Formation of the Solar System — Reading Comprehension

The solar system is a complex system of planets, moons, asteroids, and comets orbiting our Sun. All these objects formed about 4.6 billion years ago, but how did this incredible transformation occur? Scientific evidence supports the solar nebula theory, which explains the step-by-step process that shaped our planetary neighborhood. Understanding this process helps us see how natural forces, like gravity and energy, create organized systems from chaotic beginnings.

From Cloud to Spinning Disk
According to the solar nebula theory, the solar system began as a massive, cold cloud of gas and dust called the solar nebula. This cloud may have started collapsing under its own gravity after a shockwave from a nearby supernova—an exploding star—disturbed it. As gravity pulled the particles closer, the cloud shrank and began spinning faster, a result of the conservation of angular momentum. This process is similar to how a figure skater spins faster when pulling their arms in. The spinning nebula flattened into a disk, with most material concentrating at the center. As the core grew dense and hot, it became a protostar: our young Sun.

Building Planets and Moons
In the disk around the protostar, tiny dust grains collided and stuck together, gradually forming larger objects called planetesimals. Over time, planetesimals grew by attracting more material through gravity. In the hot, inner part of the disk, only metals and rocks could survive, so small, rocky planets like Mercury, Venus, Earth, and Mars formed there. In the colder, outer regions, ices could remain solid, allowing giant planets like Jupiter and Saturn to develop thick layers of gas and ice. The leftover material became asteroids and comets, which still orbit the Sun.

Evidence and Scientific Understanding
Scientists support the solar nebula theory with several lines of evidence. Nearly all planets revolve around the Sun in the same direction and in a flat plane, matching the predicted shape of the original disk. The age of meteorites—about 4.6 billion years—matches the estimated age of the solar system. Modern telescopes have also observed young stars with spinning disks and forming planets, providing real-time examples of similar processes elsewhere in the universe.

The formation of the solar system is an example of how systems can organize from disorder through natural laws. This understanding connects to the broader scientific principle that the universe follows predictable patterns, from the orbits of planets to the cycles of stars. As astronomers continue to study other star systems, they gain new insights into how common planets like ours may be in the universe.

Interesting Fact: Some meteorites found on Earth contain grains older than the Sun itself, offering clues about the materials that built our solar system!

What is the solar nebula theory?

Approximately how old is the solar system?

What caused the solar nebula to start collapsing?

What is a protostar?

What are planetesimals?

What does 'conservation of angular momentum' mean as used in the passage?

Why are the inner planets rocky and the outer planets mostly gas and ice?

Which observation supports the solar nebula theory?

True or False: Meteorites found on Earth are about the same age as the solar system.

True or False: Scientists have seen young stars with spinning disks and forming planets in space.