I heard that water was discovered in the atmosphere of an extrasolar planet. Does this mean that life is possible there?
     Water has never been observed in the atmosphere of any object, other than the Earth. Water vapor has been detected in the atmospheres of several Solar System objects, and the atmospheres of a number of stars. Its detection in extrasolar planetary atmospheres is more controversial, but irrelevant to the question of the existence or nonexistence of extrasolar life.
    In general, the discovery of water vapor in such an atmosphere means nothing, except that advances in observational techniques (and good luck) happen to have allowed its detection. Water is one of the most abundant compounds in the Universe, and water vapor should be present in every place with an atmosphere, and temperatures which allow its existence. It is difficult to detect water in the atmospheres of extrasolar planets because (1) it is difficult to detect such planets in the first place, and (2) usually, such detection only says that something is there, and nothing about its physical nature, let alone the nature of its atmosphere. Even then, as already noted, water itself is never detected in atmospheres -- only water vapor, which can be present in the atmospheres of planets which have no liquid water, at all. The only (controversial) observations of water vapor in extrasolar planetary atmospheres have been for objects with temperatures of thousands of degrees, which makes the existence of (liquid) water impossible.
     Of course, the fact that we cannot detect water elsewhere does not mean that life does not exist elsewhere; life is probably a fairly common disease of planetary surfaces which have suitable conditions for its existence. And if we could detect water elsewhere, it wouldn't necessarily mean that life exists there; it would merely increase the number we assign to the probability of its existence.

How can black holes spit out material, if nothing ever escapes from a black hole?
     Under normal circumstances, once something goes into a black hole, it can't get out again; it is doomed to be torn to pieces and crushed out of existence at the singularity at the center of the hole. But if a lot of gas is falling towards a black hole, a swirling disk of gas, called an accretion disk, forms around the black hole, and as the material swirls slowly inwards, inexorably pulled by the gravity of the black hole, the gas is compressed, more and more, until it becomes incredibly hot, allowing nuclear reactions to occur in the disk. The energy of these reactions, and powerful magnetic fields generated by compressing the inward-moving gas, cause huge amounts of light and relatively large amounts of high-energy particles to be ejected at the poles of the accretion disk. In extreme cases, one solar mass of material being powerfully compressed in this way can emit as much as a thousand times as much light as the Sun does during its entire ten-billion-years long lifetime; and in fact quasars are thought to be just this sort of thing, as we can think of no other way to explain their incredible brightness. However, all the material and light ejected from the disk is thrown out into space by material that is falling toward the hole, and is not yet inside it; so the materials involved are never actually inside the hole, and the "law" that says nothing can get out of a black hole is not violated.
      In addition, there are circumstances in which very weak radiation can escape from a nearly infinitely small black hole through a quantum-mechanical process referred to as "tunneling". This radiation was predicted by Stephen Hawking, and is therefore called Hawking Radiation; but would only be observable with current technology if a microscopic black hole passed through or very close to our Solar System; and to date, no such radiation has ever been observed.

How big are stars at different times in their lives?
     Stars have different sizes at different times during their lives. When a star is first forming, it starts off as a cloud of gas many times larger than the Solar System. During this time it is too cool to be considered a star, and gives off no visible light. As it shrinks, either because of external forces or its own gravity, it becomes smaller, denser, and hotter, and eventually becomes a visible star.
     When this happened to the Sun, it would have been about a third of the size of the orbit of Mercury; much bigger than now, but not nearly as large as our orbit. However, much more massive stars would, at that same stage of their formation, have been larger than the orbit of Mars.
     During most of a star's life, referred to as its Main Sequence lifetime, it maintains a fairly constant size, which is much smaller than the orbit of Mercury, even for the largest stars. However, all stars heavier than about a quarter of the mass of the Sun eventually swell up, as they begin to die, to become red giants, subgiants, or supergiants. In the case of the Sun, this will happen in about 8 billion years, and at that time, it will certainly become larger than the orbit of the Earth, and perhaps even larger than the orbit of Mars, although that is less likely. Whether it will swallow the Earth is uncertain, as the Sun may lose mass as it swells up, and its surface gravity decreases, and if that happens, our orbit will slightly increase in size, and there is a small possibility that we might not be consumed by the dying star.
nbsp;    Other stars, however, which are more massive than the Sun, become much larger, and any planets surrounding those stars would almost certainly be consumed, or, when the star ends its life, in a supernova explosion, be vaporized and blasted to smithereens.
     Finally, after the stars die, they become very small. Stars like the Sun, and less massive stars, become white dwarfs, stars a few thousands of miles in diameter. More massive stars become either neutron stars, which are only a few miles in diameter, or singularities, which have no size at all, but are surrounded by small regions, called black holes, where gravity is so large that nothing, including light, can escape. The sizes of such black holes are a few miles or tens of miles in diameter, depending upon the mass of the singularity hidden inside them.
     So, to summarize the answer to your question, the sizes of stars do depend upon their ages. They tend to be fairly large when forming, and very large when dying, of in-between size when Main Sequence stars, and very small when they finally die. But their sizes also depend upon how massive they are, more massive stars being larger at every stage of their formation, life and dying, and incredibly tiny when finally dead, while less massive stars are much smaller during their formation, life and dying, but only fairly small, when they finally die.

