NASA’s James Webb Space Telescope (JWST) is a remarkable machine capable of many wondrous things: It can peer at galaxies that formed just after the Big Bang, examine distant planets, and zoom in on the worlds and moons of our own solar system. New research, published this month in Nature, has found that it’s also surprisingly good at spying small space rocks—including some just dozens of feet in length, the tiniest ever discovered in our solar system’s main asteroid belt between Mars and Jupiter.

The JWST wasn’t designed to spot undiscovered asteroids; it’s more of a sniper’s scope used to get a close-up look at curious objects extremely far from Earth. “The average exoplanet person doesn’t care about asteroids,” says study coauthor Artem Burdanov, a planetary scientist at the Massachusetts Institute of Technology.

To those studying far-flung galaxies and planets, space rocks are usually more of an annoyance than anything. “Astrophysicists have had to deal with asteroids photobombing their datasets ever since they started using photography in the 1800s and termed them ‘vermin of the skies’ as a result,” says Andy Rivkin, a planetary astronomer at Johns Hopkins Applied Physics Laboratory in Maryland who was not involved with the new study.

2024 YR4 set a new record a week ago for having the highest probability of hitting Earth. (Nasa/NMIT pic)

PARIS : The chance that a football field-sized asteroid capable of destroying a city will strike Earth in 2032 has fallen to 0.001%, the European Space Agency said today.

A week ago, the asteroid set a new record for having the highest probability of hitting Earth – 3.1% according to Nasa and 2.8% according to the ESA.

The planetary defence community has been scanning the skies.

However, as had been widely expected, fresh observations from telescopes around the world narrowed the area of uncertainty where the asteroid could strike, increasingly ruling out the odds of a direct hit.

The ESA said the chance was now down to 0.001%, adding that the threat level on the Torino Impact Hazard Scale was now at zero – after hitting level three out of a possible 10 last week.

The asteroid, called 2024 YR4, was discovered in December.

It is estimated to be 40m-90m wide, which means it has the potential to devastate a city.

The impact date would have been Dec 22, 2032 – but it is now extremely likely the asteroid will simply zoom past Earth.

Despite the plummeting risk, the James Webb Space Telescope will still observe the asteroid in the coming months, the ESA said.

Scientists had emphasised that even if the asteroid had been heading our way, Earth is now capable of fighting back.

In the first test of our planetary defences, Nasa’s DART mission successfully altered a harmless asteroid’s trajectory in 2022 by smashing a spacecraft into it.

Richard Moissl, head of the ESA’s planetary defence office, told AFP that observing the asteroid – then ruling out a direct hit – was “a very exciting and educational exercise”.

Praising the early detection of the asteroid, he emphasised that “there is still ample room for improvement”.

Several new telescopes, such as the Vera Rubin and Flyeye, which are near becoming operational will enable astronomers to spot asteroids more quickly, Moissl said.

So will Europe’s planned early warning mission Neomir, he added.

The last time an asteroid bigger than 30m wide posed such a significant risk was Apophis in 2004, when it briefly had a 2.7% chance of striking Earth in 2029 – a possibility also ruled out through additional observations.

Asteroids fly by Earth on a regular basis, and most of them are of no concern whatsoever. But sometimes a space rock gets flagged as a potential threat because there is a slim chance that it may collide with Earth. A newly discovered near-Earth asteroid called 2024 YR4 is one possibly perilous object: It’s a 130 to 300-foot long rock that could impact somewhere on Earth on December 22, 2032.

To be clear, there is no need to hurriedly invest in a hardened bunker. This asteroid is certainly worth watching because it could devastate a city with a direct hit—even on the small side of its size estimate. At one point, the rock had a 3.1 percent chance of a violent rendezvous with Earth—the highest ever recorded. The odds have since fallen to 1.5 percent and will most likely, drop precipitously to zero, as astronomers gather more data on the future orbit of 2024 YR4. (There’s also small chance, 0.8 percent, that the rock could hit the moon.)

The detection shows that the system for defending Earth from lethal space rocks works like a well-oiled global machine. Observatories all over the world contribute to finding near-Earth objects. And both NASA and the European Space Agency (ESA) have developed automated software programs that can, with extreme precision, track every single potentially hazardous asteroid and comet found to date.

