What is the nearest planet to the sun

Which planet is nearest to the sun?

a. Neptune B. Jupiter C. Venus D. Mercury

ANSWER: MERCURY

That’s why its surface is ragged and scarred with relatively small to large craters, just like the moon.

Interesting Facts about Mercury

\u2022 The Smallest Planet

\u2022 Has the largest core, relative to its size than any other planet in the Solar system

\u2022 Doesn’t have an atmosphere

\u2022 The first and strongest evidence of Eintein’s theory of Relativity, due to its irregular orbit around the Sun.

Click the link below to read more about the Solar System

NEAREST PLANET TO THE SUN

ANSWER: MERCURY

Planet Mercury is the first and closest planet from the sun (67.893 million km). Planet Mercury is too small to hold its own legitimate atmosphere, so there is nothing to protect it from large chunks of interstellar bodies, such as meteors.

That’s why its surface is ragged and scarred with relatively small to large craters, just like the moon.

Interesting Facts about Mercury

• The Smallest Planet

• Has the largest core, relative to its size than any other planet in the Solar system

• Doesn’t have an atmosphere

• The first and strongest evidence of Eintein’s theory of Relativity, due to its irregular orbit around the Sun.

Mercury: The smallest and closest planet to the sun

Mercury orbits the sun faster than all the other planets in the solar system.

Mercury is the closest planet to the sun and the smallest planet in our solar system. The tiny planet has no moon of its own and zips around the sun faster than all the other planets, which is why the Romans named it after their swift-footed messenger god.

The Sumerians also knew of Mercury since at least 5,000 years ago. It was often associated with Nabu, the god of writing, according to a site connected to NASA’s MESSENGER (Mercury Surface, Space Environment, Geochemistry and Ranging) mission. Mercury was also given separate names for its appearance as both a morning star and as an evening star. Greek astronomers knew, however, that the two names referred to the same body, and Heraclitus, around 500 B.C., correctly thought that both Mercury and Venus orbited the sun, not Earth.

Mercury is the second densest planet after Earth, with a huge metallic core roughly 2,200 to 2,400 miles (3,600 to 3,800 kilometers) wide, or about 75% of the planet’s diameter. In comparison, Mercury’s outer shell is only 300 to 400 miles (500 to 600 km) thick. The combination of its massive core and composition, which includes an abundance of volatile elements, has left scientists puzzled for years.

Mercury: Temperature, size and surface activity

Because the planet is so close to the sun, Mercury’s surface temperature can reach a scorching 840 degrees Fahrenheit (450 degrees Celsius). However, since this world doesn’t have much of a real atmosphere to entrap any heat, at night temperatures can plummet to minus 275 degrees Fahrenheit (minus degrees 170 Celsius), a temperature swing of more than 1,100 degrees Fahrenheit (600 degrees Celsius), the greatest in the solar system.

Mercury is the smallest planet — it is only slightly larger than Earth’s moon. Since it has no significant atmosphere to stop impacts, the planet is pockmarked with craters. About 4 billion years ago, an asteroid roughly 60 miles (100 km) wide struck Mercury with an impact equal to 1 trillion 1-megaton bombs, creating a vast impact crater roughly 960 miles (1,550 km) wide. Known as the Caloris Basin, this crater could hold the entire state of Texas. Another large impact may have helped create the planet’s odd spin, according to research in 2011.

As close to the sun as Mercury is, in 2012, NASA’s MESSENGER spacecraft discovered water ice in the craters around its north pole in 2017, where regions may be permanently shaded from the heat of the sun. The southern pole may also contain icy pockets, but MESSENGER’s orbit did not allow scientists to probe the area. Comets or meteorites may have delivered ice there, or water vapor may have outgassed from the planet’s interior and frozen out at the poles.

Average distance from the sun: 35,983,095 miles (57,909,175 km). By comparison: 0.38 Earth’s distance from the sun

Perihelion (closest approach to sun): 28,580,000 miles (46,000,000 km). By comparison: 0.313 times that of Earth

Aphelion (farthest distance from sun): 43,380,000 miles (69,820,000 km). By comparison: 0.459 times that of Earth

Day length: 58.646 Earth days

Color: Gray

As if Mercury isn’t small enough, it not only shrank in its past but is continuing to shrink today, according to a 2016 report. The tiny planet is made up of a single continental plate over a cooling iron core. As the core cools, it solidifies, reducing the planet’s volume and causing it to shrink. The process crumpled the surface, creating lobe-shaped scarps or cliffs, some hundreds of miles long and soaring up to a mile high, as well as Mercury’s «Great Valley,» which at about 620 miles long, 250 miles wide and two miles deep (1,000 by 400 by 3.2 km) is larger than Arizona’s famous Grand Canyon and deeper than the Great Rift Valley in East Africa.

«The young age of the small scarps means that Mercury joins Earth as a tectonically active planet with new faults likely forming today as Mercury’s interior continues to cool and the planet contracts,» Tom Watters, Smithsonian senior scientist at the National Air and Space Museum in Washington, D.C., said in a NASA statement.

