Asteroids and meteorites

Gustav Witt studied mathematics and the natural sciences, particularly astronomy. For years, his main job was as a stenographer. But astronomy was his passion. He searched for unknown objects at the Urania Observatory in Berlin.

On August 13, 1898, he and his assistant Felix Linke exposed a photographic plate. When they examined it, they discovered a celestial body that we now know is a near-Earth asteroid. Its shape is similar to a potato, and it is over 30 kilometers long. It was named Eros. It orbits the Sun every 1.76 years and can come as close as 22 million kilometers to Earth. From 2000 to 2001, it was orbited and photographed by an American space probe.

Eros is just one of the many millions of celestial bodies that, like the planets, orbit the sun. We know of 8 major planets and several dwarf planets, such as Pluto and Ceres. Many smaller celestial bodies also orbit the sun. The larger ones are called asteroids, the smaller ones comets and meteoroids. There are many millions of them.

Some are only a few centimetres across, while others are more than 100 kilometres wide. Every day, the Earth, the Moon and the other planets are hit by rocks of varying sizes. On Earth, we usually see a shooting star when this happens. That is because a celestial object burns up as it enters Earth’s atmosphere. At most, only small fragments reach the ground. Scientists call meteoroids that burn up in Earth’s atmosphere meteorites.

There is a lot of space in our Solar System. That is why a large asteroid or meteoroid very rarely hits Earth. But when one does, it can cause enormous destruction. On the morning of 15 February 2013, a meteoroid exploded above the Russian city of Chelyabinsk. It is estimated to have weighed about as much as a loaded truck. Much of its mass burned up as it entered Earth’s atmosphere. The rest broke into many small fragments that reached the ground. One of them tore a six-metre-wide hole in the ice covering a frozen lake. A powerful shock wave swept across the ground. Thousands of windows shattered, roofs and walls were damaged, and the roofs of large buildings collapsed. Flying fragments injured more than 1,000 people.

That evening, an asteroid named "2012 DA14" by scientists passed Earth at a distance of only about 27,000 km. It was much larger than the meteoroid that broke apart over Russia that morning. It would certainly have caused far greater destruction if it had collided with Earth.

The most consequential asteroid impact occurred about 66 million years ago. An object more than 10 kilometers in diameter struck the Gulf of Mexico. The rock melted, a huge crater formed, and debris was hurled kilometers into the air. Tsunamis raced across the sea. Enormous fires broke out thousands of kilometers away, and the impact triggered volcanic eruptions and earthquakes in various places on Earth.

As a result, the climate cooled sharply. Seventy-five percent of the animal and plant species living at the time died out over the following millennia, including the dinosaurs. But that was not all: the catastrophe paved the way for mammals to become the dominant life forms on Earth over the millions of years that followed. This includes us humans.