Pilar Montanes-Rodriguez is a research professor at the New Jersey Institute of Technology in Newark. She has found that earthshine is more than just light. It contains signs of life that might also be present in the light reaching us from distant planets.
For example, there are days when distinctive signs of Earth's chlorophyll—the green pigment that allows plants to turn sunlight into energy—can be easily detected in the light wavelengths of earthshine, she says.
Another astronomer, Wesley Traub, has found signs of Earth's oxygen, ozone, chlorophyll, and water vapor in earthshine. All of these are important indicators of life.
Traub is chief scientist for NASA's Navigator Program, which searches for planets outside our solar system. He has determined what earthshine likely looked like at various times in the Earth's evolution.
Traub predicts that scientists might be able to compare light from extrasolar planets with his "snapshots" of earthshine throughout Earth's history. The distant planets' oxygen, ozone, chlorophyll, or water-vapor signatures could give some idea of what the planets are like and even whether they might harbor extraterrestrial life.
"You could see the stage of evolution of a planet by comparing its spectrum with what we know of Earth," Traub said.
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