First day of spring - on Mars

[LongTomH]

Phil Plait is reminding readers of his great Bad Astronomy blog that today, September 14, is the vernal equinox for Mars southern hemisphere: Happy first day of spring...Mars:

If you want to be technical, it’s the time when the axis of Martian rotation is perpendicular to the direction of the Sun, and the northern hemisphere is headed into summer (making it the autumnal equinox for the southern hemisphere). When this happens here on Earth, it’s called the first day of spring (here in the US at least, in other countries it’s considered the middle of the season — a tradition with which I agree).

Mars, like Earth, is tilted with respect to its orbit around the Sun; Earth is canted at an angle of roughly 23°, while Mars is at 25°. That’s why we (and Mars) have seasons! Over the course of the year, the angle of sunlight hitting the surface of the planet changes, heating it more efficiently in the summer and less in the winter. Boom! Seasons.

On Earth, that’s most dramatically seen as polar ice shrinks and grows over the year. Same with Mars! The picture above is from the European Space Agency’s Mars Express orbiter, and shows the northern polar cap in May 2010, during the last summer. The north pole of Mars is icy, but it’s actually two kinds of ice: water, and frozen carbon dioxide. CO2 turns directly from a solid into a gas (a process called sublimation), and does so at much lower temperature than water ice melts. This means the CO2 goes away first as temperatures rise in the northern hemisphere, leaving the water ice behind. In that picture, the ice is essentially all water.

In other words: the north pole of Mars is sublime*.

Where does the CO2 go? Into the atmosphere! So much of it adds to the air there that the atmospheric pressure on the planet increases measurably, by about 30%. That much extra carbon dioxide adds a small but significant greenhouse effect to the planet as well, warming the surface. Estimates vary, but I’ve seen quotes of a few degrees Celsius for the effect.

More at Phil's blog, at the Planetary Society and ESA sites.

[mehamgul101]

1. nice share

wow its very nice sharing thanks for it 

[byronius]

2. So damned beautiful.

Kim Stanley Robinson, who wrote the Red Mars trilogy, lives in my home town. His description of the passion the Reds feel for their planet is quite moving. I am certain he is describing a near-future, possibly The Future.

I want to go. Privation and danger, meh. I want to go.

First man to die on Mars is an honor.

[LongTomH]

3. If only I thought there was a chance of that happening during my lifetime!

Sadly, I just don't see it!:cry:

[Odin2005]

4. I have all three books, great trilogy.