Phoenix - Scouting for Water on the Red Planet

Phoenix Mars Lander in testing (credit: NASA)

NASA selected the University of Arizona to lead the Phoenix mission back in August 2003, hoping it would be the first in a new line of smaller, low-cost “Scout” missions in the agency’s exploration of Mars (the cost is about $75 million cheaper than the Spirit/Opportunity rovers, and less than a third the cost of the Viking landers of 1976). The selection was the result of an intense two-year competition with proposals from other institutions. The $325-million NASA award is more than six times larger than any other single research grant in University of Arizona history.

Viking I model (Credit: NASA)

Besides taking photographs and collecting other science data on the Martian surface, the two landers conducted three biology experiments designed to look for possible signs of life. These experiments uncovered unexpected and enigmatic chemical activity in the Martian soil, but provided no clear evidence for the presence of living microorganisms in the soil near the landing sites. According to scientists, Mars is self-sterilizing. They believe the combination of solar ultraviolet radiation that saturates the surface, the extreme dryness of the soil and the oxidizing nature of the soil chemistry prevent the formation of living organisms in the Martian soil.

The Viking mission was planned to continue for 90 days after landing. Each orbiter and lander operated far beyond its design lifetime. Viking Orbiter 1 functioned until July 25, 1978, while Viking Orbiter 2 continued for four years and 1,489 orbits of Mars, concluding its mission August 7, 1980. Because of the variations in available sunlight, both landers were powered by radioisotope thermoelectric generators—devices that create electricity from heat given off by the natural decay of plutonium. That power source allowed long-term science investigations that otherwise would not have been possible. The last data from Viking Lander 2 arrived at Earth on April 11, 1980. Viking Lander 1 made its final transmission to Earth November 11, 1982.

There was a 21-year gap between the Viking missions and the next mission to Mars by the U.S.: the Pathfinder mission.

Mars Pathfinder model (Credit: NASA)

Mars Pathfinder was originally designed as a technology demonstration of a way to deliver an instrumented lander and a free-ranging robotic rover to the surface of the red planet. Pathfinder not only accomplished this goal but also returned an unprecedented amount of data and outlived its primary design life.

Mars Pathfinder used an innovative method for directly entering the Martian atmosphere, assisted by a parachute to slow its descent through the thin Martian air and a system of giant airbags to cushion the impact. The landing site, an ancient flood plain in Mars’s northern hemisphere known as Ares Vallis, is among the rockiest parts of Mars. It was chosen because scientists believed it to be a relatively safe surface to land on and one which contained a wide variety of rocks deposited during a catastrophic flood.

The lander, formally named the Carl Sagan Memorial Station, following its successful touchdown, and the rover, named Sojourner after American civil-rights crusader Sojourner Truth, both outlived their design lives - the lander by nearly three times, and the rover by 12 times.

Between its landing and its final data transmission on September 27, 1997, Mars Pathfinder returned 2.3 billion bits of information, including more than 16,500 images from the lander and 550 images from the rover, as well as more than 15 chemical analyses of rocks and soil and extensive data on winds and other weather factors. Findings from the investigations carried out by scientific instruments on both the lander and the rover suggest that Mars was once warm and wet, with water existing in a liquid state and had a thicker atmosphere.

Phoenix Mission - a True Team Effort

The Phoenix Mars Mission has a collaborative approach to space exploration. As the very first of NASA’s Mars Scout class, Phoenix combines legacy and innovation in a framework of a true partnership: government, academia and industry. Scout-class missions are led by a scientist, known as a Principal Investigator (PI), whose role is to manage all the scientific data gathered by the spacecraft and lead the mission’s technical and scientific teams.

Pathfinder Airbags in a test (Credit: NASA)

The lander will land the same way the Viking landers did, slowed primarily by landing rockets, shifting from a recent trend of using air bags for softening landings, as was demonstrated in the Pathfinder, Spirit and Opportunity missions, as well as Europe’s ill fated probe—the Beagle 2. In 2007, a report was filed at the American Astronomical Society by Washington State University professor Dirk Schulze-Makuch that made a claim that rocket exhaust contaminated the Viking landing sites, potentially killing any life that may have been there. The hypothesis was made long after any modifications to Phoenix could be made without delaying the mission significantly. One of the investigators on the Phoenix mission, NASA astrobiologist Chris McKay merely stated that the report “piqued his interest.” Experiments conducted by Nilton Renno, mission co-investigator from the University of Michigan, and his students, have specifically looked at the how much surface dust will be kicked up when Phoenix lands. It was determined, however, that the robotic arm could reach undisturbed soil, for sampling and analyzing.

