Pluto is no longer a planet, it has been recatogarized in a dwarf planet. According to the new definition, a planet is an object that orbits the sun and is large enough to have become round due to the force of its own gravity. In addition, a planet has to dominate the neighborhood around its orbit. Pluto has been demoted because it does not dominate its neighborhood. Charon, its large "moon," is only about half the size of Pluto, while all the true planets are far larger than their moons.

The correct answer is: nobody knows. According to general relativity, Einstein's theory of gravity and our best understanding of what governs the early universe, there is no such thing as "before the Big Bang" -- it is the point at which space and time come into existence. However, it is also a "singular" point, at which our theories break down. It is possible that some future reconciliation of general relativity will help us understand the origin of the Big Bang, just as it is possible that we may come to believe that the universe had an interesting history even before what we now call the Bang. Both possibilities are being actively pursued by cosmologists

No precise answer can be given, but the most reliable answer is 140 billion

about 1.7 x 10^77 hydrogen atoms. Other atoms are near impossible to calculate.
In the TOTAL universe, including the part outside our horizon, the answer is infinity.

One way to help visualize the relative distances in the solar system is to imagine a model in which the solar system is reduced in size by a factor of a billion (109). The Earth is then about 1.3 cm in diameter (the size of a grape). The Moon orbits about a foot away. The Sun is 1.5 meters in diameter (about the height of a man) and 150 meters (about a city block) from the Earth. Jupiter is 15 cm in diameter (the size of a large grapefruit) and 5 blocks away from the Sun. Saturn (the size of an orange) is 10 blocks away; Uranus and Neptune (lemons) are 20 and 30 blocks away. A human on this scale is the size of an atom; the nearest star would be over 40,000 km away!

They are rocky lumps of material, sometimes known as the minor planets. Most of the asteroids lie between Mars and Jupiter. The biggest known asteroid Ceres, which was classified as a dwarf planet in 2006 has a diameter of about 1000 kilometres.

Jupiter, Saturn, Uranus and Neptune have no solid surfaces so that eliminates them as potential landing sites. Venus has such a thick atmosphere it would crush you like an eggshell. The rest of the bodies such as Mercury, Mars, Pluto, and the satellites of the giant planets, are possibilities, but you would have to provide your own atmosphere to breath and probably live below the surface to protect yourself from the harmful radiation and cosmic rays from the Sun. The surfaces of the icy moons would be a challenge. Humans require heat, and this would eventually cause any colony to slowly sink into the icy crust if not properly insulated from the ground. By far, the least expensive planet to visit is Mars.

Mars seems to be a good candidate because 'all' you would have to do is release the water and CO2 trapped in the polar permafrost layer to rebuild an atmosphere a little bit less thick than the earth's. This would also make the Martian surface temperature much more earthlike. Some engineers have proposed that all that would be needed is a few megatons of black graphite sprinkled on the North and South Poles of Mars. This dark stuff would absorb solar radiation and heat up the surface to release the CO2. The problem is, can this be done so fast that the atmospheres won't leak away in the meantime? After the martian atmosphere is reestablished, you still have the problem that Mars is just not massive enough to be able to hang onto such an atmosphere. Within a few thousand years, surface dwellers would probably notice a significant change in the atmospheric pressure as the last vestiges of the ancient martian atmosphere leaks away; this time for good.

Even Venus has been looked at. This time, you would seed the atmosphere with the appropriate bacteria which would gobble up the acid and over the course of a few thousand years, gradually reduce the CO2 to non-greenhouse levels.