In our quest for the search of life elsewhere in the universe, the observational bias from our one sample of life – our own planet – runs rampant.

Earth is indeed the only body currently known to hold and sustain life, and several concepts in astrobiology are centred around our planet’s current characteristics and on the Earth’s biome. Grounding our expectations in previous observations is, of course, important, although it can also be limiting when our observations involve only one sample – planet Earth.

For this reason, examining niche environments that we consider extreme on Earth might prove useful in broadening the boundaries of environments where we can look for life elsewhere.

The habitable zone, also called the Goldilocks zone, traditionally represents a range of distances away from a parent star where water would exist in a liquid state at the surface. This interpretation omits possible options for the proliferation of lifeforms, including the presence of sustained oceans of water below the surface and the possibility that other biomes might have very different forms of life, with different sustaining requirements. We know today, for example, that an extended habitable zone is more accurate since it also takes in to account the possibility of havens for life in regions such as the outer solar system, provided that they have underground reservoirs of a solvent like water.

Examining niche environments that we consider extreme on Earth might prove useful in broadening the boundaries of environments where we can look for life elsewhere

Until recently, very little was known on some of the most remote extreme locations on Earth, such as hydrothermal vents, which are notoriously hard to reach, let alone sample. We do, however, now know of several extremophilic organisms that not only survive but also thrive.

Some examples of such extremophile groups include acidophiles (organisms thriving in acidic conditions), thermophiles (those thriving in heat), psychrophiles (those thriving in cold), xerophiles (those thriving in arid conditions), and radiophiles (those thriving in high-radiation environments). Extremophiles can sometimes thrive in multiple such extreme conditions, in which case they are called polyextremophiles.

Deinococcus radiodurans is one such polyextremophile, being able to survive high-radiation conditions as well as cold, vacuum, acidic and arid conditions. With an ability to survive doses of over 5000Gy, a question regarding the reason for the high-radiation resistance persists, with different possibilities considered. One plausible reason is that the high-radiation resistance exhibited by this bacterium is a side effect of its evolved ability to remain viable after desiccation.

However, experiments involving Deinococcus radiodurans being placed outside the ISS have shown the bacterium to remain viable even after a year of space exposure, thus entertaining the possibility that radiation-resistance evolution might have been driven by past exposure of the Deinococcus radiodurans to the space environment.

More research is still required to understand more about such radio-resistant polyextremophiles, which may be vital in assisting us in understanding the mechanisms that lead to cancer and aging in humans.

Josef Borg completed a PhD in astronomy at the Institute of Space Sciences and Astronomy, University of Malta, and is currently a post-doctoral researcher at the Faculty of Health Sciences at the University of Malta. He is also Malta’s representative on the European Astrobiology Network Association (EANA) council.

•        The Artemis 3 mission, which will see the return of humans to the surface of the moon, is unlikely to launch before 2026.

Originally slated for 2024 and 2025 respectively, Artemis 2 and Artemis 3 have now been pushed back to September 2025 and September 2026. Issues discovered include a battery problem as well as a faulty circuitry component, responsible for ventilation and temperature control systems. Since astronaut safety remains a priority, the decision to delay the Artemis missions by a year was deemed the safest route forward.

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DID YOU KNOW?

•        Extremophilic organisms have also been found deep in the ocean. In places such as hydro-thermal vents, a flourishing ecosystem of extremophiles can be found, typically based on chemosynthetic organisms that convert chemicals released from such vents into energy as opposed to energy from the sun (as is done in photosynthetic organisms).

•        The famous tardigrades are better categorised as extremotolerant organisms, as opposed to extremophiles. While they can indeed survive extended periods of time in extremely harsh environments in a dormant ‘tun’ state, they cannot really thrive well under these conditions, doing best under normal conditions.