This Monday and Tuesday, two smaller sized comets will come very close to earth. The two rocks probably have a common descendant - a larger comet that broke up some time ago.
The two comets will not look as beautiful as comet "Lovejoy" in January 2015Image: Alan Dyer/amazingsky.com/dpa
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Threat from above
About 10,000 asteroids loom close to Earth. This year has already witnessed a lot of astronomical activity. And Europe is building what could become an asteroid early warning system.
Image: AP
European early warning system
About 10,000 asteroids loom close to Earth. They could be dangerous. The European Space Agency (ESA) is building an early warning system in Frascati, Italy. Data from telescopes like this one on Tenerife will be collated there.
Image: IQOQI Vienna
Passing blast
If you're wondering how important early warning systems are, think of the meteorite that struck Earth near Chelyabinsk in Russia on 15 February 2013. The blast was estimated to have been as strong as between 100 and 1000 kilotons of TNT explosives. Almost 1500 people were injured.
Image: picture-alliance/dpah
A big splash
Before it had burned up in the Earth's atmosphere, the meteorite is estimated to have had a diameter of 20 meters. All that was left was a piece weighing only about a kilogram. But it still managed to smash a six meter wide hole in the ice.
Image: Reuters
Bigger and badder
But an asteroid named "2012 DA14" was much more dangerous. It weighed 130,000 tons. On the same day as the Chelyabinsk strike, 2012 DA14 flew passed our planet at a distance of just 27,000 kilometers. That is closer than some satellites.
Image: NASA/Science dpa
Whizz by Earth
A number of other asteroids and comets are expected to come close to Earth this year. Scientists are keeping a close eye on them because even the smallest rocks can be dangerous.
Image: picture-alliance/dpa
Comets and shooting stars
Comets consist of a cloud of gas and a huge tail of gas, stones and particles of dust. When the tiny grains of dust from a comet scrape the Earth's atmosphere, they can get as hot as 3,000 degrees Celsius. They start to glow and become a shooting star.
Image: picture alliance / dpa
The most famous meteor shower
The Perseids are a prolific meteor shower, associated with the comet Swift-Tuttle. Every summer, the meteor shower crosses the Earth's orbit. The Perseids are named after the constellation they are closest to when they can be seen. It is derived from Perseus, a character from Greek mythology.
Image: AP
When meteoroids don't burn up
Meteors dust burns up in our atmosphere. Most meteorites (meteoroids that survive falling through the atmosphere) are harmless and are often no bigger than a stone. But large meteorites can cause a lot of damage. One of the largest meteorite craters is the Barringer Crater in Arizona. It has a diameter of 1,000 meters and is 50,000 years old.
Image: cc-by/LarryBloom
End of an era
About 65 million years ago, a giant meteorite slammed into the Yucatan Peninsula (simulated in the image to the right). It led to the creation of the Chicxulub Crater, which is more than 180 kilometers in diameter. Experts believe the impact wiped out the dinosaurs. More recent evidence suggests that debris from a collision between two asteroids 160 million years ago led to the event.
Image: picture alliance/dpa
Burnt rocks from outer space
Meteorites look like burnt rocks. Their crust is formed when the meteorite melts upon entering the Earth's atmosphere. Other planets are also struck by meteorites. NASA's Opportunity Rover discovered the first extraterrestrial meteorites on Mars in 2005.
Image: picture-alliance/ dpa/dpaweb
Dust and gas
It's not just the dust from comets that reaches Earth - but the comets do, too. Experts believe comets to be bits leftover from the creation of planets. They may also hold secrets about the beginnings of our solar system.
Image: AP
Large chunks of rock
Almost all of meteorites found on Earth have come from asteroids - that is 99.8 percent of the more than 30,000. And just like comets, asteroids are created when a planet is being formed. They have no permanent atmosphere and hardly any gravity.
Image: picture-alliance/ dpa
And after all that...
... the chance of a large asteroid hitting Earth in the next 100 years is (said to be) quite small.
Image: AP
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On Monday, March 21, comet 252P/LINEAR will pass the Earth at a distance of 3.3 million miles (5.2 million kilometers). It is about 14 times the distance of the moon. Then, shortly afterwards, another comet, called P/2016 BA14, will follow. That rock will get even closer to earth - only about 2.2 million miles (3.5 million kilometers). That's equal to nine times the lunar distance.
The first of the two, which is also the larger one, has been known since April 7, 2000. Astronomers from the Massachusetts Institute of Technology (MIT) then discovered the rock with a diameter of about 750 feet (230 meters). The other one was discovered much more recently. Researchers from the University of Hawaii discovered it with their PanSTARRS telescope this year - on January 22. Its diameter is estimated at about 300 feet (100 meters).
Break up during fly-by close to the Sun or to Jupiter
NASA astrophysicists think that P/2016 BA14 could be a large fragment of 252P/LINEAR. "The two could be related because their orbits are so remarkably similar," said Paul Chodas, manager of NASA's Center of Near Earth Object Studies (CNEOS) at the Jet Propulsion Laboratory in Pasadena, California. In a statement, NASA suggests that the comet may have broken up either during a previous passing through of the inner solar system or during a fly-by of Jupiter.
NASA will observe the two comets during the fly-by of Earth with its Space Telescope Hubble and ist Infrared Telescope Facility. The scientists hope to further clarify the twin comet thesis.
Not visible for laymen
Hobby astronomers will not be able to spot the two comets. Only with special telescopes will the event become visible. The fly-by poses no danger for us on Earth, but it is possible that during the two days there may be an increased activity of shooting stars.
Nonetheless, astronomers consider the fly-by an extraordinary event, which happens only every few hundred years. According to NASA, it is the third closest approach of a comet to Earth since the beginning of systematic human celestial observations. Only the comets D/1770 L1 (Lexell) in 1770 and C/1983 H1 (IRAS-Araki-Alcock) in 1983 came closer than that.
Much more common than even small comets are comparably large asteroids. On March 8, 2013 TX68 got as close to earth as 13 lunar orbits. And for Halloween last year, the "Great Pumpkin" was much closer still at only 1.3 times as far as the moon.
