An Ancient Ocean on Mars?
Bad Astronomy has a post today about possible evidence for an ancient ocean on Mars, based on this press release. It’s an interesting post, but all the hype confused me. The results that supposedly suggest an ocean on Mars are old, it’s just the interpretation that is new, and that is not very convincing to me. The basis of the argument is that potassium, thorium and iron were transported to the northern lowlands, leeched out of the rocks and re-deposited in a thin layer. The detections of these elements tend to be below the “shorelines” that people have drawn on Mars, and therefore this is claimed as support for an ocean.
My questions is: why not just put the volcanic rocks in the lowlands to begin with and skip the whole business with the transport, leaching and re-deposition? It’s certainly possible that the elements were deposited by oceanwater, but I don’t think it’s necessarily the best explanation.
Don’t get me wrong, I love the idea of an ocean on Mars. But that’s why I’m so cautious about people claiming to discover one. There are so many scientists (and others) who want Mars to once have been Earth-like, that they start to see evidence for it everywhere, even if it isn’t really there, or isn’t very compelling. The more you want to find something, the more cautious you need to be when claiming that you have found it.
I know, I know. The headline: “Oceans on Mars are One of Many Possible Explanations for Observations” doesn’t have quite the same ring to it. But I think it’s important to save the big headlines for the big discoveries. These results and their interpretation are fascinating! But I’m not convinced yet.
Explore posts in the same categories: Oddysey, Water on Mars
The Martian Chronicles 
November 18, 2008 at 1:12 pm
Amen!!
November 19, 2008 at 1:52 am
what would be a really solid find on mars to indicate an ancient ocean? aside from fish fossils of course…
November 19, 2008 at 1:30 pm
Very good question…
Here are a few ideas offhand:
One would be large deposits of carbonates, but there are thoughts that carbonates on Mars might have been dissolved by a period of acidic waters, plus life on earth rapidly accelerates carbonate formation, so maybe these aren’t necessary.
I would expect oceans to leave behind large salt deposits as they evaporated. There is some recent evidence of “chlorite” (chlorine-bearing salt) deposits, but its still very new and I don’t think it’s being detected in the putative ocean basin. Problem is, salts are soft and would erode easily, so not finding them is again not conclusive.
Lava that gets extruded into ocean waters forms “pillow basalt”, where the rock solidifies in bulgy shapes known as “pillows”. If we found that, it would be very good evidence for a large body of water. If we studied the “pillows” up close and found that they had very few bubbles it would indicate that they formed under high pressure in a deep ocean.
So that would be pretty conclusive but also phenomenally difficult to find unless we got really lucky.
I honestly don’t know enough about geochemistry, but I suspect that there are some geochemical signatures that would be conclusive. Particularly isotope ratios. This may be the topic for a future blog post if I find the time to do a little reading about it…
The difficult thing is finding evidence from orbit. It’s possible that even if there was an ocean that we couldn’t find it from orbit. I don’t know, maybe these GRS results are more convincing to experts in geochemistry. And I’m sure there are clues that I haven’t thought of, or that nobody has though of yet.
November 21, 2008 at 5:19 pm
One bit I would add to this is that there is tons and tons (literally) of geologic evidence for water-based transport from the highlands into the northern basin. Even just looking at MOLA, you can see evidence for massive debris flows extending into the depths of the northern basin from outflow channels.
From recent radar results, we know that at least the upper several 100 m of the northern plains is composed of sediments. While some or all of these sediments may have been deposited by debris flows, which involves some water, this don’t necessarily mean that there was a ocean. Some people claim that the morphology of the flows indicates that they happened under water (e.g. that the morphology changes when they pass the putative “shorelines”), but that’s really unclear right now.
And on the geochem/mineral side, there are massive salt deposits in the northern basin! The gypsum deposit in the northern dunes has a volume of at least 100 cubic km, and we have no idea how far it really extends. Also, the perchlorate salts that Phoenix found were probably created by exposing salt to UV at the surface (if they were natural). Who knows what lies underneath!
So, I guess what I’m trying to say is while there isn’t any direct evidence for a northern ocean on Mars, there is plenty of potentially indirect evidence, including the K/Th result above. And while none of these results individually deserve a headline, they each are adding to the growing pile of “maybes”.
November 21, 2008 at 10:19 pm
[…] the new evidence for Oceans on Mars. Bad Astronomy is all for it, and is very excited about it. But the Martian Chronicles has a different take, and expresses skepticism about interpreting the evidence. The Meridiani […]
December 8, 2008 at 1:50 pm
is there an ocean on mars or not ???
December 8, 2008 at 1:58 pm
Is there? No.
Was there? Nobody knows.
September 13, 2009 at 3:38 pm
A recent paper uses an accurate three-dimensional model of Mars (using MOLA data) to analyze the “shorelines” reported by Clifford and Parker (2001) and shows that the lines define the perimeters of basins that could hold water.
The lines are, in fact, equipotential lines – like a bathtub ring – in the northern polar depression. Go to the site linked below.
http://mysite.verizon.net/rickmsmith/MarsOceanProject.html