I read an article that says the Law of Gravity may be wrong. Is this really possible?
     It is always possible that there may be errors in our understanding of any "law" of physics, including the Law of Gravity. In fact, Einstein's theory of general relativity provides a very different view of gravity than the traditional Newtonian view. However, Einstein's theory does not actually change the predictions of Newton's Law of Gravity, except in very special circumstances, such as when gravitational forces are very, very large (as in a black hole), or when there is so little mass in a very large region that a weird sort of anti-gravity (responsible for the expansion of the universe) is produced.
     The article in "Discover" magazine that you refer to is concerned with, among other things, the fact that Pioneer 10 and 11, which are now well beyond the orbit of any planet, have been slowing down, for years, by a little more than would be expected, based on standard Newtonian or Einsteinian theories of gravity. The acceleration is very small (about a hundred-millionth of the Earth's gravitational acceleration), but apparently quite real. A number of different theories have been advanced to explain the anomalous slowing of the spacecraft, including the possibility that the Law of Gravity is not quite accurate for objects at such large distances.
     There is actually a precedent for this, a little over two hundred years ago, when Uranus was discovered. Calculations of how it should move did not agree with its actual movement, leading to the suggestion that Newton's Law of Gravity was incorrect. By the 1840's, however, it was shown that the errors in Uranus' motion were due to the effect of a previously unknown planet -- Neptune -- and in fact, the position of Neptune was predicted, on the basis of the errors, and used to find it, on the very first night that it was seriously looked for, within one degree of the predicted position.
     In the current situation, the most likely explanation is that, as these spacecraft move through the inner Kuiper Belt, they are running into small dust particles, of the order of a few ten-thousandths of an inch in size, which are, as a result of the velocity of their collision with the spacecraft, gradually slowing them down. There is no doubt that there is a considerable amount of dust in the Kuiper Belt, as a faint infrared glow, caused by sunlight absorbed and then re-radiated by that dust, can easily be observed. The main question is whether there is enough dust in the Belt to explain the slowing. However, given the amount of dust that pervades interplanetary space, and the relatively low density (about one microscopic particle per 25,000 cubic meters of space) required to explain the observed slowing of the spacecraft, this may be the most reasonable explanation to date.
     Even if this explanation is not the correct one, it is unlikely that the correct explanation involves an error in the Law of Gravity, because gravity acts the same on all objects, large or small, whereas the slowing of the spacecraft does not correlate with any error in the motion of other solar system objects, such as the planets. In fact, that is one of the most attractive features of the idea that dust grains are responsible for the slowing -- they would be too small to affect objects as large as asteroids, moons or planets, but could still affect small objects, such as spacecraft.

