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Planetary News: Phoenix (2008)Phoenix Detects Falling Snow, Digs Up Evidence for Past Water, and Snares Mission ExtensionBy A.J.S. Rayl
Scientists working on the Phoenix mission’s meteorological team have -- for the first time in Mars exploration history -- detected snow falling from clouds passing over the north polar region of the Red Planet, even as their colleagues studying the top soil and ice layer, on which the spacecraft fortuitously landed May 25, are beginning to rewrite the books on Martian geochemistry. Using a laser instrument known as LIDAR (Light Detection and Ranging) that is designed to gather data on how the atmosphere and surface interact at Mars, the mission's meteorologists recently recorded snow from clouds above the spacecraft's landing site. "Nothing like this view has ever been seen on Mars," said Jim Whiteway, of York University in Toronto, lead scientist for the Canadian-supplied Meteorological Station on Phoenix, as he presented the graph showing the data during a press conference held at NASA headquarters yesterday. LIDAR is a remote sensing system used by NASA, as well as the National Oceanic and Atmospheric Administration (NOAA), generally to collect topographic data, however, it can also be used to study the structure of the atmosphere and the anatomy of clouds. At the heart of the device is a laser, which emits pulses of light 100 times per second upward into in atmosphere. The instrument then detects and records the light that is scattered back, which is the information scientists analyze. “It is able to show us the structure within the cloud,” explained Whiteway. The cloud they studied, it turns out, was composed of ice crystals that started out at a height of 4 kilometers (2.5 miles). “By the end of the measurement, the ice crystals have fallen all the way down to 2.5 kilometers (1.5 miles).” The ice crystals and snow they recorded, Whiteway suspects, probably fell closer to Earth, but the team had preprogrammed the instrument and it shut off after the prescribed time. “While we're taking measurements on Mars, we don't know what's happening. If we would have had a choice, we would have continued measuring for another hour,” he explained. Phoenix, like the Mars Exploration Rovers, relies heavily on solar power, so the team designed the mission to land in late spring, early summer to take advantage of the months during which the Sun never sets. Now, as the mission wraps up its fourth month on Mars, the Sun is dipping below the horizon on average four hours a day and the already frigid Martian temperatures are beginning to drop, according to Phoenix Project Manager Barry Goldstein, of NASA's Jet Propulsion Laboratory (JPL).
Even before they detected the falling snow, the meterological team had been seeing the signs during their observations of water condensing in the atmosphere, in frost, ground fog, and clouds. Although the data recorded by Phoenix’s LIDAR show that the snow vaporized before reaching the ground, Whiteway and the other team members are hopeful they’ll see snow hit the ground before the mission ends in a few months. The ice crystals and snow, he noted, are “very important factor in the hydrological cycle on Mars, with the exchange of water between the surface and the atmosphere. Since landing during Memorial Day weekend, Phoenix has confirmed that a hard subsurface layer at its far-northern site contains water-ice. Determining whether that ice ever thaws would help answer whether the environment there has been favorable for life, a key objective of the mission. "We are still collecting data and have lots of analysis ahead, but we are making good progress on the big questions we set out for ourselves," Phoenix Principal Investigator Peter Smith, of the University of Arizona (UA), told reporters in Washington DC and journalists from around the country who gathered via teleconference Phoenix, the first soft lander since Viking more than 30 years ago, is the first mission to land in the Martian arctic and also the first to actually touch Martian water. In fact, it was sent to uncover the ice-rich environment that data from an instrument onboard NASA’s orbiting Mars Odyssey indicated some 7 years ago was there. And as fate would have it, Phoenix actually landed right on the paydirt … err, payice.
