The solar system formed 4.6 billion years ago from a collapsing cloud of gas and dust. How it formed, what lies at its edge, and how it ends with the Sun.
By The Orbital Record editorial teamPublished Last reviewed
The solar system formed about 4.6 billion years ago when a cloud of gas and dust collapsed under its own gravity; most of the material became the Sun and the rest flattened into a disk that built the planets. Meteorites date its first solids to 4.567 billion years ago. The Sun will swell into a red giant in about 5 billion years.
This guide follows the solar system across deep time: how it formed, what lives at its edge, the visitors from other stars, and how it will end. For the far future of everything else, see Deep Time.
The solar system formed from the collapse of a cold cloud of gas and dust, and the planets grew in the flat disk left around the young Sun. Immanuel Kant (1755) and Pierre-Simon Laplace (1796) proposed this “nebular hypothesis” in its first form, and modern observations of planet-forming disks around young stars confirm it. The main steps:
Collisions finished the job. Earth’s Moon probably formed when a Mars-sized body struck the young Earth (the giant impact hypothesis). JWST now sees similar violent eras around other young stars, in dusty disks left by planet-shattering collisions (Webb’s extreme debris disks).
The solar system is 4.567 billion years old. The clock is radioactive decay in the oldest solids we have: calcium- and aluminum-rich inclusions, pale grains inside primitive meteorites that condensed from the hot gas around the newborn Sun. Uranium decays to lead at a known rate, so the ratio of lead isotopes in these grains gives their age. A 2012 study by James Connelly and colleagues dated them to 4,567.3 million years, with an uncertainty of only about 160,000 years.
That is about one third of the age of the universe, 13.8 billion years. The Sun is a latecomer, built from gas already enriched by generations of stars that lived and died before it (how stars make elements).
Eight planets orbit the Sun, in two families: four small rocky worlds and four giants.
| Planet | Type | Average distance from Sun (AU) | One fact |
|---|---|---|---|
| Mercury | Rocky | 0.39 | BepiColombo, two orbiters in one, arrives in November 2026 |
| Venus | Rocky | 0.72 | Hottest surface of any planet, under a thick carbon dioxide atmosphere |
| Earth | Rocky | 1.00 | The only world known to host life |
| Mars | Rocky | 1.52 | Ancient lake beds now searched for signs of past life |
| Jupiter | Gas giant | 5.2 | Its moon Io is the most volcanic world in the solar system |
| Saturn | Gas giant | 9.5 | A new ten-sided wave is forming around its south pole |
| Uranus | Ice giant | 19.2 | Spins on its side, tilted about 98 degrees |
| Neptune | Ice giant | 30.1 | Found in 1846 from its pull on Uranus, before it was seen |
An astronomical unit (AU) is Earth’s average distance from the Sun, about 150 million kilometers.
Beyond the planets are the dwarf planets, including Ceres in the asteroid belt and Pluto, Eris, Haumea and Makemake beyond Neptune. NASA’s New Horizons showed in 2015 that Pluto, far from being a dead ice ball, has young plains of nitrogen ice and an active surface (New Horizons at Pluto).
The planets are still surprising us. In 2026 Juno took the first temperature readings beneath the surface of Io (Juno at Io), Hubble tracked a new ten-sided wave forming around Saturn’s south pole (Saturn’s decagon), ESA’s BepiColombo began its arrival at Mercury (BepiColombo’s arrival phase), and in October Solar Orbiter traced a magnetic “switchback” in the solar wind back to the Sun’s surface (Solar Orbiter and the switchbacks).
The solar system has no single edge; there are three boundaries, each farther out than the last.
Maybe, but it has not been found. In 2016 Konstantin Batygin and Mike Brown showed that several distant objects beyond Neptune have orbits clustered in the same direction, with only a 0.007% chance of happening at random by their analysis. They proposed a planet of roughly 10 Earth masses or more on a distant, eccentric orbit herding them (Batygin and Brown 2016).
As of October 2026 Planet Nine has not been detected. Searches of old infrared survey data produced at least one unconfirmed candidate in 2025, and some astronomers argue the clustering is a bias in where surveys have looked. The Vera C. Rubin Observatory, which began its ten-year survey of the southern sky in mid-2026, is expected to help test the idea by finding many more distant objects.
Three interstellar objects have been seen passing through the solar system, each on a hyperbolic path that proves it came from another star system and will leave forever.
Rubin is expected to find many more, perhaps early enough for a spacecraft to meet one.
The Sun is about halfway through its stable life and will leave the main sequence in about 5 billion years. It brightens by roughly 10% every billion years, which in about a billion years will likely make Earth too hot for liquid oceans. Later it will swell into a red giant about 1.2 AU across in radius, probably engulfing Mercury, Venus and, according to a widely cited 2008 model, Earth (Schröder and Smith 2008).
The Sun will never become a black hole or explode as a supernova; it is far too light. It will shed its outer layers as a planetary nebula and end as a white dwarf of about half a solar mass, roughly the size of Earth. The full timeline, with a table of stages, is in when will the Sun die.