What is current thinking about dark matter, and the expansion of the Universe?
     As shown in my discussion of Dark Matter In Galaxies and The Expansion of the Universe, a few years ago it was shown that the dark matter could not possibly be as abundant as people wanted to believe, or else the Universe would have had to be far younger than the stars. But how this problem would be solved was uncertain. Basically, there were two ways.
      First, the Universe might not be, as commonly stated, "flat". In the Inflationary Model of the Universe, the idea is proposed that the Universe starts off incredibly small, and expands incredibly fast to a virtually infinite larger size. When small, it is "round", but as it grows, it becomes "flatter". Think of the Earth as an example. It is round, but it looks flat, because it is so large. In the standard Inflationary Model, it is presumed that the Universe, as it grows, gets so large that it must be incredibly flat. But things are not quite that simple. In our experience, as round things get bigger, they can only become flatter. But in Einstein's theory of General Relativity, if things grow enough, they can go beyond "flat" to "hyperbolic", and if the Universe has grown enough to have such a shape, then the mass of the Universe is much less than the so-called "critical" mass, and the amount of dark matter is no longer a problem.
      If this is true, then the Universe cannot be either slowing down, or "coasting" along, at nearly constant speed, to larger sizes, but must be growing bigger and bigger at a faster and faster rate. And until recently, although that was considered a theoretical possibility, it seemed impossible to ever prove that it might be right, at least with anything resembling current technology.
      However, about 2 years ago, a new way of fairly accurately measuring the brightnesses of a particular type of supernova, referred to as a type Ia supernova, was discovered. (A type Ia supernova results from the catastrophic explosion of a white dwarf which has a companion which has covered the white dwarf with nuclear material, and the white dwarf suddenly, violently, burns all of that material and its previous material, and blows itself to smithereens.) Since then, several studies of the brightnesses of type Ia supernovae at various distances (and, therefore, different look-back times in the past history of the Universe) have shown beyond any doubt that the Universe is expanding faster and faster, and has been doing so for at least the last 10 billion years of its history. As a result, the Universe is not "flat", in the sense that it had been considered to be, but "hyperbolic", and its mass is much less than the critical mass.
      Now, because visualizing hyperbolic space is difficult for non-mathematically minded students, current texts and media discussions still pretend that the shape of the Universe is "flat", but say that it is made of three types of stuff. One is normal material, visible and invisible, which makes up somewhere between 1 and 5% of the "critical" mass of the Universe, depending upon whose numbers you believe. Another is "dark matter", which is by definition completely unobservable in any way that we can currently imagine, but makes up between 20 and 20% of the "critical" mass of the Universe, according to most estimates. We literally don't know if this stuff even exists at all, but there are some compelling reasons (beyond the scope of this brief discussion) to think that it might exist. These two forms of matter, "real" normal matter, and "real or imaginary" dark matter, are the only matter in the Universe, and together, they make up at most 20% of the critical mass, and perhaps less than 10%. If you use a hyperbolic geometry for the Universe, that's the end of the story, but if you want to pretend the Universe is flat, you have to add another 70 to 90% of "non-mass", which is called "dark energy" or "funny energy", and is an imaginary number which corresponds to the current rate of expansion and acceleration of the Universe. Regardless of which way you look at things, however, one thing is certain -- the Universe will expand, faster and faster, for the rest of eternity, and eventually, everything that is now more than a few tens of millions of light years away from us will be too far away to observe, and the "observable" Universe will shrink to the few galaxies and clusters of galaxies which are so close to us that our mutual gravity can overcome the overall expansion of the Universe.

What is current theory about the origin and nature of the Universe?
      Current theory is that the Universe began as a point of zero size and infinite density, within an apparently empty part of some prior Universe. In modern physics, the apparently empty space which fills most of the Universe is, at the sub-sub-sub-sub-microscopic level, a sea seething with infinitesimal energy fluctuations. Normally, these fluctuations would amount to nothing, but occasionally they can become quite large, providing that they disappear, or average out to zero, in too small a time for anyone to notice. If the time scale involved is short enough (less than the Planck Time, or 10 to the minus 43 seconds), energy fluctuations might even become larger than the entire rest-mass energy of the Universe. If they do, however, although they might 'disappear' in some ways, they could create entire new Universes, such as ours, providing that the space-time-mass-energy of the new Universe instantaneously becomes detached from, and therefore, completely unobservable from, the old Universe. If this idea is correct, then the empty space time of one Universe can create, over time, an infinite number of other Universes, each of which, as they grow and age, would create an infinite number of other Universes. None of these Universes would, however, be in any way connected to any of the others, so there would be no way to observe any of the others. The space-time of the Universe which you happen to be in would seem to be all of existence, and the only way to tell whether this theory has any possibility of being correct would be to see whether the properties of the Universe match the predictions of the theory. At the moment, a particular variation of this theory, called the Inflationary Big Bang Theory, seems to correctly predict certain characteristics of the Universe, and so this is the most popular theory of the origin of the Universe. Unfortunately, in physics, no theory can ever be proven to be correct (although, if it makes incorrect predictions, it can be proven to be incorrect), so we cannot know whether this will still be the preferred theory a decade, a century, or a millennium from now.

