Meteor in Chelyabinsk impact was twice as heavy as initially thought

(NATURE – 06.11.2013)

A three-dimensional simulation of the 15 February airburst over Chelyabinsk/Russia

The asteroid that exploded on 15 February this year near the city of Chelyabinsk in the Urals region of Russia was the largest to crash to Earth since 1908, when an object hit Tunguska in Siberia. Using video recordings of the event, scientists have now reconstructed the asteroid's properties and its trajectory through Earth’s atmosphere. The risk of similar objects hitting our planet may be ten times larger than previously thought, they now warn.

The fireball’s early-morning flight through the sky over the Urals was observed by many people and captured by numerous video cameras. To observers on the ground, it shone 30 times brighter than the Sun, and had an energy equivalent to more than 500 kilotons of TNT. An analysis of calibrated observations now provides a precise picture of the asteroid’s last ride and reveals surprising details of its likely cosmic origin.

The rock was an ordinary chondrite from the asteroid belt located between the orbits of Mars and Jupiter, as revealed by its trajectory and by its elemental and mineral composition, mainly silicates that formed the Solar System billions of years ago. At the time it entered the atmosphere, its mass was of the order of 12,000–13,000 metric tonnes, report two studies published online today in Nature and another study published at the same time in Science. This is nearly twice as heavy as initial estimates had suggested and also larger than revised estimates published in June.

The asteroid roared through Earth’s upper atmosphere at an initial speed of around 19 kilometres per second — more than 50 times the speed of sound. At an altitude of between 45 and 30 kilometres, the heavily fractured, and hence rather fragile, body broke into pieces and finally burst into gas and dust at around 27 kilometres' altitude.

“Luckily, most of the kinetic energy was absorbed by the atmosphere,” says Jiří Borovička, an asteroid researcher at the Astronomical Institute, part of the Academy of Sciences of the Czech Republic in Ondřejov, near Prague. ”A more solid rock that might have blasted closer to the ground would have caused considerably more damage.”

(artigo/parcial – nature.com)

Meteor smoke makes strange clouds

A key ingredient for 'night shining clouds' comes from outer space. Scientists have detected bits of 'meteor smoke' imbedded in them.

Noctilucent clouds or NLC in 1880 and 1990 – increasing over time

They look alien. The electric-blue ripples and pale tendrils of NLCs reaching across the night sky resemble something from another world.

“We've detected bits of 'meteor smoke' imbedded in noctilucent clouds. This discovery supports the theory that meteor dust is the nucleating agent around which NLCs form.”

Noctilucent clouds near the top of Earth's atmosphere

Noctilucent clouds are a mystery dating back to the late 19th century. Northern sky watchers first noticed them in 1885 about two years after the eruption of Krakatoa.

"We found that about 3% of each ice crystal in a noctilucent cloud is meteoritic."

When meteoroids hit our atmosphere and burn up, they leave behind a haze of tiny particles suspended 70 km to 100 km above Earth's surface.

The small size of the ice crystals explains the clouds' blue color.

How methane, a greenhouse gas, boosts the abundance of water at the top of Earth's atmosphere

"When methane makes its way into the upper atmosphere, it is oxidized by a complex series of reactions to form water vapor. This extra water vapor is then available to grow ice crystals for NLCs."
Noctilucent clouds are a sort of "canary in a coal mine" for one of the most important greenhouse gases.

"They might look alien, but they're telling us something very important about our own planet."

(NASA)