But the Spitzer discovery opened the door to the possibility that our galaxy should contain rocky "carbon planets" with a coal-black tarry landscape perhaps with silicon carbide ceramic-hard outcroppings.
A trip to the local hardware store or car shop illustrates how tough silicon carbide is. Because it is so heat-resistant silicon carbide is used on all types of cutting and drilling devices, and inside motorcycle engines.
The surface of a carbon terrestrial planet would be, well, charcoal black. Carbon compounds would be synthesized by the star's ultraviolet light. Carbides would be chemically broken apart water to create carbon monoxide and methane rain. Diamonds might literally rain out of the sky after being dredged up from the mantle through volcanic eruptions.
Living on such a planet would be like living in Los Angeles, with nothing but smog and asphalt. Because silicates would be less abundant, glass would be a rare substance.
The gooey carbon-chemistry of life could be miles-deep on such worlds. Despite the lack of water, life might arise in hydrocarbon oceans. Organisms on such a world would be much more exotic that the arsenic-munching Mono Lake bacteria announced last week. There might be creatures that eat silicates or oxides, and use carbon instead of oxygen for metabolism.
If a carbon terrestrial planet is ever discovered, astronomers will be tempted to nickname it "Lucy" after "Lucy in the Sky with Diamonds," a song from the 1968 Beatles album "Yellow Submarine." But the lyrics would have to be changed to: "Picture yourself on a methane river, with tarry mountains and carbon monoxide skies."
Illustation credits: STScI/Bacon, R.Villard