For most people on Earth, nothing seemed unusual.
The night sky looked the same.
The stars were where they had always been.
But millions of miles away, a relatively obscure comet was doing something astronomers hadn’t expected.
Comet 220P/McNaught suddenly erupted.
Material surged away from its frozen nucleus. A glowing green cloud expanded around it. Its brightness jumped dramatically.
And this wasn’t even the first time it had happened in 2026.
After two extraordinary outbursts, NASA says the comet became roughly 20,000 times brighter than it normally is — transforming an object usually requiring a telescope into one that could be detected with binoculars under suitable observing conditions. (NASA Science)
The strangest part?
Scientists still don’t know exactly what caused the eruptions.
Meet Comet 220P/McNaught
220P/McNaught is what astronomers call a periodic comet.
Rather than visiting the inner solar system once and disappearing forever, it repeatedly travels around the Sun.
Its orbit takes a little more than 5.5 years, carrying it through a path roughly between the regions of Mars and Jupiter. (NASA Science)
Most of the time, it isn’t spectacular.
In fact, NASA describes the comet as normally so faint that observing it requires a telescope.
That’s what made its behavior in 2026 so surprising.
It suddenly stopped behaving like the quiet, difficult-to-see object astronomers expected.
The first eruption came around the end of May
Around May 31 and June 1, observers noticed an enormous change.
The comet underwent a major outburst.
Its brightness increased dramatically, with observational reports putting the increase at thousands of times its previous level. (Sky & Telescope)
Something had apparently happened on or beneath the comet’s surface.
But eventually its brightness began declining again.
That could have been the end of the story.
It wasn’t.
Then it erupted again
In early August, 220P/McNaught surprised astronomers for a second time.
Observations indicate another major eruption occurred around August 4–5.
Astrophotographer Mike Olason reported that this second event increased the comet’s brightness by roughly 650 times compared with immediately beforehand. (Sky & Telescope)
The comet once again became dramatically brighter.
NASA now says the combined effect of this year’s unusual activity has made 220P about 20,000 times brighter than its normal state. (NASA Science)
That’s the number that really puts this event into perspective.
Not 20 percent brighter.
Not twice as bright.
About 20,000 times brighter than usual.
And astronomers captured the transformation
The photograph accompanying this story reveals what telescopes could see.
Against a field filled with distant stars is a brilliant green object.
That’s 220P/McNaught.
Its glowing head — called the coma — surrounds the comet’s nucleus.
Behind it stretches a faint tail of material released as the comet interacts with solar radiation.
NASA’s Astronomy Picture of the Day on August 24 featured a long-exposure photograph taken from South Africa about ten days earlier, showing the comet’s bright green head and dust tail. (NASA Science)
Without a long exposure, the view can be far less dramatic.
But cameras can collect light over time, revealing faint structures our eyes would struggle to detect.
Why is the comet green?
The color is one of the most striking things about photographs of active comets.
Comets contain frozen materials mixed with dust and rock.
As one approaches the Sun, heating can release gases from the nucleus.
Sunlight then interacts with molecules surrounding the comet.
Certain molecules can emit strongly at wavelengths our eyes perceive as green, producing the characteristic emerald glow seen around some active comets.
The result can look almost artificial.
But the color in astronomical photographs is associated with real emissions from material surrounding the comet.
And after 220P’s eruptions, there was suddenly much more activity to observe.
But what actually exploded?
This is where the story becomes a mystery.
NASA says the reason for 220P/McNaught’s impressive outbursts is unknown. (NASA Science)
Astronomers do have possible explanations.
One involves gas trapped beneath the comet’s surface.
Imagine a comet as much more than a simple solid rock.
It contains volatile frozen material.
As sunlight heats different regions, subsurface material can warm and turn into gas.
If gas becomes trapped beneath a crust or layer of material, pressure can build.
Eventually, that pressure may break through.
Gas and dust can then erupt outward.
NASA lists the release of built-up subsurface gas as one possible explanation for what happened to 220P. (NASA Science)
But there’s another fascinating possibility.
A “comet quake”
NASA also mentions something that sounds almost like science fiction:
Comet quakes.
A comet’s surface isn’t necessarily stable.
Heating and cooling can produce stresses.
Cracks can develop.
Sections of material can shift or fracture.
A structural event could expose fresh volatile material to sunlight, suddenly triggering intense activity.
If that happened on 220P, a physical change to the comet itself may have contributed to its dramatic brightening.
But right now, that’s a hypothesis — not a confirmed explanation. (NASA Science)
Somewhere on that small frozen world, something changed.
Astronomers saw the consequences.
They just haven’t yet seen the culprit.
That’s what makes the second eruption especially interesting
One unexpected eruption would already attract attention.
