(The Hill) — An asteroid the size of a football stadium cut a path between Earth and the moon Saturday morning — the second of two astronomical near-collisions in three days.
Near miss is a relative term in this case: Saturday’s asteroid, 2024 MK, came within 300,000 kilometers of Earth. On Thursday, asteroid 2011 UL21 flew within 6.5 million kilometers.
But the Saturday passage of 2024 MK – 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, dangers from space, and Saturday’s near-flyover.
What is an asteroid?
Asteroids are rocks in space that orbit the sun, similar to the planets they occasionally cross paths with.
Like planets, asteroids formed more than 4.6 billion years ago from the condensing cloud of dust and gas that formed the solar system – essentially making them time capsules of the distant time before the formation of the Earth or the Sun.
Scientists have identified about 1.3 million of them, located mainly in the vast space between Mars and Jupiter. Both individually and in total, they are generally small: the total weight of all asteroids in the solar system is expected to be less than that of the moon.
Throughout history, asteroid impacts may also have played an important role for life on Earth.
In other asteroid news from last week, scientists on Wednesday announced results from a 2023 mission to the asteroid Bennu that returned with samples, suggesting the possibility that it was loaded with the ingredients for water.
These findings suggested a benefit to asteroid impacts. “Asteroids like these may have played a key role in providing water and the building blocks of life on Earth,” said co-author Nick Timms of Curtin University.
What happens if one hits the Earth now?
An asteroid doesn’t have to be particularly big to cause damage. In 2013, for example, an asteroid about 20 meters in diameter that disintegrated nearly 30 kilometers above Siberia released 30 times as much energy as the atomic bomb that hit Hiroshima.
While 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.
Asteroid Day on Sunday 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, which 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 was heard (not thunder), as if large stones were falling or artillery was being fired. All the buildings were shaking. 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 and thinking it was the end of the world.”
If MK 2024, with a diameter of 150 to 240 meters, 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 in the 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 context, the explosion would be 10 to 20 times larger than that of most hydrogen bombs tested, which are in the 50 megaton range.
“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. While 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 2.4 kilometers in diameter, this asteroid was about a quarter the size of the asteroid that struck Earth 65 million years ago, wiping out all walking dinosaurs and most life on Earth.
How likely is a collision?
Research shows that this is very, very low. NASA has estimated that a civilization-ending event (such as Thursday’s asteroid hitting Earth) would only have to happen every few million years.
And such an impact from an asteroid half a mile in diameter or larger would be virtually impossible for a very 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 the MIT Technology Review. “As far as we know, there is 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 that passed between Earth and the moon on Saturday — and which could destroy a city if they hit the planet — is only 40 percent complete, the magazine reported, according to Big Think.
How do scientists detect and track asteroids?
They do this by continuously scanning the sky, looking for relatively small, fast-moving objects. The Asteroid Terrestrial-impact Last Alert System that detected 2024 MK is one of several studies 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 that 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 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 letting it shatter 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 reason why the passage of 2024 MK is so disturbing: scientists only discovered it this month.
Earlier this week, NASA announced plans to deflect an asteroid that still showed “high-level gaps,” USA Today reported.
“We’re using the capabilities that we have to hopefully eliminate this 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.
Could Americans see Saturday’s asteroid?
Yes, if they are in the right region and are well prepared and lucky.
Americans in the Southwest US – or Hawaii – who were bothered by light pollution and were willing to get up in the early morning hours may have a chance to see 2024 MK as a fast-moving dot that will make its closest approach to Earth at around 9:46 a.m. Eastern Time.
That’s 90 minutes before sunrise in Hawaii and about an hour after sunrise on the west coast. However, the asteroid will be faintly visible before it passes by.
For anyone outside these areas, there is a live stream of the passage via the Virtual Telescope Project.
Even those in the right region may find it challenging to view the passage, Queen’s University’s Fitzsimmons told CBC. Skywatchers need a telescope and should be prepared to observe a faint, fast-moving object. “You have to know exactly where to look,” he said. “It’s driving.”