What Will Humanity Do If a Dangerous Asteroid Takes Aim at Earth?

News like “Astronomers have noticed an asteroid the size of a football field flying towards Earth” sometimes appears on the web. In most cases, such space objects do not pose a danger to life on the planet, especially since their existence is known long before they appear near us.

But how exactly? And what should we do if there is an asteroid that is dangerous for the Earth?

We tell you how researchers assess such risks and what the “planetary protection system” has to do with it.

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The milestone is 7.5 million kilometers

That is the threshold distance from the earth, according to information posted in a special section of the official website of the European Space Agency (ESA).

Everything about asteroids

They claim that at the end of last year, about 30,000 near-Earth asteroids were found in the Solar System — rocky bodies orbiting the Sun along a trajectory close to Earth’s orbit.

An asteroid is a relatively small celestial body moving in orbit around the Sun. Asteroids are significantly inferior in mass and size to planets, have an irregular shape, and do not have an atmosphere, although they may also have satellites.

Near-Earth asteroids (NEAs) are asteroids with orbits that bring them within 1.3 astronomical units from the Sun. Only those that are capable of approaching within a distance of 7.5 million kilometers (or 0.05 astronomical units) from Earth in the foreseeable future are considered potentially dangerous objects.

Near-Earth asteroids account for about a third of all asteroids discovered in the Solar System. Moreover, most of them are located in the asteroid belt between Jupiter and Mars, according to the ESA.

However, this is not the only place where they are concentrated. About 40,000 asteroids with unstable orbits and a size of more than one kilometer are constantly moving between the orbits of Jupiter and Neptune. They are also called Centaurs. Such objects can also be found in the Kuiper Belt beyond the orbit of Neptune.

New asteroids are discovered every week

How are asteroids discovered? They are detected thanks to ground-based survey telescopes. For example, the Catalina Celestial Survey of the University of Arizona discovers new asteroids almost every week. Such systems are designed to scan huge areas of the sky in search of unknown objects moving against the background of conventionally fixed stars.

For further observations, as a rule, more “focused” telescopes like the Very Large Telescope (VLT) are used. With their help, astronomers are able to better track the trajectory of asteroids, as well as study their size and even deduce their composition.

Gaia, ESA’s space telescope, also helps to better understand the danger of asteroids.

“Because of Gaia, we know more about the stars in the Galaxy which act as a backdrop for observations of asteroids,” explained the specialists working at the observatory.

“Asteroid’s positions are obtained against these background stars, so, the better one knows where the stars are, the more precisely the orbits of asteroids can be computed.

“Any asteroid discovered near Earth qualifies as a near-Earth asteroid, but many are found far from home,” added Marco Micheli, an astronomer at the ESA Near-Earth Object Coordination Centre.

New asteroids issue

“New objects are observed over time, their movements are studied and with just a handful of data points from different nights their future positions can be predicted. Depending on the number and quality of observations, this can extend decades, even hundreds of years into the future.”

Simply put, astrophysicists and other researchers are using a network of telescopes around the world to observe new asteroids and determine the potential risk of their collision with the planet, as well as tracking “old” asteroids that have not been recognized as safe.

Could any of these asteroids collide with Earth?

Large asteroids over one kilometer in diameter are considered potentially destructive objects. However, most of them have long been known to scientists, and “none of them poses a risk of collision, at least in the coming centuries.”

One of the most famous examples of a large space object striking the earth is the Chicxulub crater, created when an asteroid with a diameter of ten kilometers collided with Earth 66.5 million years ago, causing a cascade of powerful earthquakes, and bringing an end to the era of dinosaurs. The impact crater, with a diameter of about 180 kilometers and an initial depth of 17–20 kilometers, is located on the Yucatan Peninsula in Mexico.

The priority now is “medium” asteroids with a diameter of several hundred meters. Many of them are still waiting to be discovered because they are not so easy to detect due to their relatively modest size. “The good news is that more than half of today’s known near-Earth asteroids were discovered in the last six years, showing just how much our asteroid eyesight is improving,” explains Richard Mosle, head of ESA’s Planetary Defense department.

To sum up, today about 1,500 asteroids with a “non-zero” probability of collision with Earth are under constant observation and are included in the “Asteroid Risk” list.  But we must understand that while the risk is designated “non-zero,” the real danger of impact in the coming decades tends to be zero.

Could an asteroid collide with the Earth?

For example, the maximum risk of a collision with a planet from tracked asteroids today is assigned to (101955) Bennu. But even for him, the score according to a specialized logarithmic model is —1.59. In other words, the probability is 38 times lower than the background danger.

Is it possible to artificially change the asteroid’s trajectory?

In September last year, NASA conducted the first ever experiment to change the direction of an asteroid using the “directional collision” method. The DART space probe, moving at a speed of 22,500 km/h, crashed into the Dimorphos asteroid (the smallest object of the Dimorphos-Didymus binary system), located at a distance of about 10 million kilometers from Earth.

The detailed results of the experiment published a few months ago showed that “kinetic impact technology is a viable method of potentially protecting the Earth if necessary.” It was possible to change the orbit of the Dimorphos asteroid around Didymus such that it became shorter by 33 minutes. Moreover, this was achieved not so much due to the impact itself, but due to the recoil from the material ejected by the asteroid, which turned into a “tail” of debris one and a half kilometers long. It could be observed for almost a month.

But it is important to understand that the success of DART is only the first, and so far the only, demonstration of humanity’s ability to protect the Earth from the threat of potentially dangerous asteroids. The researchers add that the sooner we interfere with the orbit of such an asteroid, the less change will need to be made to avoid its collision with Earth.


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