Alien Oceans' Glint Could Reveal Habitable Water Worlds (space.com)

An image of Earth, taken by NASA's LCROSS satellite, shows the planet in its crescent phase. The smaller light to the left is the moon.

The bright glint of alien oceans may be visible from afar, allowing astronomers to flag potentially habitable exoplanets.
As Earth travels around the sun, it moves through phases much like the moon when seen from afar. The planet's oceans reflect a great deal of light, especially during the crescent phase. The same principle should apply to exoplanets, researchers say.
"Seeing excessive brightness at the crescent phases could be a telltale signal of ocean planets," Tyler Robinson, of NASA's Ames Research Center in Moffett Field, California, said at the Astrobiology Science Conference in Chicago in June. [‪10 Exoplanets That Could Host Alien Life]
Although a host of satellites monitor Earth, few eye the planet as a whole. As a result, many exoplanet scientists turn to models to understand how Earth might appear if it were a distant alien world. However, the accuracy of these models can be difficult to gauge without observations to verify them.
Scientists have made a few attempts to address this issue. In 1993, for example, Carl Sagan and other researchers used observations made by NASA's Jupiter-studying Galileo spacecraft during a 1990 flyby of Earth to search for signs of life on our planet.
And in 2009, NASA's Lunar Crater Observation and Sensing Satellite(LCROSS) moon mission observed Earth at several phases, including near-full and crescent, in order to calibrate its instruments. Robinson and his colleagues analyzed these data, and found that the near-infrared and ultraviolet/visible light observations provided an approximation of how Earth might appear through extreme phases across various spectrums. Their study was published in 2014 in The Astrophysical Journal.
"LCROSS looked at Earth for calibration, but its measurements were good for science," Robinson said.
The results showed that, although less of Earth's surface was visible during its crescent phase, the brightness of the planet increased due to the light reflecting off its oceans. In visible light, the glint increased the planet's brightness by as much as 40 percent; in the near-infrared, Earth shone nearly 80 percent more brightly, Robinson said.
Robinson was also a co-author on a different paper that examined similar, though less detailed, observations of Earth using NASA's Deep Impact spacecraft (which performed up-close examinations of two different comets, in 2005 and 2010).
The observations performed by LCROSS — the first high-spectral-resolution observations of Earth in its crescent phases — lined up well with predictions based on existing models, Robinson said.
However, similar results gained from observations of an exoplanet would not automatically be signs of an ocean, he cautioned; clouds and ice could also affect the brightness of a planet. Follow-up studies of the exoplanet's atmospherecould reveal more about the world's potential habitability.
Still, an apparent glint from an exoplanet ocean would be an exciting find, Robinson said.
"We conclude that the detection of such a feature would be intriguing, and would certainly indicate that a more detailed observational follow-up of the planet was warranted," he and his colleagues wrote in their 2014 LCROSS paper.

Alien Oceans May Flow on 'Super-Earth' Planets

 SEATTLE — Alien worlds more massive than Earth could harbor long-lasting oceans, according to new research.

Scientists have used computer modeling to show that so-called "super-Earth" planets — worlds that are up to five times more massive than Earth — can play host to long-lived oceans. The modeling shows that the oceans can potentially remain on the planet for billions of years, possibly allowing life to develop on the alien planet. Researchers presented the new super-Earth findings during a news conference at the 225th meeting of the American Astronomical Society here in Seattle.

"When people consider whether a planet is in the habitable zone, they think about its distance from the star and its temperature," lead author of the super-Earth study Laura Schaefer of the Harvard-Smithsonian Center for Astrophysics (CfA) in Cambridge, Massachusetts said in a statement. "However, they should also think about oceans, and look at super-Earths to find a good sailing or surfing destination."

Scientists think that Earth's oceans have existed for almost the entire history of the planet, and water is key to life as humanity understands it. Therefore, finding other worlds with long-lived oceans could help scientists narrow down planets that might have a good chance of hosting life.

Earth's oceans are recycled. Water from the planet's oceans is pulled into the mantle from the crust due to geological activity, but water is also released from the mantle and back into the surface oceans through volcanic activity. The new computer model produced by Schaefer and her team was designed to test if this water recycling can occur on super-Earths with plate tectonics as well, according to the CfA.

In fact, some planets larger than Earth could be even better at maintaining oceans than this planet. Schaefer's model shows that a planet two to four times the mass of Earth could host oceans continuously for 10 billion years. The largest planet in the study, which was about five times more massive than Earth, didn't develop an ocean in the computer model for about 1 billion years, but those planets' oceans, once formed, continue to persist on the surface for a long amount of time. .

Schaefer and her team suggest that it might be better to hunt for life on older super-Earths. Researchers might have a better chance of finding complex life on planets that are 1 billion years older than Earth, the team said.

"It takes time to develop the chemical processes for life on a global scale, and time for life to change a planet's atmosphere," the CfA's Dimitar Sasselov, a co-author on the study, said in a statement. "So, it takes time for life to become detectable."