Phoenix on Mars, this is the north!


Eric Bottlaender

Space specialist

May 14, 2023 at 5:00 p.m.

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NASA Phoenix Mars lander © NASA/University of Arizona

A “selfie” of Phoenix captured thanks to the robotic arm on board the lander. Credits NASA/University of Arizona

Arrived in 2008 while Opportunity and Spirit were rolling briskly thousands of miles away, the Phoenix lander was aimed at the north of March. Light mission, but risky, it nevertheless succeeded in detailed chemical analyzes of the soil of the red planet, and studied its climate for five months.

We had to fit all that into a very small envelope.

Looking for a cheap platform

In the early 2000s, NASA faced a problem that only applied to it. She managed to land two small rovers (Spirit and Opportunity) on Mars, but is now looking for ways to send more ambitious instruments to the red planet… and above all, for less. Indeed, there is already the Mars Science Laboratory project (MSL, Curiosity) which is gaining momentum and will absorb several billion dollars. The American agency wants to explore and discover the Martian soil on the Great Plains, at very high latitudes near its ice cap. Fortunately, it can rely on two old projects: the Mars Polar Lander, which crashed on Mars the day of its arrival, September 3, 1999, and the Mars Surveyor 2001 Lander concept, canceled in a difficult budgetary context at the turn of the decade. Finally, the University of Arizona, Phoenix project was chosen. The latter is responsible in partnership with NASA, and receives an envelope of 320 million dollars.

Phoenix NASA landing site © NASA

The Phoenix landing site, very close to the Martian North Pole. NASA Credits

You have to be efficient

However, what may seem like a lot actually represents a very limited budget, in particular for developing and sending new scientific instruments. Thus, the team of decision makers quickly freezes the idea of ​​a fixed lander, and not of a rover. For what ? Because mobility is lost mass, while it is already planned to place Phoenix in an absolutely flat landscape. Above all, it is necessary to save as much weight as possible in order to be able to land with a platform which weighs practically twice the Oppy and Spirit rovers, which requires more energy to operate its instruments and which will be in a more hostile region, in particular at because of the temperatures. No more question of using the “bunch of grapes”, these huge sets of airbags, to land. This time, it will take a controlled descent with a sequence between heat shield, parachute and thrusters. The margin of error is limited.

Preparing the Phoenix lander (which is upside down in this photo). Credits NASA/University of Arizona

small science lab

In return, Phoenix embeds a high-performance scientific “package”. A 2.3 m long robotic arm ending in a bucket for digging, a mast with cameras as well as a weather station also with a LIDAR laser, a gas analyzer (the samples are burned in a furnace then the gases are analyzed by spectroscopy) and a chemical analyzer with microscope, and finally something to dilute samples and examine them. Three large instrumental suites that come in addition to imagery. A camera called MARDI (Mars Descent Imager) is also supposed to observe the underside of the lander, from the ejection of the shield until the moment of touching the surface, the day of the arrival on Mars. Unfortunately, the teams discovered shortly before departure that this data could corrupt the recording and reading of the values ​​of the inertial unit… MARDI was therefore deactivated, for lack of time to deal with the problem before its trip to Mars.

NASA InSight artist vision landing © NASA

Only the Viking landers landed in this way on Mars, before Phoenix… Credits NASA (artist’s view)

Asked, once and for all

Phoenix blasts off August 4, 2007 aboard a Delta II rocket from Florida for a nine-month journey to the Red Planet. An uneventful journey, which ended on May 25, 2008, when it landed near the North Pole, in an area called “Green Valley”, with record water ice concentrations outside the ice caps measured by orbiters from the NASA and ESA. The approach and landing are closely followed by these vehicles from orbit, and at the end of the suspense (the parachute deployed, for example, 7 seconds late) the teams can exult: the Americans have succeeded again to land a vehicle correctly on Mars! 15 minutes later, when the dust has settled, Phoenix begins to expand its two large disc-shaped solar arrays, then begins its science operations. On May 28, a day late, the robotic arm was successfully deployed. This is important: depending on the conditions on site, the teams then only planned 90 days of survival for the mission.

A great scientific harvest

Fortunately, thanks to the results and the activation of the various instruments, the scientists know that she will probably be able to survive a little longer. The month of June is dedicated to the first experiments, but also to the calibration of the instruments. The most capricious is undoubtedly the TEGA gas analyzer (Thermal and Evolved Gas Analyser), for which it was difficult to bring the samples from the collection cup to the opening… And as it took several days, the results appeared to be biased due to the potential evaporation or sublimation of materials such as water ice. Because there is ice cream! From the first shovels, the NASA teams observed on the pictures the sublimation of water ice around the site, which can now be described as permafrost. This great desert covered in sand and dust is in fact rather a gigantic muddy expanse, frozen for billions of years. Temperatures on site fluctuate between -20 and -98°C…

NASA Phoenix on Mars shoveling samples © NASA/University of Arizona

Nice view of the landscape, but also of the many “shovels” carried out at the foot of Phoenix during the mission. Credits NASA/University of Arizona

The exploitable results are not long in coming. The mission delivers detailed images of the most northerly site ever visited on Mars, information on Martian meteorology (including sightings of water and snow clouds), the ground and its composition. Phoenix allows in particular to isolate perchlorates, which amply lowered the possibilities of finding bacterial organisms on the surface of the red planet. The perchlorate salts have since been found by Curiosity, including in its drilling of the Gale Crater floor. This does not prevent finding traces or bricks of past life, but seriously complicates their appearance today. Conversely, this is good news: there is little risk that terrestrial bacteria could really contaminate the Martian environment.

NASA Phoenix ice on the ground of Mars © NASA/University of Arizona

One of the shots that allowed, by showing the ice to sublimate, to show that the ground was rich in water ice. Credits NASA/University of Arizona

We extend, we extend, and then…

The Phoenix lander managed to exceed its expected lifespan, and was still operating as of September 2008. However, its far northern position is sensitive to seasonal variations, and it receives less and less sunlight, particularly to power its the most greedy instruments, gas and soil analyzers. On October 28, even if they expected it, the teams deplored a first cut in communications: Phoenix was placed in backup mode before again receiving enough energy to regain contact with Earth. A ballet that will not last, and on November 2, the lander sends its data one last time. NASA will attempt to contact him until the 10th, after which the mission is declared complete. The agency, for the sake of conscience, will also try to reconnect when the sunshine conditions return to good weather at this site in 2010, but to the great surprise, Phoenix will not rise again from its ashes.

Little known despite its solid scientific results, the mission is now overshadowed by other laboratories (on wheels this time) such as the famous Curiosity and Perseverance. However, Phoenix showed great performance, washed away the insult of the failed Polar Lander mission, and validated a platform that would be used ten years later for a similar mission despite other instruments: InSight (ironically the latter cost much, much more expensive). And if it is not currently planned to reuse a similar one, because the concepts of Mars missions evolve, Phoenix remains a “deliverer of scientific experiments” which has proven itself on Mars. Few can say the same.



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