Japan's priceless asteroid Ryugu sample got 'rapidly colonized' by Earth bacteria

It seems like the researchers should have analyzed the DNA of those microbes. It would have provided more conclusive evidence of terrestrial origin..

With recent evidence that microbes can colonize and survive in rock deep within Earth, we should not be assuming that they cannot also do that in other rocky materials off-Earth. And it should not be surprising if extraterrestrial microbes revive and begin to colonize on Earth, only to soon die from competition with terrestrial competitors or some sort of poisoning from an environmental factor unfamiliar to them.

That was basically the original premise for "War of the Worlds", where the invaders were able to easily defeat human military defenses but soon succumbed to terrestrial microscopic infections. So, it is not a novel concept.
 
Dec 29, 2019
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@Unclear Engineer

Not DNA analysis but thorough examination earlier showed no presence of microbes. I don't think their contamination-not-ryugu-origin conclusion lacks a sound basis -

Disappointingly, the team has successfully and conclusively ruled this out.

"Before we prepared the sample, we performed nano-X-ray computed tomography, and no microbes were seen," Genge said. "In any case, the change in population suggests they only appeared after the rock was exposed to the atmosphere, more than a year after it was returned to Earth."
 
I think it is probably terrestrial contamination.

But, I think the evidence stops short of "conclusiveness", given that we don't actually have any idea how extra-terrestrial life would work.

Just looking at the outside surface with an electron microscope does not rule out something on the inside that propagates to the outside, but then dies.

Considering that we are frequently being surprised by what microscopic terrestrial life forms can do, it is hard to develop conclusive logic about what extraterrestrial life forms might be able to do, especially when exposed to a new (to them) environment (ours).
 

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