A schematic of the environment nearest Jupiter, showing magnetically trapped particles in a portion of Jupiter's extensive radiation belts in red, the neutral gas of the Io torus in green, and the neutral gas of the Europa torus in blue. The picture is derived from data taken by the Cassini spacecraft.
The Atmosphere of Europa
The Galileo mission
discovered an amazing thing. Europa has its own atmosphere, although it is very, very thin. This atmosphere is created when fast moving molecules in Jupiter's magnetosphere
hit the surface of Europa and knock out a water molecule. This process is known as "sputtering". The surface may also evaporate, or "sublimate" when the Sun
is shining, the way a comet
does. Because there is little gravity however, a small moon cannot hold onto an atmosphere for very long.
Water molecules lost from the surface are quickly separated into the constituents oxygen and hydrogen. These molecules can also be quickly ionized by ultraviolet radiation
and charged particles in the vicinity. Thus Europa has a neutral atmosphere as well as an ionosphere. These molecules may float around Europa for awhile, but because of Europa's weak gravity, the "atmosphere" rapidly drifts away.
A neutral component of oxygen near Europa was detected by the Cassini spacecraft
as it flew by Jupiter in the year 2000, and is illustrated in the drawing to the left. This suggests that the components of Europa's atmosphere that float away create a torus of material inside Jupiter's magnetosphere
. This belt of material is called the "Europa torus". Io also has a torus
. Even though Ganymede
also have thin atmospheres, they do not seem to produce torii in Jupiter's inner magnetosphere. This probably has something to do with the shape of Jupiter's magnetosphere.
Shop Windows to the Universe Science Store!
Our online store
includes issues of NESTA's quarterly journal, The Earth Scientist
, full of classroom activities on different topics in Earth and space science, as well as books
on science education!
You might also be interested in:
The Galileo spacecraft was launched on October 19, 1989. Galileo had two parts: an orbiter and a descent probe that parachuted into Jupiter's atmosphere. Galileo's primary mission was to explore the Jovian...more
Jupiter's magnetosphere is a unique object in the solar system. It is the biggest object in the entire solar system. Not only is it big enough to contain all of Jupiter's moons, but the sun itself could...more
The Cassini probe began its journey to Saturn on October 15, 1997. It flew by Earth in August, 1999, before heading towards the distant planet. Cassini passed Jupiter in 2000 and then burned towards its...more
A satellite which has an atmosphere, such as Jupiter's moon Io, and which also is inside a magnetosphere (unlike the Earth's moon), will leave a cloud of particles behind as it orbits the planet. This...more
Callisto was first discovered by Galileo in 1610, making it one of the Galilean Satellites. Of the 60 moons it is the 8th closest to Jupiter, with a standoff distance of 1,070,000 km. It is the 2nd largest...more
Europa was first discovered by Galileo Galilei in 1610, making it one of the Galilean Satellites. Europa is Jupiter's 4th largest moon, 670,900 km from Jupiter. With a diameter that is about half the distance...more
The Galileo spacecraft, which has been orbiting Jupiter since 1995, has finally reached the end of its road. On September 21, 2003, Galileo will make a fiery plunge into Jupiter's atmosphere and be vaporized....more