Indeed, a 2016 study of cliffs on Mercury’s surface suggested the planet may still rumble with earthquakes, or «Mercuryquakes.» In addition, in the past, Mercury’s surface was constantly reshaped by volcanic activity. However, another 2016 study (opens in new tab) suggested Mercury’s volcano eruptions likely ended about 3.5 billion years ago.

One 2016 study suggested that Mercury’s surface features can generally be divided into two groups — one consisting of older material that melted at higher pressures at the core-mantle boundary, and the other of newer material that formed closer to Mercury’s surface. Another 2016 study found that the dark hue of Mercury’s surface is due to carbon. This carbon wasn’t deposited by impacting comets, as some researchers suspected — instead, it may be a remnant of the planet’s primordial crust.

Mercury’s magnetic field

A completely unexpected discovery made by Mariner 10 was that Mercury possessed a magnetic field. Planets theoretically generate magnetic fields only if they spin quickly and possess a molten core. But Mercury takes 59 days to rotate and is so small — just roughly one-third Earth’s size — that its core should have cooled off long ago.

«We had figured out how the Earth works, and Mercury is another terrestrial, rocky planet with an iron core, so we thought it would work the same way,» Christopher Russell, a professor at the University of California, Los Angeles, said in a University of California, Los Angeles statement.

An unusual interior could help to explain the differences in Mercury’s magnetic field when compared to Earth. Observations from MESSENGER revealed that the planet’s magnetic field is approximately three times stronger at its northern hemisphere than at its southern. Russell co-authored a model that suggests that Mercury’s iron core may be turning from liquid to solid at the core’s outer boundary rather than the inner.

«It’s like a snow storm in which the snow formed at the top of the cloud and middle of the cloud and the bottom of the cloud too,» said Russell. «Our study of Mercury’s magnetic field indicates iron is snowing throughout this fluid that is powering Mercury’s magnetic field.»

Although Mercury’s magnetic field is just 1% the strength of Earth’s, it is very active. The magnetic field in the solar wind — the charged particles streaming off the sun — periodically touches upon Mercury’s field, creating powerful magnetic tornadoes that channel the fast, hot plasma of the solar wind down to the planet’s surface.

Does Mercury have an atmosphere?

The atmosphere of Mercury is a «surface-bound exosphere, essentially a vacuum.» It contains 42% oxygen, 29% sodium, 22% hydrogen, 6% helium, 0.5% potassium, with possible trace amounts of argon, carbon dioxide, water, nitrogen, xenon, krypton and neon, according to NASA.

Mercury’s orbit

Mercury speeds around the sun every 88 Earth days, traveling through space at nearly 112,000 mph (180,000 km/h), faster than any other planet. Its oval-shaped orbit is highly elliptical, taking Mercury as close as 29 million miles (47 million km) and as far as 43 million miles (70 million km) from the sun. If one could stand on Mercury when it is nearest to the sun, it would appear more than three times as large as it does when viewed from Earth.

Oddly, due to Mercury’s highly elliptical orbit and the 59 Earth-days or so it takes to rotate on its axis, when on the scorching surface of the planet, the sun appears to rise briefly, set, and rise again before it travels westward across the sky. At sunset, the sun appears to set, rise again briefly, and then set again.

Research and exploration

The first spacecraft to visit Mercury was Mariner 10, which imaged about 45% of the surface and detected its magnetic field.

NASA’s MESSENGER orbiter was the second spacecraft to visit Mercury. When it arrived in March 2011, it became the first spacecraft to orbit the planet. The mission came to an abrupt end on April 30, 2015, when the spacecraft, which had run out of fuel, purposely crashed onto the planet’s surface for scientists to observe the results.

In 2012, scientists discovered a group of meteorites in Morocco that they think could have originated from the planet Mercury. If so, it would make the rocky planet a member of a very select club with samples available on Earth; only the moon, Mars and the large asteroid Vesta have verified rocks in human laboratories.

In 2016, scientists released the first-ever global digital-elevation model of Mercury, which combined more than 10,000 images acquired by MESSENGER to take viewers across the wide-open spaces of the tiny world. The model revealed the planet’s highest and lowest points — the highest is found just south of Mercury’s equator, sitting 2.78 miles (4.48 km) above the average elevation of the planet, while the lowest point resides in Rachmaninoff basin, the suspected home of some of the most recent volcanic activity on the planet, and lies 3.34 miles (5.38 km) below the landscape average.

In 2018, a new Mercury explorer was launched. The BepiColombo mission jointly operated by the European and Japanese space agencies is composed of two spacecraft — Mercury Planetary Orbiter and the Mercury Magnetospheric Orbiter — that, after a long trek to Mercury, will split up to better understand the tiny world. The European Space Agency’s segment of the mission will focus on studying Mercury’s surface while the Japan Aerospace Exploration Agency’s portion will focus on the planet’s strange magnetosphere.

