I also fear missing something by not looking for everything.

But this is how I explain it to myself: "During heating", as the temperature is constantly rising, there is no time for a five minute full scan. Each portion of the scan would occur at a different temperature range and really complicate -- as well as miss -- things. 10 - 20 measurements is perhaps the most that can be made in a reasonable time/temperature range as the temperature is rising. When a temperature plateau is reached, then there is time for a full scan at one temperature.

So, slowly scanning through all possible masses as the temperature is rising may actually miss more information than the method described above.

Another good summary of the telecon:

http://www.spaceflightnow.com/mars/phoenix...805telecon.html

Nice to see Mars back in the spotlight in the media, e.g.
http://www.latimes.com/news/science/la-sci...0,6944593.story

Has anyone any insight if this can affect MSL landing site? I remember it was supposedly to be finalized one year before launch and - gasp - we are almost there.

Thanks for those helpful articles.
I found the one containing the quote, "That's why we had trouble getting dates in high school," hilarious. That wasn't my high school experience, though.

This MECA brouhaha has been fascinating. I continue to chuckle over the stories describing "perchlorate" as if this ionic radical is a stand-alone substance, or mineral, recently discovered on Mars.

AFAIK, we don't yet know which positive ion/s it's associated with, nor do we know its concentration in that sample. ...looking forward to more news...

Knowing the results from the Labeled release experiment aboard the Viking probes, they suggest that there's a powerful oxidant in the soil. There is speculation about the chemical nature of the oxidant. Some sources suggest that the oxidant may be Iron(VI), while others suggest it's not. By sources I mean scientific journals, peer-review.

The results of both Viking 1 and Viking 2 are similar. Viking 2 landed in the northern plains of Mars. That means (probably) that the supposed superoxidant may be widespread. The results of Phoenix suggest the presence of perchlorates.

Could this explain the results of the LR experiment? Phoenix scientists say that the perchlorates are not strong enough to destroy organics. But is there anything specific of the way the LR experiment was done?

Radical? How so?

I believe that was asked at the press conference and the answer was no, perchlorates would not have produced the results seen in the Viking experiments.

'Radical' in the chemical sense - it's a term that means couple of atoms that make up part of a bigger molecule... i.e. perchlorate is usually part of aluminium perchlorate or other perchlorates.

AP story:

http://en.wikipedia.org/wiki/Radical_%28chemistry%29

Oh and while I'm at it

http://en.wikipedia.org/wiki/Perchlorate

Yes, but my point is that the term is only ever really used in the context of species with unpaired electrons. You can generate short lived perchlorate radicals ie ClO4 (eg by radiolysis of perchlorate anion), but perchlorate in this context is (presumably) [ClO4]-, and has no unpaired electrons.

This is much of an astrobiology topic. There are a lot of energetical sources used on Earth. Even the photosynthesis differs when it comes to different species. For example we have a Calvin cycle, Arnon cycle and so on ... While the energetical source on Mars is most probably a chemical component, why not perchlorate?

Mars is not Earth and Earth is not Mars.

That's a free radical though isn't it?

Free radical and radical means the same thing: unpaired electrons.
[ClO4]- is an anion.

ClO4- is part of the reactive oxygen species family, though it's not radical. That family includes ions, peroxides and free radicals. ClO4- is an anion. Phoenix scientists say it's quite stable and it's so - the Cl is in the center while the O atoms surround it. It can however release oxygen under suitable conditions. That's why I view the molecule as a potential energy source, close to nitrate reduction.

A list of different perchlorate salts can be found here. A number of these seem to be lab synthesized and don't occur naturally. Perchlorate salts are grouped. More here.

If the composition and amount of the stuff in the soil is right, would chemical oxigen production via perchloric acid be a viable way to produce oxigen on Mars, using the sulfuric acid also occuring naturally there? And how big an if is this? Or would it be a lot easier to produce O2 from the ice or the martian atmosphere?

The reduction of the molecule may occur in that way:

Perchlorate (ClO4-) -> Chlorate (ClO3-) -> Chlorite (ClO2-) -> Chloride (Cl-)

If this is *indeed* the pathway, future missions should be dedicated to searching these products.

