HiRISE Science Theme: Seasonal Processes
By:
Candy Hansen
Explanation
of the theme.
Mars' seasonal polar caps are composed primarily of
CO2 frost. This frost
sublimates (changes from solid directly to gas) in the spring, boosting the
pressure of Mars' thin atmosphere.
In the fall the CO2 condenses, causing the polar caps to
reach as far as ~550 latitude by late winter. In the study of seasonal processes we
observe the caps as they wax and wane to investigate both large scale effects
on Mars as well as the local details of the sublimation and condensation processes. By learning about current processes on
a local level we can learn more about how to interpret the geological record of
climate changes on Mars. Mars
Observer Camera (MOC) images from the Mars Global Surveyor spacecraft have
shown an astonishing array of exotic landscapes as the southern seasonal cap
sublimates, including spots, "spiders", and fans. A region we plan to investigate near the south pole has been
called the "cryptic" terrain because it seems to stay quite cold even after the
disappearance of bright frost.
Major
science questions for this theme.
What happens in the spring as the seasonal cap
sublimes? What happens in the fall
as frost condenses? What controls
the extent of the seasonal polar cap each year? What controls the sublimation and condensation of the
seasonal frost on a local level (topography, albedo of underlying
terrain)? What is going on in the
cryptic terrain at the southern polar cap? How do dust storms affect the local weather at the polar cap
edge? What are the wind patterns
and how do they change over the course of a season? Are geysers active as the caps sublimate? Is that what causes the spots and fans?
Relationship
to other science themes.
This theme is closely related to the climate change
and polar geology themes. Polar
geology is primarily focused on the permanent polar deposits in contrast to
this theme which is concerned with behavior of the seasonal cap. Climate change is an extension of
seasonal processes in which we look for long-term trends that surpass seasonal
variability.
Features
of interest potentially visible at HiRISE scale.
One
example of many phenomena we would like to observe is the evolution of a "spot"
to a "fan" as the seasonal cap retreats in the spring. Is a spot formed in a locally dark
region that gets warmer faster than its surroundings, then grows? Is the darker material very fine and
does it get blown across the surface of the brighter surrounding ice to form a
fan? Or is the darker material
lofted by Triton-like plumes such as those observed by Voyager 2? The high resolution and high
signal-to-noise ratio of the HiRISE images along with stereo coverage will give
us our best ever view of these unearthly terrains.
Figure
1. This is an example of a MOC
image of the spots and fans that form on the south polar cap as the seasonal
CO2 begins to sublimate.
Return to HiRISE Learning and Activities Page