In 2021, BepiColumbo captured its first views of Mercury during a gravity assist flyby. BepiColumbo is scheduled to arrive at Mercury in late 2025, and gather data during its one-year nominal mission with the possibility of a one-year extension, according to ESA.

Mercury quiz

Additional resources

Bibliography

Strom, Robert G., and Ann L. Sprague. Exploring Mercury: the iron planet. (opens in new tab) New York: Springer, 2003.

Hauck, Steven A., and Catherine L. Johnson. «Mercury: Inside the iron planet. (opens in new tab) » Elements: An International Magazine of Mineralogy, Geochemistry, and Petrology 15.1 (2019): 21-26.

Join our Space Forums to keep talking space on the latest missions, night sky and more! And if you have a news tip, correction or comment, let us know at: community@space.com.

Scott is a staff writer for How It Works magazine. He holds a masters degree in science and environmental journalism and a bachelor’s degree in conservation biology from the University of Lincoln.

Planets In Order: By Size And Distance From The Sun

Kate Broome PRO INVESTOR

The planets in order from the sun are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and finally the dwarf planet Pluto.

Most people have at least heard about our solar system and the planets in it. Our solar system is usually gone over in elementary school, so you might just need a refresher course about the planets in order in our solar system. Check out this guide to learn all about the planets, their size, and their order in the solar system.

Without Jupiter cleaning out the early solar system, the Earth would be pock-marked with meteor collisions. We would suffer from asteroid impacts every day. CNN studios would probably be a gigantic crater it if wasn’t for Jupiter. – Michio Kaku

Our Solar System’s Planets in Order

Our solar system revolves around the sun, hence the name solar system. In our system, we have 4 terrestrial planets, 4 gas giants, and a mysterious 9th planet. Let’s go over them, but first, here’s a quick rundown of each planet in order of size and distance from the sun.

Planets In Order Of Size:

Planets in order of distance from the Sun:

Planets In Order Of Mass:

The Terrestrial Planets In Order

1. Mercury

The planet Mercury. Image source: NASA

The first planet in our solar system is Mercury. It is slightly smaller than Earth’s moon and is extremely hot. As in 850 Fahrenheit or so. NASA launched the MESSENGER probe in 2004 to learn all about Mercury since we don’t really know much about it.

Facts:

2. Venus

Venus is the second planet in our solar system and is named after the Roman goddess of love. Venus is actually hotter than Mercury and is abundant in greenhouse gasses. Venus is similar to Earth in size and general structure. The Soviet Union sent the probes in the Venera series to learn more about Venus that helped us learn a bit about Venus’ atmosphere, and Venera probes are actually the first manmade devices to enter another planet’s atmosphere. Cool, huh?

3. Earth

The Earth. Image source: NASA

The Earth is the third planet from the sun and is the planet that we call home. It is the only planet, that we know of, that can maintain and support life. Earth was formed around 4 billion years ago and has gone through many changes in that time period. Earth has 4 seasons because of the tilt of Earth’s axis, and our oceans have tides because of the gravitational pull of the moon. The moon is our only natural satellite.

Facts:

4. Mars

The planet Mars. Image source: NASA

Mars is the fourth planet from the sun and is the last terrestrial planet. Mars is the focus of NASA and SpaceX because it is the only planet that humans can somewhat survive on (with the help of technology and science, of course). Mars is very cold and is currently inhabited solely by robots. Mars’ gravity is 1/3 of that on Earth, but it is enough for humans to live on.

Facts:

The Gas Giants

The remaining planets are separated from the terrestrial planets by the asteroid belt. All of the gas giants have some type of ring surrounding it.

5. Jupiter

Jupiter as seen from the Voyager space probe. Image source: NASA/JPL

Jupiter is the first of the gas giants and is the largest planet in our solar system. We got our first images of Jupiter up close from the space probe Voyager, which is actually still flying through space outside of our solar system. Jupiter is comprised primarily of hydrogen and helium and it is still unknown if Jupiter’s core is solid or not. If Jupiter were about 80 times its size then it would be considered a star, just like our sun. Jupiter has a lot of natural satellites surrounding it, which are believed to be from meteors. Jupiter actually protects the Earth from meteors, so in a way, Jupiter is kind of Earth’s protective big brother.

Facts:

6. Saturn

Saturn as seen from Voyager. This is our first up-close image of Saturn. Image source: NASA

Saturn is the second gas giant and is our second largest planet. Saturn was also seen by Voyager as you can see in the picture above. Saturn is most recognizable by its rings that are made up of ice and space debris. Saturn is comprised of hydrogen and helium, but it is unknown whether Saturn has a solid core (just like Jupiter). Saturn also has quite a few natural satellites as well.

Facts:

7. Uranus

Uranus as seen by Voyager. Image source: NASA

Uranus is the seventh planet from the sun and is the third of the gas giants. Just like Jupiter and Saturn, the Voyager probe gave us our first look at the planet in 1986. Our first images of Uranus came on the same day that the Challenger blew up, killing the 7 astronauts on board.

