People have been observing the sky for thousands of years. Ancient Greeks drew patterns in the sky and associated myths of their gods and goddesses to the constellations. Further, the word “planet” is Greek for “wanderer.” The Romans named the planets after their deities, which remains today. While a large part of space is unexplored, much of our solar system is known. Our solar system is comprised of the Sun and eight planets, which, in order of closest to the Sun, are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.
Mercury, Venus, Earth, and Mars are called the inner planets because they are on the inside of the asteroid belt. They are also considered terrestrial planets due to their solid rocky surfaces. Jupiter, Saturn, Uranus, and Neptune are the outer planets and are gas giants. Uranus, Neptune, and Pluto are also considered modern planets because they were not discovered until the invention of the telescope.
Distance from the Sun: 57,909,175 km
Equatorial Radius: 2,439.7 km
The smallest planet experiences extreme variations in temperature due to the lack of atmosphere. During the day, temperatures can reach 430 degrees Celsius. At night, on the other hand, it can drop to -170 degrees Celsius. Mercury is difficult to observe except during twilight because of its close proximity to the Sun. Thirteen times each century, planet Mercury can be observed indirectly as it passes the Sun, known as the transit.
Distance from the Sun: 108,208,930 km
Equatorial Radius: 6,051.8 km
Venus is the most similar to Earth of all the planets in terms of size, mass, and distance from the Sun. However, it is covered with thick clouds that trap the heat in a greenhouse-like effect bringing temperatures high enough to melt lead. The clouds also reflect sunlight making Venus the brightest body in the sky.
Distance from the Sun: 149,597,890 km
Equatorial Radius: 6,378.14 km
Earth is the only known planet in the universe to sustain life. It is made up of diverse and complex systems, such as air, water, and land, that work together to protect life from the inhospitable void of outer space.
Distance from the Sun: 227,936,640 km
Equatorial Radius: 3,397 km
There is much speculation about the possibility of the former existence of life on Mars and the potential for colonizing. Mars has evidence of changing environments in the layered soils near the poles, and the polar ice caps also grow and recede with the changing seasons. Further, occasional dust storms will overtake the planet, forming giant dunes.
Distance from the Sun: 778,412,020 km
Equatorial Radius: 71,492 km
Jupiter is the largest of all the planets with four planet-sized moons. It is so large that some of its 62 moons are asteroids that were drawn into orbit by Jupiter’s gravitational pull. As a gaseous planet, it does not have a solid surface. Rather, the gas merely becomes more and more dense the closer it gets to the center. The different colors of gas correlate with the cloud’s altitude. The Great Red Spot (GRS) has clouds that are higher and colder than the surrounding area.
Distance from the Sun: 1,426,725,400 km
Equatorial Radius: 60,268 km
Saturn is the sixth planet from the sun and was originally thought by Galileo to be triple-bodied. Over time, though, scientists identified it as rings surrounding the planet and even differentiated between A (outer) and B (inner) rings.
Distance from the Sun: 2,870,972,200 km
Equatorial Radius: 25,559 km
Scientists first considered Uranus to be one of the blandest planets. However, they later discovered rings, a phenomenon originally thought to be unique to Saturn. Uranus also has the brightest clouds that are blue due to the methane in the atmosphere.
Distance from the Sun: 4,498,252,900 km
Equatorial Radius: 24,764 km
Neptune was discovered through mathematical calculations, not through observation. Scientists considered Uranus’s elliptical orbit and was able to derive the effect of Neptune’s gravitational pull on the orbit. Because of Pluto’s unusual orbit, Neptune is the furthest body in the solar system for 20 Earth years out of 248 Earth years.
Pluto (Demoted as a planet)
Distance from the Sun: 5,906,380,000 km
Equatorial Radius: 1,151 km
In 2006, Pluto was demoted from planet to dwarf planet. The International Astronomical Union (IAU) adjusted the criteria of planet status to include “[having] cleared the neighborhood around its orbit.