A Christmas star without a tail | Science| In-depth reporting on science and technology | DW | 23.12.2015
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A Christmas star without a tail

An asteroid is going to pass by Earth for Christmas. However, it has no shining tail like the star of Bethlehem. And it may be difficult to spot - even for hobby astronomers, because the asteroid won't get that close.

The asteroid with the number 163899, also known under the name 2003 SD220, will fly by planet Earth at a safe distance of 11 million kilometers on New Year's Eve. That's equivalent to 28 times the distance between us and the moon.

As a comparison: The last asteroid that flew by Earth on a holiday came much closer to our planet. "The great pumpkin," also known as "2015 TB145," came as close as only 500,000 kilometers to our planet right on Halloween this year.

And in 2013 the asteroid 2012 DA14 flew by Earth as close as 28,000 kilometers. That's lower than some geostationary communication satellites are orbiting the Earth.

No unusual asteroid

The New Year's Eve asteroid falls into a class of celestial objects that are not uncommon. There are several per year, and they are not considered a threat to us. Only asteroids that approach Earth closer than 300,000 kilometers deserve special attention from astronomers.

2003 SD220 has an estimated diameter of about 700 meters. Objects of such size would cause global damage if they struck Earth. However, astronomers estimate that such an impact would happen only once in about 100,000 years.

Asteroiden Kollision

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Keeping an eye on objects in space

Astronomers from the world's large space agencies are constantly keeping an eye on such threats from space. For the next 100 years, they exclude the possibility of such a severe meteorite hitting out planet.

The largest asteroids in our solar system are known to us, and their orbits have been calculated for decades to come. More problematic are smaller objects, even just over ten meters in size, as those can race towards earth undetected. Suddenly they can come out of the darkness and strike the Earth, like the 40-meter large rock that landed near the Siberian town of Chelyabinsk in 2013. The shockwave that ensued ultimately destroyed windows all over the town - and injured as many as 1,500 people.

The next spectacular fly-by of a big asteroid is expected in April 2029. That's when Apophis will pass Earth at a distance of only 30,000 Kilometers. That is roughly one tenth of the distance of the moon. Apophis is several hundred meters in diameter, and the asteroid is set to return once again after that - in 2036.

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