“The crew of the space shuttle Challenger honored us by the manner in which they lived their lives. We will never forget them, nor the last time we saw them, this morning, as they prepared for their journey and waved good-bye and ‘slipped the surly bonds of earth’ to touch the face of God. ” — Ronald Reagan

Uranus has a very serious tilt to where the equator is actually at a right angle to the orbit. It is believed that Uranus had a collision with another planet, causing its tilt. The planet is made up of helium and hydrogen and is believed to have icy elements on its surface. Uranus’ core is thought to be extremely icy, instead of being molten like other planets.

Facts:

8. Neptune

Neptune as seen from Voyager. Image source: NASA

Neptune is the eighth planet from the sun and is the last of the gas giants. It is comprised of hydrogen and helium primarily and is surrounded by a thick cloud layer that houses winds faster than the speed of sound. The blue coloring is produced by an abundance of methane and it is unknown if Neptune’s core is solid. Neptune was predicted to exist by math before we actually saw it, making it the first predicted planet.

Facts:

Pluto

The dwarf planet Pluto. Image source: NASA

Pluto used to be the ninth planet in our solar system but was removed in 2006 because in all the time we’ve known about Pluto is has yet to complete an orbit around the sun. Now people have petitioned to bring Pluto back to its planet-hood, but who knows if that will happen. Pluto is only 1,400 miles wide, making it smaller than the United States. NASA sent a probe to Pluto in 2006 named New Horizons and it completed its Pluto flyby in 2015.

Planet Nine

The “last” planet on our list is Planet Nine. We have never seen this final planet, but scientists are predicting it exists (just as they did with Neptune). Nothing is actually known about Planet Nine, just that it probably exists. In the image above the bright star is representative of the sun, which is pretty dang far. This planet was predicted in 2014 after astronomers noticed that Neptune’s orbit was slightly different than some other planets. There is a theory that this planet is massive and at one point had a collision with Jupiter that “bounced” it farther away. It is merely a theory, but it’s fascinating nonetheless.

About Kate Broome PRO INVESTOR

Kate is a graduate of Texas A&M University with a Bachelor’s degree and is currently working on getting her Master’s degree at Southern New Hampshire University. She loves to read and learn about all things space, a fanatic of NASA and the latest space science news. She currently lives in Texas with her two pit bulls, Lennox and Bentley.

The Latest

From the surface of Mercury, the Sun would appear more than three times as large as it does when viewed from Earth, and the sunlight would be as much as seven times brighter. Despite its proximity to the Sun, Mercury is not the hottest planet in our solar system – that title belongs to nearby Venus, thanks to its dense atmosphere.

Because of Mercury’s elliptical – egg-shaped – orbit, and sluggish rotation, the Sun appears to rise briefly, set, and rise again from some parts of the planet’s surface. The same thing happens in reverse at sunset.

Go farther: Explore Mercury In Depth ›

10 Need-to-Know Things About Mercury

Small World

Mercury is the smallest planet in our solar system – only slightly larger than Earth’s Moon.

Inside Track

Mercury is the planet that orbits the closest to the Sun.

Fastest Planet

Mercury is the fastest planet in our solar system – traveling through space at nearly 29 miles (47 kilometers) per second. The closer a planet is to the Sun, the faster it travels. Since Mercury is the fastest planet and has the shortest distance to travel around the Sun, it has the shortest year of all the planets in our solar system – 88 days.

First Look at Mercury’s Previously Unseen Side

Rough Surface

Mercury is a rocky planet, also known as a terrestrial planet. Mercury has a solid, cratered surface, much like the Earth’s moon.

Can’t Breathe There

Mercury’s thin atmosphere, or exosphere, is composed mostly of oxygen (O2), sodium (Na), hydrogen (H2), helium (He), and potassium (K).

Moonless

Mercury has no moons.

Ringless

There are no rings around Mercury.

Tough Place for Life

It is unlikely that life as we know it could survive on Mercury due to solar radiation, and extreme temperatures.

Big Sun

Standing on Mercury’s surface at its closest approach to the Sun, our star would appear more than three times larger than it does on Earth.

Robotic Visitors

Two NASA missions have explored Mercury: Mariner 10 was the first to fly by Mercury, and MESSENGER was the first to orbit. ESA’s BepiColombo is on its way to Mercury.

Mariner 10’s First Image of Mercury

Pop Culture

The smallest planet in our solar system has a big presence in our collective imagination. Scores of science fiction writers have been inspired by Mercury, including Isaac Asimov, C. S. Lewis, Ray Bradbury, Arthur C. Clarke, and H. P. Lovecraft. Television and film writers, too, have found the planet an ideal location for storytelling. In the animated television show «Invader Zim,» Mercury is turned into a prototype giant spaceship by the extinct Martians. And in the 2007 film «Sunshine,» the Icarus II spacecraft goes into orbit around Mercury to rendezvous with the Icarus I.

