The hypothesis of Panspermia states that life exists through the cosmos, and is distributed between planets, stars and even galaxies by asteroids, comets, meteors and planetoids.
In this respect, life began on Earth about 4 billion years ago after microorganisms hitching a ride on space rocks landed on the surface. Over the years, considerable research has been devoted towards demonstrating that the various aspects of this theory work.
The latest comes from the University of Edinburgh, where Arjun Berera offers another possible method for the transport of life-bearing molecules.
According to his recent study, space dust that periodically comes into contact with Earth's atmosphere could be what brought life to our world billions of years ago. If true, this same mechanism could be responsible for the distribution of life throughout the Universe.
For the sake of his study, which was recently published in Astrobiology under the title Space Dust Collisions as a Planetary Escape Mechanism, Berera examined the possibility that space dust could facilitate the escape of particles from Earth's atmosphere.
These include molecules that indicate the presence of life on Earth (aka biosignatures), but also microbial life and molecules that are essential to life.
Fast-moving flows of interplanetary dust impact our atmosphere on a regular basis, at a rate of about 100,000 kg (110 tons) a day. This dust ranges in mass from 10-18 to 1 gram, and can reach speeds of 10 to 70 km/s (6.21 to 43.49 mps).
As a result, this dust is capable of impacting Earth with enough energy to knock molecules out of the atmosphere and into space.
These molecules would consist largely of those that are present in the thermosphere. At this level, those particles would consist largely of chemically disassociated elements, such as molecular nitrogen and oxygen.
But even at this high altitude, larger particles – such as those that are capable of harbouring bacteria or organic molecules – have also been known to exist. As Berera states in his study:
"For particles that form the thermosphere or above or reach there from the ground, if they collide with this space dust, they can be displaced, altered in form or carried off by incoming space dust.
This may have consequences for weather and wind, but most intriguing and the focus of this paper, is the possibility that such collisions can give particles in the atmosphere the necessary escape velocity and upward trajectory to escape Earth's gravity."
Of course, the process of molecules escaping our atmosphere presents certain difficulties. For starters, it requires that there be enough upward force that can accelerate these particles to escape velocity speeds.
Second, if these particle are accelerated from too low an altitude (i.e. in the stratosphere or below), the atmospheric density will be high enough to create drag forces that will slow the upward-moving particles.
In addition, as a result of their fast upward travel, these particle would undergo immense heating to the point of evaporation.
So while wind, lighting, volcanoes, etc. would be capable of imparting huge forces at lower altitudes, they would not be able to accelerate intact particles to the point where they could achieve escape velocity.
On the other hand, in the upper part of the mesosphere and thermosphere, particles would not suffer much drag or heating.
As such, Berera concludes that only atoms and molecules that are already found in the higher atmosphere could be propelled into space by space dust collisions.
The mechanism for propelling them there would likely consist of a double state approach, whereby they are first hurled into the lower thermosphere or higher by some mechanism and then propelled even harder by fast space dust collision.