On the force of vertical winds in the upper atmosphere: consequences for small biological particles

Abstract

For many decades, vertical winds have been observed at high altitudes of the Earth’s atmosphere, in the mesosphere and thermosphere layers. These observations have been used with a simple one-dimensional model to make estimates of possible altitude climbs by biologically sized particles deeper into the thermosphere, in the rare occurrence where such a particle has been propelled to these altitudes. A particle transport mechanism is suggested from the literature on auroral arcs, indicating that an altitude of 120 km could be reached by a nanometre-sized particle, which is higher than the measured 77 km limit on the biosphere. Vertical wind observations in the upper mesophere and lower thermosphere are challenging to make and so we suggest that particles could reach altitudes greater than 120 km, depending on the magnitude of the vertical wind. Applications of the larger vertical winds in the upper atmosphere to astrobiology and climate science are explored.

Detecting Microbiology in the Upper Atmosphere: Relative-Velocity Filtered Sampling

“…If naturally occurring biology is to be found in the MLT it is most likely to be on the scale of viruses or smaller bacterial organelles or possibly fungal spores [25] [26]. If one recovers viable biological material then one could use such samples, together with the flight data, to better quantify the proportion of particles that are viable as a function of altitude.…”

“…Using the natural winds to sample the biosphere is, in our opinion, likely to be a more efficient and lower risk strategy than is currently achieved with rovers. An added advantage is that being at ground level, if there is any biology on the planet, it is more likely to be found closer to the surface, assuming the planet has a similar atmospheric structure to Earth [4] [25].…”

“…Meteoric smoke particles are neutrally charged and nanometre in size, making them challenging to detect. Berera et al 2022 hypothesised that MLT large vertical winds could potentially be strong enough to push particles of this size to around 120 km in rare events [25] [3]. The main difficulty with sampling particles of this size is that they tend to follow the flow around the payload, not into the detector [35] due to the low air density complicating the aerodynamics.…”

“…These should be launched months apart to avoid inter-launch contamination. Geospatial separation of the launch sites would also be ideal as [25] identified the poles as more likely to have biological material, since these areas experienced stronger vertical winds due to geomagnetic activity.…”

“…The purpose of this paper is to entirely re-open the question of what the upper limit of the Earth's biosphere is with practical calculations and suggestions for field campaigns. Our paper builds on the pre-existing observations of the lower atmosphere and on recent work which has identified strong vertical winds, amongst other mechanisms such as volcanic eruptions, as capable of ejecting nanometre sized particles into the MLT [25].…”