That Odyssey team was led by William Boynton, also of the UA, who is the principal investigator for the Thermal and Evolved Gas Analyzer (TEGA) instrument, which bakes and analyzes the compositions of soil and water-ice samples for Phoenix mission. TEGA features 8 small ovens that heat up the soil samples delivered to it by Phoenix’s robotic arm. Once the samples are heated, the evolved gas analyzer “sniffs” the gases given off as the sample is heated. “Knowing the nature of gases given off is useful for identifying what's in the oven,” Boynton explained. “It’s very much as if you walk into a kitchen where chocolate chip cookies are baking and you can immediately tell from your nose what's in the oven.” In recent days, Boynton and his TEGA team – along with Michael Hecht, of JPL, who leads the Microscopy, Electrochemistry and Conductivity Analyzer (MECA) team of scientists -- have found evidence of past interaction between minerals and liquid water, processes that occur on Earth. “We have been enjoying a feast of data during the last four months,” said Hecht. “We've identified several minerals that are indicators for interaction with water in the past,” Boynton said. “Some of these minerals have been found by remote sensing by orbiters, but only in areas on the planet where there has been evidence for flowing water in the past. What's new here is that we have seen evidence in the northern plains -- kind of in the wide-open spaces -- where there really is no evidence for flowing water and that's one of the things we're really excited about.” The minerals found include calcium carbonate, the main composition of chalk as well as those antacids you pop when your stomach goes wonky, and particles that are likely clay. Most carbonates and clays on Earth form only in the presence of liquid water. A high temperature release of water vapor from one of the samples is, Boynton said, “most likely” due to a clay mineral “in the class of minerals called sheet silicates.” While the best known example of a sheet silicate on Earth is mica, in this case on Mars, he said, we're not looking at mica but a different type in which a form of water is actually in the crystal structure between the different sheets.” It’s the water between the sheets that makes the clay minerals “much softer” than mica. The team’s identification of a clay mineral is somewhat ambiguous, he cautioned. “There are a few other minerals that could release water vapor at high temperatures, but we think the sheet silicates or clays are probably most likely.” The calcium carbonate – which distinctly indicates episodes of interaction with water in the past – came from soil samples dug up from the Snow White White trench by the robotic arm and was confirmed both by TEGA and the tiny wet chemistry labs of the MECA.
“This mineral was identified by TEGA on the basis of a high temperature release of carbon dioxide (CO2) gas,” Boynton said. “In this case, our identification is unambiguous. The release of CO2 gas could only come from a carbonate and the fact that it was released from this high temperature means it's a calcium carbonate, as opposed to some other forms, such as iron or magnesium carbonates.” Carbonates are very common minerals on Earth and commonly form by the interaction of liquid water with CO2 gas. “And that's just what we think is going on, on the surface of Mars,” said Boynton. The MECA evidence came from a buffering effect characteristic of calcium carbonate assessed in wet chemistry analysis of the soil. “One of first findings we announced at the beginning of the mission was the pH of the soil and it turns out to be a little lower than we initially thought – pH 8.3,” said Hecht. “That turns out to be almost exactly the pH of ocean water on Earth. Ocean water is at that pH, because it is held there by a lot of undissolved calcium carbonate by the buffering process. One of the ways you know you have a buffered solution is when you add acid – which we do in the MECA experiment -- the pH doesn't change very much. So we saw exactly that response suggestive of carbonate and the way we know its calcium carbonate is that there should be a certain amount a certain concentration in the solution and we see exactly that concentration,” he explained. Thus, using two different methods – the thermal method from TEGA and a solution chemistry method from MECA – the Phoenix team has confirmed presence of calcium carbonate. “If you combine that with our previous discovery of perchlorate salt in the soil, we really now have enough information -- between carbonates and perchlorates -- to begin rewriting the book on Martian geochemistry,” said Hecht. Bolstering the TEGA evidence for clay minerals, the microscopy instrument on MECA, has turned up hints of a clay-like substance. "We are seeing smooth-surfaced, platy particles with the atomic force microscope, not inconsistent with the appearance of clay particles," Hecht said.
