The solar system includes eight official planets, from Mercury to Jupiter, that vary in composition, conditions and other aspects.
Mercury, our closest planet to the Sun and one of its smallest planets, measures only slightly larger than our moon. Mercury boasts extremely extreme temperatures that range from daytime highs of 800 Fahrenheit (430 Celsius) to nighttime lows of -290 Fahrenheit (180 Celsius).
Mercury is the smallest planet in our Solar System and was named for Roman messenger of the gods, Hermes. However, with its closest orbit to the Sun -perihelion- it is also one of the fastest moving objects. From time to time Mercury crosses Earth’s orbit and can be seen crossing into view as a tiny black dot crossing the Sun’s bright disk (see eclipse).
Due to a lack of atmosphere, Mars remains cold at night, featuring only an extremely thin exosphere composed of atoms blown off by solar winds. Furthermore, its surface features steep cliffs hundreds of miles tall as well as narrow ridges similar to those on Earth and Mars.
Earth has been transformed by various asteroid impacts, which are easily identifiable by bright streaks of crater rays left behind from them. Crater rays form when an asteroid or comet impacts with our planet and crushes the rocks beneath its surface, leaving behind bright streaks.
Scientists consider these crater rays evidence of geological activity on Mercury. It’s likely they were formed when its core and mantle contracted over billions of years, as Mercury’s temperature decreased and contracted.
Venus, our nearest planetary neighbor, is a rocky planet with an approximate diameter of 12,103.6 km. Although slightly smaller and heavier than Earth, many refer to Venus as being our “sister planet” or “twin planet.”
As Galileo Galilei noted in 1610, Venus is unique among planets in that its orbit around the Sun matches up exactly with that of Earth – and therefore displays phases of the Moon like any other planet does – providing irrefutable evidence against an earlier geocentric model for our solar system that was developed some 15 centuries prior.
Mars’ atmosphere consists of carbon dioxide at 92 times greater pressure than Earth, creating a greenhouse effect and trapping the Sun’s heat, creating an extremely hot surface.
At 880 degrees Fahrenheit (471 degrees Celsius), the surface is hot enough to melt lead. Any time water molecules land on it, they vaporize instantly – creating a potentially hazardous landing site for spacecraft.
Due to these reasons, no spacecraft missions to Venus have been launched for almost three decades – until recently when a team of scientists announced they were working on a Venus probe capable of withstanding an intense five-minute plunge through carbon dioxide clouds below its surface.
Earth, our fifth-largest planet in our Solar System, measures 12,756 kilometers (5,400 miles). With an approximate diameter of 12,756 kilometers and mass of 5.8 million tons, it is the densest rocky planet with an abundance of heavy metals in its core.
Earth has two kinds of crust: dry land made up of light silicate minerals like granite and oceanic crust comprised of dense volcanic rock called basalt. Continental crust averages 25 miles (40 km), while oceanic crust can range anywhere between 5 miles (8 km).
Earth has been struck by hundreds of large asteroids during its 4.5 billion-year existence, leaving massive scars across its surface. Unfortunately, not all space rocks make their way down into our planet’s orbit and strike its surface directly.
Our Sun, the focal point of the solar system, spans 432,000 miles (695,000 km). That makes its diameter nearly 109 times greater than our planet; to fill its entirety would require over one and one half million Earths!
Mars, the fourth planet from the Sun, is easily visible with naked eye. Like Earth, Mars features clouds, winds, 24-hour days and seasonal weather patterns similar to our own; as well as polar ice caps, volcanoes, canyons and much more.
Owing to its cold, thin atmosphere and lack of liquid water, Mars does boast evidence of salty surface water that was likely present millions of years ago but eventually evaporated due to lack of protection by an atmosphere. Scientists speculate that mars once held liquid water that has since been lost into space due to lack of protection by an atmosphere.
Mars contains an expansive canyon system called Valles Marineris that measures more than 3,000 miles (4,800 kilometers) long and four times deeper than its American counterpart. As one of the largest known canyons in our solar system, Valles Marineris may once have supported lakes or oceans.
Jupiter, the largest planet in our solar system, primarily composed of hydrogen and helium elements, was formed when our Sun pushed these heavier elements toward its outer parts.
As with other gas giants, Jupiter features an atmosphere rich in nitrogen and an equally strong magnetic field, and has a faint four-part ring system thought to have been replenished with material from small moons such as Amalthea, Thebe, Metis and Adrastea (which ESA’s Juice mission will investigate in depth).
Earth is covered in colorful latitudinal bands, atmospheric clouds and storms which change every few hours or days. One such complex weather system is the Great Red Spot; an oval-shaped storm that rotates counter-clockwise four times larger than our Earth’s hurricanes.
Jovian’s gravity plays an essential part in how its four biggest moons, known as Galilean satellites, orbit and interact. New work by astronomers at University of Maryland shows how this impacts mass distribution among them.
Saturn is the second-largest planet in our solar system with an astronomical diameter of 72,000 miles (116,000 km), dwarfing Earth by nine times.
Venus is another gas giant similar to Jupiter in composition. The atmosphere contains approximately 75% hydrogen and 25% helium, along with trace amounts of methane, water, and ammonia.
NASA’s Cassini probe will orbit Saturn and send back detailed images in 2004.
Saturn boasts a complex system of rings composed of thousands of particles of ice and rock that orbit independently from each other, covering an expanse of 6,630 to 120,700 kilometers (4120 to 75,000 mi). They average about 20 meters thick.
Uranus, commonly referred to as an “ice giant,” is the third-largest planet in our solar system and one of its coldest; with an atmosphere composed of mostly methane gas.
Day and night temperatures on this gas giant range from 840 degrees Fahrenheit to minus 290 degrees F, while it also rotates opposite of other planets in its solar system, leading to extreme seasons on both ends.
Jupiter, Saturn, Uranus and Neptune all contain mostly hydrogen and helium atmospheres with small traces of ammonia, phosphate, nitrous oxide and water vapor — providing vivid colors ranging from yellow-brown through red to blue-green hues.
Saturn features an extensive ring system comprised of ice and rock particles with various sizes and speeds of orbital speeds, just as other planets in our solar system do. Saturn also boasts several moons that orbit it.
Uranus stands out amongst planets due to its distinctive rings, which appear to wiggle much like those on some moons of Earth. Evidence indicates that Uranus’ rings were created through a massive collision approximately 4 billion years ago with another object.
The planets in our solar system, from Mercury through Mercury, Venus, Earth Mars Jupiter Saturn Uranus and Neptune can be seen. Mercury was followed by Venus Earth Mars Jupiter Saturn Uranus Neptune making up nearly one-third of our sun’s mass yet remain out of view to the naked eye due to their distance.
Neptune’s distance from Earth makes its orbit around it take 165 years; its diameter spans 15,299 miles (39,000 kilometers). That makes Neptune approximately three and one half times bigger than Earth itself!
Neptune boasts some of our solar system’s strongest winds despite its immense distance from Earth. These gusts propel clouds of frozen methane over Neptune at speeds exceeding 1,200 miles per hour!
Neptune’s atmosphere consists of hydrogen, helium and methane gasses; its core is made up of rocks. Scientists think there might be liquid ocean underneath its cold clouds but its pressure prevents its boiling off due to such high pressure levels. Neptune boasts an extremely powerful magnetic field – 27 times stronger than Earth’s! – which tilts 47 degrees from its axis of rotation for every rotation and causes unpredictable changes to occur within its magnetosphere each time Neptune spins around.