(the other is astrobio stuff)

Interesting questions. I saw a reference to ammonium nitrate decomposing with temperature (~300C) into Cl2, H2O, O2, NO and N2O (nitrogen monoxide and nitrous oxide). Wouldn't that be a laugh? Granted, ammonium nitrate probably isn't the form here, unless it's contamination.

There's a paper, Low-temperature thermal decomposition of large single crystals of ammonium perchlorate, with a chart showing a mass spec analysis of NO and N2O coming off ammonium perchlorate with temperature:



Nice quick spike ~250-350C--seems like that should be in the capabilities of TEGA to absolutely rule out rocket fuel contamination?

A word of warning now that perchlorates are in the news, be careful! Many an old-school chemist got maimed by them detonating (I seem to recall an undergrad lecture from Geoffrey Wilkinson saying how in the early days of his Nobel winning work on metallocenes they lost a student to ferrocenium perchlorate; make any other salt of the ferrocenium cation and it'll sit there and just look at you - not so the perchlorate). Indeed, though all our research stuff is on explosive materials (sulfur and selenium nitrides), I never introduce perchlorate as a counterion, just because you can't trust it! It's non-ccoordinating and tends to improve crystal growth (both very good points) but is perfidious and temperamental.

I doubt the result is from contamination. An important question is how much perchlorate is actually present.

If there is just a small amount, it might not mean a whole lot on a planetary scale. If there is a lot, then this discovery is very significant in terms of chemistry on Mars.

One of the biggest mysteries about Mars is "Where is the Nitrogen?" Mars should have received much more nitrogen during accretion than has so far been detected. It is presumed that most of the former atmospheric nitrogen originally present must have either been lost to space or been bond in the soil.

I noticed in the conference call that chlorine was not found at the same time as the oxygen. That suggests the anion is not Iron, Magnesium, or Calcium. Particularly, iron being ruled out would be very significant.

Let's assume that the elemental ratios during accretion were actually more similar to Earth than so far observed on Mars. That's a lot of potentially bond Nitrogen in the soil. So given that, why not ammonium perchlorate?

Granted, there are a lot of ifs in the equation at this moment; but, this development is cause to get me very excited.

How does the presence of NH4ClO4 match with the measured high pH??

NH4ClO4 is a so-called "acidic salt" and by itself in water solution it would produce a pH of say 4.5

We don't know yet what the counterion of perchlorate on Mars soil is.
Ammonium perchlorate was used as a propellant for Phoenix, that's why people discuss its identification with TEGA.

On the LV though- while PHX was inside its aeroshell and the RA was in it's bio-barrier. I'd be astonished if you could explain way this via rocket contamination.

Doug

Can I just say that although I feel like a dog listening to someone reading out "A Brief History of Time" as I scan this in-depth discussion about the chemistry here, I am VERY impressed with everyone's level of knowledge of and passion for the subject, and so pleased that speculation has turned into discussion about hard science. Great work guys.

Can I also ask a question which might strike some as naive or stoopid, but hey, no change there then... I've read a lot about how these perchlorates are found in "fireworks and rocket fuel", but it sounds like the chances of these perchlorate traces being down to contamination by Phoenix's own launch hardware are very small, but what about other probes and other rockets? Did the Viking landers' braking rockets use a fuel that contained this stuff? Or could it have come from discarded rocket stages or boosters or whatever of other probes that hit Mars, unseen? Wouldn't have to have landed here, just near enough for their gunk to be blown here by the wind... ?

As usual, just thinking aloud as I read off the back of an envelope, and I'm quite prepared to be corrected. Just don't slap me. We don't all know this stuff!

Totally agree, my reply was in response to Harder's question about the acidity of ammonium perchlorate solutions. Personally, I don't believe for a second there is is a contamination issue. In fact, I think the Phoenix team plays the contamination card (we have to make sure etc.) to buy the time needed to fully unravel the perchlorate discovery.

