Asteroid 2003 MH4: The Colossal Stranger Slipping Past Earth

May 20

There are giants out there.

Massive bodies of ancient rock…cold, indifferent, and older than our oceans…drifting through the void.
They don't rage or plot.
They simply move.
And sometimes, they come very, very close.

On May 24, NASA is closely monitoring the flyby of Asteroid 2003 MH4, a behemoth roughly the size of three football fields hurtling toward our planetary neighborhood at 14 kilometers per second…about 31,000 miles per hour.

It won’t hit us.
But it won’t miss by much.

And that space between impact and miss…that’s where our fascination lives.
That’s where science, anxiety, and awe all converge.

What We Know About Asteroid 2003 MH4

Let’s start with the raw details.

Discovered in 2003 and tracked ever since, MH4 belongs to a group of objects known as Near-Earth Objects (NEOs). These are celestial bodies (mostly asteroids and comets) that orbit close enough to pose potential threats.

MH4:

Is estimated to be 300–350 meters in diameter
Weighs millions of tons
Has an elliptical orbit that crosses Earth’s path every few years
Is officially categorized by NASA as a “Potentially Hazardous Asteroid” (PHA) due to its size and its proximity

On May 24, it will pass within roughly 4.5 million miles of Earth.

That might sound like a lot…but in cosmic terms, it’s a near whisper.

Why It’s Called “Potentially Hazardous”

NASA doesn’t use the word “hazardous” lightly.

To earn that title, an object must:

Be larger than 140 meters
Come within 7.5 million kilometers (4.65 million miles) of Earth

MH4 checks both boxes.
Its orbit is close. Its mass is enormous. And even though the trajectory this time is safe, the nature of orbits is that they can change…nudged by gravitational forces from planets or other asteroids.

That’s why NASA’s Planetary Defense Coordination Office watches objects like MH4 with such intense scrutiny. A slight deflection could turn a near-miss into a direct hit decades from now.

And when you're dealing with a rock moving 10 times faster than a bullet, there are absolutely no do-overs.

What Would Happen If It Hit?

Let’s play that out.

If MH4 were to strike Earth, the results would be catastrophic, but not extinction-level.

This isn’t a dino-killer (that asteroid was 10+ kilometers wide).
But it is more than enough to:

Flatten an entire metropolitan area
Release more energy than hundreds of nuclear bombs
Trigger massive fires, shockwaves, and tsunamis if it landed in the ocean

The Tunguska event of 1908…where an asteroid flattened 800 square miles of Siberian forest…was caused by a body only 50–60 meters wide.

MH4 is six times larger.

How We Track It

NASA doesn’t just point a telescope and hope.
They use a combination of:

Optical telescopes (to track movement across the sky)
Radar systems (like Goldstone in California, to bounce signals off the surface and calculate shape, speed, and spin)
Infrared sensors (to detect heat signatures in space)
And orbital modeling software (to predict future paths and potential impacts)

The data is plugged into the Sentry system, which runs continuous calculations for over 28,000 known NEOs.

So far, MH4 has shown no sign of veering toward Earth.
But they’ll keep watching.
Because one wobble…one gravitational nudge…and everything changes.

How Many of These Are Out There?

Too many.

NASA estimates there are:

Over 1,200 known Potentially Hazardous Asteroids
Around 26,000 NEOs total
And possibly hundreds of thousands more we haven’t spotted yet

Every few weeks, new asteroids are added to the list. Some slip by unnoticed until after they’ve passed.

In 2019, an asteroid the size of a football field passed within 45,000 miles of Earth, and no one saw it until it was too late to react.

It’s like cosmic hide and seek.
Except we’re not playing.
We’re just trying not to lose.

What We’re Doing to Defend Earth

In 2022, NASA ran its first-ever planetary defense test mission called DART (Double Asteroid Redirection Test). The idea? Smash a spacecraft into an asteroid and see if it can change its orbit.

It worked.

DART collided with asteroid Dimorphos, reducing its orbital period by 32 minutes. It was a landmark moment…a proof of concept that if we spot danger early enough, we might be able to stop it.

But the key word is early.

We can’t deflect what we can’t detect.

That’s why missions like NEO Surveyor (scheduled to launch by 2028) are critical. It will use infrared telescopes to find asteroids before they sneak up on us.

A Story as Old as Earth

Our planet bears scars.

Meteor Crater, Arizona: A mile-wide impact site from a 50-meter iron meteorite 50,000 years ago.
Chicxulub Crater, Mexico: A 110-mile wide crater left by the asteroid that ended the reign of the dinosaurs.
Chelyabinsk, Russia (2013): A 20-meter asteroid exploded in the atmosphere with the force of 30 Hiroshima bombs. Over 1,500 people were injured…mostly from shattered windows.

Space is not empty.
It’s a shooting gallery.
And Earth…is not always lucky.

Why We’re Drawn to These Stories

There’s something deeply human about asteroids.

They remind us we’re not the center of anything.
That life can be disrupted in an instant.
That the universe doesn’t owe us warning.

And yet…there’s beauty in that too.

Because with every near miss, we gain knowledge.
With every flyby, we calibrate our maps.
With every chill down our spine, we remember that we’re part of something vast, ancient, and wild.

Did You Know?

Asteroid 2003 MH4 is likely a C-type asteroid, made of carbonaceous material, some of the oldest stuff in the solar system.
The Yarkovsky effect (a subtle force caused by sunlight heating one side of a rotating asteroid) can alter orbits over decades.
NASA classifies any object over 1 kilometer wide as a planet killer. MH4 is not in that range, but close enough to worry.
Most of Earth’s meteorites come from the asteroid belt, flung inward by gravitational tugs from Jupiter and Mars.

Affiliate Pick

Want to track space from your own backyard?
Explore the stars with this highly rated beginner telescope for deep sky viewing.
Track the Moon, Mars, and maybe one day, spot your own asteroid.

We’re not in control.
Not really.

We launch satellites.
We predict eclipses.
We run calculations so precise they make your heart ache.

But in the end, we’re still a spinning blue dot…suspended in a universe that does not flinch when a rock the size of a skyscraper whistles past our cheek.

And maybe that’s why we keep looking up.
Because it reminds us we’re still here.
Still breathing.
Still watching the shadows pass…and whispering prayers into the void.

Michele Gargiulo http://michelegargiulo.com