So you've heard that an asteroid could crash into Earth and wreak all kinds of havoc, but how many space rocks actually threaten our planet?
It's complicated because the answer depends on what you mean by threats.
Let's start with the most important thing: NASA is not aware of any asteroids large enough to cause significant damage to Earth that are currently on the verge of colliding with our planet any time soon. But big asteroids orbiting Earth? We've discovered many, and scientists are discovering new near-Earth asteroids almost every day, with more than 27,000 identified so far.
Related : What Time Is SpaceX's 1st Starship And Super Heavy Launch On April 17?
“We are building numbers for these populations, but at the same time there are no known threats to Earth at this time,” said Kelly Fast, director of the Near-Earth Object Observing Program at the Earthquake Coordination Office. NASA planetarium defense. space.com. "To our knowledge, no asteroid poses a significant threat to Earth."
And while it may seem paradoxical, the steady increase in the number of near-Earth asteroids turns out to be the best possible news if you're worried about a possible asteroid impact.
The two parts of planetary defense
The art of protecting Earth from an asteroid impact is known as planetary defense, and there are two key steps in the process. NASA's Double Asteroid Redirection Test (DART), launching later this month, is a mission designed to test the second tier of planetary defenses and prevent a threatening asteroid from traversing Earth.
But before anyone can attempt to deflect an asteroid, scientists must find the space rock and map its orbit many years in the future to see if it will or could hit Earth.
"People might think planetary defense is about deflecting asteroids, but it's not," Nancy Chabot, a planetary scientist at Johns Hopkins University's Applied Physics Laboratory in Maryland, told Space.com and director of DART coordination. "To be able to do something about this in the future, it's really crucial to track the actual asteroids, identify them and find them."
Scientists have identified around 750,000 asteroids so far, but they suspect there are millions of space rocks floating around the solar system. Fortunately, many of them stay very, very far from Earth; Think, for example, of the inhabitants of the main asteroid belt or the Trojan asteroids that flank Jupiter in its orbit.
At the edge of Earth's forests, that number dwindles somewhat: scientists have identified more than 27,000 near-Earth asteroids, and new ones are being discovered every day.
A bonanza of discoveries
These discoveries are due to a team of instruments on Earth and in space that spend some or all of their time discovering and cataloging asteroids. The vast majority of these discoveries have been made since the late 1990s, although experts have previously warned of the threat of asteroids, with little success.
"If you talk to scientists who studied this in the 80s, there's a phrase they refer to a lot called the laughter factor," said Carrie Nugent, a planetary scientist at Olin College in Massachusetts, at Space.com. "They're basically saying they can't talk about this scientific subject without people laughing at them."
The job was hard enough at the time, with measurements based on photographic film developed in a darkened room and then used with a device that helped a human brain spot asteroids moving in front of background stars. Today, modern cameras and computer software can do much of the identification work.
So the increase in asteroid detections was partly a matter of technology. But fundraising was also crucial, so reducing the laugh factor was key.
A milestone was the impact of Comet Shoemaker-Levy 9 on Jupiter in 1994, which unexpectedly left an Earth-sized imprint on Jupiter's clouds that lasted for months. "People started thinking, 'Wow, if this happened to Jupiter, what if it hit Earth?'" Nugent said.
Congress decided to make asteroid hunting a priority and asked NASA to identify at least 90% of the largest asteroids, followed by intermediates. Today, there are a variety of projects that discover near-Earth asteroids, whether it's their top priority or an opportunity to be exploited.
Leading the current load are programs such as Arizona-based Catalina Sky Survey, which specializes in detecting smaller asteroids, the Pan-STARRS observatory in Hawaii, which excels in detecting faint objects , the NEOWISE space telescope, which lets you see the whole sky, and the ATLAS telescopes in Hawaii, which are tuned to the fastest moving objects.
"It's like the ecosystem, everyone has their role," Nugent said. "Each working together with their own power to truly cover the sky."
Others contribute if luck permits. "Widefield telescopes are deployed for other purposes, such as astrophysical research, and then capture asteroids, which they bombard," Fast said.
And asteroid hunters hope new instruments will soon join the team. Defenders of the planet are particularly excited that the Vera C. Rubin Observatory in Chile will begin observing in 2023; A space mission called NEO Surveyor is also in development and is expected to launch later this decade.
"A lot of work has been done to predict how many items the two [missions] will find, and those numbers are incredibly high," Nugent said. "The number of discovered asteroids and comets is expected to increase dramatically, and that's always very exciting."
