Monday, October 25, 2010

Meteorite tea, and the failures of genius

ResearchBlogging.orgIn the early 1970’s, Io, the innermost large moon of Jupiter, was somewhat of an enigma. Unlike Europa and Ganymede, it did not exhibit water ice adsorption bands it its IR spectra. Its density suggested that it was a rock and metal planet, but the surface reflectance was unlike anything known to science. This problem was addressed brilliantly in a Science paper by Fanale, Johnson, and Matson, researchers at the Jet Propulsion Laboratory. These scientists explained all the anomalous features of Io in a single stroke of genius.

By that time, it was known that meteorites were primitive condensates of the primordial solar nebula, even though the detailed work describing their subtle differences had not yet been completed. Since the outer moons of Jupiter were known to contain water, the study hypothesized that Io lost its primordial water and never accreted any ice later on. They then tested this hypothesis. Fanale et al. took a piece of the very primitive CI meteorite Orgueil, and made meteorite tea by boiling the piece of Orgueil in water. They then evaporated off the water and looked at the precipitate. What they found was mostly magnesium and sodium sulfate salts, with some halite and other elements mixed in. The reflectance spectra of these precipitates more closely matched that of Io than other hypothesized frosts, especially when treated with radiation. AS the evaporite was enriched in sodium, this process also efficiently transported sodium to the surface, where it can be ionized by ambient radiation, producing the Na ionization halo which was known around Io at the time.

So basically, the theory goes like this: during accretion, Io was too warm for ice to condense. Accretion from meteorites comprised of hydrous silicates released water as the planet grew and the interior increased in heat and pressure. This fluid then leached the rock, escaped to the surface, sublimed or evaporated, and left salts behind, which was what we see today. In other words, Io is an evaporite planet.

This theory explained everything know about Io so well that it would be another five years before Voyager one- at the time the most advanced robotic space probe ever launched- took pictures of Io as it flew past Jupiter which instantly and completely proved the evaporate hypothesis to be false.

The history of science is often taught as a series of breakthroughs generated by men of immense intellect who are smart enough to see the world as it is. But the reality is that the world doesn’t really care about genius. There are many incredibly brilliant scientific deductions- like the hypothesis of Fanale et al. of the evaporitic Io, which are spectacularly and brilliantly wrong. But science education has a powerful selection criteria that ignores all of the stunningly clever, but completely incorrect deductions. Instead, proponents of discarded theories are often depicted as dim, or close minded, or stuck in their ways. But in cases such as this one, they simply had no way of acquiring the data needed to disprove their hypothesis, as flying to Jupiter and looking at Io up close was science fiction in 1974. Five years later, it was history, and so was their wonderful model.

Fanale, F., Johnson, T., & Matson, D. (1974). Io: A Surface Evaporite Deposit? Science, 186 (4167), 922-925 DOI: 10.1126/science.186.4167.922


Lockwood said...

Another example of "brilliantly wrong" that impresses me is the phlogiston theory of combustion- it makes such wonderful sense... as long as you don't know anything about chemistry and elements. But we don't often ask students to put themselves in the shoes of people who didn't know and take for granted the observations that have been made in the intervening time.

rod said...

“The great tragedy of Science: the slaying of a beautiful hypothesis by an ugly fact”

andy said...

That's a pretty neat experiment actually. And even if it doesn't apply to the real Io, maybe there are evaporite planets out there somewhere.