The also calculated a habitability index for the various sites landers have explored on Mars. If a site has a probability of supporting life greater than 50%, it is considered reasonable to go looking for life using dedicated experiments.

To calculate the Habitability Index, they create something similar to the Drake Equation. Here, the habitability index is the product of the probability that liquid water has been present, the probability of a biologically abailable energy source, the probability that chemical building blocks available, and the probability that the environment is benign and nontoxic.

The problem is there is no way to assign an absolute value for any factor. The best that can be done is to make an educated guess from multiple approaches and to compare sites that do not have similar measurement types. This gets really complicated when direct measurements of each of the probabilities isn’t actually made and theory must be invoked (for instance, Phoenix didn’t get all the needed data). Additionally, data that does exist often has more than one interpretation.

All that said, let’s consider the situation at the Mars Phoenix site:

Liquid Water – Evidence: segregated ice, macroscopic evidence for melting at some time. Additionally the volume fraction of ice in soil exceeds what the pore space would allow via vapor deposition, and minerals that can only form in liquid water are present (eg carbonates at 5% level).

Energy: Solar and chemical energies are both good, but there is a need for shielding from UV for life to use solar energy (It’s a bit destructive to organics). Shielding in the form of transparent glassy grains that block UV and admit other wavelengths were found, and this offers a chance for tiny hiding life. Also, on Earth perchlorate is metabolized by many chemoautotrophs and could be chemical source for life on Mars as well.

Chemistry: The presence of Carbon, Oxygen, Nitrogen, Hydrogen, Phosphorus, and Sulfer are all thought to be needed. At this stage C and O are known to exist, but we’re not sure Nitrogen is there – can’t get a reading on nitrate with lots of percholorate around. Phosphorus also was not seen with Phoenix’s wet chemistry lab, but it couldn’t have been seen with the WCL setup. Sulfer is possible; the data is still work being worked on and early results are ambiguous. While not everything we’d like to see were there, many biologically interesting Ions were located (Na+, K+ Ca+ Mg2+ Cl- C004-).

Benign and NonToxic: They found the pH levels are non stressful, and the environment contained no poisens. All is good.

Put together, they feel that at the pole, there is the highest value for the habitability index- searching for life justified.

NOTE – this value is for now and it is hapitable *today.*

Kind of cool. Yes?

Phoenix Lander on Polygon Structure as seen by HiRISE

(disclosure: I left my cellular internet dongle in my room, so I’m twittering sessions live and posting blog entries on a semi random basis when I can go out and find internet)

I’m leaning against the back wall of a packed ballroom filled with the brim with silent and attentive geophysicists who are absorbing all they can about the Mars Phoenix Lander.

This fairly large (5,5m or 18 ft long) and heavy (350kg or 770lb) spacecraft parachuted to the surface of Mars on May 25, 2008 and poked, prodded and dug into the surface until it froze to death on November 10. While this seems like a short period, the original plan was to wind up operations in August, so the craft had been living on borrowed time. While it is unexpected that the craft will be able to turn back off when it thaws in the next Martian Spring, the lander is programmed to phone home should it survive.

If you want to go back and see what the mission knew in the moment, it’s all recorded on twitter. Check out: http://twitter.com/MarsPhoenix

Today is all about what we can now say with certainty.

The session started with a broad overview of the results everyone was waiting to hear: Is there evidence of past liquid water and is their the possibility Mars can (at other temperatures) support life. The answer is a qualified yes.

For Water:

• The soil Phoenix dug up was clotted/cemented (this is geology speak for what happens when you mix dirt and water, stir, and then let it “dry” out.)
• There is Calcium Carbonate at 3-4% level in some of the samples. This is a mineral that only forms in wet environments
• In addition to Calcium Carbonate, there are other aqueous minerals
• And, to give the most obvious case, there is water ice 5cm below the surface, and this ice is segmented in the same way as a stream that has frozen and thawed and refrozen

For Habitability:

• There are the materials needed to process energy and to get nutrients from the environment
• The 1-2% perchlorate is not a life killer
• The 7.7 pH is friendly

It just happens to be a bit too cold at the moment…

Additional work looking at the variation of ice with depth found that it matches models, and that based on the fact that the rocks aren’t frozen into the ice, but rather are capable of getting flung out of place by casual assualt by alien space laboratories, the ice is old. (Over time the ice contracts, loosening around the rocks).

There was also work that showed that the fascinating polygon structures surrounding the lander are likely caused by seasonal cracking that occurs when the ice contracts and sand and small rocks fall in between the gaps in the ice. The “flat” part of each polygon typically measured 4-5 meters in diameter and have multiple lumps and peaks indicating there is multiple events building these structures. Unlike on Earth, where these can be caused by frost heaves, these patterns are caused by sand wedges.

Sadly, I know need to go play scientist and be part of a telecon. More to come on the other side…

Let me state for the record that watching ice on Mars sublimate from up close is just cool. Being able to say, ice behaves on Mars the way we thought it would, is important.

Having said that, I also have to say that I really wish folks would quite saying that Phoenix discovered ice on Mars. Folks, if you’ve got a 10 inch or larger telescope, take it outside next time Mars is in the sky. If you see a big white blob toward the end of one of the poles, you have observed ice on Mars.

For the past several decades – since before I was born – we have known that Mars’ poles have ice caps that grow and shrink with the seasons in a manner consistent with a mixture of water ice and dry ice. As early as 1976, scientists were reporting on measurements of atmospheric water vapor on Mars using Viking data (see here). With the more recent rounds of rovers, we’ve seen clear evidence of sub-surface ice from neutrons the ice fails to jettison when hit with cosmic rays (see here), and the mars rovers have found all sorts of minerals that could only have formed in water. Thus, we have evidence of past liquid water, current water vapor, and current water ice.

This means, we knew that there was water ice on Mars. Really. We had all the evidence we needed.

What is so valuable about this latest discovery is it takes that knowledge to the next step. Science is a building process and we grow our understanding one data point at a time. From Earth we knew Mars had polar caps, but we also thought it had seas. Once we started getting there with space probes, we learned it is a desert world whose only moisture is frozen, or perhaps under high pressure beneath the surface (where maybe it occasionally spurts out of gully walls). We could identify what acted in every way like ice when viewed from space, so we sent probes first to bright sunny areas near the equator to dig around for minerals that required water to form (fairly low risk as far as going to Mars with a rover was concerned). Having found those minerals, we then sent a lander to go sit on the ice (higher risk since sunlight is at a premium and the seasons are more extreme.) Now, we have seen the ice really seriously up close. We still haven’t been able to do a chemical analysis of the water however. We’ve still only looked at it.

The next big break through will come in technologically tasting the ice to see what flavors – what minerals, isotope combos, and inclusions of gas – permeate the ice (never taste the yellow snow). We’re going to get there in the coming days and it is the result of that test that I’m waiting for.

We are building knowledge. This is good. We aren’t discovering Mars has ice. That’s old news. Instead, we’re discovering the characteristics of that ice, which is its own kind of cool.