An asteroid the size of a football stadium will pass between Earth and the moon on Saturday morning – the second of two astronomical near-misses in three days.
Near miss in this case is a relative term: Saturday’s asteroid, 2024 MK, will come within 110,000 miles of Earth. Meanwhile, on Thursday, asteroid 2011 UL21 flew within 4 million miles.
But the Saturday passage of MK 2024 – which scientists discovered just two weeks ago – coincides with a sobering reminder of threats from space.
Sunday is Asteroid Day, the anniversary of the explosion of a boulder from space over a Russian city in 1908. Astronomers warn that such dangers always lurk as Earth hurtles through space.
Here’s what you need to know about asteroids, the risk from space and Saturday’s near miss.
What is an asteroid?
Asteroids are rocks in space that orbit the sun, just like the planets they occasionally cross paths with.
Like planets, asteroids formed over 4.6 billion years ago from the condensing cloud of dust and gas that created the solar system – making them essentially time capsules of the distant past before the formation of the Earth or the Sun.
Scientists have identified about 1.3 million of them, most of which orbit the vast space between Mars and Jupiter. Both individually and collectively they are generally small; the total weight of all asteroids in the solar system is believed to be less than that of the moon.
Throughout history, asteroid impacts may also have been crucial to life on Earth.
In other asteroid news from last week, scientists on Wednesday announced the results of a 2023 mission to the asteroid Bennu that had returned with samples, suggesting the possibility that it was packed with ingredients for water.
These findings suggest a bright side to asteroid impacts. “Asteroids like this may have played an important role in delivering water and the building blocks of life to Earth,” said co-author Nick Timms of Curtin University.
What happens if someone hits the Earth now?
An asteroid doesn’t have to be particularly big to cause damage. In 2013, for example, an asteroid about 60 feet in diameter broke apart nearly 20 miles above Siberia, releasing 30 times as much energy as the atomic bomb that hit Hiroshima.
Although most of the impact energy was absorbed by the atmosphere, the explosion created a shock wave that blew out windows and injured more than a thousand people.
On Sunday, Asteroid Day commemorates an even bigger impact: the 1908 Tunguska event, which also occurred over Siberia.
In that case, the Russian newspaper Sibir (Siberia) reported that farmers looking up saw a “strange bright (impossible to look at) bluish-white celestial body, which moved downwards for 10 minutes.”
The body appeared to be a “pipe” cylinder that began to “stain” as it hit the denser atmosphere above the forest and dissipated into clouds of black smoke,” the article said.
“A loud knock (not thunder) was heard as if large stones were falling, or guns were fired. All buildings shook. At the same time the cloud began to emit flames of uncertain shapes. All the villagers panicked and took to the streets, women were crying, thinking it was the end of the world.”
If 2024 MK, with a diameter of 500 to 800 feet, were to hit Earth instead of passing by on Saturday, it wouldn’t be the end of the world — at least not completely. Such an impact would have “the equivalent impact energy of hundreds of megatons approaching a gigaton,” Peter Brown of Canada’s Western University told the Canadian Broadcasting Service.
That’s a huge potential impact. For comparison, the explosion would be 10 to 20 times bigger than most hydrogen bombs tested, which have a force of 50 megatons.
“It’s the kind of thing that if it were to hit the East Coast of the US, you would have catastrophic effects on most of the East Coast. But it’s not big enough to affect the entire world,” Brown said.
The impact of a hypothetical collision with 2011 UL21, the asteroid that flew past on Thursday, would be far more catastrophic. Although it was comfortably far out in space and had no chance of hitting Earth, it was also very large: about the size of Mount Everest.
At 2.5 kilometers in diameter, the asteroid was about a quarter the size of the asteroid that hit Earth 65 million years ago, wiping out all the dinosaurs that walked the Earth, as well as most life on Earth.
How likely is a collision?
Research suggests it is very, very low. NASA has estimated that a civilization-ending event (such as Thursday’s sized asteroid colliding with Earth) should occur only once every few million years.
And such an impact by an asteroid with a diameter of 800 meters or larger will be virtually impossible for a long time, according to findings published last year in The Astronomical Journal.
“It’s good news,” study leader Oscar Fuentes-Muñoz of the University of Colorado Boulder told MIT Technology Review. “As far as we know, there’s no impact in the next 1,000 years.”
NASA’s catalog of large and dangerous objects like 2011 UL21 is now 95 percent complete, Technology Review reports.
But as the explosions of 1908 and 2013 suggested, a relatively small asteroid can still “do a lot of damage”, Áine O’Brien of the University of Glasgow warned in the Technology Review.
The map of asteroids the size of the one passing between Earth and the moon on Saturday — which could destroy a city if it struck the planet — is still only 40 percent complete, according to Big Think magazine.
How do scientists detect and track asteroids?
They do this by constantly scanning the sky for relatively small, fast-moving objects. The Asteroid Terrestrial-impact Last Alert System that detected 2024 MK is one of many surveys looking for risks.
These studies provide early warnings that could help prevent asteroid impacts, Alan Fitzsimmons of Queen’s University Northern Ireland told the CBC.
“It’s the only natural disaster we can stop. You can’t stop a tsunami, you can’t stop an earthquake, you can’t stop a volcano,” he said. “You can actually stop or prevent an asteroid impact, at least in theory.”
NASA managed to knock an asteroid off course in 2022, when its Double Asteroid Redirection Test (DART) slammed a satellite weighing the estimated weight of a small car into Dimorphos, a rock about the same size as 2024 MK – slightly altering its orbit.
The DART mission, which required NASA to perform a precise collision 7.1 million miles away, showed “NASA is trying to be ready for whatever the universe throws at us,” agency director Bill Nelson said at the time. briefing.
But there’s an old adage in science that while in theory there’s no difference between theory and practice, in practice there is. Accomplishing a feat like the DART mission to stop an asteroid from hitting Earth “is certainly possible, but would be a difficult and expensive task,” astronomer Alistair Gunn of the University of Manchester wrote for the British Broadcasting Corporation.
“The key would be to deflect the asteroid from its collision course with Earth, rather than bursting it into equally dangerous debris,” Gunn added.
He also noted that it would take at least five years to accomplish that — which is why early warning is “vital.”
That need for early warning is one of the reasons why the approval of MK 2024 is so troubling: scientists only discovered this this month.
Earlier this week, NASA announced plans to deflect an asteroid, with “high-level gaps” still visible, USA Today reported.
“We’re using the capabilities that we have to hopefully eliminate that hazard, to understand what’s out there and know if anything poses a threat,” Kelly Fast, NASA’s acting planetary defense officer, told the outlet.
Will Americans be able to see Saturday’s asteroid?
Yes – if they are in the right region and both are very prepared and lucky.
Americans in the Southwest US (or Hawaii) who are far from light pollution and are willing to get up in the early morning hours may have a chance to see 2024 MK as a fast-moving dot, which will make its closest approach to Earth at approximately 9:46 a.m. Eastern time.
That’s 90 minutes before sunrise in Hawaii and about an hour after sunrise on the West Coast. The asteroid will be faintly visible before it passes, though.
For anyone outside these areas, the Virtual Telescope Project will stream the passage live.
Even those in the right region may find it tricky to see the passage, Fitzsimmons of Queen’s University told CBC. Stargazers will need a telescope and be prepared to spot a faint, fast-moving object. “You have to know exactly where to look,” he said. “It’s like driving.”
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