Phoenix Mars Lander mission – Københavns Universitet

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Full-circle panorama view of the Phoenix Mars Lander site. Click here for more information. Image credit: NASA/JPL-Caltech/University of Arizona/Texas A&M University/NBI-University of Copenhagen.

Phoenix Mars Lander mission

The Phoenix Mars mission was launched in 2007 and was the first mission that provided conclusive evidence of the presence of water-ice in the subsurface on Mars. It did so by identifying the melting and boiling points of water in soil samples in a small oven.

Phoenix landed at 68 degrees northern latitude not very far from the Martian North pole and was the first mission to return data from Mars' polar regions.
It was the first of NASA's ‘scout missions’, which are small and low-cost missions. The scout program, and hence the Phoenix mission, is part of the NASA Mars Exploration Program. The mission was led by Peter Smith, University of Arizona, with several contributions from around the world.

Purpose

The Phoenix Mars Lander was designed to conduct investigations of ice and soil and its interaction with the atmosphere in the Martian arctic. The two overall objectives of the mission were:

  • To study the dynamics and history of water by examining the interface between atmosphere and surface and to study water-ice below the Martian surface
  • To determine if the Martian arctic soil could support life (habitability)

Results

The Phoenix mission did find water-ice in the subsurface and gained several other insights into Mars and its polar regions. The main findings of the mission are:

  • Water-ice
  • The oxidant perchlorate
  • Calcium carbonate
  • Clouds and snow of water
  • Non-magnetic dust

Details on the results and their impact on the habitability of the landing site can be found under Phoenix results, scientific publications under Key papers.

Mission background and operations

Artist's rendition of the Phoenix Lander on Mars. The robotic arm is in front of the lander in this image. Click here for a high-resolution version. Image Credit: NASA/JPL.

Because of Mars' thin atmosphere and hence very low surface pressure, liquid water can not exist at usual conditions on the surface of the planet at present. But much scientific evidence indicate that liquid water once covered large areas of Mars, and as water is believed to be one of the main prerequisites for life, the remains of this water is of keen interest to the scientific community.
In 2002 investigations by the orbiter Mars Odyssey revealed a considerable amount of subsurface water-ice in the northern arctic plains. This is where Phoenix landed.

The 4th of August 2007 the successful launch of the Phoenix spacecraft set an impressive array of scientific instruments en route to Mars. The spacecraft cruised the interplanetary space between Earth and Mars for 10 months before touching down at the arctic plains of Mars on 25th of May 2008.

Despite the success of the airbag landing systems used earlier by Pathfinder and the two Mars Exploration Rovers, the Phoenix lander used rocket thrusters and legs to touch down softly on the Martian surface. This was a necessary decision because the Phoenix lander at 350 kg (770 lb) is heavier than the Exploration Rovers and Pathfinder.

Artist's rendition of Phoenix on Mars. Click here for a high-resolution version. Image Credit: NASA/JPL-Caltech/University of Arizona.

Because the goal was to study atmosphere-surface interactions and since the subsurface ice was believed to be ubiquitous in the landing area there was no need for the lander to be mobile. Instead it was equipped with a 2.35 m (7.7 ft) long robotic arm to reach and investigate the water-ice table, which before the mission was believed to be located just a few centimeters below ground in the circumpolar region of Mars. The arm was capable of digging up ice-soil samples and delivering them to the science instruments on the lander deck for analysis.

As well as analyzing the ice beneath the soil, the Phoenix lander performed other studies to complement the four long term science goals of NASA's Mars Exploration Program:

  • Determine whether life ever arose on Mars
    The Phoenix lander studied the habitability potential of Mars, i.e. whether the environment could support life, presently or at some point in the past - here especially focusing on the history of water on Mars.
  • Characterize the climate of Mars
    The Phoenix lander featured a meteorological station to examine the weather of Mars.
  • Characterize the geology of Mars
    As well as a wide assortment of on-board scientific tools to examine the soil, the Phoenix lander also boosted a high resolution stereo imager, capable of sampling through 12 filters to examine wavelength regions from the optical to the infrared. When properly calibrated it was used to examine airborne dust as well as rocks and sediments on the surface of Mars.
  • Prepare for human exploration
    The Martian ice could become important for future manned missions to Mars. The Phoenix lander was ideally suited to examine the Martian ice and asses the value of the arctic region as a possible area for human exploration.

Phoenix was active through October 2008. From May through September that year most of the Niels Bohr Institute Mars group stayed and worked at the Phoenix Science Operations Centre in Tucson, Arizona, and participated in surface mission operations and interpretation of data from the lander.

Payload with Danish contributions

The Mars group had two types of magnetic properties experiments on Phoenix:

The experiments were part of the following two science instruments:

Surface Stereo Imager (SSI)
The stereo imager is an advanced stereographic panoramic camera mounted on a mast reaching to approximately 2 meters above ground. From this vantage point it can create stereographic color pictures and virtual 3d views (and digital terrain maps) of the immediate environment and the lander itself. This helped operators pick good digging locations and control the lander through its period of operation where one-way radio transit times ranged from around 15 to 20 minutes.

12 filters of geological and atmospheric interest for each eye allows the SSI to image the optical and infrared region with a wider range of spectral information than any animal on Earth.

Because of the dusty atmosphere on Mars and the light scattering properties of the dust suspended in the air the sunlight reaching the surface is reddish. Also surfaces of the lander will accumulate sedimenting airborne dust with time. In addition, the imager was likely to lose accuracy during its interplanetary cruise and operation period on Mars. For these reasons it is necessary to calibrate the spectroscopic capability of the SSI using a reference color target which is well calibrated in white light in a laboratory on Earth. Therefore images obtained by the imager was periodically calibrated against radiometric color reference targets (CalTargets) developed by the Mars/Mössbauer group. These reference targets remain relatively clean from dust by exploiting magnetic properties of the Martian dust discovered by magnetic properties experiments on Pathfinder and the Mars Exploration Rovers. The stereo imager not only served as the eyes of the Phoenix lander, it was also used to examine the soil and atmosphere. For that purpose it incorporates 12 different color filters sampling the visual and infrared spectrum including the absorption bands of atmospheric water.

Microscopy, Electrochemistry, and Conductivity Analyzer (MECA)
The MECA is a combination of several instruments. One of them is an AFM microscope, which maps a surface by moving a very sharp tip on a microscopic cantilever in a zig-zag pattern in close proximity to the surface. Atoms in the tip interact with atoms in the surface creating minute forces that bend the cantilever. These deformations are measured by reflecting a laser beam off the top of the cantilever and measuring its deflection. The measurements are used to create a three dimensional map of the surface topography with nanometer resolution, much finer than could ever be achieved with an optical microscope.

The MECA features, besides the AFM microscope with 8 disposable tips, also an optical microscope and a wheel with 10 identical sets of substrates, each containing 6 different types, to hold samples for the microscopes. This variety of substrates, ranging from sticky polymers to magnets, help scientists discover as many properties of each sample as possible.

The Mars/Mössbauer group has contributed specialized insets to the MECA experiment: magnet substrates and a calibration target for fluorescence measurements.