Other solar systems contain a new class of planets, dubbed "super-Earths" that can maintain liquid water on their surfaces, making them potentially habitable, scientists say.
Observations made through space- and ground-based telescopes in the past few years have discovered the planets, described as worlds that are anywhere two to 10 times the Earth's mass and up to two times larger than its radius, orbit Sun-like stars outside our solar system, according to findings reported at NASA-sponsored Astrobiology Magazine
In our own solar system, the Earth is the only planet at the optimum distance from the sun to sustain life. But in other systems, some planets orbit around M-class stars, which are cooler and less bright than the Sun. This means they can possibly maintain water and sustain life, the magazine reports.
The M-class stars are abundant in the Sun's part of the universe, the findings report, meaning there may be super-Earths in "our solar neighborhood."
The first super-Earths were discovered in 1992, and further discoveries have come in part through the NASA Kepler space telescope, which spent nearly four years hunting for planets in the Sygnus constellation. Its mission ended this year, but still has provided a great deal of data about super-Earths.
Most of the ground discoveries are done through instruments in La Silla, Chile and Mauna Kea, Hawaii.
Kepler's mission is on hold because two of its four reaction wheels failed, Astrobiology reports
Meanwhile, a successor mission, the Transiting Exoplanet Survey Satellite (TESS) will have both advantages and disadvantages while searching for super-Earths, said Nader Haghighipour, a member of the NASA Astrobiology Institute and the University of Hawaii-Manoa's Institute for Astronomy.
"Because TESS is going to cover the entire sky, as opposed to Kepler that focused on only one portion of the sky, it may be able to find more [exoplanets]," he said. "As far as accuracy and precision, because it’s not going to stay on one region of the sky for as long as the Kepler did, the accuracy may not be as high as that of the Kepler."
Another group, led by the University of Göttingen in Germany, found that there may be many of the super-Earths. One M-star alone was discovered to have six or seven planets, including three to five super-Earths that may support life.
But the researchers said the planets can have very short years — as little as 20 to 50 days — in which one side may almost perpetually face the host star, but life could still survive on them.
"It's the most reliable detection [of potentially habitable exoplanets] that we’ve had," Haghighipour said.
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