Two in the same year makes the comet much more intriguing.
After the first major event, the comet began fading toward its more ordinary brightness.
Then suddenly:
Another eruption.
Another enormous increase.
Another cloud of material around the nucleus.
Astronomers observing it in early August measured the comet through multiple optical filters, documenting its brightness and colors following the outburst. (The Astronomer’s Telegram)
Each measurement provides another clue about what material was released and how the comet changed.
Comets are leftovers from the solar system’s beginning
Part of the reason scientists care so much about objects like 220P is their age.
Comets preserve primitive material dating back to the formation of the solar system roughly 4.6 billion years ago.
Long before Earth looked anything like it does today, the ingredients that would eventually become planets, moons, asteroids and comets were orbiting the young Sun.
Much of the material inside a comet has remained relatively primitive compared with the constantly recycled surfaces of worlds such as Earth.
That means every eruption can expose material that has spent immense periods locked beneath the surface.
It’s almost like opening a container from the solar system’s earliest history.
Except the container is moving through space.
The nucleus itself isn’t what you’re seeing
This is another strange thing about comet photographs.
That huge glowing green object isn’t the solid comet nucleus itself.
The actual nucleus is far smaller.
What becomes visually spectacular is the material surrounding it.
As gas and dust escape, they create the coma, an enormous temporary atmosphere around the nucleus.
Solar radiation and the solar wind then push some material away, creating tails.
So when an outburst occurs, the comet can appear to transform almost overnight.
The solid nucleus hasn’t suddenly become gigantic.
Its surroundings have.
Could you see it with your own eyes?
NASA says the recent outbursts made 220P/McNaught bright enough to be observed with binoculars and long-duration photographic exposures, rather than requiring the more powerful telescope normally needed to detect it. (NASA Science)
That doesn’t mean everyone can simply walk outside and see a giant green comet hanging overhead.
Visibility depends heavily on observing location, darkness, atmospheric conditions and the comet’s position in the sky.
And photographs can reveal far more detail and color than the unaided human eye.
Still, for an object normally confined to telescopic observation, the change has been remarkable.
In August, it briefly became one of the sky’s standout comets
Following the second eruption, observers reported brightness around magnitude 7, with astronomical imaging revealing the green coma and faint narrow tail.
One Sky & Telescope observation from August 7 estimated the comet at magnitude 7.2 after the eruption. (Sky & Telescope)
A separate observing report placed it around magnitude 7 on August 5. (aerith.net)
For comet watchers, this was a dramatic transformation from the extremely faint object seen before the eruption.
And it happened quickly.
Now it’s coming closer to Earth
The story isn’t finished yet.
220P/McNaught continues moving through its orbit.
NASA says that in October 2026, it will pass Earth at a distance of roughly one astronomical unit — approximately the average distance between Earth and the Sun. (NASA Science)
That sounds enormous because it is.
One astronomical unit is about 93 million miles.
So this is not a dangerous close approach.
The comet isn’t heading toward Earth.
There is no collision threat associated with this story.
Instead, astronomers will continue watching how the comet behaves as it moves along its orbit.
And there’s one particularly interesting question:
Will it erupt again?
Nobody can promise that.
The first two outbursts were already unexpected.
Eventually, the show will end
NASA expects the comet to fade quickly after its October passage as it begins traveling back toward the more distant portion of its orbit. (NASA Science)
The activity should decrease.
The glowing coma will weaken.
The comet will once again become difficult to observe.
And eventually, 220P/McNaught may return to being exactly what it was before all of this began:
A faint periodic comet that most people have never heard of.
Until its next journey around the Sun.
But something happened out there
That’s what makes this story so compelling.
Nothing crashed into Earth.
There was no giant fireball over a city.
No spacecraft landed on the comet.
Instead, astronomers simply noticed that an object they thought they understood had suddenly changed.
A frozen world moving silently between the regions of Mars and Jupiter erupted.
Then it did it again.
Its brightness increased enormously.
Its green coma expanded.
Its tail became visible in long-exposure photographs.
And scientists were left asking why.
Maybe gas accumulated beneath the surface until it broke free.
Maybe the comet fractured.
Maybe a “comet quake” exposed fresh material.
Or perhaps continued observations will reveal something researchers haven’t yet considered.
For now, the official answer remains refreshingly simple:
We don’t know. (NASA Science)
And sometimes that’s the most exciting sentence in science.
Because 220P/McNaught has given astronomers something every scientist hopes to encounter:
A familiar object doing something nobody expected — and a mystery still waiting to be solved.
For more surprising transformations, check out what happened when I Ate Sardines Every Day for 5 Days or discover the Onion Shock: What Raw Onion Really Brings to Your Diet.
