Seasons

Mars has an axial tilt of 25.2°. This means that there are seasons on Mars, just as on Earth. The eccentricity of Mars' orbit is 0.1, much greater than the Earth's present orbital eccentricity of about 0.02. The large eccentricity causes the insolation on Mars to vary as the planet passes round the Sun (the Martian year lasts 687 days, roughly 2 Earth years). As on Earth, Mars' obliquity dominates the seasons but, because of the large eccentricity, winters in the southern hemisphere are long and cold while those in the North are short and warm.

The seasons present unequal lengths are as follows:

Season	Sols (on Mars)	Days (on Earth)
Northern Spring, Southern Autumn:	193.30	92.764
Northern Summer, Southern Winter:	178.64	93.647
Northern Autumn, Southern Spring:	142.70	89.836
Northern Winter, Southern Summer:	153.95	88.997

Precession in the alignment of the obliquity and eccentricity lead to global warming and cooling ('great' summers and winters) with a period of 170,000 years.^[49]

Like Earth, the obliquity of Mars undergoes periodic changes which can lead to long-lasting changes in climate. Once again, the effect is more pronounced on Mars because it lacks the stabilizing influence of a large moon. As a result the obliquity can alter by as much as 45°. Jacques Laskar, of France's National Centre for Scientific Research, argues that the effects of these periodic climate changes can be seen in the layered nature of the ice cap on the planets north pole.^[50] Current research suggests that Mars is in a warm interglacial period which has lasted more than 100,000 years.^[51]

Because the Mars Global Surveyor was able to observe Mars for 4 Mars years, it was found that Martian weather was similar from year to year. Any differences were directly related to changes in the solar energy that reached Mars. Scientists were even able to accurately predict dust storms that would occur during the landing of Beagle 2. Regional dust storms were discovered to be closely related to where dust was available.