The mission has two goals. One is to study the geologic history of water, the key to unlocking the story of past climate change. The second is to search for evidence of a habitable zone that may exist in the ice-soil boundary, the “biological pay dirt.” Phoenix’s instruments are suitable for uncovering information on the geological and possibly biological history of the Martian arctic. Because Phoenix will be the first mission to return data from either of the poles, it will contribute to NASA’s main strategy for Mars exploration of “follow the water.” The primary mission is anticipated to last 90 sols (a Martian day, almost 24 hours).

Phoenix will carry improved versions of University of Arizona’s panoramic cameras and volatiles-analysis instruments from the ill-fated Mars Polar Lander (MPL), as well as experiments that had been built for the Mars Surveyor 2001 lander, including a JPL trench-digging robot arm and a chemistry-microscopy instrument. The science payload also includes a descent imager and a suite of meteorological instruments.

Phoenix robotic arm (Credit: NASA)

The Robotic Arm Camera will be attached to the Robotic Arm, just above the scoop. It will be a full-color camera that will be able to take pictures of its surroundings, as well as verify the samples that the scoop will return, and it will be able to examine the grains of the area where the Robotic Arm has been digging. The camera is being made by the University of Arizona a nd Max Planck Institute of Germany.

The Surface Stereo Imager will be the primary camera on the spacecraft. It is a stereo camera that is described as “a higher resolution upgrade of the imager used for Mars Pathfinder and the Mars Polar Lander.” The instrument will use a charged-coupled device that produces high-resolution 1024-by-1024-pixel images. But the SSI will also include infrared filters, allowing multispectral imaging at 12 wavelengths of geological interest and atmospheric interest. It is expected to take many stereo images of the Martian Arctic. It will also be able, using the Sun as a reference, to measure the atmospheric distortion of Mars caused by dust and other features. The camera is being provided by the University of Arizona in collaboration with the Max Planck Institute for Solar System Research.

The Thermal Evolved Gas Analyzer is a combination of a high-temperature furnace with a mass spectrometer. It will be used to bake samples of Martian dust, and determine the content of this dust. It has eight different ovens, each about the size of a large ball-point pen, which will be able to analyze one sample each, for a total of eight different samples. Team members can measure how much water vapor and carbon dioxide gas is given off, how much water-ice the samples contain, and what minerals are present that may have formed during a wetter, warmer past climate. The instrument will also be capable of measuring any organic volatiles, up to 10 ppb. TEGA is being built by the University of Arizona and University of Texas at Dallas.

Mars Descent Imager (MARDI) built by Malin Space Science Systems (Credit: NASA)

Mardi will be the lightest camera ever to land on Mars, as well as the most efficient. It only uses three watts of power during the imaging process, as compared to the many watts used by most other space cameras.

The Microscopy, Electrochemistry, and Conductivity Analyzer (MECA) is a combination of a wet chemistry lab, optical and atomic-force microscope, and a thermal and electrical conductivity probe. It is being built by the Jet Propulsion Laboratory.

Using this instrument, researchers will examine soil particles as small as 16 micrometers across. They will measure electrical and thermal conductivity of soil particles using a probe on the robotic arm scoop. One of the most interesting experiments is the wet chemistry laboratory.

The robotic arm will scoop up some soil, put it in one of four wet chemistry lab cells, where water will be added, and while stirring, an array of electrochemical sensors will measure a dozen dissolved ions such as sodium, magnesium, calcium and sulfate in the water that have leached out from the soil. This is important because it will give us information as the biological compatibility of the soil, both for possible indigenous microbes and for future Earth visitors. Sensors will also measure the pH and conductivity of the soil-water mixture, telling us if the wet soil is super acidic or alkaline and salty, or full of oxidants that can destroy life.

Dr. Christopher McKay

An Interview With NASA Scientist Dr. Chris McKay

To learn more about the Phoenix Mission, TFOT had a quick talk with Dr. Chris McKay, a research scientist with the NASA Ames Research Center who has been working on various NASA projects, including the Phoenix Mission, for many years now.

