First evidence of planet-wide groundwater system on Mars

Well that's a big difference.

Yeah, like billions of years.

But hey, maybe there's still lots of ice, here and there.

I have very little knowledge of this, but I will say chemicals have different properties. For instance the solid of H2O floats as opposed to sinks in its liquid form.

I suspect we can narrow out options for the formations. However, we will never be 100% confident (but maybe 80+% confident) in what has occurred.

I think its a fair question. According to the article it seems most modeling is based on known occurrences on Earth which makes sense. Yet do we really know if these interactions work in a totally different planet environment? There are a lot of assumptions that go into this modeling work. No question it's good work. Yet it would be nice if the underlying assumptions and modeling data is open to public peer review. Especially since this is coming from a publicly funded institution.

All that said I think its really fascinating and hope the hypothesis holds up.

From what I have read they look at different factors like chemical composition and visual, not just a single factor. So if you have something to be made of x AND look like Y then there is a high probability it has been caused by Z.

This was my question too. These articles never seem to mention how they know the formations were caused by water specifically.

From a geology point of view, many of these features all over Mars are pretty clearly fluvial in origin. They have very specific characteristics, different from aeolian (wind) landforms such as dunes, which are also present. There's really a good deal known about Martian geology. For surface processes, it is (or was) more like Earth than different.

Definitely caused by presence of a liquid, almost certainly water. Considering Mars absolutely has a great deal of water, it's the only reasonable explanation.

There's also glaciers on Mars currently, as well as glacial landforms such as eskers and moraines from much more extensive previous glaciation, which only could have occured with a more vigorous hydrologic cycle. It's pretty hard to believe all of these landforms weren't formed by hydrological processes.

There's also not much methane on Mars. It's way too warm to be a solid or liquid. There's CO2, but it's either gas or solid. Water is really the only known liquidy thing there.

Some minerals only form when the reagent minerals are wet. So if they can identify these mineral it's a good indication that there was water.

As a home experiment, you can get some cement power (for home masonry) and put a small amount in two discardable plastic glasses. Then you mix one with a small amount of water and the other with a small amount of cooking oil [1]. After a while, you will get a hard rock in one glass and a horrible goo in the other. I'm not sure how geologically accurate this is, I hope it is somewhat similar. (Discard the plastic glasses after this.)

More details from an accurate source: https://en.wikipedia.org/wiki/Water_on_Mars#Evidence_from_ro...

[1] Actually gasoline or kerosene is much more similar to liquid methane than cooking oil, but cooking oil is more safe, so please forgive the chemical inaccuracy.

Mars is too warm for liquid methane (-162°C). Mars ranges from -125°C to +20°C.