In the comic strip «Calvin and Hobbes,» Calvin and his classmate Susie give a presentation about Mercury, in which Calvin’s contribution is full of questionable information: «The planet Mercury was named after a Roman god with winged feet,» says Calvin. «Mercury was the god of flowers and bouquets, which is why today he is a registered trademark of FTD florists. Why they named a planet after this guy, I can’t imagine.»

Kid-Friendly Mercury

Mercury is the smallest planet in our solar system. It’s a little bigger than Earth’s Moon. It is the closest planet to the Sun, but it’s actually not the hottest. Venus is hotter.

Along with Venus, Earth, and Mars, Mercury is one of the rocky planets. It has a solid surface that is covered with craters like our Moon. It has a thin atmosphere, and it doesn’t have any moons. Mercury likes to keep things simple.

Mercury spins slowly compared to Earth, so one day lasts a long time. Mercury takes 59 Earth days to make one full rotation. But a year on Mercury goes fast. Because it’s the closest planet to the sun, it goes around the Sun in just 88 Earth days.

Visit NASA Space Place for more kid-friendly facts.

Solar system planets, order and formation: A guide

Explore our solar system’s planets from the nearest to the sun to the furthest.

The order of the planets in the solar system, starting nearest the sun and working outward is the following: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and then the possible Planet Nine.

The solar system extends from the sun, called Sol by the ancient Romans, and goes past the four inner planets, through the asteroid belt to the four gas giants and on to the disk-shaped Kuiper Belt and far beyond to the teardrop-shaped heliopause.

Scientists estimate that the edge of the solar system is about 9 billion miles (15 billion kilometers) from the sun. Beyond the heliopause lies the giant, spherical Oort Cloud, which is thought to surround the solar system.

Ever since the discovery of Pluto in 1930, kids grew up learning that the solar system has nine planets. That all changed in the late 1990s when astronomers started arguing about whether Pluto was indeed a planet. In a highly controversial decision, the International Astronomical Union ultimately decided in 2006 to designate Pluto as a «dwarf planet,» reducing the list of the solar system’s true planets to just eight.

If you insist on including Pluto, it would come after Neptune on the list. Pluto is truly way out there and on a wildly tilted, elliptical orbit (two of the several reasons it was demoted).

Astronomers, however, are still hunting for another possible planet in our solar system, a true ninth planet, after mathematical evidence of its existence was revealed on Jan. 20, 2016. The alleged «Planet Nine,» also called «Planet X,» is believed to be about 10 times the mass of Earth and 5,000 times the mass of Pluto.

Types of planets in the solar system

The inner four planets closest to the sun — Mercury, Venus, Earth and Mars — are often called the «terrestrial planets» because their surfaces are rocky. Pluto also has a rocky, albeit frozen, surface but has never been grouped with the four terrestrials.

The four large outer worlds — Jupiter, Saturn, Uranus and Neptune — are sometimes called the Jovian or «Jupiter-like» planets because of their enormous size relative to the terrestrial planets. They’re also mostly made of gases like hydrogen, helium and ammonia rather than of rocky surfaces, although astronomers believe some or all of them may have solid cores.

If you were to order the planets by size from smallest to largest they would be Mercury, Mars, Venus, Earth, Neptune, Uranus, Saturn and Jupiter.

What is (and isn’t) a planet?

The IAU defines (opens in new tab) a true planet as a body that circles the sun without being some other object’s satellite; is large enough to be rounded by its own gravity (but not so big that it begins to undergo nuclear fusion, like a star); and has «cleared its neighborhood» of most other orbiting bodies.

But that restrictive definition helped isolate what should and should not be considered a planet — a problem that arose as astronomers discovered more and more planet-like objects in the solar system. Pluto was among the bodies that didn’t make the cut and was re-classified as a dwarf planet.

The problem with Pluto, aside from its small size and offbeat orbit, is that it doesn’t clear its neighborhood of debris — it shares its space with lots of other objects in the Kuiper Belt. Still, the demotion of Pluto remains controversial.

The IAU planet definition also put other small, round worlds into the dwarf planet category, including the Kuiper Belt objects Eris, Haumea and Makemake.

Ceres, a round object in the Asteroid Belt between Mars and Jupiter, also got the boot. Ceres was considered a planet when it was discovered in 1801, but it was later deemed to be an asteroid. That still didn’t quite fit because it was so much larger (and rounder) than the other asteroids. Astronomers instead deemed it a dwarf planet in 2006, although some astronomers like to consider Ceres as a 10th planet (not to be confused with Nibiru or Planet X).

Below is a brief overview of the eight true planets in our solar system, moving from that closest to the sun to the farthest from the sun:

The sun

The sun is by far the largest object in our solar system, containing 99.8% of the solar system’s mass. It sheds most of the heat and light that makes life possible on Earth and possibly elsewhere. Planets orbit the sun in oval-shaped paths called ellipses, with the sun slightly off-center of each ellipse.