@Stu
Highly unlikely

No. Perchlorates are used in solid fuel, whereas the Vikings used liquid fuel descent engines, as did Phoenix. The Surveyor lunar landers, however, did use solid braking engines (along with liquid fueled vernier engines).

They would have had to have landed very close, close enough to be "in the picture". Assuming they even had significant amounts of unburned propellant left in them.

What implications would a Perchlorate of some flavor have for cross-contamination considerations on future missions? At a minimum it seems to me that it renders the fear of a Terrestrial bacterium running rampant throughout the planet far less likely.

The Register:

Terrestrial bacteria that eat perchlorate aside, the compound has been described as relatively inert.

THIS is the most salient comment I've seen to date on this issue!

One observation: It is tempting to extrapolate any soil chemistry findings to the entire planet, but is this at all wise? Terrestrial soil chemistry has enormous variation, and the more we see of Mars the more varied it seems at local scales in both topography and past history.

I submit that it might be reasonable not to draw conclusions about an entire planet from very localized sample analysis.

How do the Phoenix people know that the oxidizing compound is a perchlorate and not a hypochlorite? It seems to me, a better assumed substance would be something that matched BOTH the Viking and Phoenix results. Of course the Viking and Phoenix observed oxidizer might(?) be two different substances.

Ah, "El Reg", the closest thing to the UK newsprint media I know of online. Often amazing right, yet sometimes - oh so very wrong...



But the main rationale for Phoenix being an immobile lander which digs down, rather than a rover, was that the sub-polar region is assumed to be highly homogenised horizontally. Then again, until assumptions are tested...

Clearly we need more landers and rovers - lots more, preferably. (And yes, a telecoms orbiter! and Doug wants a pony... )

Instead we're getting Mars Science Lab and for the US that'll probably be it (sure hope the Europeans do ExoMars)...

The Wet Chemistry Lab has a special ISE (Ion Selective Electrode) for [ClO4]-

http://planetary.chem.tufts.edu/Phoenix/WetChemLab.html

Oh well, never mind... (tosses aforementioned envelope in bin) Thanks for the feedback.

Michael Hecht explained to me that the ClO4 ISE was originally called the "perchlorate sensor" but at some point they switched to calling it the "nitrate sensor" because that is what the sensor is typically used for commercially -- for testing the concentration of nitrate in things like food and agricultural soils that really should not contain any perchlorate. However he said that as sensors go it's not the most sensitive nitrate sensor, and that if any perchlorate should appear, the sensor is about 1000 times more sensitive to perchlorate than it is to nitrate.

--Emily

I was wondering that myself. Cold enough year round for it to be stable until we add water and heat. But the fact that they did not find chlorine in theTEGA sample does make this low probability. I am sure they reviewed and then rejected the possibility.

Edit. sorry just saw the above.

Thanks for the correction, folks. It may have something to do with the fact that I learned basic chemistry back in the 60s. I didn't recall unpaired electrons having anything to do with radicals. As fortune would have it, my first chemistry book is still in my library, so I referred to it, to see how "radicals" were defined back in the day.

From the glossary, in Modern Chemistry, by Dull, Metcalfe, and Williams, 1962:
radical: A group of atoms that usually behaves as if it were a single atom.

Although the "group" of atoms known as the perchlorate anion can change if it is involved in a redox reaction, the "behaves-as-a-single-atom" definition is the sense in which I used the word in that post. I am glad to finally learn the modern definition, even if it is rather lately.

Excellent write-up of "The MECA Story" over on The Planetary Society website by AJS Rayl, probably the definitive "come on, let's put it to bed" piece. Seriously, her writing puts the work many better known space journalists to shame.

It was a nice summary of a lot of things, but I think it is somewhat premature regarding some of the conclusions. I would have left Hansen out of the Mars discussion. The "big alien snowball headed right toward Washington" comment seemed totally inappropriate to me. Am I missing something?

You know, I wondered what had caused all that noise and laughing from the team's end of the phone during the telecon.
Now we know it was Stu's 'chocolate strawberries on Mars' image that got them going.
Well done Stu! BTW, isn't it nice to know that they were reading UMSF at the same time as doing the press conference.

