How is it Known that Europa Has a Subsurface Ocean?

It is estimated that Europa has more than twice as much water as Earth. The ocean is believed to be below the surface ice and has been inferred from measurements of the magnetic field around the moon and what appear to be shifts of the surface ice.

In an August 25, 2000, press release, NASA/JPL announced: "NASA researchers have the strongest evidence yet that one of Jupiter's most mysterious moons hides an ocean of water underneath its icy coat. This evidence comes from magnetic readings by NASA's Galileo spacecraft, reported in the Friday, Aug. 25, edition of the journal Science."

"Europa, the fourth largest satellite of Jupiter, has long been suspected of harboring vast quantities of water."

Interestingly enough, the Galileo probe used a 6502 computer chip, the same chip that was used in Apple IIe and Commodore 64 computers. Even though the chip has been around since the 1970's and much faster chips with more control capacity were available in the years before Galileo launched in 1989, it was the 6502 that was used on the probe. It's extraordinary what can be done with technologies that are widely available and inexpensive.

The magnetometer on the Galileo probe provided crucial evidence of a subsurface ocean.

The press release continues: "'The direction that a magnetic compass on Europa would point to flips around in a way that's best explained by the presence of a layer of electrically conducting liquid, such as saltwater, beneath the ice,' explained Dr. Margaret Kivelson (of UCLA), principal investigator for Galileo's magnetometer instrument... ice is not a good conductor, and therefore we infer that the conductor may be a liquid ocean."

"The direction of Jupiter's magnetic field at Europa reverses predictably as the moon's position within the field changes. During Galileo's flyby in January, the direction of Jupiter's field at Europa was the opposite of what it had been during passes in 1996 and 1998. Kivelson's team predicted how that would change the direction of Europa's magnetic polarity if Europa has a saltwater layer, and Galileo's measurements matched their prediction."

"'It makes a very strong case that the source of the magnetic signature is a conducting layer near the surface,' Kivelson said."

So there are the first two bits of evidence of Europa's ocean: the behavior of Jupiter's magnetic field and the surface features. But there is a third piece of the puzzle that will be discussed in Part 2 of this series.

Source:

NASA Press Release