NASA has a fleet of spacecraft observing the sun, such as the Parker Solar Probe, to learn more about its composition, and to make better predictions about space weather and its effect on Earth.

Mercury: The closest planet to the sun

Mercury is the closest planet to the sun and the smallest planet in the solar system — it is only a little larger than Earth’s moon. Mercury zips around the sun in only 88 days and because it is so close to our star (about two-fifths the distance between Earth and the sun).

Mercury experiences dramatic changes in its day and night temperatures. Mercury temperatures can reach a scorching 840 F (450 C) in the day, which is hot enough to melt lead. Meanwhile, on the night side, temperatures drop to minus 290 F (minus 180 C).

— Discovery: Known to the ancient Greeks and visible to the naked eye

— Named for the messenger of the Roman gods

— Diameter: 3,031 miles (4,878 km)

— Orbit: 88 Earth days

— Day: 58.6 Earth days

— Number of moons: 0

Mercury’s atmosphere is very thin and primarily composed of oxygen, sodium, hydrogen, helium and potassium. Because the atmosphere is so thin it cannot incoming meteors, its surface is therefore pockmarked with craters, just like our moon.

Over its four-year mission, NASA’s MESSENGER spacecraft revealed incredible discoveries that challenged astronomers’ expectations. Among those findings was the discovery of water ice and frozen organic compounds at Mercury’s north pole and that volcanism played a major role in shaping the planet’s surface.

Venus: Earth’s solar system twin

Venus is the second planet from the sun and is the hottest planet in the solar system. Its thick atmosphere is extremely toxic and composed of sulfuric acid clouds, the planet is an extreme example of the greenhouse effect.

— Discovery: Known to the ancient Greeks and visible to the naked eye

— Named for the Roman goddess of love and beauty

— Diameter: 7,521 miles (12,104 km)

— Orbit: 225 Earth days

— Day: 241 Earth days

— Number of moons: 0

The average temperature on Venus’ surface is 900 F (465 C). At 92 bar, the pressure at the surface would crush and kill you. And oddly, Venus spins slowly from east to west, the opposite direction of most of the other planets.

Venus is sometimes referred to as Earth’s twin as they are similar in size and radar images beneath its atmosphere reveal numerous mountains and volcanoes. But beyond that, the planets could not be more different.

The Greeks believed Venus was two different objects — one in the morning sky and another in the evening. Because it is often brighter than any other object in the sky, Venus has generated many UFO reports.

Earth: Our home planet, filled with life

Earth, our home planet, is the third planet from the sun. It is a water world with two-thirds of the planet covered by water. Earth’s atmosphere is rich in nitrogen and oxygen and it is the only world known to harbor life.

— Name originates from «Die Erde,» the German word for «the ground.»

— Diameter: 7,926 miles (12,760 km)

— Orbit: 365.24 days

— Day: 23 hours, 56 minutes

— Number of moons: 1

Earth rotates on its axis at 1,532 feet per second (467 meters per second) — slightly more than 1,000 mph (1,600 kph) — at the equator. The planet zips around the sun at more than 18 miles per second (29 km per second).

Mars: The solar system’s Red Planet

Mars is the fourth planet from the sun. It is a cold, desert-like planet covered in iron oxide dust that gives the planet its signature red hue. Mars shares similarities with Earth: It is rocky, has mountains, valleys and canyons, and storm systems ranging from localized tornado-like dust devils to planet-engulfing dust storms.

Substantial scientific evidence suggests that Mars at one point billions of years ago was a much warmer, wetter world, rivers and maybe even oceans existed. Although Mars’ atmosphere is too thin for liquid water to exist on the surface for any length of time, remnants of that wetter Mars still exist today. Sheets of water ice the size of California lie beneath Mars’ surface, and at both poles are ice caps made in part of frozen water.

— Discovery: Known to the ancient Greeks and visible to the naked eye

— Named for the Roman god of war

— Diameter: 4,217 miles (6,787 km)

— Day: Just more than one Earth day (24 hours, 37 minutes)

— Number of moons: 2

Scientists also think ancient Mars would have had the conditions to support life like bacteria and other microbes. Hope that signs of this past life — and the possibility of even current lifeforms — may exist on the Red Planet has driven numerous Mars missions and the Red Planet is now one of the most explored planets in the solar system.

The asteroid belt

Between Mars and Jupiter lies the asteroid belt. Asteroids are minor planets, and according to NASA there are approximately between 1.1 and 1.9 million asteroids (opens in new tab) in the main asteroid belt larger than 0.6 miles (1 km) in diameter and millions more smaller asteroids.

The dwarf planet Ceres, about 590 miles (950 km) in diameter, resides here. A number of asteroids have orbits that take them closer into the solar system that sometimes lead them to collide with Earth or the other inner planets.

Jupiter: The largest planet in our solar system

— Discovery: Known to the ancient Greeks and visible to the naked eye

— Named for the ruler of the Roman gods

— Diameter: 86,881 miles (139,822 km)

— Orbit: 11.9 Earth years

— Day: 9.8 Earth hours

— Number of moons: 79 (53 confirmed, 26 provisional)

Its swirling clouds are colorful due to different types of trace gases including ammonia ice, ammonium hydrosulfide crystals as well as water ice and vapor.

