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A quick Mars timeline: 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.
by jpxxx 14y ago
A quick Mars timeline:
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.
- samspot 14y agoI 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.
- jpxxx 14y agoI'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.
- domdelimar 14y agoWhat do you mean by "pithatician"? Really, absolutely no results searching the web or trying to translate it. O_o
- aneth4 14y agoI'd guess an expert in being pithy.
- 001sky 14y agoI'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. Or, maybe Not. =D
- jpxxx 14y agoDing ding ding! A stuffed animal for the man. :]
- domdelimar 14y agoThank you @001sky for explaining and @jpxxx for confirming. :)
- 14y ago
- IgorPartola 14y agoI 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.
- derefr 14y agoEverything 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.
- 1123581321 14y agoThe 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.
- samspot 14y agoThank you for that explanation. My basic issue is that it is difficult to tell statements with great scientific certainty apart from pure conjecture.
- thaumaturgy 14y agoDisclaimers make for bland reading. There's a time and place for them. I don't think this was it.
- nikcub 14y agoI 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.
- netcan 14y agoI 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."?
- rootbear 14y agoNice 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.
- jpxxx 14y agoThe 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: Major: 96.5% Carbon Dioxide (CO2), 3.5% Nitrogen (N2) Minor (ppm): Sulfur Dioxide (SO2) - 150; Argon (Ar) - 70; Water (H2O) - 20; Carbon Monoxide (CO) - 17; Helium (He) - 12; Neon (Ne) - 7 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. Venus had no such luck. She suffocates forever. http://nssdc.gsfc.nasa.gov/planetary/factsheet/venusfact.html http://nssdc.gsfc.nasa.gov/planetary/factsheet/venusfact.htm...
- iwwr 14y agoThe 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.
- ionwake 14y agonot to piss on your parade, but can you explain this? thnx http://www.flickr.com/photos/europeanspaceagency/3694512868/ http://www.flickr.com/photos/europeanspaceagency/3694512868/
- 001sky 14y agohttp://www.flickr.com/photos/europeanspaceagency/3694621916/in/photostream/ http://www.flickr.com/photos/europeanspaceagency/3694621916/... Check the lat/long co-ordinates.
- jpxxx 14y agoOh 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.
- novaleaf 14y agoi don't see how some icy materials in the perm shadow of a crater pisses on his parade....
- verelo 14y agoLike 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 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.
- junto 14y agoThanks you. I really enjoyed reading this.
- davedx 14y agoHi, just want to say I really enjoyed reading all of your comments on this thread. Thanks for taking the time to write them.