快猫短视频

IF THERE is an ocean on Jupiter鈥檚 moon Europa, any probe sent to explore it
will need to be gold-plated to avoid corrosion, say astronomers who have found
sulphuric acid lurking in the moon鈥檚 icy crust.

Europa鈥檚 surface consists mainly of water ice, but observations from a
spectrometer on the Galileo spacecraft hint that there are other minerals there
too. Bob Carlson of NASA鈥檚 Jet Propulsion Laboratory in Pasadena, California,
hoped to make a chemical mix that resembles conditions on Europa. They found
that the infrared spectrum of sulphuric acid most closely matches the pattern
Galileo saw (Science, vol 286, p 97).

The team suggests that the acid is there thanks to Europa鈥檚 neighbour Io,
which belches sulphur from its volcanoes. The sulphur forms an atmosphere around
Io, then is ionised and whipped away by Jupiter鈥檚 magnetosphere. When the ions
hit Europa, they react with hydrogen peroxide in the ice to form sulphuric
acid.

鈥淪ulphuric acid, sulphur polymers and sulphur dioxide are part of a
continuing cycle on Europa鈥檚 surface,鈥� says Carlson. 鈥淢ost of the sulphur exists
as sulphuric acid because it is the most stable.鈥�

Although this process occurs on the moon鈥檚 surface, Carlson believes the acid
could be pushed down into the ocean that may lie beneath the icy surface (
快猫短视频, 18 September, p 41). Sulphur may also come from Europa鈥檚
interior, an idea proposed by Jeff Kargel of the US Geological Survey in
Flagstaff, Arizona.

鈥淲e don鈥檛 know the concentration of sulphuric acid that might occur in the
ocean, but it could be fairly corrosive,鈥� says Carlson. The acid in his
experiment was concentrated enough to corrode lab equipment. 鈥淚鈥檇 use
nonreactive coatings for any probes,鈥� he says. Gold plating would do nicely.