Michael Swanwick's Periodic Table of Science Fiction

Palladium

106.42

War of the Worlds

Palladium metal has one unique property: Hydrogen can filter through it.

Thus, it was a crucial component of the Viking landers' GC-MS (gas

chromatograph-mass spectrometer) experiments. The gas chromatograph which

separates out volatile substances and the mass spectrometer which detects

ions were divided by a palladium separator. The function of the palladium

was to allow organic molecules transported by the hydrogen "carrier gas"

(but nothing else) to pass from the gas chromatograph to the mass

spectrometer.

All three Viking lander biology experiments indicated the presence of

life within the Martian soil. However, because the GC-MS analysis showed

no evidence of organic molecules, most scientists concluded that the

first three tests had been false positives and, regrettably, there was no

life on Mars.

Alas, the experiment was flawed. Palladium is "poisoned" by sulfur, an

element abundant in the Martian soil. The sulfur was heated and released

by the chromatograph's oven, after which nothing was able to pass through

the palladium separator. Which means that instead of having one true

reading and three false positives, the tests resulted in three true

readings and one false negative.

There was life on Mars.

As we all found out in 2008 when a soil sample scooped up from the

Martian surface by a NASA robot probe was returned directly to Earth

without undergoing quarantine at Space Station Alpha.

The scrappy Martian microbes, used to a harsh, resource-poor environment,

ripped through Earth's ecosphere like a slum kid who abruptly finds

himself transported to a finishing school for pantywaists. Human beings,

fortunately, were not directly vulnerable to any of the alien

microorganisms.

Algae, unfortunately, were.

Algae were formerly responsible for something like ninety percent of the

world's oxygen production. When they died, the props were knocked out

from under almost all Terrestrial plant and animal life. Outside of our

sealed habitats, only the Martian invaders remain.

Which is why it's so important that you always check your oxygen tanks

before leaving the house.