|WikiProject Solar System / Mars||(Rated B-class, Mid-importance)|
|WikiProject Geology / Meteorites||(Rated B-class, Mid-importance)|
- 1 Untitled Comment
- 2 Untitled Comment 2
- 3 ALH84001
- 4 Determination that Meteorite is from Mars
- 5 Page needs renaming
- 6 Number of specimens
- 7 Comment on the History Section
- 8 New section on cosmic radiation exposure ages
- 9 how a martian meteorite can have escaped the martian gravity field?
- 10 Black Beauty, the oldest known Martian meteorite is older than 2.1 billion years
- 11 A new standard for the minimum size of a life-form?
An article that discuss a recent research that asserts Mars has always been a cold desert. 
Untitled Comment 2
Is there any source for this paragraph?
"It should be pointed out, however, that the isotope ratios do not actually match Mars ratios especially well, to the extent that Mars ratios are known..."
"Although common wisdom is that the SNC meteorites are from Mars, the Mars origin theory does have some problems. The isotope ratios are not an especially good match. A widely published graph showing a near-perfect match is alleged to be constructed from examples selected to "prove" the hypothesis and to be a poor representation of the real data. For example, the Ar40/Ar36 ratio for one meteorite (1650) is almost exactly half-way between Earth (300) and Mars (3000). Carbon dioxide, the predominant gas in the current Mars atmosphere, is unaccountably rare in the trapped gases in the SNC meteorites. The SNC meteorites do not show shock artifacts that would be expected in small objects ejected with enough velocity to escape Mars. The majority of SNC meteorites are quite young by geologic standards and seem to imply that volcanic activity was present on Mars only a few hundred million years ago. Cosmic ray traces in the meteorites indicate relatively short stays (3 to 3.5 million years) in space. It is asserted that there are no large young craters on Mars that are candidates as sources for the SNC meteorites."
Searches of the web found nothing close, except a couple of references to recent volcanic activity. The paragraph also includes weasel terms "is alleged to be" and "it is asserted that" with no sources as to who is alleging or asserting. Ken Arromdee 20:20, 13 September 2005 (UTC)
- In the absence of references, I've deleted this material. Ken Arromdee 21:53, 25 January 2006 (UTC)
In the article ALH84001 is described as a shergottite, but I don't know of anyone in the planetary science community who would classify it that way. McSween and Treiman  says, "this meteorite does not fit into any of the previously established SNC categories." It should probably be its own category.--Will.i.am 21:52, 19 September 2006 (UTC)
Determination that Meteorite is from Mars
It is not clear to me how this is determined. Could they possibly be from another planet, moon, or other body? Also, has any meteorite from Venus, Mercury, or the moons of Jupiter ever been found? --Eraticus 04:20, 21 April 2007 (UTC)
They're definitely from Mars - I'll add a section explaining all this. As for your question, there's tonnes of meteorites known from the Moon, and a few (Angrites) that *might* be from Mercury. Venus meteorites should be impossible, and there are no candidates anyway.
This page is a bit messy, I'll give it a proper overhaul when I get the time - just finished a master's project on the Shergottites so I've got a reasonable idea what's going on... Ezkerraldean (talk) 13:54, 6 June 2010 (UTC)
Page needs renaming
Although there are a few prominent NASA websites that call these objects Mars meteorites, e.g., http://www2.jpl.nasa.gov/snc/ and http://curator.jsc.nasa.gov/antmet/mmc/, the overwhelming usage among scientists is martian meteorites. In the NASA ADS bibliographic website, there are 26 publications listed that use the former term in the title and 636 publications that use the latter. In light of this, there is little doubt about the preferred term, so this page should be renamed. Unless there are reasonable objections that I can't think of, I will rename it. JeffG (talk) 01:21, 7 April 2010 (UTC)
Number of specimens
- The reference given for the 99 number is now showing 114. Perhaps we should update this number (and date), and expect to have to do this again in a few years. Watchwolf49z (talk) 00:37, 9 January 2013 (UTC)
- Done - Would someone please review the edit, I made a few changes to the prose that should be looked at. That dataBase gives the 61,000 number as well. This is really one of the best articles I come across in a while, especially concerning HIGHLY controversial subject material. Well done !!! Watchwolf49z (talk) 15:01, 12 January 2013 (UTC)
Comment on the History Section
This section states the following, "Then in 1983, various trapped gases were reported in impact-formed glass of the EET79001 shergottite, gases which closely resembled those in the martian atmosphere as analyzed by Viking. These trapped gases provided direct evidence for a martian origin."
The last sentence that the trapped gasses provide direct evidence is not true since it cannot be proven merely from the resemblence to the current Martian atmosphere that they (the trapped gasses) actually came from it; especially from an object with an undetermined time of origin. (The article goes on to give speculations about when shergottites were actually formed.) It seems to me that you cannot obtain facts from speculations, no matter how reasonable they might be. This is not to say the meteorites could not have come from Mars, or even that it is unlikely that they have. But, based on what is written in this article, there is still no direct evidence.
