Viking lander and Mars life

[Jarhyn]

In eukaryotes. Prokaryotes don't have organelles other than ribosomes, and those are about twenty times smaller than a visible light wavelength

What we can't find doesn't impact the list of things we can. We just have to hope for something interesting being findable in the ways we may.

but the proposal I was challenging was to use a conventional microscope, not a PCR machine

I propose a decent way to use an automated package the size of a breadbox to take a sample.

I'm curious as to why it's feasible for randomly chosen bacteria to survive

Because you propose randomly chosen bacteria to survive to contaminate after being autoclaved on purpose.

A good impact can straight up yeet a lucky stone shotgun style on a brief tour.

 

[Loren Pechtel]

I'm curious as to why it's feasible for randomly chosen bacteria to survive (1) a meteor impact big enough to launch debris to escape velocity, (2) millions of years floating around interplanetary space being exposed to vacuum and radiation, waiting for dumb luck to bring them to another planet, (3) uncontrolled reentry, and (4) lithobraking, but not feasible for them to survive (5) a gentle launch, a seven-month carefully guided trip, a soft landing, and "a thorough autoclaving".

Thorough autoclaving is the part that gives them big problems. Most of them won't survive either way, but some stuff that lives in rocks isn't going to mind a trip through space. And bacteria are very acceleration-tolerant, being blasted off a planet isn't going to bother them. The survival issue is heat. Bake the rock to the core and everything dies--but aerobraking doesn't heat the core, only the surface. Meteorites land cold.

 

[steve_bank]

There is certainly the possibility of some form of life on Mars.
Two miles down.

Newly Discovered Microscopic Worm Thrives in Gold Mines a Kilometer Underground

High temperature, low oxygen and permanent darkness are no problem for a previously unknown species of nematode

www.scientificamerican.com

The Sciences

Newly Discovered Microscopic Worm Thrives in Gold Mines a Kilometer Underground​

High temperature, low oxygen and permanent darkness are no problem for a previously unknown species of nematode

• By David Biello on June 1, 2011

Deep in South Africa's gold mines water can be found in rock fractures, hosting bacteria that feed off the stone itself and form biofilms on the hard surfaces. Now new samples pulled from these sunless pools show that nematodes—roundworms of varying size that are essentially tubes with a digestive tract and thrive everywhere on the planet—likely graze on these bacterial films, surviving more than a kilometer underground. In fact, an entirely new species of nematode—dubbed Halicephalobus mephisto for a lifestyle reminiscent of Faust's underworld demon, Mephistopheles, or "he who loves not the light"—makes its home only in the deep subsurface, suggesting that life, even complex, multicellular life, may populate sulphate-loving ecosystems in the planet's unexplored depths.

 

[Bomb#20]

Thorough autoclaving is the part that gives them big problems.

According to NASA,

"Planetary protection technologies are for cleaning and sterilizing spacecraft and handling soil, rock, and atmospheric samples.

In the study of whether Mars has had environments conducive to life, precautions are taken against introducing microbes from Earth. The United States is a signatory to an international treaty that stipulates that exploration must be conducted in a manner that avoids harmful contamination of celestial bodies.

The primary strategy for preventing contamination of Mars with Earth organisms is to be sure that the hardware intended to reach the planet is clean. Each Mars Exploration Rover complied with requirements to carry a total of no more than 300,000 bacterial spores on any surface from which the spores could get into the martian environment. Technicians assembling the spacecraft and preparing them for launch frequently cleaned surfaces by wiping them with an alcohol solution. The planetary protection team carefully sampled the surfaces and performed microbiology tests to demonstrate that each spacecraft meets requirements for biological cleanliness. Components tolerant of high temperature, such as the parachute and thermal blanketing, were heated to 110 degrees Celsius (230 Fahrenheit) or hotter to kill microbes. The core box of each rover, containing the main computer and other key electronics, is sealed and vented through high-efficiency filters that keep any microbes inside. Some smaller electronics compartments are also isolated in this manner."​

 

[Swammerdami]

Given the age of the rocks, it's quite possible that earth life is in fact martian... Which would make telling the difference between them through genetic markers difficult.

Or worse that the variety of life on earth owes to a repeat exchange.

Did ancient Mars have an ocean? With alkaline thermal vents (probably made of pyrite) spewing warm water from the hot mantle?

Chapter 3 ("Energy at Life's Origin") of Nick Lane's The Vital Question discusses prerequisites for life's origin. (SPOILER: It wasn't easy.) The chapter concludes that the alkaline thermal vents where earliest life evolved on Earth may be unique! No other proposed venue would be capable of originating life.

Lane's view may be unpopular here and deemed unimaginative, but I think he makes a strong case.