CAUGHT IN THE ACT - AVALANCHES ON MARS’ NORTH POLAR SCARPS: MRO’s High Resolution Imaging Science Experiment (HiRISE) camera has the ability to im-
age small-scale, short-term changes in the Martian surface, including recent impact craters only a few metres across, dust devils and seasonally-changing flow structures on
steep slopes. Here it has captured avalanches of debris in action on the edge of the dome of layered deposits centred on Mars’ north pole. It is very rare to catch such a
dramatic event in action. Material, probably including fine-grained ice and dust and possibly even large blocks, has detached from the 700 m (2300 ft) tall 60 degree scarp
to the left and cascaded to the gentler slopes below. The largest cloud is about 180 meters (590 feet) across. The top part of the scarp is still covered with bright (white)
carbon dioxide frost which is disappearing from the polar regions as spring progresses. Credit: NASA/JPL-Caltech/Univ. of Arizona
Mars Reconnaissance Orbiter (MRO)
NASA’s Mars Reconnaissance Orbiter was launched in 12th August
2005, on a quest for evidence that water may have been present on
the Martian surface for a long period of time. While other Mars missions
have shown that water did indeed flow across the surface at vari-
ous times during the Red Planet’s history, it remains a mystery whether
water was ever around long enough to provide a habitat in which life
could originate and develop.
In its survey of Mars, MRO is looking particularly at small-scale fea-
tures. One of its cameras – the High Resolution Imaging Science Experi-
ment (HiRISE) camera - is the largest ever flown on a planetary mission,
and has a resolution of just 0.3 m per pixel from a height of 300 km.
‘Though previous cameras on other Mars orbiters could identify objects
no smaller than a school bus, this camera can spot something as small
as a dinner table…. Its imaging spectrometer could identify key (water-
related) minerals in patches as small as a swimming pool at a few thou-
sand carefully chosen sites, while covering the whole planet at a resolu-
tion of 200 meters (650 feet)’ (NASA Fact Sheet).
The spacecraft is more than its camera though, and carries six sci-
ence instruments for examining Mars in various parts of the electromag-
netic spectrum from ultraviolet to radio waves. (Two other investigations
use the spacecraft movements as a means of sounding out both the
atmospheric structure and internal structure of the planet.) Their main
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