- That statement threw a red flag for me too. However, after finishing the article I found it made sense. These trapped gases are direct evidence, but not direct proof. I don't think the article is stating this as fact above what is well referenced and notable. Science should certainly be investigating alternative speculations, just that it's not our job as encyclopedia editors. Watchwolf49z (talk) 00:08, 9 January 2013 (UTC)
If one means to distinguish between evidence and proof then I would venture to say it is unnecessary to use the adjective "direct" to modify the word evidence. A fact is either evidence of something or it is not. Perhaps the term "strong evidence" is better? But I would go a bit further and say that while the trapped gasses may be samples of the Martian atmosphere at the time the meteorite was formed, it still remains to show that the atmosphere then resembles the atmosphere now. How confident are we of that? If we are confident (and we have to provide other evidence to support our confidence), then we may say the evidence is strong otherwise it is not strong. I would say that the uncertainty about the time of formation weakens the evidence provided by trapped gasses.
Here's a question, asked naively by a layman: If I brought you a cylinder containing a sample of the atmosphere over Antartica but happened to mention that in transit, it had been heated to 5000K, subjected to various intense pressures and that the possiblity existed that the lining of the cylinder might not be completely inert, would you say the sample is direct evidence (or even strong) evidence of the composition of the Antartic atmosphere? (sorry for the run-on sentence!)
- The key is the referenced paper. Does the 1983 Science article by Bogard and Johnson support the statement given in the article. We can only go by what the references provide, and not add our own speculations. Read the sources - if the sources support the article content, then all is good. If you disagree with the sources - then go argue with them elsewhere, or find other reliable sources which disagree. Vsmith (talk) 22:30, 9 January 2013 (UTC)
- Further, does the reference support the "direct evidence.." bit that follows? That could possibly be problematic, but we need to go to the reference to see. Vsmith (talk) 22:37, 9 January 2013 (UTC)
- OK - I don't have acces to the 83 Science article, but "direct evidence of a martian origin came with the discovery of trapped atmospheric gases in one meteorite." quote from Combining meteorites and missions to explore Mars, by Timothy J. McCoy, et. al., PNAS, vol. 108 no. 48 . So the article text is valid - just might need to add the PNAS source as a reference for the line. Vsmith (talk) 23:18, 9 January 2013 (UTC)
New section on cosmic radiation exposure ages
I came here looking for this information and didn't find anything, so added a table based on a 2006 book about meteorite exposure ages which has a section on Martian meteorites. It's obviously just a starting point and needs to be updated with the most recent research.
Since they all originate apparently from only a few distinct impact events, I feel that it shouldn't be too much overload to the article to have a complete table of all the exposure ages determined so far. Robert Walker (talk) 09:41, 14 July 2013 (UTC)
how a martian meteorite can have escaped the martian gravity field?
Black Beauty, the oldest known Martian meteorite is older than 2.1 billion years
News article says it is 4.4 billion years old: http://edition.cnn.com/2013/11/20/tech/innovation/mars-meteorite/ — Preceding unsigned comment added by 220.127.116.11 (talk) 12:03, 22 November 2013 (UTC)
A new standard for the minimum size of a life-form?
The evidence for life on martian meteorites has been largely discounted because "the structures are too small to be Earthly bacteria." This is flawed for two reasons:
1. It has already been established that the meteorite is not from Earth. Consequently, what is possible on Earth should not constitute what is possible on Mars. Micropaleontologist Schopf also commented that, "the structures don't look especially like lifeforms to him." This statement should be deleted, as opinions aren't worth much in science.
2. According to an article published in Nature Communications, (6, Article number: 6372) "Diverse uncultivated ultra-small bacterial cells in groundwater", Bacteria from phyla are widespread in natural systems and some have very small genomes. Metagenomic analysis of groundwater that passed through a ~0.2-μm filter reveals a wide diversity of bacteria from the WWE3, OP11 and OD1 candidate phyla. Cryogenic transmission electron microscopy demonstrates that, despite morphological variation, cells consistently have small cell size (0.009±0.002 μm3)
This recent discovery would appear to alter the perception of the minimum possible size of life on Earth. It is difficult to find documentation on the exact size of the structures found on ALH 84001. So far the best description is, "an unusual tube-like structure that is less than 1/100th the width of a human hair".
A comparative description of the "ultra-small bacteria" says, "150 of these bacteria could fit into the better-known E. coli, and 150,000 or more of them could sit on the tip of a human hair." This would appear to illustrate that the structures found on ALH 84001 are larger than these bacteria, and those structures may now fit the new criteria for possible life.