Mars was formed around the time Earth was, but it was blessed with only 11% of Earth's mass and less than 40% of Earth's gravity field. Shortly after cooling solid, its "Noachian Era" was similar to proto-earth: warm, a thick atmosphere, plenty of liquid water on the surface, and probably a significant magnetic field.
But this era was still during the era of the Late Heavy Bombardment, a time in which the last dregs of the solar system were still settling out. Large asteroids still pounded the planets with regularity.
Unlike Earth, Mars had trouble maintaining its liquid iron magnetic field. Since it's much smaller, it cooled and thus congealed faster. And there's growing evidence that asteroid impacts were able to drive enough heat beneath the surface that interior convection was quelled, leading to a fragmented magnetic field.
Without an adequate magnetic field to deflect solar wind, the atmosphere was prone to shedding off pieces of itself into space. This was amplified by the lower gravity which meant holding on to lightweight gasses was even harder.
Over time, Mars cooled to the point where the major forms of tectonics ceased. The water locked up beneath the ground, rusted out pulverized basalt dust from the asteroid impacts, and frizzled in the radiation-baked atmosphere, floating off.
The seas and lakes dried, the rain stopped, and that... was that.
Three billion years later, we arrive on the scene and find out we have a little sibling. Then we send robots. We hope to find life, or evidence that it once lived. Characterizing how water worked in the Martian past is a part of answering that question.
I really dislike when scientific theory is presented this way. You imply too much when instead of using phrasings like "We have evidence that suggest X" you say "X happened."
> The seas and lakes dried, the rain stopped, and that... was that.
We think there was water on mars, therefore it is true. Is it too much to put a disclaimer somewhere that explains this is the current consensus but we have more to learn? The truth is that this story is riddled with assumptions, and readers need to know that.
Everything is evidence and consensus. It lengthens and weakens the prose to hedge every statement, making the actual message much less clear. Yes, people need to be disclaimed from believing everything they read, but you know whose responsibility that is? The public school system, teaching people to learn how to learn. One of the main things you should have taken from high-school science classes is that every time we had some understanding of something, we got more evidence and replaced it with a better understanding of that thing--and so everything is just a best-guess given current knowledge.
So: "A positive correlation was found between X and Y"--why are you even telling me? What's the message? "There is evidence that X might cause Y"--okay, how strong is this evidence? Is it enough to care? "X probably causes Y"--that is what you're really trying to say. I will hear that and put it though my own Bayesian updating to give slightly more credence to the statement that X causes Y (more or less depending on the trustworthiness of the source, where I read it, what other supporting statements were made, etc.) The previous two forms don't change this mental process one bit, except to make it harder to dig out the thing you were actually trying to get across.
The problem is that humans are not trying to answer one question like a Bayesian filter, even if they think they only are right now. Every assumption in your post, if it is believed, is remembered for a long time and can be combined with other knowledge to form nearly an infinite number of new associations and opinions. When you play with facts to make a point in a tone that suggests what you write is true, you poison those associations and conclusions and increase the chance that somebody will. Elieve the wrong thing.
Also, while it is true you will give up some brevity while you practice accuracy, eventually you will learn to write better and either shorten your posts again or present them in a more compelling way so that your readers do not notice the length much.
I like when scientific theory is presented this way. It is self-evident that it is scientific theory: anything in science can be prefixed with "We have evidence that suggests that..." You must follow that formalism in some forums, such as publications, but when having a coffee table discussion, when someone says "Mars formed around the same time as Earth", mentally add a note that says "We think..."
The nugget of truth in your statement is that some assumptions we are more sure of than others. We can probably say how old Mars is with more certainty than how much water there was on there. That may or may not need to be clarified, depending on what the focus of the conversation is.
I'm not a scientist, just a pithatician. I have no formal or informal education in this matter and my understanding is strictly derived from pleasure reading. But I think there's enough evidence to back up this general narrative without throwing asterisks everywhere.
Agreed. I've been looking at ways of communicating complex science-based or data-driven insights in compelling ways, and I think easily digestible narratives, like this one, are a great way to get broad range of people interested. I would love to ask you some questions and get your advice on how to better do this. If you're interested, please drop me an email: jake at insightdatascience.com.