Q: How was the Phoenix Mission born?

A: Here is my recollection of the events leading up to the Phoenix Mission. I wrote this up a few months ago due to many requests about the history of Phoenix.

SSI has a 12-position color filter wheel ranging through optical and infrared wavelengths (Credit: NASA)

Peter Smith and Mike Hecht were Co-I’s, NASA Ames was the lead institution and would manage the mission, and I was the P.I. At the time of this review of Scout ideas, the word within NASA was HQ would “never let the 2001 lander fly.” Many people thought we were wasting our time trying to reuse that hardware and those instruments.

We were not selected for seed funding at this point, but NASA Ames agreed to provide us with in-house support to develop a proposal for the real Scout competition.

However, soon after the real Scout competition started it was clear that HQ was deciding that essentially all planetary missions would have to be managed by JPL. (In fact the four Scouts selected a year later for further study were all JPL managed). In light of this, Carol and I had a meeting to review the prospects for Ameba and concluded that it had no chance of being selected with an Ames lead. We (correctly) concluded that the only way the 2001 lander would fly again if it was proposed with a highly qualified and experienced member of the original 2001 team as P.I. and with JPL as the managing institution. Peter Smith was the obvious choice. We both know Peter well and we just called him up and had a three-way teleconference, and Peter agreed to be the P.I. Peter did several important things that made the proposal successful: He steered the science rationale into line with the selection criterion combining parts of the 2001 and 1998 landers, he worked effectively with the instrument teams and JPL, and he presented the mission to HQ. The rest, as they say, is history.

Q: The phoenix has a very similar task to the Viking 1/2 of the mid 1970s—how is the phoenix different than those previous missions?

A: Phoenix will go to the polar regions and examine ice-rich samples. Both Vikings were only able to analyze dry soils.

Q: The last three (successful) NASA Mars lenders had wheels, Phoenix is a static craft—don’t you feel that this design is too restricting given the task at hand?

A: Phoenix has the capability to dig deeper than any previous mission. In my view going below the surface on Mars is more important now than going across.

Q: Don’t you fear that a static craft will find nothing, while a few meters away life might thrive?

A: Phoenix will not be able to detect life. It will detect and characterize soil and ice. We know that soil is everywhere and are pretty sure that ice-cemented ground below the surface is everywhere as well. It is much more useful for Phoenix to be able to dig than to be able to roll.

The first half of the fairing is installed around the Phoenix spacecraft (Credit: NASA)

A: It may come as a surprise to many that after Viking, we no longer sterilized spacecraft that landed on Mars. Pathfinder, ESA’s Beagle 2, the Mars Polar Lander, and the two MERs were not sterile. Nor will the upcoming Phoenix or MSL rover be sterile. These missions were assembled in special rooms under remarkably clean conditions, but it is known that they carried microorganisms. For Phoenix the arm is sterilized and kept in a biobarrier bag until after landing.

The committee that determines the protocol for spacecraft cleanliness is COSPAR (the international Committee on Space Research). After the Viking results indicated that the surface of Mars was inhospitable to life, COSPAR, following the recommendation of the U.S. National Academy of Sciences, lifted the requirement for sterilization and replaced it with a requirement for a high level of cleanliness but not sterility. Thus was Mars contaminated with life from Earth. 

Q: Doug McCuistion was quoted by Space News as saying “It’s important to understand that we bought a used car” when he referred to Mardi, and the fact that the Phoenix will not photograph the landing site as it was originally planned—what do you say about that?

A: Virtually every mission has some parts the do not work completely—on Viking the seismometers, on Galileo the high gain antenna, on Huygens Titan probe one of the radio links, etc. If the worse that happens to Phoenix is the loss of the Mardi images (other than the final one) this is hardly a problem. Especially since MRO can take these pictures for us.

Q: Why did you choose not to include instrumentation capable of detecting life (at least to some degree of accuracy)?

A: It was really just a matter of cost, not lack of interest. There is the cost of the instruments, but note that an additional cost is incurred with life-detection instruments because of the COSPAR requirement of sterilization when doing life detection.

Tal Inbar is the acting head of the space research center of Israel’s Fisher Institute for Air and Space Strategic Studies.