Of the approximately 1,800 planets that have been hunted down by the astounding Kepler Space Telescope and other scientific instruments, less than two dozen reside in the Goldilocks zone where the temperature is just right for liquid water to exist, having the best chance to support life. Add to that small number, the fact they’re all much larger than Earth, whereby their more powerful gravity would most likely attract a thick hydrogen-helium based atmosphere, which is not very conducive to life as we know it here on Earth, not to mention that those of type planets wouldn’t being particularly inviting to humans—a 175 lb. person landing on a planet 2.5 times more massive than Earth, would weigh 438 lbs.
WWWAccording to Space.com, the ten planets most likely to harbor life are:
1. Gliese 581g In the constellation Libra, 20 light-years away. it’s two to three times the size of Earth, and orbits its sun every 30 days.
2. Gliese 667Cc In the constellation Scorpius, 22 light-years away, is about five times the size of Earth, taking 23 days to orbit its M-class dwarf star which is only a third of the mass of our sun.
3. Kepler 22b In the constellation Cygnus, 600 light-years away and 2.4 time the size of Earth. If it has a greenhouse effect like Earth, its surface temperature is approximately 720 F.
4. HD 40307g In the constellation Pictor, 42 light-years away. It’s so massive it’s known as a super-Earth, and orbits its star at 56 million miles away.
5. HD 855125d In the constellation Vela, 35 light-years away and 3.6 times more massive than Earth.
6. Tau Ceti e In the constellation Cetus, is another super-Earth at least 4.3 times the mass of Earth, is 11.9 light-years away.
7. Gliese 163c In the constellation Dorado, a real super-Earth, seven times more massive than Earth, circling its star every 26 days, is 50 light-years away.
8. Gliese 581d Sister planet to Gliese 581g, is a super-Earth orbiting a dwarf star 20 light-years away in the constellation Libra.
9. Tau Ceti f Super-Earth like its sister Tau Ceti e in the constellation Cetus.
10. Kepler-186f Finally, the very first Earth-size planet ever found, only 10%
larger than Earth, and in the habitable zone of its M-class dwarf star, making it the top contender for life to exist. It is 490 light-years from Earth.
Kepler-186f is the most Earth-like planet ever discovered. It’s historic. Not only is it in the Goldilocks zone and about the same size as Earth, but it may have liquid water. It is the outermost planet of five, orbiting at a distance of 32.5 million miles from its dwarf sun, a little closer than Mercury is to our sun, and completes an orbit every
130 days. While it orbits in the outer part of the habitable zone, any water existing
on it may freeze, but because of it’s slightly larger size, it cold hold a thicker atmosphere, thereby insulating the planet with warmer temperatures, preventing
its water from freezing.
WWW Scientists have learned that when a planet reaches about 1.5 the mass of Earth, there’s a tipping point at which it starts accumulating a thick hydrogen and helium atmosphere, like that of gas giants such as our neighbor Jupiter. Kepler-186f is smaller and has a good chance of being a terrestrial rocky planet.
M-class dwarf stars tend to emit more radioactive flares of harmful radiation than G-type stars like our sun. Kepler-186f though resides at the outer edge of the habitable zone keeping it at a safe distance from intense radioactive assault. M-dwarfs are also dimmer and cooler than G-types, and what also makes it safe for Kepler-186f to be closer than Mercury is to our sun. That is really a Goldilocks distance, a perfect balance act of heat and radioactivity. M-dwarf planets are easier to find because as the planet passes across its dwarf sun, they block more of it light, rendering the decrease in its light output much more detectable to the Kepler Space Telescope. Measuring that amount of differential in light would be analogous to measuring the difference in light output caused by a moth flying in front of a lighthouse beam.
WWWGiven that M-class dwarf stars account for 75% of the stars in the Milky Way Galaxy, where every red dwarf has at least one planet circling it, there very probably could be billions of Earth-sized planets out there.
Are we a lone life ship in the Milky Way Galaxy or just one among million, perhaps billions? The question is
as universal as the one that asks, is there life after death? Dimitar Sasselov,
planetary astrophysicist at the Harvard-Smithsonian Center for Astrophysics expresses it this way,
Whether we are an extremely rare fluke—a phenomenon that only happens once in a universe—or in a galaxy teeming with life is a very basic question not only of science, but for our existence. [This is] the first time in human history we have a good shot at answering that question.
© Joe Arrigo