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Astroboffins' discovery gives search for early life a left hand. Or right

Sagittarius B2 a veritable plastic factory

By Richard Chirgwin, 15 Jun 2016

For the first time, astronomers have made an interstellar observation of a molecule that can exist in left- and right-handed versions – which could help unravel how life can come to exist.

The discovery was made using two radio telescopes: Green Bank in the USA, and Parkes in Australia.

What Brett McGuire (US National Radio Astronomy Observatory) and P. Brandon Carroll (California Institute of Technology) are presenting to the American Astronomical Society is evidence of chirality – the existence of left- and right-handed versions of the same molecule – away from Earth.

The molecule of interest is propylene oxide (CH3CHOCH2), and it's been spotted in Sagittarius B2, an active star-forming gas cloud near the centre of the Milky Way.

Although the researchers don't yet know the left/right distribution, it's the first time a molecule that can have both forms has been detected outside the Solar System.

As Science notes, on Earth, we use propylene oxide to make polyethylene plastics.

"Chiral molecules have been found in meteorites and comets in our own solar system, and the material they’re made of likely came from the cloud of gas and dust our solar system formed from, so chiral molecules may not be uncommon, but they are extremely hard to detect," Brandon Carroll told The Register's Katyanna Quach.

"We know the Earth acquired a lot of material, including a small amount of amino acids, from comets and meteors as it formed. By detecting a chiral molecule in a region like Sagittarius B2(N), which is actively forming stars and from which planetary systems will eventually form, we now have a place to search for a primordial excess of one enantiomer over another," Carroll added.

However, chirality is important in organic chemistry. While the mirror-image molecules will behave the same in some ways – melting and freezing points, for example, or their reactions to light – they combine with other molecules differently. The left-handed version of a molecule might react readily, while the right-handed version not at all.

All the amino acids in living creatures are left-handed, which is the bit that interests astrophysics: why did Earth end up with those molecules and not others?

Chiral molecules have been found in bits of asteroid, and left-handed forms typically dominate. With Sagittarius B2 observation in hand, astroboffins now have a candidate for further study to see if there's a left/right imbalance in the dust cloud as well.

That would let them work out whether chirality arises at an earlier stage of development than we can determine from anything in the solar system. ®

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