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Although Captain Kirk and crew could zip over to a planet at warp speed and teleport down to the surface to check if it was inhabited, current-day scientists will generally have to search for life from a distance. New research gives some hope that we could detect a "handedness" beacon from a planet full of microbes.
This handedness, or homochirality, is characteristic of life on Earth. The molecules that make proteins and DNA all have either a left-handed or right-handed orientation. Both orientations are made in equal quantities by non-biological processes, but life prefers to have just one type of hand over the other.
"Homochirality is a fundamental aspect of self-replication," says William Sparks of the Space Telescope Science Institute. "It is a reasonable proposition that life on other planets will exhibit a particular handedness."
Many of the molecules in organic chemistry come in left and right-handed varieties. When life starts building up larger compounds from these organic ingredients, scientists suspect that having only one hand to deal with is an advantage, if not a necessity.
Detecting homochirality in purified samples is easy in the lab, but could we see the signal if we stepped back 40 light-years and looked at an entire planet?
"We are testing whether we can remotely sense something that we think is a generic aspect of life," says Sparks.
The classic biosignature is an atmosphere far from equilibrium. Certain molecules can only survive for a short time, so if astronomers detect them in the spectrum of light coming from a distant planet, we might assume that living things are replenishing the supply.
Another calling card of life might be the vegetation red edge, which is due to plants absorbing strongly in the visible wavelengths but reflecting infrared light. Alien plants may capture the light from their host star in a similar fashion.
However, there are geological phenomena that can mimic these supposed biological indicators. Volcanoes can replenish the atmosphere with short-lifetime gases, and some minerals have a red-edge-like reflection spectrum.
This ambiguity led Sparks and his colleagues to consider an alternative biosignature.
All told its an interesting idea... the only flaw I see in it is what if other life does not react the way ours does... for example it does not do Photosynthisis but acquires its energy the way fungi or the life in the deep trenches of the ocean does.
I had heard before that all life has a preferred handedness... even if it doesn't have hands...