Poster Abstract
Is there ice on Mars? Yes. But where is it now, how did it get there and where will it go? The water cycle is a crucial element of the Martian climate, past and present, and it has a significant effect on the planet’s geology. The water cycle changes as the climate changes. And the climate changes on Mars have been considerable, due to extreme variations in the planet’s orbital parameters. For example, the obliquity, or tilt of the planet’s axis, has changed considerably over the millennia, affecting where the sun’s radiation hits the planet’s surface. So the amount of solar heating that areas of the planet receive changes over time, which impacts on where the ice forms, how it behaves and how water vapour is transported around the planet. Computer models can simulate the Martian climate and provide insight into the behaviour of the water cycle and the surface ice. These models can show how the water cycle functions when the planet is experiencing different obliquities. Ice, such as the polar ice caps, glaciers and other icy features, can move from the poles to the equator and back again over the millennia. These changes leave marks on the planet’s surface, which can be shown by the climate model and compared to actual features on the planet today. Studies can also be made of certain significant locations, such as deep craters which have microclimates – that is, small restricted areas where the climate is different to that of the surrounding area. In these locations we can study in detail the relationship between the water cycle and the ice-rich deposits found in and around the crater, and how they have changed over time.
Plain text summary
Is there ice on Mars? Yes. But where is it now, how did it get there and where will it go in the future? The water cycle is a crucial element of the Martian climate and it has a significant effect on the planet’s geology. The water cycle changes as the climate changes. And climate changes on Mars have been considerable, due to extreme variations in the planet’s orbital parameters, such as obliquity (the tilt of the planet’s axis), eccentricity (how much the orbit deviates from a circle) and perihelion (the time of year when the planet is closest to the sun). For example, the obliquity has changed extensively over the millennia, with the planet moving from being nearly upright to being tilted up to 55 degrees or more. Obliquity affects where the sun’s radiation hits the planet’s surface, so the amount of solar heating that different areas of the planet receive changes with obliquity changes. This impacts on where the ice forms, how it behaves and how water vapour that comes from sublimating, or evaporating, ice is transported around the planet. Computer models can simulate the Martian climate and provide insight into the behaviour of the water cycle and the surface ice. These models can show how the water cycle behaves when the planet is experiencing different obliquities. When the planet is nearly upright, the poles get very little solar heating and only small amounts of water vapour sublimate and enter the atmosphere. There is little water vapour to move around the planet and what there is recondenses at the poles, so the ice caps there grow larger over time. Craters today in the high northern latitudes still contain water ice. When the planet is at a moderate obliquity, of about 25 degrees like today, the poles receive more solar heating. So in the northern summer more water vapour sublimates into the atmosphere. It is transported over the equator to the south pole, where some condenses. But most of the water vapour comes back to the north pole, where it recondenses during the winter there. This process builds up icy layers, which can be seen in photographs of the northern polar ice cap. At higher obliquities, when the planet is even more tilted over, the poles receive much more solar heating and most of their ice caps sublimate. The water vapour travels to the equator, which gets much less solar heat than today, meaning ice can condense and form ice caps on the high ground there. Glaciers from these times of higher obliquity can be seen today in the tropics, covered in dust which has helped protect them from the solar heating. So icy features can move from the poles to the equator and back again over the millennia. These changes leave marks on the planet’s surface, where the ice has affected the geology. The output from climate models run at different obliquities can be studied to see where it shows icy features at different times in the planet’s history. And these results can be compared to actual features photographed on the planet today, by orbiters circling around the planet and rovers on the ground. Studies can also be made of certain significant locations, such as deep craters like Lyot crater in the northern hemisphere, which have microclimates – that is, small restricted areas where the climate is different to that of the surrounding area. In these locations we can study the relationship between the water cycle and the ice-rich deposits found in and around the crater, and how they have changed over time.