The MECA team has been using the power of the atomic force microscope and the optical microscope – both of which are part of the instrument Hecht designed and which was for the mission by JPL – “to see the different animals in the zoo of Martian mineralogy,” as Hecht put it. “When you look at sand on beach, you see whitish stuff and it's not until you look up close, under a magnify ing glass or under a microscope, that you really see all the mineral grains and sizes and shapes and colors that make them so interesting and tell you about the mineralogy of Earth. The same is true of Mars,” Hecht said. “We have finally gotten to the bottom of pile and we see what all these tiny particles look like, what they're made of, and what kind of shapes and crystalline forms they have.” In coming weeks, the MECA team will be creating a catalogue of the different types of particles, crystal and salts, “and hopefully silicates,” he informed. Amidst their work with the MECA’s various instruments, Hecht and crew have turned up a real Martian mystery with the thermal and electrical conductivity probe (TECP), a fork-like device located at the end of the lander’s robotic arm. While this instrument has sensed humidity rising and falling beside Phoenix, when it has been stuck into the ground, its measurements indicate that the soil is thoroughly – and perplexingly – dry. “We have been busy sticking the TECP needles into soils looking for signs of ice, almost liquid water, and water vapor, but we didn't find very much ... no dampness, no traces of not quite frozen water, not even the humidity in the air above the soil that you might expect to rise from the ice,” confirmed Hecht. “In other words, what we learned from the TECP is that the soil in our little corner of Mars is very, very dry.” The Phoenix mission, which was originally planned for three months on Mars, is now entering its fifth month and facing a decline in solar energy that is expected to curtail and then end the lander's activities before the end of the year.
Before power ceases, the Phoenix team will attempt to activate a microphone on the lander to possibly capture sounds on Mars. “This instrument was turned off for 4 months, so we’re not sure if it’s going to work, but we’re going to change software and turn it on and try to listen to Mars,” Smith announced. At this juncture, no matter when it ends, Phoenix has successfully “risen from the ashes” of the lost Mars Polar Lander and lived up to its mythical name. “The vehicle has been operating tremendously well all this time,” said Goldstein. “We originally designed this mission to last 90 sols and clearly we're doing much better than that. We have actually commanded this vehicle 120 of the 123 sols that we have been on the surface and the health of the vehicle is exceptional. Every day it's waking up as per command and communicating with Odyssey as well as MRO and doing its job well.” The Mars Exploration Rovers – Spirit and Opportunity – were also supposed to last for just 90 days, but four and a half years later, they're still going. That's something that has caused a lot of people to wonder if Phoenix could live longer and prosper too. It's a question that Goldstein said he's been asked "frequently." Alas, the answer, though, is no. “Fundamental to our termination of this mission is where we've landed," Goldstein said. "We're way up above the Arctic Circle on Mars. Much like on Earth, when you’re above the Arctic Circle, sometimes the Sun is up all the time and other times during the year the Sun is down all of the time. When we landed on May 25 we landed in the late spring, early summer to try and maximize the amount of time we would have the Sun above of the horizon.” Once the Sun goes and stays below the horizon for winter, it's lights out for the Phoenix lander. The Sun dipped completely below the horizon for the first time since the spacecraft touched down just after Phoenix completed its primary mission, on Sol 93, and the amount of time it's below the horizon will only increase from here on, Goldstein informed. "Now it is gone [below the horizon] for more than four hours each night, and the output from our solar panels is dropping each week," he said. "Before the end of October, there won't be enough energy to keep using the robotic arm."
Beyond producing less energy in coming weeks, Phoenix will also have to draw more power to use heaters in order to keep the electronics from freezing. “Both these things conspire against us,” Goldstein explained. “When we landed in late May, we were generating 3,500 watt-hours per sol. Last Friday, on Sol 120, Phoenix produced 2,100 watt-hours and it's slowly going down to point where we will become a weather station [taking] occasional pictures. It is possible -- though not really probable -- that they could wake Phoenix up and restart it after the winter passes “The vehicle will probably not survive the harsh winter and there probably will not be enough power on the vehicle [for it] to come back to life, so we’re not really hopeful we can [resurrect it]," Goldstein said. "But we’ll sure give it a try." In the meantime, Phoenix has miles to go before it sleeps and team members are working “to try and squeeze every bit of science out of this mission,” said Goldstein. “We're now literally trying to make hay as the Sun shines, to get most out of the science instruments before the end of the mission.” All in all, the Phoenix team has packed an awful lot into the last four months. “During the first couple months of the mission, we were able to determine that the robotic arm could scrape through the surface soil only a few inches deep and reveal an ice layer,” said Smith, by way of summary. Through the climate research they've also found that the ice at the surface is in close contact with the atmosphere and, as Jim Whiteway pointed out, there is definitively a very close connection between ice under the surface, and water vapor and ice crystals in the atmosphere,” Smith added.
