Panspermia. No, it’s not the name of the alien world explored in the new series of Dr Who. It is the idea that life could spread throughout the Universe, transferred by material floating through space.
One theory goes like this: If a planet supporting life is struck by a large-enough asteroid, it’s impact could be sufficient to throw material from the planet’s surface into space. If that material has micro-organisms on it, and they are able to survive the impact, a subsequent journey through space and ultimately an entry through another planet’s atmosphere, then panspermia could work. So, taking into account all those ‘ifs’, there is the possibility that this process could spread life between planets or even different star systems. This particular theory is known as lithopanspermia – where life is transferred across space within rocks.
But where could this happen? Well, to transport life from one place to another, you’d better make sure that the start and end points are habitable. Astronomers still haven’t ruled this out for our own Solar System, as there are several candidate bodies that have the potential to host life. This even includes an old favourite: Mars.
Conditions need to be suitable for life in order to deem a planet ‘habitable’. Though the formation of life is yet to be fully understood, most agree that liquid water and an energy source are the key components to a habitable environment as we know it. Planets where things are ‘just right’ for liquid water to exist are said to be in the Goldilocks Zone, though this is far from definitive. All life on Earth is carbon-based, but there is even speculation about this as a requirement. It would also help to have an atmosphere in place, to offer protection against harmful radiation from the star.
The list of potentially habitable planets has shot up in the past couple of years. One planetary system, however, has caused particular excitement among the exoplanet community. TRAPPIST-1 is a system of seven temperate planets transiting a small, ultra-cool star. Originally thought to host three planets, a further four were announced in early 2017. With all of the planets similar in size and mass to Earth and Venus, and three orbiting in the so-called Goldilocks Zone, the system continues to fascinate researchers. To top it all off, the planets are remarkably close together.
The perfect test case
Cue James Blake, a PhD student at the University of Warwick who, while studying for his undergraduate degree in the Department of Physics, decided to undertake a research project to see if lithopanspermia could be plausible in the TRAPPIST-1 system.
He explains: “The discovery of the TRAPPIST-1 planets has thrown up all sorts of weird and wonderful scenarios for astrophysicists to investigate. One of the really special things about the system is that the planets are extremely close together – so close that in each other’s night skies they’d appear similar in size to a full moon here on Earth.
“So, as we were looking to study the theory of lithopanspermia, TRAPPIST-1 seemed the perfect test case. I decided to try simulating the system to see whether, in theory, it would be possible.”
Enter the extremophiles
James used the results of experiments conducted by organisations like NASA and ESA in space, exposing micro-organisms to the harsh environment outside Earth. These organisms are aptly referred to as ‘extremophiles’. Researchers have carried out these studies for various species of bacteria, lichen, fungi and tardigrade (a charismatic micro-animal known fondly as the ‘water bear’) to test their hardiness against extremes of temperature, pressure and radiation.
“One of the longest experiments was carried out aboard NASA’s Long Duration Exposure Facility, finding that up to 90 percent of a population of the bacteria Bacillus subtilis could survive extreme conditions for six years,” explains James. “We used this alongside several other studies as benchmarks for our own. After tracking the amount of UV radiation that test particles (asteroids) were exposed to throughout our simulation, we were able to compare against the doses that have been tested in space.
The results were really promising. The simulation showed journey times for the test particles in the TRAPPIST-1 system to be tens of thousands of times shorter than those for our Solar System – so it would take rocks years to travel between planets instead of millions of years. This kept the dose of UV flux way below many of the thresholds found to be survivable by missions like Biopan and LDEF. If there were habitable planets in a system like TRAPPIST-1, it’s plausible that a colony of Bacillus subtilis or some other extremophile could survive the journey from planet to planet in strong numbers, if conditions were right.”
Consider the caveats
Plausible – but not definite then?
“As with the majority of results in astronomy, there are caveats,” says James. “We’ve not taken into account the initial impact or final atmospheric entry. Other studies have been optimistic about these stages and their potential effects on microbial life, but as of yet there’s nothing conclusive.
“There’s also the issue of the system’s habitability in general. This will continue to generate speculation for years to come. Planets around stars of this kind are likely to be subjected to strong winds of high-energy particles and intense X-ray radiation, possibly extreme enough to completely strip them of their atmospheres. Stars like TRAPPIST-1 also tend to flare a lot, so the situation is probably much more violent than it is on Earth around our Sun.
“But as a first look, the project showed us that within the parameters of what we already know about the survival of extremophiles in space-like conditions, panspermia in a compact system like TRAPPIST-1 is at least plausible. And who knows? It may have already happened somewhere in the Universe - it’s so vast, I wouldn’t be surprised!”
James presented his research this week at the International Conference of Undergraduate Research, hosted annually by the University of Warwick and its partner Monash University in Australia. The conference aims to showcase the best of undergraduate research on an international platform, linking students to universities all over the world.
“I think undergraduate research should be a key part of any university’s agenda,” adds James. “Getting students involved in research from an early age can only lead to more world-class researchers and that’s exactly what we need to continue pushing the boundaries further and further.”
For more information about ICUR and how to submit your own research in the coming year, visit https://www.icurportal.com/.
28 September 2018
James Blake is a PhD student in the Astronomy and Astrophysics group at the University of Warwick, under the supervision of Prof. Don Pollacco. His PhD project focuses on the imaging and tracking of space debris in geostationary Earth orbit (GEO). This is his fifth year in the department.
Watery asteroid. Credit Mark Garlick
EM image of Milnesium tardigradum in active state. Via Wikimedia Commons
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