Hoaxes, Rubbish, Delusions, Misunderstandings and Fraud

The discovery of chlorophyll on Europa -- misunderstanding
      The "discovery" of chlorophyll on Europa was not actually a real discovery. It was part of a fictional work, "2010", by Arthur Clarke. However, although the discussion in the book and movie was fictional, the people who work on plans for probes to Europa would love for that fictional discovery to turn out to be true, it is sometimes mentioned in press releases, and it is not always made entirely clear that it is just a story, and has nothing to do with current scientific knowledge.
      Europa's surface appears to be covered with shifting sheets of ice, separated by dark rifts which are thought to be thinner, fresher ice created when the surface shifts, and water pushes its way up from below (probably many miles below). It has been theorized that a water ocean buried beneath the surface ice may contain life, and that the dark rifts might contain some evidence of organic materials, or even micro-organisms, trapped in the upwelling material. However, there is at present no evidence that even primitive organic materials exist on Europa, let alone complex materials such as chlorophyll, which was created by lifeforms on Earth only after hundreds of millions of years of evolution. The building blocks of such materials are abundant throughout the Universe, and there is no reason that at least primitive, inorganically created carbon compounds cannot exist on Europa, but we haven't had a chance to examine the moon up close enough to make the appropriate observations.

Mars will be the closest to us in 66000 years, and look as large as the Moon -- hoax
     Mars will be relatively close to the Earth in October and November, with the closest approach on October 30, at a distance of 43 million miles. However, even at that distance Mars' apparent diameter will 80 times smaller than the Moon's, and the planet will only appear as a bright dot, without a telescope. At the closest recent approach, in August of 2003 (see The Oppositions of Mars), Mars was still almost 35 million miles away, appeared 70 times smaller than the Moon, and was still just a bright dot without optical aids. That close approach, or opposition, was the closest one in 60,000 years, by a few hundred miles; but there will be other very slightly closer approaches over the next few centuries, and when Mars' eccentricity reaches its greatest possible value a little over 200,000 years from now, it could be as close as 30 million miles -- but even then, it would still appear 60 times smaller than the Moon, and be only a bright dot in our sky. In other words, Mars can never appear anywhere near the size of the Moon, and its upcoming close approach, although considerably closer than normal ("normal" is about 49 million miles), is not nearly as close as just a couple of years ago.

Buy land on the Moon / Name a star -- fraud
     Although there are companies that are happy to "sell" land on the Moon or other celestial bodies, the "deeds" they provide are no more valid than the proverbial deed to the Brooklyn Bridge. International treaties deny ownership of any part of any celestial body by any individual or country; and as discussed immediately below, such certificates are completely worthless. Companies that promise to name a star after you are also merely trading worthless pieces of paper for your money, as the names they "assign" to stars are not recognized by any astronomical organization.
     Here is a legal summary, from the British National Space Centre: "The United Nations Outer Space Treaty, to which most countries including the UK are signatories, forbids nations from claiming ownership of outer space, including the moon. No one has the right to own land on the moon, or any other celestial body. No signatory could support or enforce a private claim to ownership of land on the moon without breaching the Treaty. So any claims to title are unenforceable. Certificates of ownership can only be that -- certificates. They do not confer title on real estate."

