Solar system

The planets

The planets

The planets they are stars that revolve around a star, the Sun. They have no light of their own, but reflect sunlight.

How do planets move?

They are never still; On the contrary, they have different movements. The most important are two: the rotation and the translation.

By that of rotation, revolve around themselves around their own axis, that is, rotate. This determines the duration of the day of each planet.

For the movement of translation, these stars describe orbits around the Sun. Each orbit is the year of the planet, and each one takes a different time to complete that round. The further from the Sun, the longer is your year. They rotate almost in the same plane, except Pluto *, which has the most inclined, eccentric and elongated orbit.

Models, shapes and sizes

The planets have an almost spherical shape, like a ball slightly flattened by the poles.

The compact materials are in the core, denser the more to the center. The gases, if any, form an atmosphere on the surface.

Mercury, Venus, Earth and Mars are small and rocky worlds, with high density. They have slow rotation, few moons (or none) and quite round shape. In contrast, Jupiter, Saturn, Uranus and Neptune, the gas giants, are huge and light, made of ice and gases. They spin fast, they have many satellites, more equatorial bulge and rings.

Data, data, data ...

Planet Radio
to the Sun (km.)
Moons Period of
of the axis (º)
orbital (º)
Mercury2.44057.910.000058.6 days87.97 days0,007,00
Venus6.052108.200.0000-243 days224.7 days177,363,39
The earth6.378149.600.000123.93 hours365,256 days23,450,00
Mars3.397227.940.000224.62 hours686.98 days25,191,85
Jupiter71.492778.330.000799.84 hours11.86 years3,131,31
Saturn60.2681.429.400.0008210.23 hours29.46 years25,332,49
Uranus25.5592.870.990.0002717.9 hours84.01 years97,860,77
Neptune24.7464.504.300.0001416.11 hours164.8 years28,311,77
Pluto (*)1.1605.913.520.0005-6.39 days248.54 years122,7217,15

* Pluto ceased to be considered a planet in the General Assembly of the International Astronomical Union (UAI) held in Prague on August 24, 2006. On this site, however, they continue to provide their data in the list of planets. Some astronomers have good arguments against this "expulsion."

How were the planets formed?

Its formation began about 4.6 billion years ago, at the same time as the Sun.

In general, light materials that were not trapped in the Sun moved away from it more than heavy ones. In the original cloud of gas and dust, which turned spirally, there were denser areas where planets would later form.

Gravity and collisions brought more matter to these areas and the rotational movement rounded them. Afterwards, the materials and forces of each planet were readjusted, and they still do. The planets and the entire Solar System continue to change their appearance. Slowly but surely.

Click on each planet to go to its page.

We have given a basic and brief review of the Solar System Planets. In the following links there is more information for restless minds.

Discover more:
• Why do planets orbit?
• How are the orbits of the planets?
• How did the solar system form?

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