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The leftovers from the formation of the solar system can be found in the snowballs thrown by the Oort Cloud and the Kuiper Belt.
As comets cross the sky, many of them turn a green color as they approach the Sun.
The green shade disappears before it reaches the one or two tails behind the comet.
Astronomers, scientists and chemists have been puzzled by this mystery for over a century. The phenomenon was thought to be caused by sunlight destroying diatomic carbon, a chemical created from the interaction between sunlight and organic matter on the comet's head.
The theory that a chemical reaction can be tested in a laboratory has been proven correct by a new study.
The senior author of the study says that they have proven the mechanism by which dicarbon is broken up by sunlight.
The comet's coma shrinks as it gets closer to the Sun, and the tail of the comet is not green.
Dicarbon is the key player at the center of the mystery and is responsible for giving many comets their green color. It's made up of two carbon atoms stuck together and can only be found in environments with low oxygen.
The comets don't have dicarbon until they get close to the Sun. The organic matter on the comet's nucleus is going to be comatose as the Sun warms it. Sunlight creates dicarbon by breaking up larger organic molecules.
The comet gets closer to the Sun and the UV radiation breaks apart the dicarbon molecules it created. The green coma will get brighter and shrink if the dicarbon is destroyed before it can move far from the nucleus.
This is the first time this interaction has been studied on Earth.
"I think it's amazing that someone thought in the 1930s that this was happening, and then 90 years later, we find out it's what's happening," says Ms Borsovszky.
Herzberg won a prize for chemistry in the 70s. It's pretty exciting to be able to prove something.
The findings help us understand dicarbon and comets, says Prof. Schmidt, who has been studying dicarbon for 15 years.
He says that carbon comes from the breakdown of larger organic molecules in the nucleus of a comet.
Understanding its lifetime and destruction will allow us to better understand how much organic material is lost off comets. Discoveries like these could help solve other space mysteries.
A laser show.
The team needed to recreate the same chemical process in a controlled environment on Earth to solve the puzzle.
They pulled it off with the help of a vacuum chamber, a lot of lasers, and a powerful cosmic reaction.
"We had to make a molecule that is too reactive to store in a bottle," says Prof. We couldn't buy it from the shops.
We took perchloroethylene and blasted it off with a high-powered UV laser.
The dicarbon molecule was sent through a gas beam in a vacuum chamber, which was around two meters long.
The team pointed two more UV lasers towards the dicarbon, one to flood it with radiation and the other to make its atoms visible. The carbon atoms flew onto a speed detector after the radiation ripped the dicarbon apart.
The team could measure the strength of the carbon bond by analyzing the speed of the atoms.
It took nine months before they were able to make their first observation due to the complexity of the experiment.
She says that they were about to give up. It took a long time to make sure everything was lined up.
There was a lot of stabbing in the dark because the lasers were invisible.
This is the first time anyone has ever observed a chemical reaction.
It's gratifying to have solved a problem that dates back to the 1930s.
Space mysteries are solved.
There are 3700 known comets in the solar system. A comet's nucleus is 10 kilometers wide, but its coma is 1000 times bigger.
Bright comets can put on amazing shows for those lucky enough to see them. One of the theories about the origin of life is that comets once delivered the building blocks of life right to our doorstep.
Professor Martin van Kranendonk is an astronomer and geologist from the University of New South Wales and was not involved in the study.
"Early Earth would have had a lot of different carbon-bearing molecules being delivered to its surface, allowing for even more complex reactions to occur in the leadup to life."
The case of the missing green tail in comets has been solved, and Prof. Schmidt wants to solve other space mysteries.
He wants to investigate diffuse interstellar bands, which are patterns of dark lines between stars that don't match any atom or molecule.
He says that the mysteries of diffuse interstellar bands are a big one. We don't know why nibbles are taken out of the light that arrives on Earth.
"This is one more mystery in a huge inventory of bizarre things in space that we're yet to discover."
Nature breaks an unusual multiple bond through photodissociation of dicarbon.
The National Academy of Sciences has a journal.
We finally know why comets' heads can be green, but never their tails, after 90 years.
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