Earth looks like such a solid and stable blue marble from outer space. But looks can be deceiving. Our planet is actually quietly leaking the equivalent of about 90 metric tons of plasma into outer space every day, according to new data collected by the European Space Agency's Cluster mission. Plasma is an invisible, electrically charged gas that forms in the upper atmosphere when air particles are heated by the Sun's ultraviolet rays. These particles travel along Earth's magnetic field lines and are able to escape Earth's gravity, but most remain trapped in an enormous bubble around the Earth known as the plasmasphere that ends about 16,000 miles outward from the planet.

Scientists observed that some plasma was escaping even further beyond this point in sporadic bursts of sudden activity known as plumes, which were first recored in the 1990s. But now the new data from ESA's Cluster missions suggests the process of plasma escape is actually more regular, supporting a theory first proposed in 1992. "Now we have finally found proof of a permanent and continuous leakage of material from the plasmasphere outwards," said Iannis Dandouras, a French scientist involved in the research, in a statement published online today.



Credit: ESA/ATG medialab

Instead of bursts, the new data suggests that plasma is flowing steadily outward from Earth in a wind-like form, and that this wind is generated by the interplay between the pressure exerted by plasma, Earth's gravity and the planet's rotation. "Imagine you buy a helium balloon and the next day you find it's falling down," said C.T. Russell, a professor of geophysics at UCLA who was not involved with this research. "You haven't got a hole in the balloon, but the helium can diffuse out through the film that makes up the ballon. That's basically what they are saying happens here with the plasma."

Fortunately, life here on Earth has nothing to worry about when it comes to plasma leakage. The daily loss of 90 metric tons of plasma is quite small when compared to the entire size of Earth's atmosphere. "The amount being lost looks large, but this is a very big planet," said Russell. "The man on the street is not going to be affected by this."