A famous feature in its swirling clouds is Jupiter’s Great Red Spot, a giant storm more than 10,000 miles wide, first observed in 1831 by amateur astronomer Samuel Heinrich Schwabe. It has raged at more than 400 mph for the last 150 years, at least.

Jupiter has a strong magnetic field, and with 75 moons, including the largest moon in the solar system, Ganymede.

Saturn: The ringed jewel of the solar system

Saturn is the sixth planet from the sun and is famous for its large and distinct ring system. Though Saturn is not the only planet in the solar system with rings.

— Discovery: Known to the ancient Greeks and visible to the naked eye

— Named for Roman god of agriculture

— Diameter: 74,900 miles (120,500 km)

— Orbit: 29.5 Earth years

— Day: About 10.5 Earth hours

— Number of moons: 82 (53 confirmed, 29 provisional)

If you put Saturn in a bathtub it would float as Saturn has an average density that is less than water. You’d just need to find a bathtub big enough…

When polymath Galileo Galilei first studied Saturn in the early 1600s, he thought it was an object with three parts: a planet and two large moons on either side. Not knowing he was seeing a planet with rings, the stumped astronomer entered a small drawing — a symbol with one large circle and two smaller ones — in his notebook, as a noun in a sentence describing his discovery. More than 40 years later, Christiaan Huygens proposed that they were rings.

The rings are made of ice and rock and scientists are not yet sure how they formed. The gaseous planet is mostly hydrogen and helium and has numerous moons.

Uranus: The tilted, sideways planet in our solar system

Uranus is the seventh planet from the sun and is a bit of an oddball.

It has clouds made of hydrogen sulfide, the same chemical that makes rotten eggs smell so foul. It rotates from east to west like Venus. But unlike Venus or any other planet, its equator is nearly at right angles to its orbit — it basically orbits on its side.

— Discovery: 1781 by William Herschel (was originally thought to be a star)

— Named for the personification of heaven in ancient myth

— Diameter: 31,763 miles (51,120 km)

— Orbit: 84 Earth years

— Day: 18 Earth hours

— Number of moons: 27

Astronomers believe an object twice the size of Earth collided with Uranus roughly 4 billion years ago, causing Uranus to tilt. That tilt causes extreme seasons that last 20-plus years, and the sun beats down on one pole or the other for 84 Earth-years at a time.

The collision is also thought to have knocked rock and ice into Uranus’ orbit. These later became some of the planet’s 27 moons. Methane in Uranus’ atmosphere gives the planet its blue-green tint. It also has 13 sets of faint rings.

Uranus holds the record for the coldest temperature ever measured in the solar system — minus 371.56 degrees F (minus 224.2 degrees C). The average temperature of Uranus is minus 320 degrees Fahrenheit (-195 degrees Celsius).

Neptune: A giant, stormy blue planet

Neptune is the eighth planet from the sun and is on average the coldest planet in the solar system. The average temperature of Neptune at the top of the clouds is minus 346 degrees Fahrenheit (minus 210 degrees Celsius).

— Discovery: 1846

— Named for the Roman god of water

— Diameter: 30,775 miles (49,530 km)

— Orbit: 165 Earth years

— Day: 19 Earth hours

— Number of moons: 14

Neptune is approximately the same size as Uranus and is known for its supersonic strong winds. The planet is more than 30 times as far from the sun as Earth.

Neptune was the first planet predicted to exist by using math, rather than being visually detected. Irregularities in the orbit of Uranus led French astronomer Alexis Bouvard to suggest some other planet might be exerting a gravitational tug. German astronomer Johann Galle used calculations to help find Neptune in a telescope. Neptune is about 17 times as massive as Earth and has a rocky core.

Trans-Neptunian region

Astronomers had long suspected that a band of icy material known as the Kuiper Belt existed past the orbit of Neptune extending from about 30 to 55 times the distance of Earth to the sun, and from the last decade of the 20th century up to now, they have found more than a thousand of such objects. Scientists estimate the Kuiper Belt is likely home to hundreds of thousands of icy bodies larger than 60 miles (100 km) wide, as well as an estimated trillion or more comets.

Pluto, now considered a dwarf planet, dwells in the Kuiper Belt. It is not alone — recent additions include Makemake, Haumea and Eris. Another Kuiper Belt object dubbed Quaoar is probably massive enough to be considered a dwarf planet, but it has not been classified as such yet. Sedna, which is about three-fourths the size of Pluto, is the first dwarf planet discovered in the Oort Cloud. NASA’s New Horizons mission performed history’s first flyby of the Pluto system on July 14, 2015.

Pluto: Once a planet, now a dwarf planet

Pluto was once the ninth planet from the sun and is unlike any other planet in the solar system.

