Usually when asked what planet is closest to Earth, most will answer Venus; however, this may not be accurate.
Mercury, Venus and Earth come first; Mars follows; then Jupiter, Saturn, Uranus and Neptune are seen setting and rising after the Sun. These inferior planets set and rise after him.
Mercury
Mercury, the closest and smallest planet to our Sun, is an intensely dense rocky world dotted with impact craters. It has an extremely thin atmosphere made up primarily of hydrogen, helium and oxygen atoms; and is tidally locked to it via its axis being in constant contact. Because its day only lasts 59 Earth days per year compared with 88 on earth; additionally its lack of tilt prevents full sun coverage at either pole, effectively eliminating seasons altogether.
Mercury, our fastest planet in our Solar System, goes through apparent retrograde motion three to four times per year. According to astrology, Mercury rules communication; those who believe in planetary horoscopes should expect communication difficulties or roadblocks during its apparent retrograde motion phase.
Since the dawn of space exploration, numerous probes have explored Mercury, Venus, Earth and Mars; Jupiter, Saturn, Uranus and Neptune; with possible signs of an additional ninth planet such as Nibiru or Planet X; with more exploration to be conducted beyond these four planets in an asteroid belt or into gas giants Neptune and Pluto.
Venus
Venus is our solar system’s hottest planet. Sometimes referred to as Earth’s twin planet, due to their similar sizes and densities, their two worlds couldn’t be any different – though their atmospheres might resemble each other closely – they couldn’t be further apart! Venus’ thick toxic atmosphere traps heat that almost matches that of the Sun itself while its surface area is 50 times drier than Chile’s Atacama Desert.
Venus may appear obscured by a thick cloud cover, yet radar observations reveal an intricate landscape filled with mountains, volcanoes and ridges. Most notable features are two bright spots rising through the clouds to nearly 11 kilometers (7 miles). These spots likely represent broken tectonic plates that have separated to form rift zones consisting of many valleys and ridges.
As with Mercury, Venus’s hostile environment renders life on this planet impossible. Its thick clouds wreak havoc with spacecraft and within minutes melt and burn any that land on the surface. Yet despite such difficulties, numerous robotic missions have visited Venus such as Soviet Russia’s Venera series and NASA’s Akatsuki missions.
Earth
According to Caltech (opens in new tab), Earth lies at just the right distance from the Sun for liquid water to remain stable on its surface, unlike Mercury, Venus, or Mars. Sunlight takes about eight minutes to reach Earth’s interior; an immense layer of silicate and basaltic rocks lies underneath a thick outer crust moving slowly due to plate tectonics.
Earth is tilted with respect to the ecliptic plane, altering how much sunlight each of its hemispheres receives throughout the year and giving us seasons. Our solar system’s only planet known to harbor life thrives thanks to abundant flora and fauna species as well as plentiful oxygen supplies as well as its magnetic field’s deflecting harmful cosmic radiation rays.
Jupiter, Saturn, Uranus and Neptune are collectively known as gas giants because their composition primarily comprises hydrogen, helium and ammonia atoms. Each planet takes approximately 84 Earth years to orbit the Sun; their rings, blue hues and unique axial tilts stand out among their competitors.
Mars
Mars is one of our closest planetary neighbors and is easily identified using a telescope. The red planet features iron oxide dust covering its surface, while its atmosphere consists of thin carbon dioxide clouds. Like Earth, Martian polar caps consist of water which vary seasonally – closer to the Sun the southern cap may become much larger; otherwise their sizes remain nearly equal throughout the year.
Mars, unlike Venus, is a true terrestrial planet and therefore habitable for short periods. It rotates every 687 days and boasts two natural satellites called Deimos and Phobos – as seen here at its closest approach to Earth.
However, Uranus falls outside the four inner planets due to its highly elliptical orbit that sometimes passes close to Earth than Neptune itself. Because of this phenomenon, astronomers use an algorithmic formula in order to identify which terrestrial planet lies closest.
Jupiter
Jupiter, our fifth planet from the Sun and a gas giant approximately twice as massive as all of our Solar System combined, features an atmosphere rich with helium that is enveloped by hydrogen-containing layers. Jupiter rotates extremely rapidly completing one day in about 10 hours which creates bands in its outer atmosphere that frequently interact with one another creating stormy and turbulent zones on its borders.
Planet Jupiter boasts a faint ring system and at least 79 moons, four of which can be spotted through binoculars or small telescopes and known as Galilean moons after Galileo Galilei in 1610. Io is home to one of our Solar System’s most active volcanic environments while Europa and Ganymede may hide liquid water oceans beneath their icy shells.
Scientists theorize that Jupiter formed from material left over from the Sun and its siblings’ creation, pulling in dust and gas as it collected in an area roughly two-and-a-half times the size of Earth before being shaped into its current form with its core of nickel and iron.
Saturn
Saturn is the second-largest planet in our Solar System and, similar to Jupiter, a gas giant. The rest of Saturn formed alongside other planets 4.5 billion years ago when gravity pulled swirling gas and dust together into our Solar System. Saturn primarily comprises hydrogen and helium molecules which gives its appearance a yellow hue.
Saturn rotates rapidly, covering one day of rotation every 10.6 hours. However, its density is extremely low – 764 times less dense than water! Furthermore, Saturn is currently locked into orbit around its parent planet Jupiter so only one side of Saturn appears visible to us.
Cassini probe identified and named 53 natural satellites of Jupiter that resemble the Solar System as part of its miniature nature, including Enceladus with an icy shell and cryovolcanoes spewing geyser-like jets of water vapor, ice particles and molecular hydrogen into space. Cassini also detected methane at fractured surfaces – perhaps suggesting an ocean of liquid water exists there! Whether or not life exists remains to be seen.
Uranus
Before recently, it was thought that there were only six planets in our Solar System; however, more dwarf planets have since been identified. Uranus is the seventh planet from our Sun and an ice giant planet.
Saturn stands out among its fellow gas giants due to its unique composition: most of its mass lies within a hot dense fluid of “icy” materials such as water, ammonia and methane that flows above a small rocky core. This gives it its distinct blue-green hue.
Uranus stands out among our Solar System planets with a dramatic 98-degree tilt that creates extreme seasons. One pole receives direct sunlight while the other experiences long, cold winters; then they swap places again.
Uranus currently boasts 27 known moons, such as Cordelia (named for the fairy queen in Shakespeare’s play, A Midsummer Night’s Dream). There is also a banded region called the southern collar which may host additional bodies but are difficult to detect from Earth. Astronomers believe there may be even more, though.
Neptune
Neptune, the eighth planet from the Sun, is an immense gas giant with an orbit that takes 165 years. Like Uranus, Neptune possesses 13 known satellites and lies 30 times further from our Sun than Earth does.
Neptune’s atmosphere consists mainly of hydrogen, helium and methane – with its absorption of red light causing its hue to change to blue – making the planet appear bluer than ever. Like Uranus and Saturn or Jupiter, Neptune also boasts rings; though their patterns are slightly diffuse.
Triton is the seventh-largest moon in our solar system and the biggest Neptune moon by volume. Unlike most of its fellow satellites, however, Triton orbits Neptune retrogradely, unlike all of its peers. Astronomers have identified 14 other Neptune satellites such as Naiad Thalassa Despina Larissa and Hippocamp. Neptune comes closest to our Sun at its perihelion while farthest at aphelion.