Mars polar cap mystery solved

Sep 22, 2008
This is a mosaic of images taken by the Mars Express’s Visible and Infrared Mineralogical Mapping Spectrometer, OMEGA. It shows the residual south polar cap at the end of northern winter on the Red Planet. The cap appears clearly asymmetric, its centre being displaced by 3° from the geographic pole. Credits: ESA/ Image Courtesy of F. Altieri (IFSI-INAF) and the OMEGA team

(PhysOrg.com) -- Scientists are now able to better explain why Mars’s residual southern ice cap is misplaced, thanks to data from ESA’s Mars Express spacecraft - the martian weather system is to blame. And so is the largest impact crater on Mars – even though it is nowhere near the south pole.

Like Earth, Mars has frozen polar caps, but unlike Earth, these caps are made of carbon dioxide ice as well as water ice. During the southern hemisphere’s summer, much of the ice cap sublimates, a process in which the ice turns straight back into gas, leaving behind what is known as the residual polar cap. The problem is that while the winter cap is symmetrical about the south pole, the residual cap is offset by some three to four degrees.

This misplacement, which has puzzled planetary scientists for years, was solved by scientists in 2005 but now, thanks to ESA’s Mars Express, new information is available to explain the misplacement.

Marco Giuranna of the Istituto di Fisica dello Spazio Interplanetario CNR (IFSI), Rome, Italy, and colleagues have used the Planetary Fourier Spectrometer (PFS) onboard Mars Express to measure the temperature of the martian atmosphere from the ground up to an altitude of 50 km above the south polar region.

The team used the profiles to chart the way the atmosphere changes in temperature and other characteristics over more than half a martian year. They monitored the way carbon dioxide builds into the southern ice cap as the martian autumn, or fall, turns into the martian winter. “It is not a straightforward process. We found that two regional weather systems developed from mid-fall through the winter,” says Giuranna.

These weather systems are derived from strong eastward winds that characterise the martian atmospheric circulation at mid-latitudes. They blow straight into the Hellas Basin, the largest impact structure on Mars with a diameter of 2300 km and a depth of 7 km. The crater’s depth and the steep rise of the walls deflect the winds and create what are called Rossby waves on Earth.

These waves reroute the high altitude winds on Mars and force the weather system towards the south pole. In the western hemisphere of Mars, this creates a strong low-pressure system near the south pole, and a high-pressure system in the eastern hemisphere, again near the south pole.

Giuranna found that the temperature of the low-pressure system is often below the condensation point for carbon dioxide, so the gas condenses and falls from the sky as snow and builds up on the ground as frost. In the high-pressure system, the conditions are never appropriate for snow, so only ground frost occurs. Thus, the south polar cap is built by two different mechanisms.

The areas that have extensive snow cover do not sublimate in the summer because they reflect more sunlight back into space than the surface frost. Frost grains tend to be larger than snow grains and have rougher surfaces. The ragged texture traps more sunlight, driving the sublimation.

So the western area of the southern polar cap, built of snow and frost, not only has a larger amount of carbon dioxide ice deposited but also sublimates more slowly during the summer, while the western area built of frost disappears completely. This explains why the residual cap is not symmetrically placed around the south pole.

“This has been a martian curiosity for many years,” says Giuranna. Thanks to Mars Express, planetary scientists now understand a new facet of this amazing, alien world.

Citation: 'PFS/MEX observations of the condensing CO2 south polar cap of Mars' by M. Giuranna, D. Grassi, V. Formisano, L. Montabone, F. Forget, L. Zasova is to be published in a forthcoming edition of the journal Icarus.

Provided by ESA

Explore further: NASA-NOAA Suomi NPP Satellite team ward off recent space debris threat

add to favorites email to friend print save as pdf

Related Stories

Under Rainier's crater, a natural laboratory like no other

Oct 03, 2014

Counting all the ups and downs, he had climbed more than 15,000 feet to get here - past yawning crevasses and over cliffs where a single misstep could send a rope team tumbling. His party was pummeled by a lightning storm ...

Curiosity Mars rover finds sandstone variations

Mar 25, 2014

(Phys.org) —Variations in the stuff that cements grains together in sandstone have shaped the landscape surrounding NASA's Curiosity Mars rover and could be a study topic at the mission's next science waypoint.

NASA Mars spacecraft reveals a more dynamic red planet

Dec 10, 2013

(Phys.org) —NASA's Mars Reconnaissance Orbiter has revealed to scientists slender dark markings—possibly due to salty water - that advance seasonally down slopes surprisingly close to the Martian equator.

Managing the deluge of 'big data' from space

Oct 18, 2013

(Phys.org) —For NASA and its dozens of missions, data pour in every day like rushing rivers. Spacecraft monitor everything from our home planet to faraway galaxies, beaming back images and information to ...

Mars: What lies beneath

Aug 13, 2013

There is much more to Mars than meets the eye. By using the radar on Mars Express, we can see several kilometres below the surface to see what lies beneath.

Recommended for you

Beastly sunspot amazes, heightens eclipse excitement

1 hour ago

That's one big, black blemish on the Sun today! Rarely have we been witness to such an enormous sunspot. Lifting the #14 welder's glass to my eyes this morning I about jumped back and bumped into the garage.

The formation and development of desert dunes on Titan

2 hours ago

Combining climate models and observations of the surface of Titan from the Cassini probe, a team from the AIM Astrophysics Laboratory (CNRS / CEA / Paris Diderot University) , in collaboration with researchers ...

'Eau de comet' is a bit of a stinker

3 hours ago

Rotten eggs, horse pee, alcohol and bitter almonds: this is the bouquet of odours you would smell if a comet in deep space could be brought back to Earth, European scientists said on Thursday.

User comments : 0