Mercury
Mercury
Mercury is the smallest planet, only 4,880 km in diameter. It's a dense, rocky planet with a massive iron core making up most of its interior. It orbits just 58 million km from the Sun. A year is only 88 Earth days, but a day (one full rotation) takes 59 Earth days. Known since antiquity, it was observed by Babylonian, Greek, and Roman astronomers.
Info:
- Volume: 6.08x1010 km3 (0.056 Earths)
- Mass:3.30x1023 kg (0.055 Earths)
- Surface Gravity: 3.7 m/s2
- Median Surface Temprature: ~ 167°C
Venus
Venus
Venus is nearly Earth's twin in size (12,104 km diameter) and is a rocky planet with a thick carbon-dioxide atmosphere and sulfuric acid clouds. It lies about 108 million km from the Sun. Its orbit takes 225 Earth days, while its rotation is extremely slow and retrograde, lasting 243 Earth days. Also visible to the naked eye, Venus has been observed since ancient times and was first studied telescopically by Galileo in 1610.
Info:
- Volume: 9.28x1011 km3(0.86 Earths)
- Mass: 4.87x1024 kg (0.82 Earths)
- Surface Gravity: 8.87 m/s2
- Median Surface Temprature: ~ 464°C
The Moon
The Moon
Earth's Moon is about 3,474 km across (just over a quarter of Earth's size). It's a rocky body made mostly of silicate minerals with a small iron core. It orbits Earth at an average distance of 384,400 km, taking 27.3 days to orbit and rotate (tidally locked, so the same side always faces Earth). It wasn't “discovered” — humans have always seen it — but the first telescopic studies were by Galileo Galilei in 1609.
Info:
- Volume: 2.1958x1010 km3 (0.02 Earths)
- Mass: 7.35x1022 kg (0.001 Earths)
- Surface Gravity: 1.62 m/s2
- Median Surface Temprature: ~ -20°C
Mars
Mars
Mars is about half Earth's size (6,779 km diameter) and is a rocky planet rich in iron oxide (rust), which gives it its red color. It orbits at 228 million km from the Sun. A Martian year lasts 687 Earth days, and a day (a “sol”) is just a bit longer than ours at 24.6 hours. Known since ancient times, it was documented by early civilizations and studied in detail with telescopes from the 1600s onward.
Info:
- Volume: 1.63x1011 km3 (0.15 Earths)
- Mass: 6.42x1023 kg (0.11 Earths)
- Surface Gravity: 3.72076 m/s2
- Median Surface Temprature: ~ -65°C
Jupiter
Jupiter
Jupiter is the giant of the Solar System, with a diameter of 139,820 km. It's a gas giant made mostly of hydrogen and helium with no solid surface. It orbits at about 778 million km from the Sun, taking 12 Earth years to complete a year, but it spins rapidly — a day is just 10 hours. Observed since antiquity, its four largest moons were discovered by Galileo in 1610.
Info:
- Volume: 1.43x1015 km3 (1321 Earths)
- Mass: 1.90x1027 kg (317.8 Earths)
- Surface Gravity: 24.79 m/s2
- Median Surface Temprature: ~ -110°C
Saturn
Saturn
Saturn is famous for its rings and measures 116,460 km across. Like Jupiter, it's a gas giant mostly made of hydrogen and helium. It orbits at 1.4 billion km from the Sun, with a year lasting about 29 Earth years, and it rotates quickly — one day is about 10.7 hours. Known since ancient times, its rings were first seen by Galileo in 1610, though Christiaan Huygens (1655) correctly identified them.
Info:
- Volume: 8.27x1014 km3 (764 Earths)
- Mass: 5.68x1026 kg (95.16 Earths)
- Surface Gravity: 10.44 m/s2
- Median Surface Temprature: ~ -140°C
Uranus
Uranus
Uranus is an ice giant about 50,724 km in diameter, made mostly of hydrogen, helium, and “ices” like water, methane, and ammonia. It orbits 2.9 billion km from the Sun. A year lasts 84 Earth years, while a day is 17 hours. Discovered with a telescope by William Herschel in 1781, it was the first planet found in modern times.
Info:
- Volume: 6.83x1013 km3 (63.1 Earths)
- Mass: 8.68x1025 kg (14.54 Earths)
- Surface Gravity: 8.69 m/s2
- Median Surface Temprature: ~ -195°C
Neptune
Neptune
Neptune is the smallest ice giant at 49,244 km across and is composed of hydrogen, helium, and a high proportion of “ices” like water and methane (which gives it its blue color). It orbits about 4.5 billion km from the Sun, with a year lasting 165 Earth years, and rotates in about 16 hours. It was discovered in 1846 by Johann Galle, based on predictions from Uranus's orbital irregularities.
Info:
- Volume: 6.25x1013 km3 (57.7 Earths)
- Mass: 1.02x1026 kg (17.15 Earths)
- Surface Gravity: 11.15 m/s2
- Median Surface Temprature: ~ -200°C