Solar system

The solar system is the retinue of objects gravitationally bound to our Sun. Traditionally, it is said to consist of nine planets and their 156 (at last count) moons; however a large number of other objects, including asteroids, meteoroids, planetoids and comets orbit the Sun along with them.

The solar system and other planetary systems

For many years, our own system was the only planetary system known, and so theories of planetary formation only had to explain one system to be plausible. The discovery in recent years of many extrasolar planets has uncovered systems very different to our own, and theories have had to be revised accordingly.

Related Topics:
Planetary system - Extrasolar planet

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Exoplanets have not been seen by astronomers yet, however we know they exist because of the gravitational tug the planets induce on the star, and hence making the star ?wobble?. Astronomers can calculate how massive the planets are by observing how much the star wobbles. Exoplanets can also be observed more directly by their occultation of the stars' discs, which dims them slightly.

Related Topics:
Exoplanet - Occultation

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

In 1996, astronomers Geoffrey W. Marcy and R. Paul Butler discovered a massive planet orbiting Upsilon Andromedae ? a star that in the constellation Andromeda. This planet was ¾ the mass of Jupiter, and had an orbital period of 4.6 earth days, due to it?s closeness to the star (0.06AU). Since then, several dozen more have been identified.

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Many external systems contain a such a hot Jupiter; a planet comparable to or larger than Jupiter orbiting very close to the parent star, perhaps orbiting it in a matter of days. It has been hypothesised that while the giant planets in these systems formed in the same place as the gas giants in our system did, some sort of migration took place which resulted in the giant planet spiralling in towards the parent star. Any terrestrial planets which had previously existed would presumably either be destroyed or ejected from the system.

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

There has also been some photographic evidence to suggest that regions in the Orion Nebula, which is 1500 light years from Earth, have solar systems forming.

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

See extrasolar planet for more information.

~ ~ ~ ~ ~ ~ ~ ~ ~ ~