Stargazing: Could Earth be struck by a doomsday rock?

IMAGINE waking one morning to find the sky torn open by a glowing fireball racing towards Earth.

It sounds like science fiction, but it isn’t.

Our planet sits in a cosmic shooting gallery.

Asteroids and comets – leftovers from the birth of the solar system – cruise through space, and sometimes their paths cross ours.

The big question is: could one of these objects wipe us out?

The short answer is yes.

It’s happened before.

Roughly 66 million years ago, a city-sized asteroid slammed into what’s now the Yucatán Peninsula in Mexico.

The impact blasted a crater 180 kilometres wide and hurled so much debris into the sky that sunlight dimmed for years. Forests burned, oceans boiled, and three-quarters of Earth’s species – including the dinosaurs – vanished.

It was not the first mass extinction linked to cosmic impacts, but it was the most famous.

Scientists count at least five major extinction events in Earth’s history; at least two of them appear to have been triggered by asteroid or comet strikes.

So, what would happen if a similar object came calling today?

Let’s take the nightmare scenario: an asteroid 10 kilometres across, the size of the dinosaur-killer.

On impact, shockwaves would ripple across continents.

Skies would rain fire.

Global temperatures could plunge into a “nuclear winter” lasting months or years.

Crops would fail, and civilisation as we know it could collapse.

A smaller asteroid – say, one kilometre wide – wouldn’t wipe out humanity but could still kill hundreds of millions, destroy nations, and trigger decades of chaos.

Before you bolt for the bunker, though, consider the odds.

Astronomers estimate that civilisation-ending strikes occur roughly once every 50 to 100 million years.

That means the chances of a dinosaur-class asteroid hitting Earth in our lifetime are vanishingly small.

Smaller, city-smashing rocks (hundreds of metres wide) are more common, arriving every few tens of thousands of years. Even then, the probability of such an object hitting Earth in any given year is less than one in a hundred thousand.

Terrifying in scale, yes – but not an everyday worry.

Here’s the hopeful part: we can see them coming.

Telescopes around the world and in space are part of NASA’s “Planetary Defence” program, scanning the skies for Near-Earth Objects.

More than 90 percent of the kilometre-sized threats are already catalogued.

And we’re not helpless.

In 2022, NASA’s DART mission deliberately slammed a spacecraft into a small asteroid, successfully nudging its orbit.

It was proof of concept and given enough warning, years or decades, we could shove an incoming asteroid off course.

Still, detection is key.

A rock just 50 metres wide could flatten a city, and we’ve only mapped a fraction of objects that size.

The infamous Tunguska event in 1908, when a small asteroid exploded over Siberia, levelled 2,000 square kilometres of forest. If it had hit a populated region, millions might have died.

So, should we live in fear? Perhaps just a little.

Cosmic impacts are part of Earth’s natural history, and the potential damage is too vast to ignore.

But we now possess knowledge the dinosaurs never had.

With vigilance, technology, and international cooperation, we may be able to stop the next world-killer in its tracks.

The sky may one day fall – but this time, we just might be ready.

We’re constantly monitoring for Earth-threatening asteroids.

NASA and global observatories track thousands of near-Earth objects daily, aiming to spot potential threats early enough for deflection or mitigation.

By Dave RENEKE, Astronomer