I'm not a "pithatician", but methinks it has something to do with the word "pith" and its Variant "pithy". A quick google of said terms yielded the following points of note:
Pith is the central idea or essence of something. If you’re in danger, you could exclaim, “I would greatly appreciate it if someone would provide assistance.” Or, you could get right to the pith of your point by shouting, “Help!”
Following along this line of inquiry, one is led to consider the possibility (however remote) of this being an example of near-humour. Possibly of the genus: Pun, species: indirect. So, if one were to dress this up, it is perhaps alluded to as a Punnus Indirrectus.
I don't think you need to throw asterisks everywhere.
I think a simple opening statement like "our current theory is" followed by the main text would be more than enough, but it is good to remind people that theories are just that - theories.
What's the common usage of the word 'theory'? Maybe it's because I'm a former scientist, but I can't imagine how the public's definition would be different from the common dictionary definition:
a proposed explanation whose status is still conjectural and subject to experimentation
to me, the common use is more like 'hypothesis' - a possible explanation, that is still waiting for "real" confirmation once the facts come in.
but the scientific usage includes the fact that lots of facts have already been evaluated, and even that the new predictions by the theory have already been evaluated and found to be true.
>but the scientific usage includes the fact that lots of facts have already been evaluated, and even that the new predictions by the theory have already been evaluated and found to be true.
It's been evaluated and found to be true...for now. Almost every major scientific discovery upends some form of thinking or fact that we had accepted up until new information is found.
that's a misreading of what I wrote. I mean, the predictions made by the theory have been found to be true, not that the theory itself is ever proven to be true.
A scientist might make a hypothesis that suspect A is the murderer; the prediction would be that the murder weapon would be found in their house, the fingerprints match, blood types match. Upon search, the murder weapon was actually found, and fingerprints and blood types match.
A layman would say that finding the weapon converted the theory into a nearly certain fact.
A scientist would say that finding it pushed the hypothesis towards being a theory.
"Pithatician" is a novel use of πείθειν, "to persuade;" it reminds me of pithiatism, which is supposed to be a form of hysteria curable by persuasive suggestion.
I like it. I think I'm critical enough to take "truths" about Mars' distant past with more than a grain of salt. I can visualize the whole thing without always going into how sure we are about different pieces.
When you react to something like this are your saying "I don't like narratives being presented to me like this. or "I don't want narratives being presented to people dumber than me like this."?
I was thinking the same thing while reading it, I have heard 10 versions of the same story in the past 15 years. There is nothing to suggest that the latest version is the correct one, and the scientists at NASA say as much.
Nice summary, thanks. If Mars never had time for life to develop, that would be a sad thing. We could have had neighbors. In some ways, Venus is even more sad. It's much closer in size to Earth with much higher gravity than Mars, which I think would be better for human colonists. But Venus is a mess, so that's that.
The deal with Venus: dat atmosphere. She's a true sister to Earth in mass, gravity, and composition. She's also good evidence that Earth had a vastly thicker atmosphere at one point. Right now Venus has 90x more atmosphere than we do. And look at the proportions:
That's interesting because if you take away the products of volcanism (a major source of sulfur dioxide and carbon dioxide here on Earth), you're left with... Nitrogen... Argon... Water... and noble gasses. Look familiar?
The best thinking right now is that Earth outgassed and held on to a similar volume of gasses as Venus. But since we had a substantial volume of liquid water on the surface, the oceans naturally absorbed CO2 and then deposited it on the sea bottom as carbonate minerals. (Life eventually learned that trick too, leading to things like shells)
So limestone, dolostone, chalks, calcite, marble, etc.... all those carbonates are likely the product of our liquid water oceans drawing out the vast bulk of the C02 in our atmosphere, leaving relict gasses in its place. Same starting point but we ended up with vastly lower pressure and vastly different final composition.
