Meteors vs space junk: Are we seeing more fireballs in the sky than there used to be?

It might be from dash cam footage or a shaky mobile phone, but reports of fireballs lighting up the night sky are now a regular occurrence on social media.

More than 436 sightings of one fireball were reported over the US and Canada earlier this week.

NASA said the fireball was not associated with the Orionids meteor shower, which peaked at the same time. 

So are fireballs becoming more common, or are we just better at spotting them?

Groups like the Desert Fireball Network have spent years tracking bright flashes across the sky, but according to the network's director and planetary scientist Ellie Sansom, people recording their own fireball findings is also an important resource.

Knowing what you're looking at, though, is harder than it appears. While most of us might assume a comet, fireball and meteor are all the same, Dr Sansom notes that they do have subtle differences. 

What is a fireball?

To understand what a fireball is, we need to start with an asteroid or a comet.

Asteroids are large space rocks that travel through the asteroid belts in our Solar System, sometimes getting kicked out of orbit and making their way towards Earth.

Comets, which are made up of dust and ice as well as rock, swing in from the edge of the Solar System.

As they get closer to the Sun, they leave a trail of debris in their wake.

This debris, smaller asteroids, and their fragments are known as meteoroids, and it's usually these that end up entering Earth's atmosphere.

Meteoroids travel so quickly that they heat the air around them to more than 1,000 degrees Celsius, producing the visual streak of light across the sky that looks like a falling star.

"Something quite small, like sand- or dust-sized grains, they're quite faint, and we call those ones meteors," Dr Sansom says. 

The difference between a meteor and a fireball comes down to brightness. As their name suggests, fireballs are significantly brighter, and because of that they are more likely to be seen in urban environments, even with light pollution.

"When they start getting bigger — centimetre size and bigger — they become a lot brighter," Dr Sansom says.

These brighter fireballs can have enough mass in them to make it through the atmosphere, and if they do land on Earth, they become a meteorite.

How can you tell if it's a meteoroid or space junk? 

It's not just bits of meteoroids that can end up lighting up our sky. Space junk, or any other other artificial space object, can burn up when it hits the atmosphere too.

According to Dr Sansom, there's an easy way to tell the difference between a natural fireball and something human-made burning up in the atmosphere: time. 

"Something five or six seconds long, that's probably a fireball, but something that's minutes long and you're able to get your phone out and start recording, that's more likely space debris." 

If you're seeing something even longer than that, you might be particularly lucky and catching a glimpse of a comet.

These are not fireballs. Instead they are lit up by the Sun and are millions of kilometres away from Earth. They stay in approximately the same spot of sky and may be visible for several days just before sunrise or after sunset as they go around the Sun.

What can I do if I see a fireball? 

To find out if there are more fireballs than there used to be, we have to catch them as they happen. 

The Desert Fireball Network tracks about 3 million square kilometre area over the Nullarbor plains and surrounds. And it's not the only network around.

"There's been meteor or fireball cameras around the world since the '60s. Some have popped up in the US. Some have popped up in Canada. There's one in Europe," Dr Sansom says.

While cameras can scan the sky all night, human eyes also regularly catch fireballs as they happen.

Groups like the Australian Meteor Reports Facebook page and the International Meteor Organization track human reports of fireballs which, if enough people report location data, can provide valuable data for scientists. 

"It's very popular in the US. Sometimes fireballs will have hundreds of reports and it allows you to get a really good sense of where that object was — almost able to do pseudo-triangulation from just people's reports."

This is particularly important for groups like Dr Sansom's, as if they know where to look, they can sometimes find a meteorite.

"We probably see, on average, one fireball a night over our 3 million square kilometre area, but maybe 10 [of those] a year would drop a rock," she said.

Finding meteorites gives geochemists a look into the early Solar System, but finding them isn't easy. 

While the network of cameras can narrow down the search to a square kilometre or two, that still requires six or eight people to search the entire area for "a black rock at your feet".

The team recently had some success using drones and machine learning to look for the meteorites instead. 

"We trained it to pick up black rocks, but it learns what 'background' looks like instead … it will pick up kangaroos, tin cans, bones and obviously black rocks."

Are fireballs happening more regularly? 

According to Phil Bland, a meteorite expert at Curtin University who set up the Desert Fireball Network in 2012, there are times of the year when you might get more or fewer meteors and fireballs in the sky. 

"That's mostly related to dust from comets," Professor Bland says.

"As the comet goes around the Sun, it leaves that trail of dust behind. And if the Earth is moving through that trail, we get a lot of meteors and fireballs all of a sudden."

This is commonly known as a meteor shower, and occur at the same time every year as we move through the comet's path.

Dr Sansom says the November Taurids meteor shower and the December Geminids meteor shower (which is the best in Australia) are known to have bigger chunks and produce fireballs. 

That doesn't mean that we're getting more fireballs year-on-year though. 

Instead, you might see more of them on your feed or in the news because we're better able to capture them. Almost everyone has a camera in their pocket, and continuously recording dash cams and home security cameras are becoming more common.

"There's just more people observing or noticing them," Dr Sansom says.

But another factor is definitely increasing: burning space junk. 

What about space junk?

Hundreds of kilometres above sea level there are satellites, leftover pieces of rocket, and plenty of other debris orbiting the Earth. 

Eventually, everything that's up there will make its way back to Earth. 

When it does, it enters the atmosphere and burns up in a similar way to a fireball. And just like a fireball, sometimes a piece makes it to the ground. 

It's this type of "fireball" that's becoming more common in our night sky, and they're only going to be more frequent over time. 

Alice Gorman, space archaeologist at Flinders University who specialises in space junk, notes that with the increase in Starlink satellites and other internet mega-constellations, the number of "re-entries" of satellites is likely to increase dramatically.

"We're likely to see a lot more," Dr Gorman says.

"With mega-constellations, the failure of a number of spacecraft are built into the system."

And Australia is likely to see more than our fair share of these space junk "fireballs".

That's because Australia is relatively close to Point Nemo: an area in the South Pacific that is commonly used as a spacecraft dumping ground because it's the furthest point from land.

"There's more than 300 spacecraft at the bottom of the ocean at Point Nemo," Dr Gorman says. 

"Controlled re-entry" to a location like Point Nemo is the space industry standard for disposing of space junk. But even spacecraft that can't do controlled re-entries still sometimes aim for the Southern Hemisphere, because there is more ocean and fewer people than the Northern Hemisphere.

"The things that most commonly will hit the ground tend to be parts of the fuel system, which are made out of metal alloys with a high burning point," Dr Gorman says.

It's these fuel systems, and other well-insulated parts of the spacecraft, that end up making landfall, like the multiple pieces of a SpaceX crew Dragon capsule that landed in a field in the Snowy Mountains in 2022.

But there is one silver lining to a piece of space junk making a surprise landing, according to Professor Bland.

"The good thing is they're really bright, and if you are looking up, you can avoid them," he laughs.

"The slow ones are going just 8 kilometres a second."