In addition, Phoenix has imaged and studied the bumpy, polygon sculpted terrain, which is different than the vast “parking lot” plains of Meridiani Planum, where the Opportunity rover is exploring or the rocky landscape that the Spirit rover has been negotiating for the last 4 years and 9 nine months. “We have dug in the centers of polygons which are typically 1-2 meters (3 to 6 feet) across, and are formed by the expansion and contraction of ice -- at least that's how it would be in the polar regions of Earth -- and find the ice layer is about 2 inches below the surface,” Smith continued. “And we have dug in the troughs and find that it is 3-5 times deeper in the troughs. If you were to sweep away this thin soil layer, you would find that it's really more like a skating rink. It's a very ice-rich environment.” Interestingly, the area this team has been studying is a much younger terrain than the landscape that either Spirit or Opportunity have been roving around near the Martian equator. The spacecraft, actually, is resting on the material that was blown out of a large nearby crater just a few millions years ago, Smith noted. “This is important. It was only a few million years ago that this crater was formed, so the terrain is not the thousands of millions of years old that is being explored by the two rovers. We're looking at modern processes that are active on Mars today and a new environment, not an ancient environment.” Among the other “facts on the table” that have come from four months of research at the landing site is that the atmosphere serves as a transport mechanism for water-ice and for vapor, Smith said. “The vapor can actually permeate and diffuse through the soil and freeze out at the ice layer. We know the ice is just near the surface.” The Phoenix team has also determined that it was warmer in this polar region in the past. “One other thing we didn't learn ourselves but had been studied by scientists over last 20 years is that the spin axis of Mars is not stable like it is on Earth,” Smith said. “It’s now at 25.5 degrees, but over 2 million years of time, it clocks back and forth and at some times it almost points toward the Sun, at a 60-70 degree tilt, putting the polar regions to face the Sun. So in the past there's been a warmer climate.”
In the cold climate in this Martian arctic region now, the scientists don't expect the ice will melt into liquid water. “But in the past, when the tilt was more and the climate warmer, we could have expected this ice went through a melt phase," said Smith. "That doesn't mean it was a lake, but even just a wetting of soil could create these carbonates and these clays that are now indicators of past climate, or the nutrients we see in the forms of salt, and the perchlorate, which on Earth is a nutrient and energy source for microbes.” Which once again brings up the $64 billion question: Is the north polar region of Mars a habitable zone? “We're approaching that hypothesis,” Smith said. “We understand Mars, though, has many surprises for us. We have not finished our investigation or laboratory analyses or our data analysis, so it's too soon to be sure of this. But we are certainly finding a lot of the indicators that we proposed to find at the beginning of this mission, which to me is bringing great excitement," he added. "Our mission now is about studying the history of this ice and soil that is within reach of the robotic arm and to determine if this is the place on Mars that is habitable," Smith expounded. "We're somewhat biased when we talk about Martian life, because we only know life as it exists on Earth. So the idea we have is to see if this is an environment that Earth microbes could live in,” he clarified. Still to be found are organics and the team has yet to look at the key isotopic signatures of the water-ice found or compared it to the water vapor in the atmosphere. “The picture is still a little blurry,” as Smith put it. “We're making good progress, but more lab work and more analysis is needed and this is what we're going to be doing on our extended mission. October is a very busy month for us.” Even when Phoenix ceases to function, the science it’s collected will keep researchers and planetary scientists busy for a long time. “The significant amount of data collected by the Phoenix mission will last the science research community for a significant number of years to come. “The little lander is terminal. It's battling the weather and the temperatures. It has a finite lifespan," acknowledged Doug McCuistion, the Mars Exploration Program director at NASA headquarters. "But the science data it is producing is going to last a lot longer than its lifespan.” As a result of Phoenix’s success and its rich bounty of data, NASA has decided to extend the mission. “We’re going to try and survive as long as possible,” McCuistion announced at the press conference. “There is an end to this mission, because of weather, but we want to see how far we can get the mission into winter to understand the climatic processes that occur.” The Phoenix mission is led by Smith at the University of Arizona, the first public university to lead a mission for NASA. Project management is being handled by JPL, with development partnership by Lockheed Martin in Denver. The Canadian Space Agency, University of Neuchatel, Switzerland, the universities of Copenhagen and Aarhus, Denmark, the Max Planck Institute in Germany, and the Finnish Meteorological Institute have also contributed to the mission. For more:
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