The water, while scarce as part of the whole atmosphere, is concentrated within the sulphuric acid clouds (25% by volume). So if you can float a balloon with a pump at that altitude, you should be able to get water fast enough. Human or robotic explorers should be very safe in the cloud deck, with low ambient pressure and temperature. You may even be able to dissociate the hydrogen from the acid itself.
That math and engineering is wildly beyond me! But one suckypoo downer once you do sequester all that CO2? No planetary magnetic field.
In short, scientists think there has to be a convecting, rotating, liquid metal core in order to create a substantial magnetosphere. Venus's planetary core is almost certainly missing one, two, or three of those things.
The fact that Venus is extremely hot on the surface (460ºC) is at least partially assisting with creating a "stagnant lid" tectonic regime where no heat-venting plate action is seen. So if the surface of the planet is nearly as hot as the mantle and the mantle is nearly as hot as the core, convection doesn't happen. Wiki "geothermal gradient" for more.
Thus no magnetosphere, thus no electromagnetic deflection of the sun's blast. Not a dealkiller, but certainly not preferable if you'd like to move in someday.
The one problem will be that once you're established in the clouds, access to resources down below will still be difficult. You'd be living in a desert. Whereas if you're set up on Mars, all its surface resources become available.
Like others have said, its not unexpected that some water remains, however its also possible (especially due to its location) that the object that caused this impact was made of ice.
I'm not sure if Mars suffers impacts from it, but impacts from sources such as the Oort Cloud (http://en.wikipedia.org/wiki/Oort_cloud) often contain ice and other materials. There are other examples if you search around.
The universe is a big and crazy thing, the possibilities of what can and have happened are almost endless.
An article from 2007 on the debate : http://www.newscientist.com/article/dn12026-mars-rover-finds... there are still some that believe at 'just the right time and place' you could get liquid water on the surface, but everyone seems to think it would be short lived.
Oh ya, there's still a bit of ice water on the surface. Also a large quantity at both poles (primarily on the South pole, whereas frozen CO2 tends to collect more on the North pole). There's even evidence of temporary crater puddles on nice days.
But it's a very small amount of the suspected former total (perhaps 10% to 1% or much less). Assuming that the Martian canyons and valleys that appear to be carved out by water were actually carved out by water, they were absolutely torrential floods - of a scale unlike ever seen on Earth. Now? Ice glaze. Polar snow flurries. Underground ices. Hypersaline water tables, perhaps. Dusty crusty dune ice at the poles.
It's not so much that the Martian hydrosphere isn't present, it's that it doesn't resemble ours much at all. And figuring out how life might fit into the present day is tricky: Mars is essentially a much drier and colder Antarctica.
Not to burst anyone's bubble, but this is not the staggering news it's being made out to be. It is good foundational geology, yes, but water has essentially been confirmed for years now.
The story of Mars in short: flop planet, can't hydrosphere.
There is extremely strong evidence that in the very early years Mars was capable of holding on to a great deal of water: Enough to cover the Southern Hemisphere. The streambed seen here is from that time.
That downer is that this was over 3 billion years ago. Through a variety of processes and for a number of reasons most of Mars' water was lost to space or trapped underground.
The billion-dollar question that would be epic to answer: Did Mars develop Or acquire life during the time it had liquid water on the surface and if so is there any trace of it left, alive or dead?
"... but water has essentially been confirmed for years now. ..."
From the article, "... This is the first time we're actually seeing water-transported gravel on Mars. This is a transition from speculation about the size of streambed material to direct observation of it ..."
Yes, it is good foundational geology being reported upon.
What's cool about that is that it allows you to directly calculate how much water flow was involved in moving this gravel (taking in to account the much lower Martian gravity), you can use the pattern in which the gravel deposited itself to determine what direction the flow was going, and more.
You do realize that the reason this find is significant is because it gives us more information to answer that last question, right? Especially as we drive our rover over there and study the ever loving crap out of these materials.
Yes, and I do realize I sound like a buzzkill - I was just trying to curb enthusiasm. "Streambed confirmed" conjures ideas of desert playas or dry gullies that are just waiting for rain, when the reality is that we're investigating a planet that hasn't seen liquid precipitation in perhaps billions of years. Condensing out all of the water currently in the Martian atmosphere would produce a layer a few microns thick. It's dry.
