http://nai.arc.nasa.gov/astrobio/index.cfm NAI Ask an Astrobiologist Black holes are common in the universe, including the very massive black holes that are found in the center of most galaxies. They are remarkable objects, predicted by general relativity and first found by astronomers in 1973. If you want more information, there is a good article in Wikipedia. There is absolutely nothing that any black holes can do to us, and no reason to be afraid of them. If people are worrying about black holes, it is probably because of the irresponsible websites that lie about astronomy, for motives that escape me. I am surprised that more people don’t make use of Wikipedia and other responsible web resources to check on such things rather than get upset about them. <br /><br /> <i>David Morrison<br /> NAI Senior Scientist</i> http://nai.arc.nasa.gov/astrobio/astrobio_detail.cfm?ID=6205 The Sun obtains its energy from the fusion of hydrogen into helium in its core. Astronomers call the lifetime of a star in this hydrogen-burning phase its “main sequence lifetime.” The main sequence lifetime for the Sun is about 10 billion years, with half of that time still to go. The problem for the future habitability of Earth is not that the Sun will collapse, but that it will swell up into a red giant and engulf the Earth some 4-5 billion years in the future. Actually, the Earth may get too hot for life sooner than that. The Sun is gradually increasing in luminosity (energy generation), and the Earth may become too hot for comfort just a couple of billion years from now. <br /><br /> <i>David Morrison<br /> NAI Senior Scientist</i> http://nai.arc.nasa.gov/astrobio/astrobio_detail.cfm?ID=6181 There are three basic approaches to the search for life beyond the Earth: (1) On the planets in our solar system, such as Mars and Europa. We are able to send spacecraft to these objects, and perhaps in the future to bring samples back to Earth for laboratory analysis. (2) On planets circling other stars. Here we can use astronomical or remote sensing techniques to search for biomarkers or biosignatures, for example changes in atmospheric chemistry indicative of life. In this case I agree with your caution; we may never know for sure. (3) On planets with technological civilizations. Here we might detect radio or optical transmissions and perhaps ultimately conduct a very-long-distance dialogue. Such a SETI signal would be an unambiguous detection of life, if you include possible artificial or computer-based life within your definition. <br /><br /> <i>David Morrison<br /> NAI Senior Scientist</i> http://nai.arc.nasa.gov/astrobio/astrobio_detail.cfm?ID=6193 It would be nice to be able to predict future scientific discoveries. Alas, it does not usually work that way, and many important discoveries are serendipitous. We do know, however, that there are several forthcoming space missions that will address astrobiology questions, including the Mars Science Laboratory rover (launch in 2011), the James Webb Space Telescope (launch in 2014), a mission to orbit Europa (launch around 2020), and of course the Kepler telescope just placed in orbit to detect Earth-like planets. <br /><br /> <i>David Morrison<br /> NAI Senior Scientist</i> http://nai.arc.nasa.gov/astrobio/astrobio_detail.cfm?ID=6194 Earth, Venus and Mars all experience greenhouse heating, mostly due to the trapping of heat by atmospheric carbon dioxide. The magnitude of the greenhouse heating has changed over time. In the case of the Earth, we think that other gases such a methane also contributed to the greenhouse effect during the first billion years of Earth history, which was considerably stronger than today. However, this was not a “runaway greenhouse effect”, which is irreversible by definition. Venus, on the other hand, did at some time in its history experience a runaway greenhouse, transforming the planet into a high equilibrium temperature state maintained by a thick carbon dioxide atmosphere, about 100 time larger than the atmosphere of Earth. We don't know when this transformation took place on Venus, but probably it was several billion years ago. Fortunately we don’t think such a runaway is possible on Earth, in part due to our active geology (plate tectonics) and in part from the oxidizing influence of life. Some people have suggested that the current rapid global warming could lead to a runaway greenhouse, but that seems very unlikely. Long before that could happen we will experience plenty of other bad effects, such as the melting of the Greenland and Antarctic ice caps, sea level rise of something like 100 m, and a modification or shut-down of the ocean thermohaline circulation system. <br /><br /> <i>David Morrison<br /> NAI Senior Scientist</i> http://nai.arc.nasa.gov/astrobio/astrobio_detail.cfm?ID=6108