Solar System

In 2006, the International Astronomical Union redefined a planet, and Pluto does not clear its orbital neighborhood of other objects.

Mercury has almost no atmosphere, so rocks from space do not burn up before hitting the surface. Its old, inactive crust has preserved impact scars for billions of years.

Venus traps heat far more effectively than Mercury because of its thick carbon dioxide atmosphere and runaway greenhouse effect. Mercury has almost no atmosphere, so it cannot hold heat in the same way.

Venus orbits the Sun inside Earth’s orbit, so we see different amounts of its sunlit side over time. That makes it go through crescent, half, and gibbous phases.

They are inner planets, so from Earth they always stay close to the Sun’s direction. Their orbits lie inside Earth’s orbit, limiting how far they can separate in our sky.

Mars is farther from the Sun and has a much thinner atmosphere, so it receives less heat and traps far less of it. Its low atmospheric pressure also allows temperatures to swing sharply.

Mars lost much of its atmosphere over time because it is small and has weak gravity, and the solar wind stripped gases away after its magnetic field weakened. The planet could not hold onto as much air as Earth does.

Mars’ low gravity and lack of moving tectonic plates let lava build up in one place for a very long time. That is why Olympus Mons grew to enormous size.

Mars has very fine, dry dust and a thin atmosphere that can still move it over huge distances once storms start. Seasonal heating can intensify winds until dust spreads across the whole planet.

Jupiter’s rapid rotation and deep, turbulent atmosphere help storms persist for a long time. The Great Red Spot is a massive high-pressure system that has likely lasted for centuries.

Jupiter is the largest planet by far and contains more mass than all the other planets combined. More mass means stronger gravity at and around the planet.

Their orbits are squeezed by Jupiter’s gravity and by resonances with one another, which flexes their interiors. That constant flexing turns orbital energy into heat.

Saturn is made mostly of hydrogen and helium, which are very light elements. Its average density is only about 0.69 g/cm³, lower than water’s 1.0 g/cm³.

The rings lie inside Saturn’s Roche limit, where strong tidal forces prevent the particles from clumping into a single body. They are also constantly shaped by moonlets and shepherd moons.

Uranus’ extreme tilt is usually explained by a giant impact early in its history, though multiple impacts or interactions may also have contributed. Its axis is tilted by about 98 degrees.

Methane in Uranus’ atmosphere absorbs red light and leaves more blue and green light to reflect back to space. That gives the planet its pale blue-green color.

Neptune’s atmosphere is driven by strong internal heat and fast jet streams, despite getting little sunlight. Winds there can exceed 2,000 km/h.

Neptune’s atmosphere is active and changeable, so large storm systems can form, evolve, and fade. These storms are influenced by winds, internal heat, and changing cloud structures.

Pluto is extremely cold, so volatile gases freeze onto its surface as ices. Its thin atmosphere can also freeze out and return as the dwarf planet moves farther from the Sun.

Pluto’s low gravity and weak atmosphere let gases leak away more easily, especially when sunlight warms the surface. Some molecules gain enough energy to drift off into space over time.

Asteroids vary because they formed in different parts of the early Solar System and experienced different heating and collisions. Their colors reflect differences in composition, metal content, and surface weathering.

The asteroid belt never formed into a planet because Jupiter’s gravity stirred up the region and prevented material from sticking together efficiently. Repeated collisions also shattered growing bodies.

The Sun appears bigger because it is far closer to Earth than any other star. Its actual diameter is similar to other stars, but distance changes how large it looks in the sky.

Mercury has almost no atmosphere to store and redistribute heat, so its sunlit side can soar to about 430°C while the night side can drop to around -180°C.

Rings form when moons, comets, or asteroids are torn apart inside a planet’s Roche limit, but they persist only if the planet’s gravity and nearby moons keep the debris spread out.

Saturn is made mostly of hydrogen and helium, so its average density is only about 0.69 g/cm³, lower than water’s 1.0 g/cm³.

Jupiter’s rapid rotation, deep atmosphere, and internal heat drive strong jet streams and long-lived storms that can persist for centuries.

The Sun is about 400 times larger than the Moon but also about 400 times farther away, so they appear nearly the same size in our sky.

The Moon’s far side has a much thicker crust and far fewer lava plains, likely because of early thermal differences and the way the Moon cooled and was shaped by Earth’s gravity.

