Haze surrounding Earth 4 billion years ago may have given the planet a pale orange hue. Photo by NASA’s Goddard Space Flight Center/Francis Reddy

Feb. 9 (UPI) -- Researchers at NASA's Goddard Space Flight Center have been studying Earth during the Archean era in an effort to understand exoplanets hidden by hazy atmospheres.

The chance of finding an exoplanet that mirrors modern Earth is slim, but Earth hasn't always looked like it does now.


Astronomers have found a number of Earth-like exoplanets, but many of these planets are shrouded in haze. New research suggests these exoplanets resemble a younger, less mature Earth -- an Earth NASA scientists are trying to better understand.

"We like to say that Archean Earth is the most alien planet we have geochemical data for," Giada Arney of NASA's Goddard Spaceflight Center in Greenbelt, Md., said in a news release.

Earth didn't look all that inviting 4 billion years ago. Though haze can be hostile, choking a planet with harsh chemicals and blocking out the sun, it can also be nurturing -- a protective layer against harmful UV rays.

Researchers modeled the atmosphere of Archean Earth to better understand how haze, sunlight and temperature would interact and evolve. Their findings suggest Earth's haze would have blocked much of the rays from a then less-powerful sun, cooling Earth. But cooler temperatures would slow the chemical reactions that produced haze.

Thus, a young Earth's haze never became so thick that it froze the entire surface of Earth. Instead, it acted like sunscreen, keeping out most of the sun's most harmful rays.

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The model showed other planets wouldn't be as lucky as Earth. A stronger star might have formed thicker haze, or if there was an excess of ultraviolet radiation, no haze at all, leaving the planet exposed and unlikely to spawn life.

Scientists now have a better a idea of what combination of factors might yield a haze beneficial to the development of life.

"Haze may turn out to be very helpful as we try to narrow down which exoplanets are the most promising for habitability," said Arney.