PUBLIC DOMAIN Space dust may carry living microbes despite lacking water and oxygen.
For centuries, humans have pondered the question of how life originated on Earth. Several theories have been developed that range from religious doctrines to scientific observations. Some propose that lightning provided the spark of life, while others suggest that life was brought from elsewhere in space.
In an article published on Nov. 12 in the journal Astrobiology, Arjun Berera of the University of Edinburgh’s School of Physics and Astronomy hypothesizes that microbial life and organic building blocks could be distributed among different planets through hypervelocity space dust collisions in the atmosphere.
The mechanism Berera depicts shares several similarities with the mechanism behind the radiopanspermia theory proposed by Svante Arrhenius in 1908. The radiopanspermia theory claims that microscopic life, such as bacteria or spores, is dispersed in space through the means of radiation.
Berera, however, believes that space dust collision is the main driving force that propagates microbial particles in space rather than radiation.
On a daily basis, space dust crashes into Earth’s atmosphere with high speeds. If high altitude particles, such as those in the upper layer of the mesosphere and thermosphere, collide with space dust, they gain enough velocity to escape Earth’s gravitational field.
On the other hand, low altitude particles, specifically those that occupy the stratosphere below, cannot escape Earth’s gravitational field because the high atmospheric density significantly reduces their speed.
In addition, fast moving space dust at micron and millimeter sizes are not the only ones that can propel microbial particles into space. Larger space dust particles and meteoroids with sufficient speed can also provide enough momentum to send these particles into space.
Although it is possible for microscopic particles to be in high altitudes, larger particles need to be propelled by other forces first before reaching the thermosphere. These forces include vertical wind and volcanic eruptions.
One of the major concerns about the space dust collision mechanism is whether particles are destroyed during the impact. Berera points out that if the microbes were packed together, some would absorb the impact while others would remain alive.
Another concern is the microbes’ survivability in space, where there is no water, no oxygen and drastic temperature changes. Berera gives the example of tardigrades to address this problem.
Tardigrades, also known as water bears, are eight-legged microscopic organisms that have demonstrated time and again their extraordinary abilities to withstand extreme environments. Researcher K. Ingemar Jönsson and colleagues demonstrated in 2008 that tardigrades can survive in space.
“Even if the escaped particle only contained organic molecules or microbes that were killed on their journey out of Earth, such complex organic systems may still act as blueprints in suitable environments to speed up the development of life,” Berera said in a press release. “[This can be done] through assisting self-replication, self-organization, abiogenesis and various other potential mechanisms.”
To improve his hypothesis, Berera suggests the need to make direct measurements on the density of microbial particles in the mesosphere and thermosphere by using high altitude balloons or sounding rockets. He also mentions the need to analyze space junk, which might house microbes that escaped Earth.
The space dust collision mechanism Berera proposes has important implications to the origin of life and could potentially explain how planets exchange information with each other.
“The proposition that space dust collisions could propel organisms over enormous distances between planets raises some exciting prospects of how life and the atmospheres of planets originated,” Berera said.
In fact, the streaming of fast space dust could be an important factor that proliferates life in many parts of space.