The Solar System consists of the Sun and the other celestial objects gravitationally bound to it: the eight planets, their moons, five currently identified dwarf planets and their seven known moons, and billions of small bodies. This last category includes asteroids, Kuiper belt objects, comets, meteoroids and interplanetary dust. In broad terms, the charted regions of the Solar System consist of the Sun, four terrestrial inner planets, an asteroid belt composed of small rocky bodies, four gas giant outer planets, and a second belt, called the Kuiper belt, composed of icy objects. Beyond the Kuiper belt lies the scattered disc, the heliopause, and ultimately the hypothetical Oort cloud. In order of their distances from the Sun, the planets are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. Six of the eight planets are in turn orbited by natural satellites, usually termed "moons" after Earth's Moon, and each of the outer planets is encircled by planetary rings of dust and other particles. All the planets except Earth are named after gods and goddesses from Greco-Roman mythology. The five dwarf planets are Pluto, Makemake, and Haumea, the three largest known Kuiper belt objects; Ceres, the largest object in the asteroid belt; and Eris, the largest known object in the scattered disc.
A dwarf planet
is a celestial body orbiting
that is massive enough to be spherical as a result of its own gravity
but has not cleared its neighbouring region
and is not a satellite
. They are smaller than planets
, but more massive than small solar system bodies
. The term was adopted in 2006 by the International Astronomical Union
(IAU) as a result of the increase in discoveries of trans-Neptunian objects
that rivaled Pluto
in size, and finally precipitated by the discovery of an even more massive object, Eris
. The IAU currently recognizes five dwarf planets—Ceres (pictured)
, Pluto, Haumea
, and Eris. It is suspected that at least another 40 known objects in the Solar System
are dwarf planets, but the number might be as high as 2,000. The 2006 definition has been both praised and criticized, and has been disputed by some scientists.
Jupiter is the fifth planet from the Sun and by far the largest within the Solar System. It is 318 times more massive than Earth, with a diameter 11 times that of Earth, and with a volume 1300 times that of Earth. Its best known feature is the Great Red Spot, a storm larger than Earth, which was first observed by Galileo four centuries ago. This picture, taken by the Cassini orbiter was one of 26 thousand images taken of Jupiter during the course of its flyby and is the most detailed global color portrait of the planet ever produced.