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Comment by danieltillett | Hacker News Reader

We are only 3.7 billion years too late to be worrying about this. Earth rocks containing viable microbes have been landing on Mars for billions of years. I can't find a reference, but my memory is the rate is around 100 kg per year.

Edit. Found some references [1 - 3].

1. http://www.ncbi.nlm.nih.gov/pubmed/11543506

2. https://arxiv.org/pdf/1011.0101.pdf

3. https://arxiv.org/pdf/0809.0378.pdf

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> Conley has a response to this argument. Even if a microbe on Mars shares the same deep origins as us, a few thousand years down a separate evolutionary pathway would still make them pretty alien indeed. But ultimately, the best case for caution, and for planetary protection, may be simply to point to all the ways in which our knowledge of Mars has changed just in the past few years. Curiosity ended up almost on top of possible liquid water because we didn’t know what we didn’t know. In a way, Conley’s deepest arguments boil down to a quote from Haldane: “The universe is not only queerer than we suppose, but queerer than we can suppose.”

But if 100kg of Earth material makes it's way to Mars every year, it means Mars has already been contaminated this year as well as in 2015, 2014 and so forth.

Personally I'm for being cautious as well but there are always trade-offs and we must understand that.

That's still the same argument. It's possible Martian life has already been decimated by microbes from earth, but does that possibility justify carelessly introducing new extremophiles? There is a short window, less than a century and perhaps only a couple decades, before we start sending humans in which we can study what may have lived on Mars, originating from there or not, prior to colonization.

Conley is not trying to prevent Mars exploration or colonization. When we contaminate Mars, we should only do so as a deliberate choice, aware of the consequences, as there is no going back.

All the life on Mars is now going to be deep underground. It really isn’t possible to contaminate this even if we were to deliberately crop dust the whole planet in bacterial spores from Earth. It is not something we need to worry about.

I would be much more cautious about some of the moons of Jupiter and Saturn that may have internal oceans. These could be contaminated if we are not cautious, but like Mars they have probably been contaminated by Earth microbes billions of years ago.

It takes easily a few million years to travel from Earth to Mars.

The interesting thing is, this represents a snapshot of Earth lifeforms over a period of a million years. If there is a mass spectra of such ejecta out there, who knows what it may yield ..

That might be the average, but some will do it in a few years. The ejecta from a large asteroid struck will be large and thrown out with enough energy for some rocks to make the journey in a short time.

All caution and no action gets us nowhere.

Some caution and some action gets us where we are.

Sending robots to Mars is hardly "no action".

How exactly does that work? Where do they get the energy from? How big are these rocks?

The rocks are ejected during large asteroid strikes. There have been many of these over the billions of years life has existed on Earth.

Do your links support your conclusion? They seem to be optimistic about mars-to-earth transfer, but not the reverse.

"The conclusion is that if microbes existed or exist on Mars, viable transfer to Earth is not only possible but also highly probable ... Earth-to-Mars transfer is also possible but at a much lower frequency."

The frequency is much higher from Mars to Earth, but you only need one Earth microbial spore to survive the journey to contaminate Mars.

Depending on where it lands, and how it interacts with the Mars environment, a large number of microbial spores can land on Mars without causing any problems.

Given that what you're saying is possible, but not probable, it totally makes sense for NASA to take precautions to ensure that they don't destroy the Mars ecosystem through their Mars landings.

There is no way earth microbes can destroy the Mars ecosystem since both will have the same microorganisms. It is unlikely that a Earth rock landing on Mars now will land somewhere productive, but in the past when Mars had surface water it was much more likely.

The really interesting thing is we know so little about the micro-organisms here on Earth that we would not even be able to tell if we find a new phylum of bacteria or archea on Mars if it was native or not.

This presents a mechanism of travel, but no proof travel has happened.

There is nothing that can prove this has happened other than to visit Mars and look for bacterial life.

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