This is part two in our feature, A Tale of Two Missions, looking at the 2001 Mars Odyssey satellite and the Phoenix lander. As we saw in part one, these missions were planned to complement each other, with Odyssey spotting the landing site for Phoenix, then acting as the communications relay for the lander. This would happen after Odyssey had already completed its mission, surveying the surface of the red planet in unprecedented detail.
The Odyssey mission went exactly as planned. Using the survey information that it had gathered, NASA scientists picked a landing site for Phoenix: a region where there was a high probability of finding frozen water just beneath the surface. Phoenix was intended to provide the final, positive proof: a sample of ice taken from the Martian soil.
We will take up our story with the launch of Phoenix from Earth.
Phoenix was launched on a Delta II rocket from Cape Canaveral, Florida, on August 4, 2007. The name was a reference to the fact that this mission was actually a resurrection of some of the equipment from two unsuccessful earlier missions. The Mars Polar Lander failed to return data after its landing, and this shattering failure caused NASA to cancel plans for Mars Surveyor 2001. Phoenix used some of the designs from each of these missions, and represented a new birth pulled from the ashes of disappointment.
The Phoenix mission had two objectives: (1) to study the history of water in the Martian arctic and (2) search for evidence of a habitable zone and assess the biological potential of the ice-soil boundary.
The spacecraft arrived at Mars after a 10-month voyage, slowed itself with airbraking and then finished its descent by parachute. On May 25, 2008, it landed successfully in the Martian arctic. (The location was at a latitude which, on Earth, would have been in northern Alaska.)
The projected mission was short, only three months. It was expected that the frigid Martian winter would cause terminal damage to the lander. As it turned out, Phoenix survived for two months longer than expected, getting in a full five months of work.
Now that the information is all in, we can see what a big success the Phoenix mission was. It found the ice it was looking for, and it also found evidence that ongoing, long-term climate cycles might sometimes provide favorable conditions for life on Mars.
Speaking in an article published in the journal Science, Phoenix Principal Investigator Peter Smith of the University of Arizona said, “Not only did we find water ice, as expected, but the soil chemistry and minerals we observed lead us to believe this site had a wetter and warmer climate in the recent past- the last few million years- and could again in the future.”
The article goes on to cite evidence that the Martian soil has had films of liquid water at times. This, plus the presence of potential nutrients in the soil, “implies that this region could have previously met the criteria for habitability” during parts of cyclic climate shifts, the article concludes.
We know from examples here on Earth that some forms of life can go into periods of dormancy that last indefinitely. Microbes which were apparently dead have been found encased in rock and made to grow in the laboratory; ancient seeds taken from archaeological sites have been shown to be viable. The possible duration of dormancy for living cells is not established, but is obviously very long. The Phoenix findings raise the tantalizing possibly that some forms of life, at least on the microscopic level and possibly larger, may have the ability to remain dormant through these long-term cycles.
It paints a beautiful picture, doesn’t it? At some time in the remote future, the Martian climate may shift, vast amounts of subsurface ice may thaw, and the plains of Mars spring into life like the desert after a rainstorm. Let your mind play with that idea for a moment: what kind of life might be buried in the Martian dust, just waiting for a little moisture to help it come alive?
Another pleasant surprise was the presence of perchlorate in the soil samples collected by Phoenix. If combined with water in the right concentrations, it could form a brine that would allow water to stay liquid at lower temperatures than normal. On Earth, some microorganisms use perchlorate as food. Humans could get oxygen from it, or process it into rocket fuel.
Phoenix also documented an event that is both scientifically interesting and aesthetically beautiful: snowflakes falling in the thin Martian air. This was the first documented precipitation on Mars. Before this, we knew that the polar caps were composed of frozen water, but we didn’t know whether it was frost that had condensed on surfaces, or precipitation that had fallen from the sky. Now we know: it actually snows on Mars.
Finally the deep cold of Martian polar winter overtook Phoenix, and the lander stopped operating.
As we said earlier, this outcome was expected. But space probes have been known to defy expectations and continue functioning long after their projected lifespans, and with this in mind, NASA has been using the Mars Odyssey satellite to listen for a signal from the lander. Odyssey listened as it passed over the site in January, then again in February, and it will try again in March. So far there have only been negative results, and hope is fading for Phoenix.
It’s the end of a great mission. Phoenix has found what it was looking for: subsurface water ice on Mars.
And where there’s water, there may be life. The first Martians that we encounter may be extremophile organisms lying in that frozen soil, waiting for the next swing of the climatic cycle.
And now we know what one of the major industries will be for future Martian colonies: ice mining. This will undoubtedly prove to be one of the most valuable natural resources on the red planet, and may form the basis of a planet-wide economy in the same way petroleum does here (but without the pollution.)
Phoenix will sit on that windswept plain for a while, but in time, people will go there and retrieve it. When they do, they should put in a museum or shrine- some place of honor, as it deserves. Phoenix has made a vital step in our march to the stars, and the world of the future will owe it a debt of gratitude.
Odyssey is still orbiting Mars and functioning fine. We will undoubtedly hear from it again.
Preview: The European Space Agency’s Mars Express probe, which was featured in a previous article at this site, has recently been conducting a series of flybys of Phobos, one of Mars’ moons. The info from these is starting to come out, and our next article will take a look at it.
Sources:
Phoenix Mars Lander: Mission Overview at NASA website: nasa.gov/mission_pages/phoenix/mission/index.html
Phoenix Mars Lander: Launch Coverage at NASA website: nasa.gov/mission_pages/phoenix/launch/index.html
Phoenix Mars Lander: Exploring the Arctic Plain of Mars at NASA website: nasa.gov/mission_pages/phoenix/news/phoenix-20090702.html
Phoenix Mars Mission: “Mars Odyssey Still Hears Nothing From Phoenix” at website of the University of Arizona: phoenix.lpl.arizona.edu/index.php
Phoenix Mars Mission: Mission Phases at website of the University of Arizona: phoenix.lpl.arizona.edu/phases.php
Space Topics: Phoenix at website of the Planetary Society: planetary.org/explore/topics/space_missions/phoenix/
Phoenix Mars Lander News: “NASA Phoenix Results Point to Martian Climate Cycles” at website of the Jet Propulsion Laboratory, California Institute of Technology: jpl.nasa.gov/news/phoenix/release.php?ArticleID=2210