Solar System Planets, Order, and Formation

Solar System Planets, Order, and Formation

The order of the planets within the system, starting nearest the sun and dealing outward, is the following: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, so the possible Planet Nine.

The solar system comprises the sun and everything that orbits around it, including planets, moons, asteroids, comets, and meteoroids. The order of the planets within the solar system, starting nearest the sun and dealing outward, is the following: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and so the possible Planet Nine.

The solar system extends from the sun, called Sol by the traditional 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 much beyond to the teardrop-shaped heliopause. Scientists estimate that the solar system’s edge is about 9 billion miles (15 billion kilometers) from the sun. Beyond the heliopause lies the giant, spherical Oort cloud, which is believed to surround the system.

Ever since the discovery of Pluto in 1930, kids grew up learning that the solar system has nine planets. that everyone changed within the late 1990s when astronomers started arguing about whether Pluto was indeed a planet. during 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 only eight.
If you impose including Pluto, it’ll come after Neptune on the list. Pluto is answered there and on a wildly tilted, elliptical orbit (two of the several reasons it absolutely was demoted).

Astronomers, however, are still looking for another possible planet in our solar system, a real 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.


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 contains 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 due to their enormous size relative to the terrestrial planets. They’re also mostly made from gases like hydrogen, helium, and ammonia instead of rocky surfaces, although astronomers believe some or all of them may have solid cores.

Jupiter and Saturn are sometimes called the gas giants, whereas the more distant Uranus and Neptune are nicknamed the ice giants. this is often because Uranus and Neptune have more atmospheric water and other ice-forming molecules, like methane, hydrogen sulfide, and phosphene, that crystallize into clouds within the planets’ frigid conditions, in keeping with the Planetary Society. For perspective, methane crystallizes at minus 296 Fahrenheit (minus 183 degrees Celsius), in keeping with the U.S. National Library of medication.


The IAU defines a real planet as a body that circles the sun without being another object’s satellite; is large enough to be rounded by its own gravity (but not so big that it begins to undergo nuclear fusion reaction, sort of a star); and has “cleared its neighborhood” of most other orbiting bodies.

But that restrictive definition helped isolate what should and may not be considered a planet — an issue that arose as astronomers discovered more and more planet-like objects within the solar system. Pluto was among the bodies that did not cut and was re-classified as a dwarf planet.

The problem with Pluto, apart from its small size and offbeat orbit, is that it doesn’t clear its neighborhood of debris — it shares its space with plenty of other objects within 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.

In the asteroid belt, Ceres, a round object between Mars and Jupiter, also got the boot. Ceres was considered a planet when it had been discovered in 1801, but it absolutely was later deemed an asteroid. that also didn’t quite fit because it absolutely was larger (and rounder) than the opposite asteroids. Astronomers instead deemed it a dwarf planet in 2006, although some astronomers prefer to consider Ceres as a tenth planet (not to be confused with Nibiru or Planet X).

Below could be 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 is far and away from the biggest object in our solar system, containing 99.8% of the solar system’s mass. It sheds most of the warmth and lightweight that creates life possible on Earth and possibly elsewhere. Planets orbit the sun in oval-shaped paths called ellipses, with the sun slightly off-center of every ellipse.
NASA features a fleet of spacecraft observing the sun, like the Parker Solar Probe, to learn more about its composition, and to form better predictions about solar activity and its effect on Earth.


Mercury is the closest planet to the sun and also the smallest planet within the solar system — it’s only a bit larger than Earth’s moon. Mercury zips around the sun in just 88 days and since it’s so near our star (about two-fifths the space between Earth and also the sun).

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

Mercury’s atmosphere is incredibly 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, a bit 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 which volcanism played a significant role in shaping the planet’s surface.


Venus is the second planet from the sun and is the kind of hottest planet within 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.

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, within the opposite direction of most of another planet.

Venus is typically named Earth’s twin as they’re similar in size and radar images beneath its atmosphere reveal numerous mountains and volcanoes. But beyond that, the planets couldn’t be more different.
The Greeks believed Venus was two different objects — one within the morning sky and another within the evening. Because it’s often brighter than the other object within the sky, Venus has generated many UFO reports.


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

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


Mars is the fourth planet from the sun. it’s a chilly, desert-like planet covered in iron oxide dust that provides the planet its signature red hue. Mars shares similarities with Earth: it’s rocky, has mountains, valleys and canyons, and storm systems starting 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 far warmer, wetter world, rivers and perhaps even oceans existed. Although Mars’ atmosphere is just 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 dimensions of California lie beneath Mars’ surface, and at both poles are ice caps made partially of frozen water.
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 also the possibility of even current lifeforms — may exist on the Red Planet has driven numerous Mars missions and also the red planet is now one among the foremost explored planets within the solar system.


Between Mars and Jupiter lies the asteroid belt. Asteroids are minor planets, and in step with NASA, there are approximately between 1.1 and 1.9 million asteroids within the main asteroid belt larger than 0.6 miles (1 km) in diameter and millions of smaller asteroids.

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


Jupiter is the fifth planet from the sun and also the largest planet within the solar system. The gas giant is quite twice as massive as all the other planets combined, in step with NASA.

