no magnetosphere, save for a few magnetic anomalies on the surface. The Moon passes through the magnetotail of the Earth during its orbit, but spends most of the time fully exposed, in a bit of an analogue to Mars, which also has crustal magnetic anomalies and exposure to the solar wind.