Huge rocks regularly spring close to Earth. Let's say in April last year when an asteroid with a diameter of about fifty meters was very close to the planet. Astronomers discovered it just 21 hours before it flew by.
Five years earlier, the Earth was actually hit by a 20-meter meteorite - it fell near Chelyabinsk, Russia. There was no major disaster - the earthquake damaged thousands of buildings and injured more than a thousand people, mostly from broken glass. But luckily there were no deaths.
Shooting asteroids?
Astronomers are convinced that they have registered increasingly large objects that fly through the universe and threaten to sink into the earth one day. They say it won't happen for at least the next hundred years.
But even an asteroid the size of a football field can cause enormous damage in some part of the world. The two mentioned examples also show that such smaller "flying rocks" are not noticed much earlier by astronomers.
That's why about 300 astronomers, space flight engineers and other experts from the USA, Russia, China, Germany, France and Israel are discussing this week in Maryland. The meeting is called: International Conference for the Defense of the Planet.
For this occasion, scientists came up with a hypothetical asteroid that would have a diameter of 300 meters, a speed of 14 kilometers per second (ie about 50.000 kilometers per hour) and rush towards the earth from a distance of 57 million kilometers. In that hypothetical model, there is a one percent chance that it will hit the exact part of the Earth you are on. One possibility is evacuation.
However, there are other ways. Let's say the DART system being developed by NASA. The first real test will be in 2022, when 150-meter asteroids fly near the Earth. The idea is to cause a collision with the object so that it deviates from its path and passes even further away from Earth.
Politicians recognized the danger
Asteroids whose orbit around the Sun approaches the Earth at less than 50 million kilometers are considered "close to the Earth". 20.000 of these are already known, and approximately 700 new ones are discovered every year.
"We have to let people know that this is not Hollywood here," NASA's Jim Bridenstine said at the start of the conference.
His colleague Detlef Košnji from the European space agency ESA added:
"The good thing about the disaster in Chelyabinsk was that political decision makers saw the dangers".
The greatest dangers are posed by objects that move near the Sun - because of the strong light, they are not visible from Earth until it is too late. In certain situations, they can only be observed with special telescopes such as those in Arizona, Hawaii, Chile, Spain and Sicily.
Astronomers are therefore discussing the construction of a new global telescope that would serve only this purpose. So far, the most interesting possible location for building such a telescope: the Moon. Scientists say the view from there would be much better.
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