Its swirling clouds are colorful because of differing kinds of trace gases including ammonia ice, ammonium hydrosulfide crystals additionally and water ice, and vapor.

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

Jupiter contains a strong magnetic field, and with 75 moons, including the biggest moon within the solar system, Ganymede.


Saturn is the sixth planet from the sun and is legendary for its large and distinct ring system. Though Saturn isn’t the only planet within the solar system with rings.

When polymath Galileo Galilei first studied Saturn within the early 1600s, he thought it absolutely 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 little drawing — a symbol with one large circle and two smaller ones — in his notebook, as a noun in an exceeding sentence describing his discovery. over 40 years later, Christiaan Huygens proposed that they were rings.

The rings are made from ice and rock and scientists aren’t yet sure how they formed. The gaseous planet is usually hydrogen and helium and has numerous moons.


Uranus is the seventh planet from the sun and could be a little bit of an oddball.
It has clouds made from hydrogen sulfide, the identical chemical that produces rotten eggs that smell so foul. It rotates from east to west like Venus. But unlike Venus or the other planet, its equator is almost at right angles to its orbit — it basically orbits on its side.

Astronomers believe an object twice the dimensions 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 also the sun beats down on one pole or the other for 84 Earth-years at a time.

The collision is additionally thought to possess knocked rock and ice into Uranus’ orbit. These later became a number 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 within the solar system — minus 371.56 degrees F (minus 224.2 degrees C). the common temperature of Uranus is minus 320 degrees Fahrenheit (-195 degrees Celsius).


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

Neptune is approximately the identical size as Uranus and is known for its supersonic strong winds. the planet is over 30 times as far away from the sun as Earth.
Neptune was the primary planet predicted to exist by using math, instead of being visually detected. Irregularities within the orbit of Uranus led French astronomer Alexis Bouvard to suggest some other planet could be exerting a gravitational tug. German astronomer Johann Galle used calculations to assist find Neptune in a telescope. Neptune is about 17 times as massive as Earth and contains a rocky core.


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

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


Pluto was once the ninth planet from the sun and is unlike the other planet within the solar system.
It is smaller than Earth’s moon; its orbit is extremely elliptical, falling inside Neptune’s orbit at some points and much beyond it at others; and Pluto’s orbit doesn’t fall on the identical 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 extremely elliptical, falling inside Neptune’s orbit at some points and much beyond it at others; and Pluto’s orbit doesn’t fall on the identical plane as all the other planets — instead, it orbits 17.1 degrees above or below, taking 288 years to complete a single orbit consistent with 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 yet again became the solar system’s most distant planet — until it absolutely was redefined as a dwarf planet. it is a cold, rocky world with a tenuous atmosphere.

Scientists thought it would be nothing over 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 could be 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 from water, methane, or ammonia.


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 haven’t seen Planet Nine. They inferred its existence by its gravitational effects on other objects within the Kuiper Belt, a section at the fringe of the solar system that’s 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 within the same direction.

Scientists Mike Brown and Konstantin Batygin at the California Institute of Technology in Pasadena described the evidence for Planet Nine during a study published within the Astronomical Journal. The research relies on mathematical models and computer simulations using observations of six other smaller Kuiper Belt Objects with orbits that aligned during a similar matter.

A hypothesis proposed in September 2019 on the pre-print server arXiv suggests Planet Nine may not be a planet in any respect. Instead, Jaku Scholtz of Durham University and James Unwin of the University of Illinois at Chicago speculate it might be a primordial black hole that formed soon after the Big Bang which our solar system later captured, consistent with 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 massive Bang, and this one would be so small (5 centimeters in diameter) that it might be challenging to detect.
Astronomers continue to come up empty in their exploration of 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 may be confirmed.


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, called the heliopause, is about 9 billion miles (15 billion km) from the sun.
The Oort cloud lies well past the Kuiper Belt, considered to be located between 2,000 and 5,000 astronomical units (AU) from the sun. The outer edge of the aggregation may reach as far as 10,000 up to 100,000 AU from the sun. One AU is adequate approximately 93,000,000 miles (150 million kilometers). The Oort cloud is home to billions, or maybe trillions of objects, consistent with NASA Science.


Approximately 4.5 billion years ago a dark cloud of gas and dirt began to collapse. because it shrank, the cloud flattened into a swirling disk called a solar nebula, consistent with NASA Science.
The heat and pressure eventually became so high that hydrogen atoms began to mix to make helium. The nuclear reactions released vast amounts of energy and our sun was formed.
The sun accumulated about 99% of the available matter and also the remaining material farther from the sun formed smaller clumps inside the spinning disk. a number 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 structure our solar system.

For millennia, astronomers have followed points of light that are perceived to move among the stars. the ancient Greeks named them planets, meaning “wanderers.” Mercury, Venus, Mars, Jupiter, and Saturn were known in antiquity, and also the invention of the telescope added the asteroid belt, Uranus, Neptune, Pluto, and lots 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 are five human-made objects up to now, Voyager 1, Voyager 2, New Horizons, Pioneer 10, and Pioneer 11, that have crossed the edge into interstellar space.


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

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