On 4 September, an asteroid was spotted curving towards Earth. Astronomers quickly established that it would impact the planet in 10 hours’ time. The Philippines island of Luzon was in the line of fire, and there was nothing they could do about it but watch. Sure enough, at 16.39 UTC (17.39 in the UK), just as predicted, the space rock plunged into the world and burst into flames.

If you’re wondering why you’re still around to read this, it’s because that meteor was only a metre in length. Far too puny to cause any damage, the asteroid instead harmlessly ignited in the upper atmosphere, temporarily painting the sky in a blue-green streak of light. As it turns out, small asteroids hit the planet all the time. They’re nothing to worry about – but it doesn’t take a massive leap in size for one to become a threat.

An asteroid just 20m long exploding in the sky could implode windows and knock people off their feet. A 50m space rock could ruin a town, causing widespread infrastructural damage, injuries and deaths many miles away from the site of the mid-air explosion. And an asteroid 140m in length would make its way to the ground, slice a hole in the face of the planet, and instantly destroy a sprawling metropolis.

For billions of years, Earth has been at the mercy of such cosmic threats – but oh, how times have changed. Today, there exists a field of applied science known as planetary defence, which is exactly what it sounds like: scientists and engineers working around the clock to protect the world from apocalyptic space rocks. One of the ways in which they do this is by spying on the heavens, scanning the night sky for asteroids that may be heading our way. In the next few years, two next-generation telescopes are coming online that will find almost all the space rocks that have been eluding even the most eagle-eyed astronomers. And if these missions achieve their considerable promise, all 8 billion of us will be significantly safer than we are now.

Planetary defence falls into two categories. The first is more offensive, using technology to deflect or destroy an incoming asteroid of those 140m-long city-killing or 50m-long town-trashing dimensions. In 2022, Nasa conducted the first planetary defence experiment in history. As part of the Double Asteroid Redirection Test, or Dart mission, it crashed an uncrewed spacecraft into a (harmless) asteroid to see if it could deflect it. Dart passed this test – a dress rehearsal for a genuine global emergency – with flying colours, suggesting that an asteroid big enough to vaporise a metropolis could be knocked out of Earth’s way, should we rush to meet it with force and precision.

There is, however, a huge caveat to this technique: we can’t deflect asteroids if we don’t know where they are. That’s why planetary defence is a tag team effort. While space agencies are building spacecraft and developing technology to deflect (or destroy) incoming asteroids, others have their eyes on the sky, seeking any near-Earth asteroids that may imperil us.

At the moment, Earth’s continued safety relies on optical astronomy: telescopes that look for sunlight glinting off space rocks that have yet to be discovered. Many observatories conduct all sorts of astronomical quests; finding asteroids is something that happens opportunistically during those surveys. Some telescopes, including a select few funded by Nasa, are solely dedicated to finding errant asteroids.

There are roughly 14,000 near-Earth asteroids with city-flattening potential still out there to be found

This method of space rock sleuthing has proved fairly effective, especially for the heftier asteroids. Nasa estimates that most of the planet killers – asteroids a kilometre long or above – zooming about near Earth’s orbit around the sun have been found. (The asteroid that swiftly ended the reign of the non-avian dinosaurs 66 million years ago was 10km long, and easily fits into the planet killer category.) It also suspects it has spotted just under half of those 140m, near-Earth, city-killer-size asteroids. (And, thankfully, none of them are on a collision course with Earth.)

But this crop of asteroid-seeking surveys is insufficient to shield the planet. There are roughly 14,000 near-Earth asteroids with city-flattening potential still out there to be found. And only a handful of near-Earth asteroids 50m long have been identified; Nasa reckons there are hundreds of thousands of town-trashing space rocks hiding nearby. Astronomers have been crying out for a better instrument to scan the stars to find these asteroids before they find us. Fortunately, they’re about to get two.

The first is Nasa’s Near-Earth Object Surveyor, or NEO Surveyor, mission. It’s essentially a sniper that is going to be hidden in outer space. Within 10 years of being launched, it will find 90% or more of those city-killer asteroids that have yet to be found by conventional means.

This planetary defence mission has been through developmental hell, having to spend years competing for attention with other space mission concepts that were purely about planetary exploration in the name of scientific curiosity. But today it is a separate, dedicated mission with its own funding stream – and Nasa recently gave the green light to begin building it. Its secret sauce comes from the fact that, instead of using reflected starlight to find asteroids, it’s going to seek out their heat signatures.

