ANSWERS: 4
  • I don't know about "Most." star. So far we have only studied a small fraction of them. What we do know is that many of them do have planetary bodies and that there is a great deal of missing mass associated with the movement of the visible star system.
  • Here's what I found on the subject: "At least 130 stars outside our solar system have been shown to have orbiting planets, based on a slight wobble in the stars' positions or a variation in intensity as planets pass in front of them." http://www.news.cornell.edu/Stories/March05/extrasolar.ws.html That's just how many we've actually observed. Here's an idea of how many solar systems there might be based on probability: "In order to determine the existence of extrasolar planets it is important to consider one minor and one major premise. The minor premise, and to a large degree a philosophical one, is to consider the existence of additional solar systems based on the probability factor. As stated above, with the number of galaxies and the number of stars contained within each of the galaxies, the probability of another solar system existing is excellent. The speculation based on probabilities is not new. Two very important books on the search for extraterrestrial life, written in the 1960's attest to this thesis. "With 10 to the 11th stars in our galaxy and 10 to the 9th other galaxies, there are at least 10 to the 20th stars in the universe. Most of them may be accompanied by solar systems. If there are 10 to the 20th solar systems in the universe, and the universe is 10 to the 10th years old -- and if, further, solar systems have formed roughly uniformly in time -- then one solar system is formed every 10 to the negative 10 yr = 3 x 10 to the negative 3 seconds. On the average, a million solar systems are formed in the universe each hour."1 "The implication is that solar systems are common, but the argument will be greatly strengthened if there is real agreement on how our solar system came about. The space exploration of the next decade should enable us to narrow down the theories to a great extent. We will have samples of the Moon and direct knowledge as to the nature of its interior. We will learn the precise compositions of other planets and their atmospheres to compare with those of our Earth. However, study of our own solar system is not the only way to learn if it is unique. Another approach is to search for clues among the other stars of our galaxy. Such observations, carried out originally without reference to the question of whether or not there are planets elsewhere, led to surprising discoveries.."2 1 from a monograph co-authored by Carl Sagan 2 Walter Sullivan, who at that time was Science Editor of The New York Times " http://www.public.asu.edu/~sciref/exoplnt.htm (really good link) This subject is hotly debated as astonomers still have a hard time coming up with a universally accepted definition of 'planet' : "The problem is that astronomers don't all agree on what it means to be a planet. Some of the objects found orbiting other stars are in fact much larger than any of the giant planets in our own solar system, weighing in at more than 10 times the mass of Jupiter (although most are less than 3 or 4 Jupiter masses). This approaches the size threshold of another type of substellar object known as a "brown dwarf", often described as a "failed star" because its too small to ignite the fusion of hydrogen in its core. Brown dwarfs are intermediate in size between planets and true stars, and the boundary lines at the upper and lower limits of brown dwarfdom are still a little fuzzy." J.R. Hurley and M.M. Shara: American Scientist 2002 90:140 http://scienceweek.com/2003/sw030207.htm In short, we know extrasolar planets exist. It seems that solar systems may, in fact, be quite common. The debate lies in how our own solar system was formed, what exactly a planet is, and how many stars there really are in the entire universe.
  • As of Oct. 1, 2005, more than 150 planets had been detected orbiting other stars. Most are much larger than Earth -- Jupiter-sized and bigger, due to technical limits of our observing systems. Future systems, such as NASA's planned "Terrestrial Planet Finder," consist of an array of spacecraft, flying in formation, that can act as a giant telescope. The spacecraft could theoretically be miles apart. The reason it's such a big deal to search for Earth-like planets is that Earth-like planets are the most likely to harbor life. By that I mean, life that humans could recognize as life. If there were some exotic form of life with no analogue on Earth, we'd have a tough time realizing we were observing something alive. So, as we start the search for extraterrestrial, we have to try looking for life that's kinda Earth-like.
  • 8-9-2017 It is mighty hard to guess whether a star has a planet or not. And it's mighty hard to see most stars. So there ya go.

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