Phoenix (Mars Phoenix Lander)

1. Historical Context and Detailed Objectives

The scientific gap that the Phoenix mission aimed to fill involved the in situ characterization of the climatic and water history in the Martian arctic, assessing the biological potential of the interface between the regolith and subsurface ice. Primary objectives focused on:

Scientific:

• Study the history of water in the Martian arctic by characterizing subsurface ice and regolith.
• Search for complex organic molecules and evaluate the biological potential or habitability of the ice-soil interface.
• Continuously monitor polar climate and meteorology.

Engineering:

• Validate a retrorocket-based landing system for a stationary high-latitude platform.
• Operate a long-reach robotic arm under cryogenic surface conditions.

2. Vehicle Architecture and Main Subsystems

The Phoenix stationary lander had a launch mass of 670 kg and a landing mass of 350 kg (with a scientific payload of 59 kg). Its platform featured a deck diameter of 1.5 m and a height of 2.2 m to the top of the meteorological mast, reaching a wingspan of 5.52 m with the solar panels deployed. Electrical power came from solar arrays complemented by nickel-hydrogen (NiH2) batteries, generating approximately 450 W under optimal conditions. Communications were established via UHF links with relay orbiters and a direct X-band link.

3. Payload and Scientific Instrumentation

The instrument suite of Phoenix included the following main equipment:

• RA (Robotic Arm): 2.35 m reach robotic arm equipped with a scoop and rasp to excavate up to half a meter in depth.
• RAC (Robotic Arm Camera): Camera mounted on the arm to document trenches and extracted samples.
• TEGA (Thermal and Evolved Gas Analyzer): System of small ovens and mass spectrometer for the thermal analysis of volatiles.
• MARDI (Mars Descent Imager): Descent camera intended to capture images during atmospheric entry.
• MET (Meteorological Station): Meteorological station provided with pressure, temperature, wind sensors, and a lidar.
• SSI (Surface Stereo Imager): Mast-mounted color stereo camera for obtaining high-resolution panoramas.
• MECA (Microscopy, Electrochemistry, and Conductivity Analyzer): Assembly composed of optical and atomic force microscopes, wet chemistry cells, and conductivity sensors.

4. Chronology and Mission Phases

Following its launch on August 4, 2007 aboard a Delta II rocket, the probe completed its interplanetary trajectory until achieving atmospheric entry and a successful landing in Vastitas Borealis on May 25, 2008. Scientific operations began in early June 2008 (with Sol 0 set on the arrival date). Having successfully exceeded the planned nominal duration of 90 sols, the mission entered an extended phase totaling 152 operational science sols. The last communication with the spacecraft was recorded on November 2, 2008, a date when the decrease in solar illumination deprived the system of power, concluding formally by NASA in May 2010.

5. Results and Discoveries

The in situ analysis provided visual and chemical confirmation of the presence of subsurface pure water ice just centimeters deep after using the robotic arm. Likewise, the MECA and TEGA instrument suite allowed the detection of perchlorates in the Martian soil, a geochemical finding of great relevance. In the atmospheric realm, the MET station recorded in detail the polar weather cycle and the fall of ice crystals in the form of snow that sublimated before reaching the surface.

6. Legacy and Significance

Phoenix demonstrated the feasibility of using stationary landers equipped with excavating arms in high-risk polar regions, substantially expanding knowledge about the distribution of volatiles and potential habitability in Mars' past and present.