Imagine that an asteroid is heading at full speed towards Earth. It is the size of the Eiffel Tower, shaped like a peanut, and is potentially dangerous. It sounds scary, and it’s not even made up. The asteroid in question, called 2024 ON, has already passed by Earth. He did not avoid us, but there was never a chance of it crashing.
Since its discovery in July 2024, media and content creators made headlines about the details of the asteroid: it was 370 meters in diameter, traveling at about 40,000 kilometers per hour, was considered “potentially dangerous” by space authorities, and was heading towards the Land.
But as soon as 2024 ON was discovered, Astronomers calculated that it would pass by our planet at a distance of one million kilometers. That’s more than double the distance to the Moon. “Publications need to have these ‘cliffhangers’ to receive visits,” said Juan Luis Cano, of the European Space Agency’s Planetary Defense Office. “But daily we receive visits from many objects.”
In fact, around 100 tons of space material impact Earth every day. Fortunately, the mass is distributed among many tiny particles, rather than one large destroying body.
Near-Earth Objects
The Office of Space Affairs of the The United Nations defines near-Earth objects (NEOs) simply as any asteroid or comet that passes close to Earth’s orbit..
In more technical terms, NEOs are objects with a perihelion (their closest orbital distance from the sun) of less than 195 million kilometers.
Since the Earth orbits the Sun at a distance of about 150 million kilometers, NEOs are well within our solar neighborhood. Scientists like Cano know of about 34,000 NEOs, but none of the largest are currently on track to impact Earth.
How likely is an asteroid impact?
While tiny NEOs hit Earth every day, larger ones do so much less frequently. Asteroids the size of 2024 ON could hit Earth once every 10,000 years.
Those more than a kilometer in diameter, like the Chicxulub asteroid that caused the extinction of the dinosaurs 66 million years ago, could do so every 260 million years.
“We estimate that there are around a thousand objects larger than one kilometer and we have discovered 95% of them,” Cano said. “They are the ones that could really cause a global disaster.”
But the smallest ones also have destructive potential. Depending on the speed and angle of entry into Earth’s atmosphere, a 40-meter-wide rock could level an entire city. Hundreds of thousands of smaller NEOs have not yet been catalogued. “We discovered around 3,000 near-Earth asteroids [NEAs] every year,” Cano said. “But we need to find them faster.”
Finding nearby objects: a ‘complicated’ task
In the last decade or so, two space telescopes have been in charge of finding NEOs. First was NEOWISE, which documented more than 158,000 NEOs before retiring in 2024 on a more than 10-year mission. Second is a mission called Near-Earth Object Surveyor.
The NEO Surveyor should begin operating in 2027. Its objective will be to find the rest of the potentially dangerous asteroids 50 million kilometers from Earth’s orbit. But finding dangerous objects in space is complicated. “One of the hardest things to do in astronomy is determine how far away something is,” said Amy Mainzer, a UCLA planetary scientist who led the NEOWISE mission and will lead NEO Surveyor.
“One might think, ‘Well, we see objects at the edge of space, why don’t we know what’s right next to us here on Earth?’ Don’t we know everything?’ and the answer is, ‘No, it’s actually very difficult.'”
Take Apophis for example. When it was first identified in 2004, the 340-meter-wide Apophis was considered one of the most potentially dangerous objects ever discovered. It was thought that it could impact the Earth in 2029, 2036 or 2068.
Subsequent calculations ruled out that possibility. Apophis will pass 30,000 kilometers from the planet, closer than the Moon and within the range of geostationary satellites. But according to current projections the impact will not occur.
What would happen if a new rogue NEO was detected on a collision course with Earth? If given enough notice, engineers could try to reroute it.
In 2022, NASA’s Double Asteroid Redirection Test (DART) mission successfully crashed a spacecraft into an asteroid called Dimorphos. It was shown that a mission based on collisions could change the direction of a celestial body and defend our planet.
ESA plans to launch a reconnaissance mission called Hera in October 2024 to inspect the aftermath left by DART.
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