But studies alone are not enough for planetary defense experts: follow-up observations are crucial in providing scientists with the data they need to accurately calculate an object's orbit. "That's the key thing there," Fast said. "You want to know if the asteroid is there, but you really want to know where it will be in the future and if Earth will be in the same place at the same time."
Recipe for a "potentially hazardous asteroid"
If all of these observations show that an asteroid is of a certain magnitude (indicating a certain size, although the two factors are not exactly correlated) and is within 4.65 million miles (7.48 million kilometers) from Earth, the object is automatically called a "potentially dangerous asteroid". (The distance is one-twentieth of the average distance between Earth and the Sun.)
But in most cases, despite the ominous terminology, "potentially hazardous asteroids" can also be referred to as "currently non-hazardous asteroids." After all, these are the objects that scientists have already found, tracked, mapped, and predicted for the future.
"It's not like looking at a potentially dangerous object and breaking into a cold sweat," Nugent said. "It just means we want to keep an eye on it."
For those who spend their careers watching the skies for an apocalypse, the still-unidentified asteroids are so much scarier; These asteroids are the ones that can appear, suddenly uncomfortably close to Earth, too late for anyone to even try to change the course of a rock.
Scientists think they've found nearly all of the biggest asteroids over 3,300 feet (1 km), and they know they're the easiest to find anyway. And while small near-Earth asteroids are plentiful and hard to find, they're also the most likely to break up harmlessly in Earth's atmosphere.
Therefore, it is the category of medium-sized asteroids, more than 140 meters (460 feet) in diameter but less than 3,300 feet (3,300 feet) that worries planetary defense experts the most. "That's where an impact is most likely to happen," Fast said. "Even with that, we're talking about time scales of centuries or millennia."
At the end of 2020, estimates indicated that scientists had found only 40% of near-Earth objects of this size; this year he added 500 to the account. While that number is impressive, NASA's Office of Planetary Defense estimates that at current speeds, it will take scientists another 30 years to identify 90 percent of objects that size, a goal Congress has given NASA and that it will continue until it is achieved in 2020.
"There are more as the size goes down, and we're still accumulating numbers every year," Fast said. "That's why the polls do their job every night so you don't get caught off guard."
Read Also : What time is SpaceX's 1st Starship and Super Heavy launch on April 17?
White Clover Markets
So you've heard that an asteroid could crash into Earth and wreak all kinds of havoc, but how many space rocks actually threaten our planet?
It's complicated because the answer depends on what you mean by threats.
Let's start with the most important thing: NASA is not aware of any asteroids large enough to cause significant damage to Earth that are currently on the verge of colliding with our planet any time soon. But big asteroids orbiting Earth? We've discovered many, and scientists are discovering new near-Earth asteroids almost every day, with more than 27,000 identified so far.
Related : What Time Is SpaceX's 1st Starship And Super Heavy Launch On April 17?
“We are building numbers for these populations, but at the same time there are no known threats to Earth at this time,” said Kelly Fast, director of the Near-Earth Object Observing Program at the Earthquake Coordination Office. NASA planetarium defense. space.com. "To our knowledge, no asteroid poses a significant threat to Earth."
And while it may seem paradoxical, the steady increase in the number of near-Earth asteroids turns out to be the best possible news if you're worried about a possible asteroid impact.
The two parts of planetary defense
The art of protecting Earth from an asteroid impact is known as planetary defense, and there are two key steps in the process. NASA's Double Asteroid Redirection Test (DART), launching later this month, is a mission designed to test the second tier of planetary defenses and prevent a threatening asteroid from traversing Earth.
But before anyone can attempt to deflect an asteroid, scientists must find the space rock and map its orbit many years in the future to see if it will or could hit Earth.
"People might think planetary defense is about deflecting asteroids, but it's not," Nancy Chabot, a planetary scientist at Johns Hopkins University's Applied Physics Laboratory in Maryland, told Space.com and director of DART coordination. "To be able to do something about this in the future, it's really crucial to track the actual asteroids, identify them and find them."
Scientists have identified around 750,000 asteroids so far, but they suspect there are millions of space rocks floating around the solar system. Fortunately, many of them stay very, very far from Earth; Think, for example, of the inhabitants of the main asteroid belt or the Trojan asteroids that flank Jupiter in its orbit.
At the edge of Earth's forests, that number dwindles somewhat: scientists have identified more than 27,000 near-Earth asteroids, and new ones are being discovered every day.
