I've asked this question before, but honestly, I just don't really understand it too well, so please forgive me for asking again.
By why don't a planet's moons crash into it, or why don't we crash into the sun?
Excellent question for which you will find that gravitational physicists have no answer other than Almighty God's divine intervention and miracleworks.
"...lest the systems of the fixed stars should, by their gravity, fall on each other, he [God] hath placed those systems at immense distances from one another." -- Isaac Newton, mathematician, 1687
Since all of them have gravity, wouldn't it make sense that Jupiter's moons should've crashed into it, or that Mercury should've burned up in the sun by now?
Excellent questions for which you will find that gravitational physicists have no answer other than Almighty God's divine intervention and miracleworks.
Gravitation is a myth.
"The example of the magnet I have hit upon is a very pretty one, and entirely suited to the subject; indeed, it is little short of being the very truth." -- Johannes Kepler, astronomer, New Astronomy, 1609
"For, by the demonstration of the Englishman William Gilbert, the earth itself is a big magnet...." -- Johannes Kepler, astronomer, New Astronomy, 1609
"It is therefore plausible, since the Earth moves the moon through its species and magnetic body, while the sun moves the planets similarly through an emitted species, that the sun is likewise a magnetic body." -- Johannes Kepler, astronomer/mathematician, New Astronomy, 1609
"But come: let us follow more closely the tracks of this similarity of the planetary reciprocation [libration] to the motion of a magnet, and that by a most beautiful geometric demonstration, so that it might appear that a magnet has such a motion as that which we perceive in the planet." -- Johannes Kepler, astronomer, New Astronomy, 1609
"The long and constant persuasion that all the forces of nature are mutually dependent, having one common origin, or rather being different manifestations of one fundamental power, has often made me think on the possibility of establishing, by experiment, a connection between gravity and electricity …no terms could exaggerate the value of the relation they would establish.'' -- Michael Faraday, physicist, 1865
"...the great truth, accidentally revealed and experimentally confirmed, is fully recognized, that this planet, with all its appalling immensity, is to electric currents virtually no more than a small metal ball...." -- Nikola Tesla, physicist, 1904
"What we call mass would seem to be nothing but an appearance, and all inertia to be of electromagnetic origin." -- Henri Poincaré, physicist, 1908
"...inertia is exclusively of electromagnetic origin...." -- Henri Poincaré, physicist, 1908
"The form of the corona and the motion of the prominences suggest that it [the sun] is a magnet." -- George E. Hale, astronomer, 1913
"Magnetism is possessed by the whole mass of the earth and universe of heavenly bodies, and is an essence of known demonstration and laws. By adopting it we have the advantage over the gravity theory by the use of the polar relation to magnetism. A magnetic north pole presented to a magnetic south pole, or a south pole to a north pole, attracts, while a north pole to another north pole or a south pole to another repels. This gives to us a better reason than gravitation can for the elliptical orbit of the planets instead of the circular. It also gives us some light on the mystery of the tides, the philosophy of which the profoundest study has not solved. Certain facts are apparent; but for the explanation of the true theory such men as Laplace and Newton, and others more recent, have labored in vain." -- C.H. Kilmer, historian, October 1915
"I hope that some reader interested in astronomical matters will take occasion to make some reply to this letter [The Myth of Gravitation] and possibly contend that electro-magnetism cannot supersede Newton's theory of gravitation in the suspension and movement of the universe of worlds." -- C.H. Kilmer, historian, October 1915
"An atom differs from the solar system by the fact that it is not gravitation that makes the electrons go round the nucleus, but electricity." -- Bertrand Russell, physicist/philosopher, 1924
"It is found that matter and electricity are very closely related in structure. ... it is self-evident that matter is connected with gravitation and it follows logically that electricity is likewise connected." -- T. Townsend Brown, physicist, Aug 1929
"The writer and his colleagues anticipated the present situation even as early as 1923, and began at that time to construct the necessary theoretical bridge between the two then separate phenomena, electricity and gravitation. The first actual demonstration of the relation was made in 1924." -- T. Townsend Brown, physicist, Aug 1929
"The earth itself is a great big magnet." -- Edward Leedskalnin, stone mason, 1945
"According to our present view every atom consists of a small heavy nucleus approximately 1O^-12 cm in diameter sur-rounded by a largely empty region 1O^-8 cm in diameter in which electrons move somewhat like planets about the sun." -- Hendy D. Smyth, physicist, 1945
"Gravitation is an electromagnetic phenomenon." -- Immanuel Velikovsky, polymath, 1946
"All planets revolve in approximately one plane. They revolve in a plane perpendicular to the lines of force of the sun’s magnetic field." -- Immanuel Velikovsky, polymath, 1946
"The picture of an atom began to look more like a miniature solar system with an atomic nucleus for the sun, and electrons for planets. The analogy with the planetary system can be further strengthened by these facts: the atomic nucleus contains 99.97 per cent of the total atomic mass as compared with 99.87 per cent of the solar system concentrated in the sun, and the distances between the planetary electrons exceed their diameters by about the same factor (several thousand times) which we find when comparing interplanetary distances with the diameters of the planets. The more important analogy lies, however, in the fact that the electric attraction-forces between the atomic nucleus and the electrons obey the same mathematical law of inverse square (that is, the forces are inversely proportionate to the square of the distance between two bodies) as the gravity forces acting between the sun and the planets. This makes the electrons describe the circular and elliptic trajectories around the nucleus, similar to those along which the planets and comets move in the solar system." -- George Gamow, physicist, 1961
"When first observed by Voyager, the spoke movements [of Saturn's Rings] seemed to defy gravity and had the scientists very perplexed. Since the spokes rotate at the same rate as Saturn's magnetic field, it is apparent that the electromagnetic forces are also at work." -- Ron Baalke, astrophysicist, 1998
"Tides are created because the Earth and the moon are attracted to each other, just like magnets are attracted to each other. " -- Keith Cooley, astronomer, 2002
Man knows not his time. Jack, may you rest in peace. 
