Event: The Origin and Role of Comets and Asteroids
Date: ~4.56 billion years ago to present

“The most interesting thing about a comet is not its tail, but its trail—what it leaves behind and where it comes from.”
— Brian May

Dear Human,

They fall from the sky, but they come from the beginning.

Comets and asteroids are not just debris—they are the leftover pages of a book that was never finished. Formed in the early violence of the solar system, they were never melted, never shaped into planets, never buried beneath crust or sea. They remain raw. Ancient. Drifting.

Asteroids dwell closer in, between Mars and Jupiter, mostly rocky and scarred. They are fragments of collisions—ruins of failed worlds. Some, like Ceres, are nearly round, holding onto secrets of water and potential. Others, like Vesta or Pallas, are jagged and beaten, reminders of a time when the solar system was still carving itself into shape. Their belt is not neat—it is broken. And some escape it entirely, crossing Earth’s path with silent intent.

Comets live farther out, born beyond the frost line. They are made of fragile mixtures—water ice, carbon dioxide, ammonia, methane, silicates, and organic molecules. These frozen ingredients, unchanged for billions of years, are among the most primitive matter in the solar system. When a comet nears the Sun, its ices sublimate into gas, creating a glowing coma and long tails of ionized particles and dust. These tails always point away from the Sun, driven by solar wind and light pressure. Yet what matters most is not the display—it’s what they’re made of. Comets may have delivered water to early Earth. Some even carry complex organic compounds, sparking theories that they helped seed life.

They are not just beautiful. They are revealing.

But how do they begin to move? Some are nudged from their slumber by distant gravitational tugs—Jupiter’s mighty pull, the passing of a star, or subtle shifts from other drifting objects. A resonance, a collision, a slow spiral of drift. Over time, these quiet forces destabilize their orbits, sending them inward from the Kuiper Belt or the scattered disc, or outward from the asteroid belt into planetary paths. Others are shaken loose by ancient chaos, by the echoes of formation and migration, long after the planets had settled. They move because gravity never sleeps, and the solar system is not static. It breathes. It changes. And sometimes, it sends a stone flying across the dark to write a sentence on Earth’s skin.

Some have names etched into human history. Halley’s Comet, the most famous, returns every 76 years, its visits recorded for millennia. Shoemaker–Levy 9 struck Jupiter in 1994, leaving massive scars in the gas giant’s clouds—visible proof of cosmic impact. Chicxulub, an asteroid from the outer solar system, is remembered not by its form but by its effect: the extinction of the dinosaurs. It ended an age and began another.

Every year, astronomers discover new near-Earth objects—asteroids that pass within striking distance. Some are small and harmless, others are measured in kilometers. While none pose an immediate threat, their presence is a reminder: Earth is not isolated. It moves through a dynamic, ancient minefield. Impact is not a question of if, but when. The Earth has been shaped, altered, even reborn by what falls from the sky.

To understand them, we’ve reached out. Giotto flew past Halley’s Comet in 1986, capturing the first close images of its nucleus. Stardust collected particles from Comet Wild 2 and brought them home. Rosetta orbited Comet 67P/Churyumov–Gerasimenko, and its lander, Philae, touched down on the surface—revealing a strange, black crust and organic compounds hidden beneath. These missions were not just scientific. They were archeological. They reached into time.

You may see them as threats. And they are. Some have scarred the Earth, ended eras, changed the story. Others have given gifts: the raw ingredients for oceans, maybe even life itself. They carry not just danger, but possibility.

Each one is a message—not in language, but in structure. Where it came from. What it carries. How long it’s traveled. Some orbit every few years, like messengers on a schedule. Others return only once, from the farthest reaches, as if summoned by fate.

They are studied now, visited even—by machines that land on their surfaces and steal their dust. But they were known long before science.

To ancient eyes, comets were never neutral. They were omens—streaks of light that tore across the sky without pattern or permission. When Halley’s Comet appeared in 1066, it was said to foreshadow the death of King Harold at Hastings. In ancient Rome and China, comets were feared as signals of political upheaval or natural disaster. Their unpredictability made them unsettling, and their brightness made them unforgettable. For millennia, people believed the sky was a reflection of the divine—so when something strange entered it, the world below prepared for change. A comet was a sign that something larger than human plans had stirred. To ancient eyes, they were omens—harbingers of war, plague, or kings. To poets, they were wanderers. To astronomers, they became windows into the past.

We track them now. We name them. We prepare for them. Every year, astronomers discover new near-Earth objects—asteroids that pass within striking distance. Some are small and harmless, others are measured in kilometers. While none pose an immediate threat, their presence is a reminder: Earth is not isolated.  Impact is not a question of if, but when.

But even with all our instruments, we do not control them.

They are the leftovers. The reminders. The messengers.

So look up. What falls may be warning—or welcome.

Pathfinder
Comet – Wikipedia
Asteroid – Wikipedia