seasonal changes
A question for the Mars experts out there. Throughout the history of telescopic Mars observations, one feature stands out: Mars appeared to undergo seasonal changes, darkening in the spring and lightening in the winter. When I was a kid, it was not considered ridiculous to assume that this was caused by plant life.
Now that Mars is being observed close up, has anyone nailed the real cause of this effect and documented it? Dust storms covering and uncovering dark features, maybe?