Mars’s thin atmosphere, dry dust, and strong seasonal heating can let small storms grow into planet-wide events that last for weeks or months.

Io is squeezed by Jupiter’s gravity and the pull of neighboring moons, and that tidal flexing generates enough heat to melt rock inside it.

Tidal heating from Jupiter keeps Europa’s interior warm enough to maintain a global ocean beneath its icy crust.

Its south polar geysers喷 out water-rich plumes from a subsurface ocean, carrying salts and organic compounds into space.

Atmospheres depend on gravity, temperature, and whether a world has been able to keep or replenish its gases. Small or hot worlds lose gas more easily than large, cold ones.

Solar heat makes frozen gases on the comet’s surface sublimate into gas, carrying dust away with them. The Sun’s wind then pushes the material into a tail pointing away from the Sun.

Earth crosses the same stream of debris along its orbit each year. When those tiny particles burn up in our atmosphere, we see a recurring meteor shower.

Jupiter’s gravity prevented the material there from forming a planet, and collisions kept the region spread out and sparse.

Mercury shrank as its interior cooled, causing its crust to wrinkle and break into huge thrust faults. Some of these scarps are hundreds of kilometres long and up to about 3 km high.

Venus rotates very slowly because its spin was probably altered over time by strong solar tides and maybe giant impacts. One Venus day lasts about 243 Earth days.

Venus's clouds are made mainly of sulfuric acid droplets formed from volcanic gases and sunlight-driven chemistry. The atmosphere is so dense that the cloud layer stays thick and global.

Mars has giant broad shield volcanoes because its lower gravity and lack of plate tectonics let lava pile up in one place for a very long time. Olympus Mons is the largest volcano in the Solar System.

Mars has a thin, dry atmosphere that lifts dust easily, and once storms start they can spread around the planet. Global dust storms can last for weeks or months.

Mars is cold enough for both water ice and dry ice to exist at the poles. Seasonal carbon dioxide frost grows and shrinks each Martian year.

Jupiter formed early and far from the Sun, where there was plenty of gas and ice for it to accumulate. Its core grew large enough to capture huge amounts of hydrogen and helium.

Jupiter's fast rotation, deep atmosphere and internal heat drive enormous weather systems. The planet emits more heat than it receives from the Sun.

Jupiter's rings are made of dust, not ice, and are much harder to see. They were discovered by Voyager 1 in 1979.

Each moon experiences a different mix of heating, geology and radiation. Io is volcanic, Europa is icy, Ganymede is cratered and Callisto is ancient and heavily battered.

Io is heated by tidal flexing from Jupiter and orbital resonances with Europa and Ganymede. That constant squeezing melts rock and fuels hundreds of volcanoes.

Europa likely has a global subsurface ocean beneath its ice shell, kept liquid by tidal heating. Liquid water, chemical energy and rock-interaction make it a prime target.

Saturn is made mostly of hydrogen and helium, so its average density is less than water. If there were a bathtub large enough, Saturn would float in it.

The rings are made of countless icy particles orbiting in the same plane, and collisions keep them very thin. From Earth, that makes them look like a narrow line when edge-on.

Titan's temperature is low enough for methane and ethane to behave like water does on Earth. That lets it have clouds, rain, rivers and lakes of liquid hydrocarbons.

Methane in Uranus's atmosphere absorbs red light and reflects blue and green light. That gives the planet its pale blue-green colour.

Both planets have methane, but Neptune also has a thinner haze, letting the blue colour appear deeper. Differences in atmospheric composition and scattering change the shade.

Triton is likely a captured object from the Kuiper Belt, not a moon that formed with Neptune. Its retrograde orbit suggests it was pulled in later.

Solar heat turns comet ice into gas, releasing dust and vapour that form a tail. The solar wind and sunlight push the material away from the Sun.

Jupiter's gravity stirred up the region and prevented the small bodies there from merging into a planet. Collisions kept breaking material apart instead of building it up.

They keep falling around the Sun because gravity pulls them inward while their sideways motion carries them forward. This balance creates an orbit instead of a crash.

The Sun contains about 99.8% of the Solar System's total mass, so its gravity dominates the motion of everything else. That makes it the natural centre of the system.

The giant planets formed with large disks of material around them and had enough gravity to capture many objects. Their strong gravity also helped keep those moons in place.