字幕列表 影片播放 列印英文字幕 While the idea of alien life might sound like science fiction, it's becoming more and more of an established scientific theory. And in the next few years, I believe it will become a scientific fact. The field of astrobiology is now well established, and it started off by looking at possible signs of fossilized life in meteorites that have fallen to Earth. In fact, there's a theory called Panspermia that says life exists throughout the universe and transports from one place to the other via asteroids, comets, and meteors. Now, as beautiful as the Earth is to us human beings, in the grand scheme of the universe, it's actually nothing special. And hence, if life can exist here, there's no reason it can't exist elsewhere in the universe. In fact, it may exist in our own backyard in our own solar system. We just need to find it. The Water of Life While alien life might take many different exotic forms, the easiest way to search for it is to look for conditions like where it already exists. And this means finding liquid water. Now, the way scientists do this is to search for a region called the Goldilocks zone around a star. Too close to a star and water boils and turns to steam, and so life can't exist. Too far away and the water turns to ice. But in this middle region, it's just perfect, and liquid water exists. This immediately gives us a number of candidates, one of which being Mars. Life on Mars The pieces of the puzzle are starting to come together. In September 2015, liquid water was found on the surface of Mars. And even more interestingly is that methane has been discovered present in the atmosphere. So, why is this exciting? Well, methane is actually a waste product that's created by living organisms, us included. So, if methane is present on Mars, there's a tantalizing prospect that it could be being created by living organisms. So, when I'm talking about alien life, I'm talking about microbes rather than little green men. Further research needs to be conducted, but if there is life on Mars, where else could it exist? Another great prospect is a moon of Jupiter called Europa. It's believed that below its icy surface there could be a vast liquid ocean kept warm by geological activity. In fact, Europa is such a good prospect for life that both the European Space Agency and NASA are sending probes there to investigate it. So where does this leave our little green men? Well, scientists aren't actually discounting them. The Search for Extraterrestrial Intelligence Program has been going for over three decades now looking for signs of alien life. And the Chinese government is taking this so seriously that they've built the world's largest radio telescope looking for signals coming from alien civilizations. However, if they were to detect any signals coming from these aliens, the vast distances between us will make it impossible for us to ever have meaningful communication.