Earth’s atmosphere is leaking into space at the impressive (but not dangerous) rate of 90 tonnes (99 tons) per day. The leakage has been investigated by the ESA’s Cluster fleet for over 15 years, but many unknowns still remain.
Cluster has observed how the solar wind interacts with Earth’s magnetic field, and found that there was a continuous wind of cold plasma escaping our atmosphere at about 1 kilogram (2.2 pounds) per second. But how the plasma ends up in the magnetosphere is not at all clear.
“There are a few different aspects to this,” said Philippe Escoubet, ESA's Project Scientist for the Cluster mission, in a statement.
“We need to know the processes involved in transporting it there, how these processes depend on the dynamic solar wind and the conditions of the magnetosphere, and where plasma is coming from in the first place – does it originate in the ionosphere, the plasmasphere, or somewhere else?”
Although the magnetosphere protects us from the charged particles in the solar winds, it is not without weak spots. At the poles the field lines are open (just like a bar magnet) and protons and electrons from the Sun can penetrate and interact with the atmosphere, forming the northern and southern lights.
The process is not a one-way street. Charged particles from Earth’s atmosphere can also escape the atmosphere in the same locations. Since the 1990s scientists have known of sporadic columns of plasma, known as plumes, reaching the edges of the magnetosphere. But thanks to Cluster, space scientists have confirmed that the there is a constant outflow.
The latest analysis suggests a subtle interaction between our planet's magnetosphere and the interplanetary magnetic field (IMF). The IMF orientation depends on the rotation of the Sun, and scientists have seen that plumes are formed when the two fields are opposite while leaking outflows happen when the IMF and the Earth’s magnetic field point in the same direction.
"While there is still much to learn, we've been able to make great progress here," said Arnaud Masson, ESA's Deputy Project Scientist for the Cluster mission.
"These recent studies have managed to successfully link together multiple phenomena to paint a better picture of Earth's magnetic environment. This research required several years of ongoing observation, something we could only get with Cluster."
Understanding our own atmosphere and how it interacts with the solar wind will help us understand better the other objects in the Solar System, as well as suggesting what to look for in our search for a habitable exoplanet.