Using visible light to spy asteroids allows astronomers to catch sight of moving objects and get an estimate of their size. But there is an issue with this method: a small asteroid that has a shiny rocky coating reflects as much light as a bigger asteroid that has a dull, charcoal-like coating. That means it’s hard to tell the size of an asteroid using reflected light, which is problematic if you’re trying to work out whether you have a town trasher or a city killer coming at you.

A second issue is that there are probably many asteroids hidden in the glare of the sun. If you try to look at it with your naked eye – which I wouldn’t advise – you’d struggle to see anything. The same applies to Earth’s telescopes: if they point towards the sun, many asteroids will be invisible, like lit matches in front of a raging bonfire.

NEO Surveyor circumvents both problems. Sitting far from Earth, and covered in a sun shield, it will be one of the coldest objects ever built. And that allows its infrared eye to be extremely sensitive to any heat sources, including those of city-killer asteroids warmed by the sun. It will be so perceptive that even asteroids concealed by the sun’s glare will quickly show up on its scopes.

View image in fullscreen An illustration of Nasa’s NEO Surveyor, which will use an infrared eye to spot asteroids. Photograph: Alamy

It is to be launched sometime in the next five years. And when it does, it will already have a ground-based partner tallying up its own near-Earth asteroid count: the Vera C Rubin Observatory, under construction now in the mountains of Chile.

Unlike NEO Surveyor, Rubin is not a dedicated asteroid hunter, and it relies on reflected starlight, not infrared emissions. But it has the most technologically advanced mechanical eye ever made. With a colossal mirror that collects even the faintest, most distant starlight, and a 3,200-megapixel digital camera the size of a car, it will see and chronicle anything that moves in the dark sky above, from distant exploding stars to interstellar comets.

It will also create a detailed inventory of pretty much everything in the solar system, including the host of objects flying around close to our planet. The first asteroid was spotted in 1801, and it took two centuries to find a million more. In the first six months of operations, which begin in 2025, Rubin will double that number. It is, in other words, a polymathic telescope; one that, among all its other tasks, will find asteroids of all shapes and sizes faster than any other spotter on Earth.

Like any ground-based observatory, Rubin must still deal with bad weather and an increasing number of reflective artificial satellites occluding its view. But, along with NEO Surveyor, it will accomplish what traditional telescopes have often struggled to do: find potentially cataclysmic asteroids. In fact, the combined power of NEO Surveyor and the Rubin Observatory means that, by the 2040s, we should know whether Earth is in danger of being hit by a city killer-sized asteroid within the next century.

If we did discover that we were in the line of fire, it would be terrifying. But at least we could do something about it: space agencies could launch a mission to deflect it – either hitting it with a Dart-like spacecraft, or aggressively irradiating one side of it with a nuclear explosion – or blast it into tiny pieces, or at the very least (and once the impact zone is more precisely known) plan to get those in harm’s way to a place of safety. And if it’s found that none of these asteroids are heading our way for the foreseeable future, then humanity can breathe a collective sigh of relief, and have one less existential risk to worry about.

For most of our species’s history, we had no dominion over space. It was something that affected us, not the other way around. Even after setting up space stations in orbit around the planet, after visiting the moon with astronauts, and after sending spacecraft into interstellar space, we have remained passive observers of the cosmos. Planetary defence makes us active participants in it. We not only live in a time in which we can make intricate maps of the night sky and everything in it, we are also able to rearrange our galactic neighbourhood to make it a more habitable place to live.

The world is besieged by conundrums: the climate crisis, war, poverty, political instability, pandemics, environmental destruction. Earth is a beautiful, troubled place. But, increasingly, it’s one protected from threats originating from beyond the firmament – and for that, we can most certainly be thankful.

Dr Robin George Andrews is the author of How to Kill an Asteroid: The Real Science of Planetary Defence (WW Norton & Company, £19.99). To support the Guardian and Observer order your copy at guardianbookshop.com. Delivery charges may apply

An illustration shows hexagon shaped footprints project on a band of asteroids representing the view of the Rubin observatory

The forthcoming Vera C. Rubin Observatory will never leave Earth itself, but the highly detailed, “big picture” view of the cosmos it will offer scientists may very well kick-start a new era of space exploration.