What is Planet X (Niburu)? Who are the Ringmakers of Saturn? -- delusion, hoax or fraud
     These questions are in some ways about totally different topics, but are closely related, as they involve complete nonsense. Basically, they involve unknown planets and/or moons, inhabited by alien beings who are infinitely above us technologically, but have an unfathomable interest in our welfare. There are certainly many unknown objects in the Solar System, most particularly in the regions beyond Pluto; but there is no evidence that any place in the Solar System is inhabited by beings of any intelligence, let alone beings more intelligent than us; and anything you read about Niburu or the Ringmakers of Saturn is fiction, labeled as fact in order to take money out of the pockets of those foolish enough to believe the tales. Unfortunately, there is a very lucrative, market for lies and hoaxes in publishing and entertainment in general. Many people would like to believe that there are strange things going on in the Universe that we don't know anything about, or, better yet, that our government knows about, and is hiding from us. (The fact that our government can't keep anything of any importance secret from either the general public or foreign spies is of course irrelevant to these all-too-willing believers.)
     Now, I'm just as happy as anyone to watch a TV show or movie about strange doings, as long as it's labeled as entertainment. In that case, the time and/or money is hopefully well spent. But please don't waste any money or mental effort on junk that claims to be real, when it is, in reality, even less real, and far less entertaining than, say, Mork from Ork. You can pretty much count on it, that if you read about this stuff on the Internet, or see it on TV (which is, nowadays, almost nothing but made-up nonsense, even on many so-called "news" programs), but it isn't in a regular newspaper or reputable magazine, it is complete nonsense.
     If you'd like to read more about this junk, there is a very entertaining website, Bad Astronomy, which debunks some of the astronomy hoaxes that fill the air waves and the Internet. Even that site doesn't cover all of the nonsense that is around, however, so, to quickly summarize the two topics above:
      Planet X, or Niburu, does not exist. The Ringmakers of Saturn do not exist, save in the perfervid imaginations of those who are foolish enough to believe such tales. I do not know whether the originators of these tales are, as has been very strongly implied elsewhere, charlatans, pranksters, or lunatics, but I am sure that the tales themselves are completely devoid of any merit.

The book/program "The Great Year" says that the Sun has a binary companion -- rubbish
     The Great Year is a term used to describe the 25,000 year cycle of precession of the Earth's axis of rotation around the pole of its orbit. This term has been used for quite a long time, but doesn't in any way refer to WHY the precession occurs (when the term was invented, it was thought to be a 'natural' motion of the stars, which occurred in additional to their daily motion around the sky).
      Precession occurs because of the gravitational effects of the Moon and Sun on our equatorial bulge. This is referred to as the 'lunisolar' theory, and is the ONLY accepted theory of precession.
     However, there is an alternative theory, based on an 1894 book which was itself based on ancient Oriental philosophies of the motions of heavenly bodies, which suggests that precession is caused, at least in part, by the Sun orbiting around some unknown stellar companion, with an orbital period of 24,000 years. This is the theory that you must have heard discussed in the program. I was, frankly, quite surprised and disturbed to hear that this program was based on such nonsense. There are small discrepancies in the lunisolar theory calculations, which is quite common in any application of theory of any sort to the real world, but the idea that some unknown companion of the Sun can be in any way responsible for these discrepancies is absolute rubbish. If there were such a star, and it was close enough so that it could have a 24,000 year orbital period, it would produce many other, very noticeable effects on our Solar System, particularly on comets and the outer planets, and there is absolutely no way that this can be true; and in any event, those effects would NOT be related to precession, which involves the axis of rotation of the Earth, and not its orbital motion.
     Frankly, this reminds me of some very similar rubbish, about 30 years ago, about a nonexistent star dubbed Nemesis, which supposedly had a 26-million year orbital period, and was responsible for periodic waves of comets being thrown into the Solar System, destroying everything in their path. At least in that case, it was possible to show that the theories involved were not only ridiculous, but also that the mathematics involved was completely faulty, without having to invest additional time in a fruitless search for the nonexistent object.
      I hope that this unfortunate incident won't put you off on watching science programs on TV. Many of them are well worth watching. It's too bad that the producers of programs such as this one don't bother to explain that the theories being pushed are controversial, and should be taken with a heaping spoonful of salt. But that might hurt their ratings, and they'd rather sell their mothers than do that, so don't expect any great effort to provide correct information. Just keep in mind that if something like this were really true, it would be in the real news (meaning major newspapers and magazines, as TV "news" is intended strictly for entertainment value, as well).