Like its namesake in ancient mythology,
the 2007 Phoenix Mars Scout mission is reborn out of fire;
created from the embers of previous missions. Phoenix returns
to flight the Mars Surveyor Programís 2001 (MSPí01) lander
with a rich and diverse scientific payload chosen from the
1998 Mars Polar Lander (MPL'98) and the MSPí01 missions.
This complement of spacecraft and payload is ideally suited
to perform a scientific analysis of the Martian arctic soils
for clues to its geologic history and potential for biology.
Phoenix is the first fully competed and investigator lead
mission as part of NASA's new Mars Scout program.
The Mars programís crosscutting theme to "follow the water"
proves to be difficult on a desert planet. Besides the traces
of water vapor in the thin atmosphere and exposed water
ice on the Northern Polar cap, only vestigial remnants mark
the flowing rivers and crater lakes from ancient times.
However, Odyssey scientists announced early in 2002 that
large amounts of water ice are clearly seen by the Gamma
Ray Spectrometer (GRS) in the circumpolar regions. Modeling
the gamma ray and neutron fluxes, they predict that high
concentrations of ice, up to 80% by volume, are to be found
within 50 cm of the surface.
The Phoenix will land in the northern plains between 65
and 75°N. Continuing GRS measurements verify that the
Martian arctic, near 70°N, is the holy grail: water
ice protected from solar UV by a thin layer of regolith.
The signatures near longitude -120°W are nearly as strong
as the exposed ice cap. In addition, high-resolution images
from the Mars Orbiter Camera (MOC) on the Mars Global Surveyor
(MGS) spacecraft show a "basketball-like" texture on the
surface with low hummocks spaced 10ís of meters apart; polygonal
terrain is also common. These geologic features are common
in Earthís polar regions indicating permafrost and an active
To Ice Layer (cm)
Phoenix will be the first scientific mission to study the
history of water in all its phases. The polar regions are
known from remote sensing to be critical to the seasonal
transport of water and carbon dioxide. Quantifying the volatile
inventory locked into the arctic soils and the water chemistry
of wet soils, even at one location, is a giant step toward
modeling the weather processes and climate history of Mars.
As on Earth, the past history of water is written in the
subsurface. Liquid water changes the soil chemistry in characteristic
ways. Obliquity wander and precession are known to strongly
influence the climate on time scales of 100,000 years or
more. In particular, the water ice may melt and wet the
overlying soil in cycles commensurate with orbital dynamics.
Phoenix will search for evidence of a habitable zone and
assess the biologic potential of the ice-soil boundary Microbial
colonies can survive in a dormant state for eons. Recent
work shows that water ice melts onto soil crystals at temperatures
as cold as Ė20° C, thus activating dormant microbes.
As temperatures increase, growth and reproduction may begin.
The Phoenix lander brings instruments to the surface that
acquire samples of this biological paydirt and test for
signatures related to biology. Organic molecules will be
easily detectable even in small concentrations. Other experiments
will determine the chemical and paleo-hydrological properties
of the soils under both dry and wet conditions.