Beware! Extraterrestrial "Assassins"

Beware! Extraterrestrial "Assassins"

In the movie "Alone on the Moon", a meteorite named "π" hits the Earth, and the Moon's shield plan to block this "assassin" fails. Eventually, the Earth's climate deteriorates, smoke and dust cover the sky, the temperature drops sharply, the ground becomes uninhabitable, and people are forced to move underground. Although at the end of the movie, the Earth's climate gradually returns to normal, but in reality, will the extraterrestrial "assassin" visit again?

01

This "Assassin" is familiar yet strange

As early as in the Bamboo Annals, there was a record of a meteorite shower more than 4,000 years ago, "In the sixth month of the eighth year of Emperor Yu of Xia, gold rained in Xiayi", which is also the earliest record of meteorites and meteorite showers in the world. In the literature, meteorite landings are common, but where do meteorites come from?

In fact, worrying about nothing is not entirely unnecessary.

There are a large number of asteroids between Mars and Jupiter, which may collide with other asteroids as they orbit in space.

If the collision is strong, it will break into pieces. The asteroid and its fragments may even be knocked out of orbit, forcing them to start a cosmic "citywalk" .

Under the influence of the Earth's gravity, some asteroid fragments become "assassins" and fly toward the Earth at a certain speed. When they fall to the ground, they become meteorites. In addition to the asteroid belt distributed between Mars and Jupiter, there are also a small number of terrestrial meteorites from the Moon, Mars and outside the solar system.

Schematic diagram of the location of the asteroid belt, source: China Digital Science and Technology Museum

It is estimated that the Earth faces 50,000 tons of meteorites falling every day. However, the Earth is the lucky child of the solar system, and it is protected by the atmosphere . Asteroid fragments continue to rub after entering the atmosphere, generating light and heat. Generally, most of the asteroid fragments burn up at an altitude of 10-40 kilometers above the ground.

Researchers have found that the study of meteorites can not only help to explore undetected celestial bodies, but also find clues about the evolution of the universe.

So they climbed mountains and crossed rivers to look for traces of meteorites. 70% of the earth's surface is covered with water, making it extremely difficult to find meteorites. Among the remaining land, Antarctica has gradually become a popular place to find meteorites. Why has Antarctica become a popular "meteorite treasure hunting site"? First, the Antarctic continent is covered with ice, and meteorites are particularly eye-catching in the vast ice and snow; second, Antarctica is cold all year round, and the preservation environment of meteorites is good.

By studying meteorite samples, we can determine their type and origin, and further deduce the material composition and evolution of the planet. Recently, a study on the meteorite GRV150277 was published. This meteorite was found in Grove Mountain, Antarctica. After petrological, mineralogy and composition analysis, it was determined that the rock came from Vesta (located in the asteroid belt). Further research found that Vesta had experienced multiple asteroid impacts, which is of great significance for studying the composition and evolution of Vesta's surface soil layer.

GRV 150277 meteorite hand specimen, the black cube on the left has a side length of 1 cm

Source: Article "Study on the First Ancient Copper-Calcium-Long Achondrite (GRV 150277) Found in Grove Mountain, Antarctica and Its Exogenous Debris"

02

The assassin's sneak attack caused a huge change in the world

Is the landing of a meteorite just as simple as bringing a piece of stone to the earth and creating a hole?

The probability of a large meteorite falling to the ground will produce a series of physical, chemical, and geological effects, and may even trigger major global changes.

For example, when a giant meteorite rubs against the atmosphere, its outer shell melts, vaporizes, shatters, and explodes due to high temperature and high pressure. The strong shock wave ignites combustible materials on the ground, triggering forest fires and generating large amounts of smoke, dust, and black charcoal. The meteorite itself and the high temperature environment in which it falls may also produce toxic substances, directly causing poisoning and death of organisms. The impact of a huge meteorite will also lead to the redistribution of materials inside the earth, which may cause changes in land and sea, such as seafloor expansion and continental drift.

The most well-known sneak attack is probably the one that caused the Earth to move from the Cretaceous to the Neogene. It is speculated that 66 million years ago, an asteroid with a diameter of 10 kilometers fell in today's Caribbean region, causing a huge change in global climate, leading to the extinction of dinosaurs and the subsequent emergence of mammals on the stage of history, completing a historic role change.

Recently, an article published in the journal Nature Geoscience pointed out that the dust produced by the asteroid impact on the earth 66 million years ago may be the cause of the mass extinction of dinosaurs. Through rock samples collected from the Chicxulub Crater in Mexico and paleoclimate simulations, the impact of silicate dust, sulfur and smoke produced by wildfires on the climate was evaluated, and it was found that silicate dust played a "ruthless role" in this climate cooling event.

The tiny particles produced by the meteorite impact may have been diffused in the air for a long time, blocking out the sun and the sky. Within two years, plant photosynthesis stopped, vegetation eventually withered, herbivores lost their food source, and the food chain was broken. From herbivorous dinosaurs to carnivorous dinosaurs, this great famine defeated this group of huge creatures that dominated the earth. The dust stayed in the atmosphere for 15 years, the climate became cold, and the global temperature dropped by more than ten degrees Celsius, making the winter on Earth last for 15-20 years. In the long and severe cold, dinosaurs, pterosaurs, ammonites, and many animals and plants were helpless, and the catastrophe came...

Three major types of dinosaurs lived in the Shanyang Basin at the end of the Cretaceous: Oviraptorosaurs, Hadrosaurs, and Tyrannosaurus

Source: Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences

03

Modern Assassin Defense

Although the probability of a near-Earth asteroid hitting the Earth is low, from a statistical point of view, the possibility of it happening in the future is quite high. Once such an event occurs, it will bring catastrophic consequences to human society. Therefore, preventing the impact of near-Earth asteroids is necessary to ensure the development of human civilization.

If faced with another meteorite of the magnitude of the one from 66 million years ago, would humans be able to withstand it?

Scientists have designed two main methods: using nuclear weapons to smash the meteorite in advance; sending a spacecraft to "send the meteorite away". The second solution that is being studied more is kinetic impact, which is to use a spacecraft to impact the meteorite, changing its speed and causing its trajectory to deflect.

“Strike stone with stone” simulation

Source: National Space Science Center, Chinese Academy of Sciences

Thanks to the progress of science and technology, humans now have the choice between survival and extinction when facing "assassins". While looking up at the stars, humans should also look down at themselves.

On November 30, 2023, the 28th Conference of the Parties to the United Nations Framework Convention on Climate Change (COP28) opened in Dubai, UAE. On the opening day of COP28, the World Meteorological Organization released the provisional version of the 2023 Global Climate Status Report and announced that 2023 was the hottest year in human meteorological records. It is an indisputable fact that the world has entered a boiling era. As the biggest "assassin" among the many global climate problems on Earth, human activities are also a more controllable factor. Can we reduce the "heat" of the climate and its climate issues through more diligent climate actions? A positive answer and positive actions will be a big step forward for the continuation of human civilization.

Author: Li Beibei, Associate Professor of the Institute of History of Science and Technology and Meteorological Civilization

Gong Xinyu, Master's student at the Institute of History of Science and Technology and Meteorological Civilization