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You sure know how to be defensive in a discussion.

I sure know how to discuss things, if that's what you mean.

Those "erosional features" could not have arisen from the occasional rain. Some are deeper then the grand canyon.

Again, a straw man argument.

Sure, there are no roots to hold soil together, but any comet-vapor-rain event would not occur every other day now, would it? We have been watching mars for a short while now and i haven't heard of it.

Mars is covered with craters, and those were caused by impacts.

Water erosional features have been seen on Mars. I'm a little surprised that you'd oppose that concept, since you think snow used to fall on Mars, and snow is made of water.

Mars' mass and density are such that its atmosphere is today about what it has been for a very very long time (not a mere 50,000 years, but millions of them), and liquid water can't exist on Mars because of the low atmospheric pressure.

Any purported snowfall on Mars would itself have to result from the impact scenario -- the vapor would lose energy some time after and distance from the impact, refreeze, and precipitate.

The seasonal growth and shrinkage of the polar icecaps would be due to the arrival of solar radiation or lack thereof. But it doesn't mean Mars can be terraformed.

Water erosional features have been seen on Mars. I'm a little surprised that you'd oppose that concept, since you think snow used to fall on Mars, and snow is made of water. When did i oppose that concept? I only disagree on the origin of the flowing water.

Mars' mass and density are such that its atmosphere is today about what it has been for a very very long time (not a mere 50,000 years, but millions of them), and liquid water can't exist on Mars because of the low atmospheric pressure.

Apparently it can exist after a comet impact. Why does the vapor not just float to space?

Any purported snowfall on Mars would itself have to result from the impact scenario -- the vapor would lose energy some time after and distance from the impact, refreeze, and precipitate. Some snow does not carve out ravines deeper then the grand canyon. Nor does the occasional rainfall resulting from the occasional meteor impact.

The seasonal growth and shrinkage of the polar icecaps would be due to the arrival of solar radiation or lack thereof. But it doesn't mean Mars can be terraformed. It still resembles earth more then any other planet in our solarsystem. It is supposedly too small to hold an atmosphere, but astronomy changes it's theories to fast to convince me yet, that Mars always was a dead world. Im not talking about jungles, just an active climate system.

Climate on Mars
Mars is a cold, forbidding planet. Although Mars is not much further from the Sun than Earth is, Mars has only a thin atmosphere, so the solar energy that reaches Mars' surface is reflected back into space without warming the surface. Earth, by contrast, has a layer of greenhouse gases in its atmosphere which absorbs the radiation reflected by Earth and reradiates some of it back to warm the surface.

Evidence from the surface of Mars collected from the Mars and Viking orbiters indicates that Mars was once warm enough to have liquid water on its surface. There is evidence on the Martian surface of ravines and other signs of erosion by water; scientists do not know how long liquid water was present, but they believe that surface water existed on Mars around 4 billion years ago. If water existed on the surface of Mars, then at some in the past Mars must have had an atmosphere warm and dense enough to sustain water in its liquid state. If Mars had enough water for a long enough period of time to cause visible erosion on its surface, then Mars had atmospheric temperatures and pressures similar to those found on Earth.

The prevailing theory is the carbon dioxide in Mars' atmosphere dissolved into its surface water and was ultimately deposited on Mars' surface as solid carbonate rock. This same process occurs on Earth. The carbon stored in Earth's crust is eventually recycled back to the surface over many millions of years when it is emitted through volcanic eruptions. However, unlike Earth, Mars' hot, molten interior cooled and its volcanic activity ceased. Carbon was removed from the atmosphere by Mars' water, but planetary carbon was no longer recycled back to the atmosphere. Mars' greenhouse mechanism weakened and the water on its surface froze or escaped into space.

Mars Weather and Climate Today
The difference in climate between Mars and Earth can help us understand the processes that shape Earth's weather and climate. Mars experiences drastic changes in temperature and violent weather phenomena such as planet-wide sandstorms. Scientists attribute this weather volatility to the lack of water on the planet. Earth's oceans absorb and store vast quantities of heat energy; the oceans remove heat from the atmosphere and, in effect, ration it back out slowly and redistribute it around the globe. Earth's atmosphere also moderates temperatures because its greenhouse gases absorb and reradiate heat back to the planet's surface. Both of these natural processes moderate temperature fluctuations. On Mars, however, with no water or atmosphere to store solar heat, the Sun's energy is absorbed only briefly by the dry, cold surface. Dry land both heats up and cools down much more quickly than water does. Therefore, the surface temperatures on Mars vary drastically from day to night.

Another feature of Mars' climate that affects it on seasonal time scales is that the tilt of its axis can be much greater than Earth's (23.5°), which results in much larger weather contrasts between its northern and southern hemispheres and within each hemisphere from season to season. At present, Mars' axial tilt of 25.2° is almost the same as Earth's, but this angle does not remain constant. Earth's axial tilt undergoes small changes (from 21.5° to 24.5°), but Mars' axial tilt changes significantly, ranging from 15° to 35° over 100,000 years. The difference stems from the fact that Earth has a moon whose gravitational pull stabilizes its orbit. Mars has two small moons with negligible gravity; without greater gravitational pull from its moons to stabilize it, Mars' orbit sways wildly in space. During periods in which Mars' axis is significantly tilted, seasonal changes in incoming sunlight for each hemisphere are drastic.

Mars' elliptical orbit also means that Mars is much closer to the sun at some times of the year and much farther away at others. This means that while Mars has seasons similar to those on Earth, they are about twice as long.

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