A bonanza of discoveries
These discoveries are due to a team of instruments on Earth and in space that spend some or all of their time discovering and cataloging asteroids. The vast majority of these discoveries have been made since the late 1990s, although experts have previously warned of the threat of asteroids, with little success.
"If you talk to scientists who studied this in the 80s, there's a phrase they refer to a lot called the laughter factor," said Carrie Nugent, a planetary scientist at Olin College in Massachusetts, at Space.com. "They're basically saying they can't talk about this scientific subject without people laughing at them."
The job was hard enough at the time, with measurements based on photographic film developed in a darkened room and then used with a device that helped a human brain spot asteroids moving in front of background stars. Today, modern cameras and computer software can do much of the identification work.
So the increase in asteroid detections was partly a matter of technology. But fundraising was also crucial, so reducing the laugh factor was key.
A milestone was the impact of Comet Shoemaker-Levy 9 on Jupiter in 1994, which unexpectedly left an Earth-sized imprint on Jupiter's clouds that lasted for months. "People started thinking, 'Wow, if this happened to Jupiter, what if it hit Earth?'" Nugent said.
Congress decided to make asteroid hunting a priority and asked NASA to identify at least 90% of the largest asteroids, followed by intermediates. Today, there are a variety of projects that discover near-Earth asteroids, whether it's their top priority or an opportunity to be exploited.
Leading the current load are programs such as Arizona-based Catalina Sky Survey, which specializes in detecting smaller asteroids, the Pan-STARRS observatory in Hawaii, which excels in detecting faint objects , the NEOWISE space telescope, which lets you see the whole sky, and the ATLAS telescopes in Hawaii, which are tuned to the fastest moving objects.
"It's like the ecosystem, everyone has their role," Nugent said. "Each working together with their own power to truly cover the sky."
Others contribute if luck permits. "Widefield telescopes are deployed for other purposes, such as astrophysical research, and then capture asteroids, which they bombard," Fast said.
And asteroid hunters hope new instruments will soon join the team. Defenders of the planet are particularly excited that the Vera C. Rubin Observatory in Chile will begin observing in 2023; A space mission called NEO Surveyor is also in development and is expected to launch later this decade.
"A lot of work has been done to predict how many items the two [missions] will find, and those numbers are incredibly high," Nugent said. "The number of discovered asteroids and comets is expected to increase dramatically, and that's always very exciting."
But studies alone are not enough for planetary defense experts: follow-up observations are crucial in providing scientists with the data they need to accurately calculate an object's orbit. "That's the key thing there," Fast said. "You want to know if the asteroid is there, but you really want to know where it will be in the future and if Earth will be in the same place at the same time."
Recipe for a "potentially hazardous asteroid"
If all of these observations show that an asteroid is of a certain magnitude (indicating a certain size, although the two factors are not exactly correlated) and is within 4.65 million miles (7.48 million kilometers) from Earth, the object is automatically called a "potentially dangerous asteroid". (The distance is one-twentieth of the average distance between Earth and the Sun.)
Read Also : What time is SpaceX's 1st Starship and Super Heavy launch on April 17?But in most cases, despite the ominous terminology, "potentially hazardous asteroids" can also be referred to as "currently non-hazardous asteroids." After all, these are the objects that scientists have already found, tracked, mapped, and predicted for the future.
"It's not like looking at a potentially dangerous object and breaking into a cold sweat," Nugent said. "It just means we want to keep an eye on it."
For those who spend their careers watching the skies for an apocalypse, the still-unidentified asteroids are so much scarier; These asteroids are the ones that can appear, suddenly uncomfortably close to Earth, too late for anyone to even try to change the course of a rock.
Scientists think they've found nearly all of the biggest asteroids over 3,300 feet (1 km), and they know they're the easiest to find anyway. And while small near-Earth asteroids are plentiful and hard to find, they're also the most likely to break up harmlessly in Earth's atmosphere.
Therefore, it is the category of medium-sized asteroids, more than 140 meters (460 feet) in diameter but less than 3,300 feet (3,300 feet) that worries planetary defense experts the most. "That's where an impact is most likely to happen," Fast said. "Even with that, we're talking about time scales of centuries or millennia."
At the end of 2020, estimates indicated that scientists had found only 40% of near-Earth objects of this size; this year he added 500 to the account. While that number is impressive, NASA's Office of Planetary Defense estimates that at current speeds, it will take scientists another 30 years to identify 90 percent of objects that size, a goal Congress has given NASA and that it will continue until it is achieved in 2020.
"There are more as the size goes down, and we're still accumulating numbers every year," Fast said. "That's why the polls do their job every night so you don't get caught off guard."