For starters, the remaining atmosphere on Mars is extraordinarily thin. Go to the top of Mt. Everest. Then go four times higher than that. That's the atmospheric pressure at "sea" level on Mars.
It's apparently relatively easy to determine atmospheric composition from afar, and of the atmosphere remaining on Mars, 210 parts per million is water. I have not done the math myself, but I'm assured the total "depth" of water left is measured in microns.
It's really dry. It's really cold. And we'd pop like a balloon stepping outside.
As for how much water is frozen below? SHRUGGGGGG Anyone could make a career answering that. The biggest confounding factor is that the planet is substantially covered in dust, many meters thick in places. It makes remotely sensing what's underneath a real pain in the ass.
The most solid answer so far appears to be "there is a nontrivial amount of ice below the ground". Think "enough to fill the great lakes".
One minor point- the temperature on Mars makes gigantic wide swings. It can get to be pretty warm there. I believe the record high is 81 degrees F, which is what it is this afternoon in Los Angeles. Of course, it also gets down to -200 F, so the swings can be huge.
Temps above freezing have been reported by Curiosity, which is interesting in itself.
"... NASA's Curiosity rover mission has found evidence a stream once ran vigorously across the area on Mars where the rover is driving. There is earlier evidence for the presence of water on Mars, but this evidence -- images of rocks containing ancient streambed gravels -- is the first of its kind ..."
Why isn't this front page, the implications are staggering.
Part of the reason may be that NASA has been crying wolf before. The 'arsenic life' announcement wasn't that long in the past. So people may be a bit wary until the images have been independently analysed.
"... So people may be a bit wary until the images have been independently analysed...."
Good point. The theory of a flowing river should support all types of evidence at large & small scale: alluvial fans,
"... The imagery shows an alluvial fan of material washed down from the rim, streaked by many apparent channels, sitting uphill of the new finds. ..."
to pebbles and rate of flow of liquids,
"... From the size of gravels it carried, we can interpret the water was moving about 3 feet per second, with a depth somewhere between ankle and hip deep... This is the first time we're actually seeing water-transported gravel on Mars. This is a transition from speculation about the size of streambed material to direct observation of it. ..."
All directly observable evidence, each piece confirming the conclusion.
I guess I'm missing the staggering implications. It's cool, and these particular rocks are fascinating, but what are the implications that are surprising?
Water has always been supposed to have played a role in the state of Gale Crater, and it must have been moving water at some point...
The staggering implication, as someone mentioned in another reply, is that it brings us one step closer to answering whether the existence of water led to existence of lifeforms, alive or dead.
Yup. And in order for there to be flowing water on Mars, conditions had to be much much warmer on the red planet in the past. Warm enough to support Earth-like life.
If life came to Earth aboard a comet (as opposed to developing here), it most likely arrived on Mars as well. In that case, the early solar system was probably teeming with life (seeds), and in that case, it could be very common elsewhere.
Quite so. It means that flowing water existed in this one spot for long enough to lay down conglomerate rocks. That's a pretty damn long time. And that just strengthens the possibility of their being conditions suitable for life that much more.
Also, if there was ever a significant amount of organic matter in that stream, we may be able to find out about it through the SAM instrument. It turns out someone was planning ahead and shipped a gas chromatagraph with a mass spectrometer and laser spectrometer attached. You know, just in case we wanted to pick up some dirt and figure out what the heck sort of complex chemicals are in it. Which we do!
"From the size of gravels it carried, we can interpret the water was moving about 3 feet per second, with a depth somewhere between ankle and hip deep," said Curiosity science co-investigator William Dietrich of the University of California, Berkeley.
Out of interest, how do we know it was water, and not some other liquid?
A good piece of evidence is that the dust of Mars is significantly composed of 'goethite', essentially hydrated iron rust. There's an awful lot of dust, and if you do the work backwards you can get a decent idea of how much water it took to make it happen.
Furthermore, most liquids found at reasonable temperatures aren't all that voluminous, and a number of the minerals scanned and inspected on Mars show evidence of water contact.
