It's a simple question: How did we get here?
What cosmic events led to the formation of the Earth? What about any of the other planets, or the Sun itself? What led to all this?
Much of the Solar System's history is still unclear. But with careful study, scientists have managed to paint a picture of our neighborhood's past — at least with broad strokes — and they've also been able to predict what it'll look like some billions of years down the road.
Let's start from the beginning and work our way forward.
Star Formation in the Circinus Molecular Cloud Complex (2010-11-02) by NASA/JPL-Caltech/UCLANASA
The Beginning — 4.5 Billion Years Ago
Everything around you began, originally, in a molecular cloud like the one pictured here.
A molecular cloud is a loose collection of gas and dust, one that is cold enough for molecules to be able to form. They are mostly made up of hydrogen gas.
Towering Infernos (2005-11-09) by IRAC Image: NASA/JPL-Caltech/Harvard-Smithsonian CfA/ESA/STScI<br />Visible Light Image: NASA/JPL-Caltech/Harvard-Smithsonian CfA/DSSNASA
Making a Star
Over time, gravity causes parts of these clouds to collapse. The clumps get denser and hotter, attracting even more material from the cloud, until finally their cores reach the conditions required to begin nuclear fusion—the power source of all stars.
Infrared Spotlight on Orion Sword (2006-08-15) by NASA/JPL-Caltech/IRAS /H. McCallonNASA
Orion
We can watch this happening in the Orion Nebula. The bright clumps on the right are regions where gigantic, massive stars are forming. The clump that became our Solar System was about 20,000 times as big as the current distance between the Earth and the Sun.
Orion Nebula (2001-12-11/2005-04-30) by Hubble Space Telescope and ESO La Silla 2.2-meter TelescopeNASA
A Closer Look At The Orion Nebula
It was in a place like this that our Sun formed, surrounded by many other stars. Over hundreds of millions of years, these stars drifted apart, leaving little evidence of their original crowding.
Hubble Sees the Force Awakening in a Newborn Star (2017-12-08)NASA
Ignition
As a star turns on, it continues to attract dust and gas. Some falls onto the star, but other bits collect into a disk that rotates around it instead. At the same time, the star's magnetic field channels some particles through powerful jets from either north/south pole.
Disk Around a Massive Baby Star Artist Concept (2010-07-14) by ESO/L. CalçadaNASA
A Planet Crucible
Once the cloud clears, some dust and gas remains leftover in the disk. Its continuous orbit keeps it from drifting into the star, like how a satellite is always falling around the Earth.
Out of this disk, planets form.
Silicate Crystal Formation in the Disk of an Erupting Star Artist Concept (2009-05-13) by NASA/JPL-CaltechNASA
Enter: Planets
Though the dust in this disk is only about a billionth of a meter large to begin with, over thousands of years it coagulates into dust bunnies, then pebbles, then boulders —and eventually, the building blocks of entire planets (called "protoplanets").
Arrokoth
486958 Arrokoth
This faraway object, also known as "2014 MU69", is thought to be a leftover of the primitive building blocks that glommed together to form the rocky cores of planets.
Birth of an Unusual Planetary System Artist Concept (2005-02-08) by NASA/JPL-CaltechNASA
Diverging Paths
Depending where and when a planet begins forming, it can end up big or small. It can be made of rock or ice or gas, or some combination of the three. It can end up anywhere between an orbit so far away that it takes centuries, or one so close that it takes less than a day.
Over time, the gas and dust in the disk falls into the star or gets blown away. In several million years, it's gone, leaving behind asteroids, comets, and protoplanets.
In the Solar System, Uranus and Neptune may have formed last, just as the disk faded away.
Building Planets Through Collisions Artist Concept (2014-08-28) by NASA/JPL-CaltechNASA
The Chaotic Era
At this point, the Solar System went through a period of instability that lasted about a hundred million years. Some protoplanets smashed into each other, like the impact that formed the Earth's moon. Others may have been ejected out of the Solar System entirely.
Haumea
Haumea
The dwarf planet Haumea, which orbits the Sun from a distance far past Neptune, is thought to have formed through the kind of giant collision that reshaped our Solar System so much.
Loops of Gas and Dust Rise from Planetary Disks Artist Concept (2014-03-06) by NASA/JPL-CaltechNASA
Moon-making
In this chaotic time, some planets captured others into their orbit, gaining moons. Others had already formed moons early on, from orbiting disks like miniature versions of the one that had surrounded the Sun.
A Distant Solar System Artist Concept (2004-12-09) by NASA/JPL-CaltechNASA
Asteroids Incoming
Most scientists agree that about 500 million years after the Solar System formed, Jupiter began migrating closer to the Sun. Its gravitational influence disturbed the asteroid belt and launched many rocks toward the inner planets, including the Earth.
High Resolution Globe of Jupiter (2001-01-30) by NASA/JPL/University of ArizonaNASA
A Shove From Jupiter
One popular theory says that as Jupiter moved, it eventually interacted with Saturn's orbit, causing a major gravitational disturbance that pushed Uranus and Neptune farther out from the Sun and even switched their order.
From a Million Miles Away, NASA Camera Shows Moon Crossing Face of Earth (2017-12-08)NASA
The "Final" Product
That brings us to today.
Planet Earth From Space (2015-07-06) by NOAA/NASANASA
But the Solar System isn't done evolving.
The Hustle and Bustle of our Solar System (2012-05-16) by NASA/JPL-CaltechNASA
Collision Course?
The orbits of all the planets are stable in the near-term. But there is a small chance that within the next billion years, Mercury's orbit could get more and more oblong until it eventually smashes into Venus or the Earth.
In several billion years, Mars could do the same.
Our Solar System Features Eight Planets (2008-11-19) by NASA/JPLNASA
But by then...
...the Sun will have already made life (and water) on Earth's surface hard to sustain. In a billion years, it'll be too hot.
And as the Sun exhausts the hydrogen it fuses for energy, it will expand, eventually swallowing Mercury. It may also consume Venus and the Earth — some calculations point to yes, others say no.
On the bright side, temperatures will rise enough in the outer Solar System that those planets could become more habitable.
But their days will be numbered as well.
Planetary Nebula NGC 7293 also Known as the Helix Nebula (2005-05-05) by NASA/JPL-Caltech/SSCNASA
Boom.
In about 5 billion years, the Sun will exhaust all its fuel and collapse in on itself. The sun isn't massive enough to go supernova or become a black hole, but the collapse will cause an explosion that either destroys any of the remaining planets or ejects them out into space.
LIFE Photo Collection
Another Kind Of Nebula
The Solar System will then be a "planetary nebula" —a misleading name, since the planets will all be gone. The Sun will have lost about half its mass, and will continue to shine as a small, hot white dwarf.
Planetary Nebula (2017-12-08)NASA
The End?
But the surrounding nebula will dissipate in mere thousands of years. Most of what used to be the Solar System will be scattered into space.
Maybe, one day, some of the remains will enrich another star, or another planet, or maybe even another form of life.
Credits: All media
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