Did life hitchhike through the Solar System?

Astronomers suggest microscopic organisms, such as tardigrades, can be transported between planets by fast-moving streams of space dust.
By | Published: November 21, 2017
ASA/ESA/M. Livio/The Hubble Heritage team
Astronomers have long believed that asteroid (or comet) impacts were the only natural way to transport life between planets. However, a new study published November 6 in Astrobiology suggests otherwise.

The study, authored by Professor Arjun Berera from the University of Edinburgh’s School of Physics and Astronomy, suggests that life on Earth may have begun when fast-moving streams of space dust carried microscopic organisms to our planet. Berera found that these streams of interplanetary dust are not only capable of transporting particles to Earth, but also from it.

Here is an example of an interplanetary dust particle measuring about 10 micrometers across. A micrometer is one millionth of a meter.
Washington University
Interplanetary dust — a combination of debris from ancient asteroid collisions, active comets, and interstellar dust — is pervasive throughout the solar system. Roughly 220,000 pounds (100,000 kilograms) of space dust fall onto Earth every day. And in interplanetary space, streams of cosmic dust can travel together at speeds of up to 44 miles per second (70 kilometers per second).

The researchers found that as these streams of dust graze Earth, they collide with organic particles found in the upper atmosphere. These small particles, which are trapped about 93 miles (150 km) or higher in Earth’s atmosphere, are then knocked out with enough force to escape Earth’s gravity altogether. Once the particles are free from the bounds of Earth, the powerful dust flows can pick up and carry the microscopic hitchhikers off through interplanetary space.

Tardigrades (also known as water bears) are one of the most resilient forms of life on Earth. These microscopic animals can go decades without food or water, can exist in the most extreme temperatures, and can survive in the harsh, radiation-filled vacuum of space.
NASA/N. Ottawa/O. Meckes/Eye of Science/Science Source Images
Since some bacteria, plants, and even small animals — known as tardigrades — can survive in space, it is possible that these organisms could also get caught in the dust conveyor belt and hitch a ride to another planet. The same mechanism outlined in the study also allows for distant planets within the same solar system to exchange atmospheric particles with one another.

“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,” said Berera in a press release. “The streaming of fast space dust is found throughout planetary systems and could be a common factor in proliferating life.”