Basically, there's not much else it could be. :) That said there's some really cool theorizing on underground carbon dioxide flows that might explain some washouts seen later in Mars's life.
Almost! The blueberries are hematite, Fe2O3, an iron oxide. Goethite is FeO(OH), an iron oxyhydroxide. Both strongly indicate water went in to making them but the blueberries imply they were submerged in water whereas goethite doesn't necessary require anything but water vapor.
How does the lower gravity affect that? Does the lower gravity mean the rocks are easier to carry, or does the lower gravity mean the water flows slower?
The real question is where did the water go and does it still exist somewhere on Mars? Finding a little bit of ice or water is one thing, finding an old streambed is another — but potentially finding an underwater ocean/ecosystem filled to the brim with undiscovered organisms makes me excited not only from a study of different organisms perspective but perhaps because the key to curing diseases that plague Earth might be found on Mars not to mention unlocking other discoveries like how to live longer and even more exciting finding organisms that don't age and have been alive since Mars was created.
My mind is teeming with excitement of the possibilities, is anyone else as excited as me?
If traces of life are found, however distant in the past, it seems quite likely that any Mars colony or even exploration would be delayed by decades, if not longer. Preservationists would be against any interaction whatsoever.
As someone who would take such a preservationist position, I think this is my best argument: It is morally inconsistent to think that super-intelligent life should leave us intact if we were found, and at the same time be willing to interfere with vastly less advanced life, for our own gain.
I totally get you; I'm really torn on it. But part of me hopes that there are signs life existed there, and that gets more people on board with wanting to get there to investigate more. Maybe it even raises interest enough to get people there quickly. I have a hope that once that starts, going there will be become more regular. But then I remember the moon...
Actually if we're going to colonize Mars a large source (like Great Lakes quantity) of accessible water would solve a number of problems. So yes, that would be quite exciting.
It would also be fun to discover that in its first billion years of existence as a wet planet Mars supported life in one form or another, simply to give us a data point in the probability function.
One of my favorite thought-experiments is to imagine what it would be like to have lived in a solar system that developed intelligent life on two independent planets in the same system.
Imagine what that would do to culture, mythology, technological development...
Without a strong magnetic field, solar winds would blow away the atmosphere -- water vapor included.
Earth has a hot, churning, iron core and therefore still has a strong magnetic field to protect our atmosphere from the solar wind. Mars cooled long ago and its magnetic field weakened.
No they didn't find a "streambed". They found a bunch of clasts, with pebbles that wind couldn't move. Perhaps they were moved by something solid rather than liquid. Perhaps that was some kind of ice.
It's tiresome hearing of the "piling evidence" for water on Mars. Find some damn water. Prove it by melting it then boiling it on camera in a container with a thermometer.
Mars was formed around the time Earth was, but it was blessed with only 11% of Earth's mass and less than 40% of Earth's gravity field. Shortly after cooling solid, its "Noachian Era" was similar to proto-earth: warm, a thick atmosphere, plenty of liquid water on the surface, and probably a significant magnetic field.
But this era was still during the era of the Late Heavy Bombardment, a time in which the last dregs of the solar system were still settling out. Large asteroids still pounded the planets with regularity.
Unlike Earth, Mars had trouble maintaining its liquid iron magnetic field. Since it's much smaller, it cooled and thus congealed faster. And there's growing evidence that asteroid impacts were able to drive enough heat beneath the surface that interior convection was quelled, leading to a fragmented magnetic field.
Without an adequate magnetic field to deflect solar wind, the atmosphere was prone to shedding off pieces of itself into space. This was amplified by the lower gravity which meant holding on to lightweight gasses was even harder.
Over time, Mars cooled to the point where the major forms of tectonics ceased. The water locked up beneath the ground, rusted out pulverized basalt dust from the asteroid impacts, and frizzled in the radiation-baked atmosphere, floating off.
The seas and lakes dried, the rain stopped, and that... was that.
Three billion years later, we arrive on the scene and find out we have a little sibling. Then we send robots. We hope to find life, or evidence that it once lived. Characterizing how water worked in the Martian past is a part of answering that question.