We’ve all wondered at some point whether we’re really alone in the universe. Over the 14 billion years since the beginning of the universe, how could we possibly be the only life-supporting planet out of this massive thing we call the universe? Many of us either avoid this question, simply assuming that if there really is extraterrestrial life-forms out there, they would have made contact with us already. Others simply say that our planet simply got it right, Earth just had the perfect conditions for life to develop and it was just a fluke. The rest, escape into science fiction, hoping one day that we will make contact with alien life-forms, build a galactic police station here on Earth and let Captain Kirk go whizzing around the galaxy, boldly going where no man has gone before. While that that idea is firmly constrained to the realm of science fiction for now, recent discoveries have shed light in this very question; we might not be alone after all.
That’s right, we might not be alone, and our new found neighbors are just a mere 590 light-years down the road from us. An absolutely amazing discovery! On December 5th, 2011, scientists announced to the world the discovery of Kepler 22b, an Earth sized planet orbiting the nearby Kepler star. The planet orbits a G-class star known as Kepler 22 (hence the planets name, Kepler 22b) in the constellation Cygnus. The star itself is composed mostly of helium and is a little smaller and cooler than our own sun. But enough about the star, we all want to know about this planet right?
Kepler 22b is about 2.4 times larger than the Earth, or just more than half the size of Neptune. But what makes this planet so special is that it is the first earthlike world discovered orbiting in what is known as the habitable zone of the star. This means that the planet is in a perfect position to support life just as our own Earth does.
But what is the habitable zone of star? This is what astronomers call the area around a star where temperatures are not to hot, a result of being too close to the sun, or too cold, a result of being to far away from the sun, and the planet is able to sustain an atmosphere and liquid water on its surface. Take mercury for example, it’s the closest planet in our solar system to the sun, mostly made of iron and rock. Due to Mercury’s close proximity to the sun, it is very hot, and also very cold, with temperature ranging from -183 C to 427C. This vast temperature range, combined with the generally hot area the planet orbits around, basically means that water is unable to form oceans, or even remain stable as liquid, which is of course the main requirement for life to begin. Alternatively, Jupiter orbits our sun beyond the habitable zone where temperatures are too low, causing any water in the planets to freeze. The habitable area of our star begins just beyond Venus, the second planet in our solar system, and ends between Mars and Jupiter, the next planets in our solar system after Earth. But knowing that Kepler 22b orbits within the habitable zone of its star raises another problem, we don’t know what its made of.
Kepler 22b could simply be a gaseous planet like Jupiter or Neptune, with a very thick, dense atmosphere that could prevent the stars light and heat from reaching the surface, assuming it has a surface of course. Alternatively it could be a rocky planet like earth, which would give it a strong possibility of containing oceans of water with continents and its own weather and climate, the ingredients necessary to support life. In fact if the planet had an atmosphere similar to that of earth, the average surface temperature would be around 22C, a perfect day here on Earth.
This all seems a little too good to be true, a planet similar in size to Earth, orbiting a star inside the habitable zone, with the possibility of containing water, the fundamental building block of life, with a perfect surface temperature similar to that of Earth. But that’s not the end of the story, there is another planet, that may be even more suited to support life than Kepler 22b. It is known as Gliese 370 b.
Gliese 370 b, or HD 85512 b is another planet that orbits its star within the habitable zone, and appears to be a rocky planet similar to earth. Gliese 370 b’s surface temperature is also estimated to be around 25C assuming it has a similar atmosphere as earth. This puts the planet in the perfect area to maintain liquid water and thus support life. The planet is about 3.5 times the size of Earth, and is classed as a Super-Earth like planet. And the best part? Its only 36 light-years away! That’s an amazing 6% of the distance to Kepler 22b.
This still leaves the same burning question, are we really alone in the universe? If we consider that so far, we have discovered at least two earthlike planets within 600 light-years of us, then there has to be billions more left to be discovered. After all, 600 light-years is nothing considering our galaxy alone is 120,000 light-years across and contains approximately 400 billion stars. Even more surprising is that scientists believe the galaxy contains at least 400 billion planets, 10 billion of which would be within the habitable zone of their star. And that’s just in our galaxy, there’s still another 200 billion galaxies in the universe we know of. How amazing is that?
It may also surprise you to learn that life has already been found on another planet, that’s right, extraterrestrials really do exists! Albeit very small. On a meteorite found in Antarctica, known simply as ALH84001, which was ejected from Mars about 17 million years ago, scientists found evidence of the remains of bacterial organisms that may have lived on Mars. Evidence of bacterial life forms have also been discovered on two other meteorites, one of which also originated from Mars, approximately 165 million years ago.
So we know that it is possible for life to exist on other planets, and that there is approximately 10 billion life supporting planets in our galaxy alone, you do the math, do you really think we are alone? I guess we’ll just have to wait until we either invent inter stellar travel, or an extraterrestrial species comes to visit us to know the answer to that question, but that still doesn’t stop scientists from trying to find the answer anyway.