Mercury
Distance from Sun: 57.9 million km
Orbital Period: 88 Earth days
Day Length: 176 Earth days
Diameter: 4,879 km
Temperature: -173°C to 427°C
Mercury is the smallest planet in our solar system and closest to the Sun. It's a rocky planet with a solid surface covered in craters, similar to our Moon's appearance. Mercury has no atmosphere to speak of, and without an atmosphere to trap heat, temperatures on Mercury's surface can swing from extremely hot during the day to very cold at night.
Despite its proximity to the Sun, Mercury is not the hottest planet in our solar system – that distinction belongs to Venus. Mercury has a very small axial tilt and consequently does not experience seasons like many other planets.
Mercury has no moons, and its orbit is highly elliptical, taking it as close as 47 million km and as far as 70 million km from the Sun. The planet has a large iron core that generates a magnetic field about 1% as strong as Earth's.
Venus
Distance from Sun: 108.2 million km
Orbital Period: 225 Earth days
Day Length: 243 Earth days
Diameter: 12,104 km
Temperature: 462°C (average)
Venus is often called Earth's twin because of their similar size and proximity to each other in the solar system. However, Venus has extreme surface heat and atmospheric pressure. Its thick atmosphere is primarily carbon dioxide and contains clouds of sulfuric acid, creating a runaway greenhouse effect that traps heat.
The surface of Venus features extensive plains marked by thousands of volcanoes, some of which may still be active today. Venus rotates very slowly and in the opposite direction of most planets, meaning the Sun rises in the west and sets in the east.
Venus has no moons and no magnetic field. Its atmosphere is so thick that the pressure at the surface is 92 times that of Earth, equivalent to the pressure at a depth of nearly 1 km in Earth's oceans.
Earth
Distance from Sun: 149.6 million km
Orbital Period: 365.25 days
Day Length: 24 hours
Diameter: 12,742 km
Temperature: -88°C to 58°C
Earth is the third planet from the Sun and the only astronomical object known to harbor life. About 71% of Earth's surface is covered with water, with the remaining 29% consisting of continents and islands. The Earth's atmosphere consists of 78% nitrogen, 21% oxygen, and 1% other gases including argon, carbon dioxide, and water vapor.
Earth's atmosphere protects us from incoming meteoroids, most of which break up before they can hit the surface. Our planet has one natural satellite, the Moon, which is the fifth largest moon in the solar system.
Earth's magnetic field, generated by its rotating iron core, shields the planet from most of the Sun's harmful radiation and solar wind. This magnetic field, along with Earth's distance from the Sun and its abundant water, has made it uniquely suitable for life as we know it.
Moon
Distance from Earth: 384,400 km
Orbital Period: 27.3 days
Diameter: 3,474 km
Temperature: -173°C to 127°C
Type: Natural Satellite
The Moon is Earth's only natural satellite and the fifth largest moon in the solar system. Its presence helps stabilize our planet's wobble, leading to a relatively stable climate over billions of years. The Moon is a differentiated rocky body, meaning it has a geologically distinct crust, mantle, and core.
The Moon's surface is covered with regolith, a mixture of fine dust and rocky debris formed by meteor impacts. Its lack of atmosphere means that temperature extremes exist on the lunar surface, and the airless environment preserves footprints and other marks left by Apollo astronauts.
The most widely accepted theory of the Moon's origin is that it formed roughly 4.5 billion years ago from debris left over after a massive collision between Earth and a Mars-sized body called Theia. The Moon is gradually moving away from Earth at a rate of approximately 3.8 cm per year.
Mars
Distance from Sun: 227.9 million km
Orbital Period: 687 Earth days
Day Length: 24.6 hours
Diameter: 6,779 km
Temperature: -87°C to -5°C
Mars is often called the "Red Planet" due to its reddish appearance, which is caused by iron oxide (rust) on its surface. It's a dusty, cold desert world with a thin atmosphere primarily composed of carbon dioxide. Mars has polar ice caps made of water and carbon dioxide ice, and evidence suggests that Mars once had flowing rivers, lakes and possibly even oceans.
Mars has two small moons, Phobos and Deimos, which may be captured asteroids. The planet features some striking geological features, including Olympus Mons, the largest volcano in the solar system, and Valles Marineris, a vast canyon system that would stretch from New York to California if located on Earth.
Mars experiences seasons similar to Earth because its axial tilt is similar to ours. It has a weak magnetic field, which suggests that it once had a molten core like Earth's. Today, Mars is being explored by multiple rovers and orbiters, with plans for human missions in the coming decades.
Jupiter
Distance from Sun: 778.5 million km
Orbital Period: 11.86 Earth years
Day Length: 9.93 hours
Diameter: 139,820 km
Temperature: -145°C (cloud top)
Jupiter is the largest planet in our solar system, more than twice as massive as all the other planets combined. It's a gas giant primarily composed of hydrogen and helium, similar to the Sun. Jupiter lacks a solid surface, gradually transitioning from gas to liquid as you travel toward the center.
