| Images taken of the North Polar region on Mars by the Mars Color Imager (MARCI) [1]
onboard Mars Reconnaissance Orbiter, during the landed operations of the Mars Phoenix
Lander provides new opportunities for interpreting data from the Lander on a global scale. In
this contribution, we make use of optical depth data [2], wind data [3], pressure data [4] and
MARCI images [5, 3] to discuss two different origins of dust activity at the landing
site.
Several “dust storms”, i.e. periods with sudden increase in atmospheric dust optical depth
were observed at the Phoenix landing site during its 150 sol mission (LS = 76º to
150º).
In the beginning of the mission (LS < 100º), two periods were observed with increased
dust load in the atmosphere, around LS Â 80º and from LS = 88º to LS = 94º. These
events were not associated with increased wind speeds. On the lander, these events
can be seen as slightly elevated pressure levels on an otherwise steadily declining
pressure curve due to seasonal condensation at the South Pole. When the latter event
is traced back in MARCI images, it is found that this event originates when the
last visible remaining CO2 frost evaporates from the polar region. The wind data
shows that none of these events are associated with storm systems. More likely there
is dust present just below the CO2 frost layer that is easily put into suspension
when the CO2 evaporates, or that the evaporation assists the lifting of dust into
suspension.
More likely there is dust just below the CO2 frost layer that is easily put into suspension
when the CO2 evaporates, or that the evaporation assists the dust to be lifted into
suspension.
In the latter half of the mission, several individual days showed elevated dust levels along
with increased wind speeds, which were generally from West. In MARCI images, these
events are associated with the passing of condensate clouds. These events became more
frequent in the latter part of the mission, and one of the strongest occurred at LS = 120º. The
pressure data shows dips from the otherwise declining pressures indicating low
pressure weather systems. Simultaneously the wind data shows elevated wind speeds
as these systems pass over the landing site. Another characteristic feature of the
passing of these systems is elevated dust-devil activity [5]. In MARCI data, it is seen
that when these weather systems approach the North Polar region, dust storms are
initiated [3]. This was also the case on sol 150, when a condensate cloud was seen just
south of the landing site. By sol 151 the cloud had reached the North Pole and a
dust storm was beginning to form. The passing of this dust storm over the landing
site led to reduced power that eventually led to loss of communications with the
lander.
References: [1] Malin M. C. (2001) JGR 106, 17651, [2] Tamppari, L. et al., (2010) JGR,
in press. [3] Holstein-Rathlou, C. et al., (2010) JGR, in press. [4] Taylor, P. et al., (2010) JGR
in press. [5] Ellehoj et al., (2010) JGR in press. |