The Potential for Bacterial Spores to Flourish on Jupiter and Saturn’s Icy Moons

In the realm of microorganisms, the boundary between life and death can appear incredibly thin. However, certain types of bacteria have managed to adapt to extreme conditions here on Earth by entering dormant phases and transforming into biological spores.

This survival mechanism is especially advantageous in cold environments. However, astrobiologists are intrigued by the possibility that bacterial spores might also exist in the frigid subsurface conditions of Jupiter and Saturn’s icy moons.

It is hypothesized that these bacteria may have originally evolved on the warm seafloors of Europa or Enceladus, and were later deposited into the icy subsurfaces or surfaces through cryovolcanism, where they formed spores.

Surprisingly, recent research conducted by planetary scientist Edith Fayolle and her team at NASA’s Jet Propulsion Lab suggests that these spores actually thrive in colder conditions. The colder the environment, the more favorable it is for these spores.

Are bacterial spores considered living organisms?

I reached out to Fayolle via email to learn more about bacterial spores. According to her, bacterial spores are indeed a form of life, albeit in a dormant state. She explains that some bacteria respond to environmental stressors by entering this dormant spore phase, during which they form a highly resilient coating around their genetic material.

Fayolle emphasizes that spores are among the most resilient life forms known to us. They can be found everywhere on Earth, and although they do not replicate or grow, the genetic material within the spores remains preserved. When conditions become more favorable, they can transform back into regular cells capable of replication.

In their study, Fayolle and her colleagues focused on a hardy microorganism called Bacillus Subtilis and examined its spores under sun-like light irradiation in a laboratory setting.

Fayolle explains that Bacillus Subtilis is a bacteria commonly found on Earth, including in our gut. It has the ability to enter a spore phase when environmental conditions are unfavorable. Studying this microorganism helps researchers gain insights into the viability limits of spores on the surfaces of icy moons.

Fayolle and her team measured the number of spores that could be reactivated and become functional by counting the bacterial colonies that grew on petri dishes.

They discovered that the spores were more viable when irradiated at cryogenic temperatures compared to room temperatures. In other words, the ability of the spores to transform back into regular cells capable of replication was enhanced in extremely low temperatures. This is because low temperatures slow down the rate of radiation-induced damage to the spores.

How long can bacterial spores survive on the surface of an icy moon?

Fayolle speculates that in the absence of radiation, microorganisms as resilient as bacterial spores could remain viable at cold temperatures for an extended period of time. On Earth, less hardy microorganisms have been found to retain viability for years when preserved in cryogenic conditions.

However, Fayolle cautions that the surface of icy moons is exposed to solar radiation and high-energy charged particles, which significantly lower the likelihood of finding viable microorganisms on the very top surface.

Which icy moon is most suitable for these spores?

According to Fayolle, Saturn’s moon Enceladus is the most promising candidate. If microorganisms were able to originate in the sub-surface ocean of Enceladus and make their way to the moon’s surface, the south pole would provide the best conditions for the survival of bacterial spores. The radiation levels are low, the long winters minimize exposure to harmful conditions, and the deposition of icy grains from the moon’s vapor plumes could shield the microorganisms from damage.

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