With the exception of Uranus and Neptune, each of these planets can be seen unaided. All eight planets can be see through the use of an inexpensive amateur telescope or binoculars.
Order of the planets
Distance of the planets from the Sun
Distance from the Sun
|Mercury||57,910,000 km (0.387 AU)||4,879 km|
|Venus||108,200,000 km (0.723 AU)||12,104 km|
|Earth||149,600,000 km (1.000 AU)||12,756 km|
|Mars||227,940,000 km (1.524 AU)||6,805 km|
|Jupiter||778,330,000 km (5.203 AU)||142,984 km|
|Saturn||1,424,600,000 km (9.523 AU)||120,536 km|
|Uranus||2,873,550,000 km (19.208 AU)||51,118 km|
|Neptune||4,501,000,000 km (30.087 AU)||49,528 km|
|Pluto (Dwarf planet)||5,945,900,000 km (39.746 AU)||2,368 km (+- 20km)|
Types of planets
Click any of the eight planets below to find out more about the remarkable objects in our solar system.
What is a planet?
The answer to this question is a highly controversial one. This has not always been the case, though. In fact, before 1978 the definition of a “planet” was not really necessary. Until that time a planet simply meant a body in orbit around the Sun, that reflected sunlight, and was not a planetary moon, asteroid, or comet.
However, with the discovery of Pluto’s moon Charon in 1978 scientists were able to calculate Pluto’s mass much more accurately than ever before and soon realized that it was much smaller than they had previously believed. At a tiny fraction of the mass of Mercury, Pluto was clearly a body much smaller than any other planet. This discovery led some to question whether Pluto was actually a planet or some other type of object.
In the 1990s and early 2000s the discovery of several objects in the outer solar system similar in size to Pluto made it all but necessary to come to a definitive definition of a planet. Such a definition was needed to separate those types of objects like Pluto into a distinct class, otherwise all of the newly found objects would have to be called planets as well.
In response to this uncertainty, the International Astronomical Union (IAU), the official governing body for matters concerning naming astronomical objects, came to a definition of the term “planet.” According to the IAU, a planet is a celestial body that meets the following criteria:
- is in orbit around the Sun,
- has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and
- has cleared the neighbourhood around its orbit.
How many planets are in the Solar System?
According to the IAU’s definition for planet above, there are 8 known planets in the Solar System: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.
Pluto is no longer considered a planet under the IAU definition.
Are there any undiscovered planets in the solar system?
There have been several additional planets hypothesized throughout history; however, none of these planets has ever been found.
The most recent of these theorized planets was Planet X, a supposedly giant planet used to explain the deviations from the predicted orbits of Uranus and Neptune. Although Planet X has never been found and scientists are still unable to satisfactorily explain the uranian and neptunian orbital discrepancies, the scientific community has almost unanimously come to the conclusion that Planet X does not exist.
It is highly unlikely that there are any planets beyond the orbit of Pluto.