Astro0

Tom Pike's take on the whole thing:
http://news.bbc.co.uk/1/hi/sci/tech/7408033.stm

Basically they were sitting on the perchlorate story. They found the chemical over a month ago and it was confirmed by the second MECA test, but they had zero press conferences between June 26 and July 31 while this was happening. The story on June 26 was that the soil was like you'd find in your back yard ("minus organics"). The real story was that it was only if your back yard was in a Chilean desert. For the July 31 press conference, MECA news/personnel were absent even though they are now reportedly almost certain that the signal is real. Craig Covault picked up on that absence, has been privy to some inside information, and because of him the story has been pried loose.

The idea that the signal is from contamination has been described time and again as an exceedingly remote possibility. So what was holding this announcement back, any more than, say, "the pH of the soil is 8.0" and "we found trace quantities of water" or any number of other preliminary results they have shared?

pH and water are easy public consumption issues, and were high-confidence-results from the get-go. It's water, it's battery acid, it's bleach - they can 'get' that nice an easy.

Perchlorates, whilst interesting and fascinating in their own way, don't mean a damn thing to joe-public - notice the press - half of them saying it's devastating for life ( when it isn't ) and so on. Furthermore, it wasn't at the same high confidence of the pH and water results.

"The press" and "the web," etc. are convenient scapegoats, but I noted an AP article previously, quoting a leading astrobiologist:



It's a toxin closely monitored by the EPA and would be particularly known in the space industry as such, because it creates big environmental protection headaches when it finds it way into groundwater--thus, perhaps, some initial (at least) non-delight and unflabbered gasts with the detection.

Looking back to June 26 press conference, we have this BBC report the next day:



Suddenly getting all condescending about the scientific process, peer review, and years of graduate study rings a bit hollow.

More from the June 27 BBC article:



Given that they had the perchlorate signal at that point, that statement is very questionable. Then came the second confirming test, no announcement, no MECA presence even on July 31. Granted that percholate may be rehabilitated into the central anion of Martian biochemistry, but wouldn't it have been better to acknowledge its presence from the start, and then work on how it fits into a highly-modified life narrative?

I think you're trying to make more out of this than there is, assuming they knew more than they did at any one time.

There is possibly another factor that now makes the WCL analysis of the soil more complicated. In experiments performed with the ISE sensors originally part of the WCL of the cancelled Mars Surveyor Program ’01, it was mentioned that perchlorate messes around with other ions.
I quote from Kounaves et al, J. Geophys. Res. 108 (2003), 5077 :



However, it could be that these perchlorate problems have been dealt with, and updated ISEs were used for Phoenix. There is an article in press in J. Geophys. Res. that describes the current Phoenix WCL suite, and might include that information :

"The 2007 Phoenix Mars Scout Lander MECA Wet Chemistry Laboratory" S. P. Kounaves,et al., J. Geophys. Res., 2008, (In Press)

Unfortunately, I have no access to that, so I don't know if perchlorate interference remains an issue.

Anyone can comment or help ?

...yes it does, and your images put it over the top! Well done, indeed! (Was gonna say something about "bloody Earthlings" here, but I desist...)

I would say that the lack of confirmation from TEGA would be a big worry to thinking you have the facts right. The "story" is still not clear. Nobody is sitting, they are still working feverishly to figure out what the story is.

You're acting as if someone is hiding the fact that percholates were found in your back yard and their silence is putting you at risk. CHILL OUT!


If you'll recall, the team's first reaction to that signal was 'there must be a fault with the sensors...'
It's a long road from that to 'OK, it's real and this is what it's telling us.' I again mention that the discrepancy between TEGA and MECA results is still unreconciled.

Interesting reading--color my gast flabbered.



And after the second test confirmed--time for a clarification at least on the "nothing toxic" comment?

It's true that extraordinary claims require extraordinary proof. Thus, we have a discrepancy between the "flabbergasting" pH and minerals results reported the day after the test while the "non-announcement announcement" of supposedly neither-here-nor-there percholates enjoyed a month of the cricket chorus.