Beyond the Sun’s death, the solar system’s long future is less stable than once thought.
For an accessible long-form overview, our video library includes SciShow’s “The Solar System Explained.”
About 4.567 billion years. The age comes from radioactive dating of the oldest solids known, millimeter-sized calcium- and aluminum-rich grains inside primitive meteorites, which a 2012 study dated to 4,567.3 million years with an uncertainty of about 160,000 years. Earth and the other planets formed over the following tens of millions of years.
A dense pocket of an interstellar gas cloud collapsed under its own gravity. Most of the material fell to the center and became the Sun; the rest flattened into a spinning disk. Dust grains in the disk stuck together into planetesimals, which collided and grew into rocky planets near the Sun and giant planets farther out.
Nobody knows. Konstantin Batygin and Mike Brown proposed it in 2016 to explain why the orbits of several distant icy bodies beyond Neptune are clustered. As of October 2026 no such planet has been detected. Some astronomers argue the clustering is a statistical artifact of where surveys have looked.
It depends on the definition. The Sun's wind of charged particles ends at the heliopause, which Voyager 1 crossed in 2012 at about 122 times Earth's distance from the Sun. The Sun's gravity dominates much farther out, through the hypothesized Oort cloud of comets, perhaps more than a light-year away.
Yes. The Sun and its planets orbit the center of the Milky Way at more than 200 kilometers per second, completing one lap every 200 to 250 million years. The whole Milky Way is also moving, along with the rest of the Local Group, relative to the cosmic microwave background.
The Kuiper belt is a broad ring of icy bodies beyond Neptune, roughly 30 to 50 times Earth's distance from the Sun. Pluto is one of its largest members. The first object other than Pluto and Charon was found there in 1992, and thousands are now known.
The Oort cloud is a vast, spherical swarm of icy bodies thought to surround the solar system far beyond the planets, proposed by Dutch astronomer Jan Oort in 1950 to explain long-period comets. It has never been observed directly; its existence is inferred from the orbits of comets that fall in from all directions.
About one third of the universe's age. The universe is about 13.8 billion years old and the solar system about 4.6 billion, so the Sun formed when the cosmos was already over 9 billion years old, from gas enriched with heavy elements forged by earlier generations of stars.
Hartmann and Davis, Icarus, 24, 504-515, 1975
Proposed in 1975 that the Moon formed from debris of a giant collision with the young Earth. Hartmann and Davis's idea explains the Moon's small iron core.
Alvarez et al., Science, 208, 1095-1108, 1980
Found in 1980 a spike of iridium where the Cretaceous ends. Luis and Walter Alvarez proposed that a 10 km asteroid caused the extinction of the dinosaurs.
Laskar, Nature, 338, 237-238, 1989
Showed in 1989 that the Solar System is chaotic. Laskar found that planetary orbits cannot be predicted beyond about 100 million years.
Jewitt and Luu, Nature, 362, 730-732, 1993
Found 1992 QB1, the first object beyond Neptune since Pluto and Charon. Jewitt and Luu's 1993 paper revealed the Kuiper belt, a vast zone of icy bodies.
Gomes et al., Nature, 435, 466-469, 2005
Proposed in 2005 that giant planet migration triggered the Late Heavy Bombardment. Gomes and colleagues' Nice model reshaped how we see the Solar System.
Stern et al., Science, 350, aad1815, 2015
Showed in 2015 that Pluto is geologically active, with a young plain of nitrogen ice. Stern's New Horizons team reported the first close look at Pluto.
Batygin and Brown, The Astronomical Journal, 151, 22, 2016
Proposed in 2016 that an unseen planet of about 10 Earth masses shapes distant Kuiper belt orbits. Batygin and Brown's Planet Nine is still undetected.
Meech et al., Nature, 552, 378-381, 2017
Found in 2017 the first object known to enter the Solar System from interstellar space. Karen Meech's team showed 'Oumuamua is red and extremely elongated.
Daly et al., Nature, 616, 443-447, 2023
Showed in 2023 how NASA's DART spacecraft hit the asteroid Dimorphos and changed its orbit. Daly and colleagues reconstructed the first deflection test.
Hank Green leads a 35-minute tour of the Solar System, its planets and moons and its unsolved questions. A friendly, wide-ranging introduction for all ages. SciShow
Covers recent simulations suggesting the Moon may have formed within hours of the giant collision that created it. A good update on the giant impact theory for viewers who know the basics. PBS Space Time
Follows NASA's New Horizons to its 2015 Pluto flyby and what it revealed about Pluto's surface, moons and atmosphere. An accessible recap of the first close look at the dwarf planet. Astrum
Becky Smethurst and Scott Manley explain why BepiColombo needed about eight years to reach Mercury when Juno took five to reach Jupiter, and the orbital mechanics behind it. Clear and beginner-friendly. Dr. Becky
Explains solar flares and coronal mass ejections, and what a major solar storm could do to our technology-dependent civilization. A short, animated introduction to space weather. Kurzgesagt - In a Nutshell