— Discovery: 1930 by Clyde Tombaugh

— Named for the Roman god of the underworld, Hades

— Diameter: 1,430 miles (2,301 km)

— Orbit: 248 Earth years

— Day: 6.4 Earth days

— Number of moons: 5

It is smaller than Earth’s moon; its orbit is highly elliptical, falling inside Neptune’s orbit at some points and far beyond it at others; and Pluto’s orbit doesn’t fall on the same plane as all the other planets — instead, it orbits 17.1 degrees above or below.

It is smaller than Earth’s moon; its orbit is highly elliptical, falling inside Neptune’s orbit at some points and far beyond it at others; and Pluto’s orbit doesn’t fall on the same plane as all the other planets — instead, it orbits 17.1 degrees above or below, taking 288 years to complete a single orbit according to ESA.

From 1979 until early 1999, Pluto had been the eighth planet from the sun. Then, on Feb. 11, 1999, it crossed Neptune’s path and once again became the solar system’s most distant planet — until it was redefined as a dwarf planet. It’s a cold, rocky world with a tenuous atmosphere.

Scientists thought it might be nothing more than a hunk of rock on the outskirts of the solar system. But when NASA’s New Horizons mission performed history’s first flyby of the Pluto system on July 14, 2015, it transformed scientists’ view of Pluto.

Pluto is a very active ice world that’s covered in glaciers, mountains of ice water, icy dunes and possibly even cryovolcanoes that erupt icy lava made of water, methane or ammonia.

Planet Nine: A planet search at solar system’s edge

In 2016, researchers proposed the possible existence of a ninth planet, for now, dubbed «Planet Nine» or Planet X. The planet is estimated to be about 10 times the mass of Earth and to orbit the sun between 300 and 1,000 times farther than the orbit of the Earth.

Scientists have not seen Planet Nine. They inferred its existence by its gravitational effects on other objects in the Kuiper Belt, a region at the fringe of the solar system that is home to icy rocks left over from the birth of the solar system. Also called trans-Neptunian objects, these Kuiper Belt objects have highly elliptical or oval orbits that align in the same direction.

A hypothesis proposed in September 2019 on the pre-print server arXiv suggests Planet Nine might not be a planet at all. Instead, Jaku Scholtz of Durham University and James Unwin of the University of Illinois at Chicago speculate it could be a primordial black hole that formed soon after the Big Bang and that our solar system later captured, according to Newsweek. Unlike black holes that form from the collapse of giant stars, primordial black holes are thought to have formed from gravitational perturbations less than a second after the Big Bang, and this one would be so small (5 centimeters in diameter) that it would be challenging to detect.

Astronomers continue to come up empty in their search for Planet 9. A recent 2022 sky survey using the 6-meter Atacama Cosmology Telescope (ACT) in Chile found thousands of tentative candidate sources but none could be confirmed.

The edge of the solar system

Past the Kuiper Belt is the very edge of the solar system, the heliosphere, a vast, teardrop-shaped region of space containing electrically charged particles given off by the sun. Many astronomers think that the limit of the heliosphere, known as the heliopause, is about 9 billion miles (15 billion km) from the sun.

Solar system formation and discovery

The heat and pressure eventually became so high that hydrogen atoms began to combine to form helium. The nuclear reactions released vast amounts of energy and our sun was formed.

The sun accumulated about 99% of the available matter and the remaining material further from the sun formed smaller clumps inside the spinning disk. Some of these clumps gained enough mass that their gravity shaped them into spheres, becoming planets, dwarf planets and moons. Other leftover pieces became asteroids, comets and smaller moons that make up our solar system.

For millennia, astronomers have followed points of light that seemed to move among the stars. The ancient Greeks named them planets, meaning «wanderers.» Mercury, Venus, Mars, Jupiter and Saturn were known in antiquity, and the invention of the telescope added the Asteroid Belt, Uranus, Neptune, Pluto and many of these worlds’ moons. The dawn of the space age saw dozens of probes launched to explore our system, an adventure that continues today.

There have been five human-made objects so far, Voyager 1, Voyager 2, New Horizons, Pioneer 10 and Pioneer 11, that have crossed the threshold into interstellar space.

Additional resources

Explore the solar system in greater detail with these interactive resources (opens in new tab) from NASA. Discover the wonders of the solar system with this educational material (opens in new tab) from ESA. See where the planets are in their current orbit of the sun with this interactive orrery (opens in new tab) from NASA.

Bibliography

Prialnik, Dina K., Antonella Barucci, and Leslie Young, eds. The Trans-Neptunian Solar System. (opens in new tab) Elsevier, 2019.

Pirani, Simona, et al. «Consequences of planetary migration on the minor bodies of the early solar system. (opens in new tab) » Astronomy & Astrophysics 623 (2019): A169.

Brown, Michael E., and Konstantin Batygin. «Observational constraints on the orbit and location of planet nine in the outer solar system. (opens in new tab) » The Astrophysical Journal Letters 824.2 (2016): L23.