It could be a milestone on the path to detecting life on other planets: Scientists detect a key molecular property of all living organisms from a helicopter flying several kilometers above ground. The measurement technology could also open up opportunities for remote sensing of the Earth.
From: University of Bern
June 18, 2021 -- It could be a milestone
on the path to detecting life on other planets: Scientists under the leadership
of the University of Bern and of the National Centre of Competence in Research
(NCCR) PlanetS detect a key molecular property of all living organisms from a
helicopter flying several kilometers above ground. The measurement technology
could also open up opportunities for remote sensing of the Earth.
Left hands and right hands are almost
perfect mirror images of each other. But whatever way they are twisted and
turned, they cannot be superimposed onto each other. This is why the left glove
simply won't fit the right hand as well as it fits the left. In science, this
property is referred to as chirality.
Just like hands are chiral, molecules
can be chiral, too. In fact, most molecules in the cells of living organisms,
such as DNA, are chiral. Unlike hands, however, that usually come in pairs of
left and right, the molecules of life almost exclusively occur in either their
"left-handed" or their "right-handed" version. They are
homochiral, as researchers say. Why that is, is still not clear. But this
molecular homochirality is a characteristic property of life, a so-called
biosignature.
As part of the MERMOZ project, an
international team led by the University of Bern and the National Centre of
Competence in Research NCCR PlanetS, has now succeeded in detecting this
signature from a distance of 2 kilometers and at a velocity of 70 kph. Jonas
Kühn, MERMOZ project manager of the University of Bern and co-author of the
study that has just been published in the journal Astronomy and
Astrophysics, says: "The significant advance is that these
measurements have been performed in a platform that was moving, vibrating and
that we still detected these biosignatures in a matter of seconds."
An instrument that recognizes living
matter
"When light is reflected by
biological matter, a part of the light's electromagnetic waves will travel in
either clockwise or counterclockwise spirals. This phenomenon is called
circular polarization and is caused by the biological matter's homochirality.
Similar spirals of light are not produced by abiotic non-living nature,"
says the first author of the study Lucas Patty, who is a MERMOZ postdoctoral
researcher at the University of Bern and member of the NCCR PlanetS,
Measuring this circular polarization,
however, is challenging. The signal is quite faint and typically makes up less
than one percent of the light that is reflected. To measure it, the team
developed a dedicated device called a spectropolarimeter. It consists of a
camera equipped with special lenses and receivers capable of separating the
circular polarization from the rest of the light.
Yet even with this elaborate device, the
new results would have been impossible until recently. "Just 4 years ago,
we could detect the signal only from a very close distance, around 20 cm, and
needed to observe the same spot for several minutes to do so," as Lucas
Patty recalls. But the upgrades to the instrument he and his colleagues made,
allow a much faster and stable detection, and the strength of the signature in
circular polarisation persists even with distance. This rendered the instrument
fit for the first ever aerial circular polarization measurements.
Useful measurements on earth and in
space
Using this upgraded instrument, dubbed
FlyPol, they demonstrated that within mere seconds of measurements they could
differentiate between grass fields, forests and urban areas from a fast moving
helicopter. The measurements readily show living matter exhibiting the
characteristic polarization signals, while roads, for example, do not show any
significant circular polarization signals. With the current setup, they are
even capable of detecting signals coming from algae in lakes.
After their successful tests, the
scientists now look to go even further. "The next step we hope to take, is
to perform similar detections from the International Space Station (ISS),
looking down at the Earth. That will allow us to assess the detectability of
planetary-scale biosignatures. This step will be decisive to enable the search
for life in and beyond our Solar System using polarization," says MERMOZ
principal investigator and co-author Brice-Olivier Demory, professor of
astrophysics at the University of Bern and member of the NCCR PlanetS says.
The sensitive observation of these
circular polarization signals is not only important for future life detection
missions. Lucas Patty explains: "Because the signal directly relates to
the molecular composition of life and thus its functioning, it can also offer
valuable complementary information in Earth remote sensing." It can for
instance provide information about deforestation or plant disease. It might
even be possible to implement circular polarization in the monitoring of toxic
algal blooms, of coral reefs and the effects of acidification thereon.
Story Source:
Materials provided by University of
Bern. Note: Content may be edited
for style and length.
https://www.sciencedaily.com/releases/2021/06/210618133959.htm
Footnote
by the Blog Author
Previous posts of this blog have dealt
with chirality. See the posts of June 8,
2020; March 2, 2020; July 10, 2017; November 27, 2015; and particularly April
5, 2011.
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