One of the key developments separating modern civilization from the hunter
gatherer societies of the past is the invention of farming, which took place
about 10,000 years ago. This began with the cultivation of wild plants and
the domestication of various animals for dairy products and meat.
The big advantage of farming is that it sustains a much larger population
than hunting and gathering. This led to the emergence of cities, the sharing
of natural resources and of ideas and innovations.
It has also had a big impact on the Earth itself. The effects of farming are
visible in the grid-like arrangement of fields, in the way light is
reflected from photosynthetic plants and in the chemicals it releases into
the atmosphere, particularly by industrial-scale agriculture.
Now a group of astronomers and astrobiologists say this atmospheric
signature must be clearly visible from space and that a similar signal could
also be generated by a farm on another planet. “The spectral signature of
such an “ExoFarm” is worth considering in the search for technosignatures,”
say Jacob Haqq-Misra at the Blue Marble Space Institute of Science in
Seattle, and colleagues. They go on to explore what such a signature might
look like and how easily it could be detected by the current generation of
space telescopes such as the James Webb.
Nitrogen Fixing
An essential element of agriculture is the application of fertilizer to
increase productivity. This gives plants improved access to nitrogen, a
crucial element of life. Nitrogen is readily available as N2 which makes up
78 per cent of the atmosphere.
But fixing it in a plant-usable form is tricky because N2 is bound together
by a highly stable triple bond. This nitrogen is naturally broken down into
more easily exploited forms in a variety of ways ranging from lightning
strikes to the microorganisms in manure.
But as the population has increased, particularly since the industrial
revolution, the demand for nitrogen fertilizers has exploded. This has led
to the development of artificial fertilizers and a global industry dedicated
to manipulating the nitrogen cycle via an industrial approach to creating
ammonia called the Haber-Bosch process.
This produces vast amounts of ammonia, some of which escapes into the
atmosphere, albeit for short periods of time since ammonia usually falls to
ground after a few days. So detectable levels of ammonia in the atmosphere
must be the result of significant ongoing agricultural activity.
Although atmospheric ammonia is short-lived, its use as a fertilizer
produces nitrous oxide (N2O), a greenhouse gas that survives in the
atmosphere for over one hundred years.
Nitrous oxides are also produced by combustion. However, Haqq-Misra and co
point out that other civilizations may discover, like us, that combustion is
not sustainable and phase it out. So in the long run, the signature of
nitrous oxides is more likely to indicate agricultural activity.
Agriculture is also the main producer of atmospheric methane on Earth. So
CH4 is another signature worth looking for, say the team. “The signature of
such an ExoFarm could only occur on a planet that already supports
photosynthesis, so such a planet will necessarily already show spectral
features due to H2O, O2, and CO2,” say Haqq-Misra and co.
Extraterrestrial Technosignature
“These calculations suggest the possibility of considering the simultaneous
detection of NH3 and N2O in an atmosphere that also contains H2O, O2, and
CO2 as a technosignature for extraterrestrial agriculture.”
It may be possible to detect this signature on other planets using today’s
observatories. The researchers point out that the James Webb Space
Telescope, currently being commissioned, should be able to detect ammonia at
the level of five parts per million in the atmosphere of a hydrogen-rich
planet orbiting a nearby red dwarf. Current levels of ammonia on Earth are
about ten parts per billion.
That makes the search for nitrogen signatures an interesting pursuit for
astrobiologists. It is likely that the hunt for this signal would be a
natural next step after the discovery of photosynthetic signatures.
What seems clear is that technosignatures are unlikely to be single WOW-type
signals but more complex patterns of evidence that require some dedicated
detective work. And with the James Webb Telescope coming online later this
year, that detective work might just be about to begin.
Reference:
Disruption of a Planetary Nitrogen Cycle as Evidence of Extraterrestrial
Agriculture :
arxiv.org/abs/2204.05360
Tags:
Space & Astrophysics
You don't need to search exoplanets for life. There are plants growing/grew on Mars. See for yourself:
ReplyDeletehttps://mars.nasa.gov/mer/gallery/all/1/p/4983/1P570553921EFFD119P2404L2M1.JPG
https://mars.nasa.gov/mer/gallery/all/1/p/4983/1P570554096EFFD119P2404R2M1.JPG
You really MUST BE A HERMIT.
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