The solar system is filled with billions of small rocky bodies and icy objects, many of which formed around 4.5 billion years ago when planets like the Earth were forming around the sun. Space missions like NASA’s OSIRIS-REx, Lucy, and Psyche have been making strides in visiting these primordial solar system bodies. They’ve been collecting images, and OSIRIS-REx even snagged a few samples, for investigation here on Earth — all informed by data collected by observatories across the globe.

Rubin, which will see its “first light” in 2025, will be capable of detecting millions of new asteroids, comets and potentially even bodies passing through our planetary backyard from other systems. Take Oumuamua, for instance, which was first spotted in 2017. After detecting these bodies, Rubin will then quickly track them as they move around the solar system and tread close to Earth — or even if they remain in the main asteroid belt between Mars and Jupiter.

Related: Dark energy is forcing the universe to expand. This new observatory may show us how

“Nothing will come close to the depth of Rubin’s survey and the level of characterization we will get for solar system objects,” Siegfried Eggl, Assistant Professor at the University of Illinois Urbana-Champaign and Lead of the Inner Solar System Working Group within the Rubin’s Solar System Science Collaboration, said in a statement. “It is fascinating that we have the capability to visit interesting objects and look at them close-up. But to do that, we need to know they exist and where they are.

“This is what Rubin will tell us.”

Picking out asteroid muses

Rubin will monitor solar system bodies and cosmic objects that quite far out, beyond even the limits of the solar system and the Milky Way galaxy, as it conducts its 10-year Legacy Survey of Space and Time (LSST).

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Scanning the entire southern hemisphere sky every few nights with an 8.4-meter, fast-moving telescope and the largest digital camera in the world, Rubin is expected to vastly increase our catalog of known solar system objects that has been built over 200 years — by at least 5 times, scientists project.

The Vera C. Rubin Observatory as it appears at twilight on the El Peñón peak of Cerro Pachón in Chile. (Image credit: RubinObs/NOIRLab/NSF/AURA/J. Pinto)

Not only will Rubin, presently under construction on the mountain Cerro Pachón in northern Chile, spot a multitude of new solar system objects, but scientists also expect it to gather more information about the broader “spacescape” of the solar system.

This could reveal whole regions that contain unique objects to consider as future space mission targets.

“If you think of Rubin as looking at a beach, you see millions and millions of individual sand grains that together constitute the entire beach. There might be an area of yellow sand, or volcanic black sand,” Eggl said. “A space mission to an object in that region could investigate what makes it different. Often, we don’t know what’s weird or interesting unless we know the context it’s in.”

The observatory will be further able to alert operators to changes in the night sky within 60 seconds of spotting them, which could help space agencies quickly plan and deploy a mission toward rapidly moving objects of interest.

This could also give scientists an early warning of an interstellar object like Oumuamua as it passes through the solar system, for instance, allowing teams to study the intruder in situ before it slips out of reach and back into deep space.

“Rubin is capable of giving us the prep time we need to launch a mission to intercept an interstellar object,” Eggl added. “That’s a synergy that’s very unique to Rubin and unique to the time we’re living in.”

An illustration of NASA’s Lucy spacecraft. (Image credit: Robert Lea/NASA)

One project that is already gearing up to take advantage of Rubin data is the JAXA/European Space Agency Comet Interceptor mission that will launch in 2029. The Interceptor will await sighting of a visitable, long-period solar system comet or interstellar object as it passes in front of the sun. Then, it will be deployed for investigtaion.

Rubin could also assist with missions concerning interesting objects located close to the passage of a spacecraft as it conducts its primary mission.

One active mission that could benefit from Rubin’s eye on the solar system is NASA’s asteroid-hopping spacecraft, Lucy. The 12-year mission is set to perform the first in situ study of the Trojan asteroids, two families of space rocks that share Jupiter’s orbit around the sun.

Rubin could spot smaller, fainter asteroids that lie near Lucy’s path to Jupiter, offering the NASA mission some new and unexpected fly-by opportunities.

“With our current telescopes, we’ve essentially been looking at the big boulders on the beach,” Eggl concluded. “But Rubin will zoom in on the finer grains of sand.”