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Comment by saiya-jin | Hacker News Reader

Article mentions another bacteria thats rated as world's toughest - Deinococcus radiodurans. Hell it survived 3 years in outer space and high doses of gamma radiation, with that logic we most probably already (re?)introduced life on Mars.

> Deinococcus radiodurans has a unique quality in which it can repair both single- and double-stranded DNA. When damage is apparent to the cell, it brings the damaged DNA into a compartmental ring-like structure where the DNA is repaired, and then is able to fuse the nucleoids from the outside of the compartment with the damaged DNA.

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> with that logic we most probably already (re?)introduced life on Mars.

It's not unlikely that all the solar system's planets have been contaminating each other for billions of years. All it takes is a big asteroid impact and some luck, and then some bacteria hitches a ride.

The tough part is of course thriving after the organism arrives. Given Mars' current climate and surface perchlorate levels, I'm not convinced it's likely that something from here takes root over there without some help.

I'm always intrigued by this. How big a rock would need to impact to throw a chunk all the way up Earth's gravity well? And does escape velocity create the same kind of atmospheric friction problems that re-entry does (so it'll need to be a big chunk or the bacterium needs to resist extreme heat)?

The whole chain of "really big rock -> chunk of Earth leaving the gravity well -> getting into some kind of stable orbit where it can be pulled into Mars -> surviving re-entry on Mars" doesn't seem like it would happen enough times to create the kind of odds of success that would be needed for a bacterium to successfully colonise Mars.

> does escape velocity create the same kind of atmospheric friction problems

Yes; but those temperatures may not penetrate deep into the body of the rock; so there still might be biology surviving.

It's also possible that life originated on Mars (back when it was young and much more conducive to life) and was then introduced to Earth. Or, that life bounced back and forth between the planets as each was affected by large sterilizing impacts in the early solar system, the other acting as a refugee from which the sterilized sister planet could be reinoculated.

Kurzgesagt recently had an interesting video on how life might have been everywhere when the universe was still young and essentially every inch of it had temperatures to support it.

The bit that sold me on the idea was when they noted that the complexity of life seems to double every 250m years. But apparently if you roll with that assumption and extrapolate all the way back to the simplest conceivable organism, you end up at time when earth didn't exist and the universe was young.

Well this is just fascinating. 280 million years is a lot of time if you only really need one instance of reheating/hydrating to grow for a bit and reset before settling in for another long sleep.

>When cultured and exposed to ionizing radiations in liquid media, Deinococcus radiodurans could survive up to 25 kGy.[40] Horne et al. (2022) have studied the effects of desiccation and freezing on the microbial survivability to ionizing radiations considering the feasibility studies to return Martian subsurface soil samples for microbial characterization and for determining the most favorable landing sites of a future robotic exploration mission.[41] They found that the desiccated and frozen cells could resist to a 5.6 higher radiation dose: up to 140 kGy. They calculated that this could correspond to a theoretical survival time of 280 million years at a depth of 33 feet (10 m) below the present Mars surface. However, this time scale is too short to allow microbial survival at a depth accessible to a rover equipped with a drilling system below the Martian surface when compared to the moment when liquid water disappeared from the Martian surface (2 – 2.5 Ga ago). Nevertheless, Horne et al. (2022) consider the hypothesis that meteorite impacts could have dispersed Martian soil and heated locally the subsurface during the geological history of Mars, heating sporadically from time to time the local environment, melting the frozen ice and giving perhaps a chance to a hypothetical distant Martian extremophile resembling its terrestrial cousin Deinococcus radiodurans to grow again for short moment before to rapidly become again frozen and dormant for millions of years. So, for returning subsurface soil samples from Mars for microbial characterization with a potentially "successful" mission like the European Rosalind Franklin rover, it would be necessary to target a relatively young impact crater to increase the chances of discovering dormant extremophile micro-organisms surviving in the dry and frozen Martian subsurface environment relatively protected from the lethal ionizing radiations.[40]

https://en.wikipedia.org/wiki/Deinococcus_radiodurans#Clues_...

It also has multiple backup copies of the genome, and there some other (more speculative?) mechanisms listed here:

https://en.wikipedia.org/wiki/Deinococcus_radiodurans#Mechan...

That's super interesting. Though I am waiting for the longevity hackers to CRISPR that into themselves. If it works out, great. If not, another lesson for the ages.

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