The most notable feature of Jupiter is the Great Red Spot, a giant storm that has been raging for at least 400 years. Jupiter has a strong magnetic field, 14 times stronger than Earth's, and at least 79 moons, with the four largest (Io, Europa, Ganymede, and Callisto) discovered by Galileo in 1610.
Jupiter's rapid rotation (a Jupiter day is just under 10 hours) causes it to bulge at the equator and flatten at the poles, making it not perfectly spherical. The planet also has faint ring systems, though they're much less spectacular than Saturn's.
Saturn
Distance from Sun: 1.4 billion km
Orbital Period: 29.46 Earth years
Day Length: 10.7 hours
Diameter: 116,460 km
Temperature: -178°C (cloud top)
Saturn is the sixth planet from the Sun and is famous for its spectacular ring system. Like Jupiter, Saturn is a gas giant composed primarily of hydrogen and helium. It's the second-largest planet in our solar system but has the lowest density – it would float in water if there were an ocean large enough to hold it.
Saturn's rings are made mostly of water ice particles, with some rocky debris and dust. They extend up to 282,000 km from the planet but are surprisingly thin, typically only about 10 meters thick. Saturn has at least 82 moons, with Titan being the largest and the only moon in the solar system with a substantial atmosphere.
Like Jupiter, Saturn has a short day, taking about 10.7 hours to rotate once. The planet's fast rotation causes it to bulge at the equator and flatten at the poles. Saturn's hexagonal cloud pattern at its north pole is a unique and still not fully explained phenomenon.
Uranus
Distance from Sun: 2.9 billion km
Orbital Period: 84 Earth years
Day Length: 17.2 hours
Diameter: 50,724 km
Temperature: -224°C (average)
Uranus is the seventh planet from the Sun and is classified as an "ice giant." It's composed primarily of water, methane, and ammonia fluids above a small rocky core. Uranus gets its blue-green color from methane gas in its atmosphere, which absorbs red light and reflects blue light.
What makes Uranus truly unique is its extreme tilt – the planet essentially orbits the Sun on its side, with an axial tilt of about 98 degrees. This unusual orientation, which may be the result of a collision with an Earth-sized object long ago, gives Uranus extreme seasons that last for decades.
Uranus has 27 known moons, all named after characters from the works of William Shakespeare and Alexander Pope. The planet also has a system of rings, though they're much fainter than Saturn's. Uranus has the coldest planetary atmosphere in the solar system, with minimum temperatures of -224°C.
Neptune
Distance from Sun: 4.5 billion km
Orbital Period: 165 Earth years
Day Length: 16.1 hours
Diameter: 49,244 km
Temperature: -214°C (average)
Neptune is the eighth and most distant planet from the Sun. Like Uranus, it's classified as an ice giant and has a similar composition of water, ammonia, and methane over a solid core. Neptune gets its vivid blue color from the methane in its atmosphere, which absorbs red light and reflects blue wavelengths.
Neptune has the strongest winds in the solar system, reaching speeds of 2,100 km/hour. When Voyager 2 flew by in 1989, it observed a large, dark storm called the Great Dark Spot, similar to Jupiter's Great Red Spot. Unlike Jupiter's storm, Neptune's dark spots come and go every few years.
Neptune has 14 known moons, with Triton being the largest. Triton is unique because it orbits Neptune in the opposite direction of the planet's rotation, suggesting it was captured by Neptune's gravity rather than forming alongside it. Neptune also has faint ring systems and a magnetic field about 27 times stronger than Earth's.
Pluto
Distance from Sun: 5.9 billion km (average)
Orbital Period: 248 Earth years
Day Length: 6.4 Earth days
Diameter: 2,377 km
Temperature: -229°C (average)
Pluto was once considered the ninth planet in our solar system but was reclassified as a "dwarf planet" in 2006. Its orbit is highly elliptical, bringing it closer to the Sun than Neptune for about 20 years of its 248-year orbit. Pluto is small, even smaller than Earth's Moon, and is primarily made of ice and rock.
NASA's New Horizons spacecraft gave us our first close-up images of Pluto in 2015, revealing a surprisingly complex world with mountains, glaciers, and plains. The most notable feature is a large, bright, heart-shaped region named Tombaugh Regio, after Pluto's discoverer, Clyde Tombaugh.
Pluto has five known moons, with Charon being the largest. Charon is so large relative to Pluto that the two bodies orbit a common center of gravity located between them, leading some astronomers to consider the Pluto-Charon system a "double dwarf planet." Pluto has a thin atmosphere of nitrogen, methane, and carbon monoxide that expands when it's closer to the Sun and collapses as it moves farther away.