Mars has gotten our attention from the ancient days, when it was Ares, the God of War, to the latest probes by rovers and orbiting spacecraft. While nowhere near Earth's size, it's the only planet in the solar system that might harbor life similar to Earth life. Therein lies the fascination.
We know the planet has no canals (remember, the search for"canals" on Mars arose from a misinterpretation of the word "canali," applied by Italian astronomer Giovanni Schiaparelli in 1877 to straight lines that, well, don't exist either). The human eye and the telescopes of the 1800s had limitations, one of which was a tendency to make separated features look like they were making a straight line.
Ever since the Mars Reconnaissance Orbiter spotted slopes and "beds" that looked like they were made by flowing water, we've been looking for more evidence. These formations might have contributed to the "canali" appearance, but one Mars scientist, American William Hartmann, had already suggested another explanation: the apparent lines, or segments of them, were plumes of dust blowing off peaks in Martian windstorms. Because of Mars' thin atmosphere, the plumes were highly visible and the dust blew a long ways. That made sense, and some such plumes have been spotted by the Hubble and other instruments, but they don't really explain what what we're seeing right now.
Amateur astronomers in 2012 were the first to spot two plumes, streaming out hundreds of kilometers long and wide and rising 250 km high. They may be dust or ice, but either way they shouldn't rise so high in the thin atmosphere and low gravity of Mars before becoming so spread out they are invisible.
I'm not going to try to offer a solution here: it's way out of my depth. But the point to be made is that this is our closest, most studied, and most Earthlike planetary neighbor, and we still don't thoroughly understand it. We don't know for sure whether it had flowing water, although most planetary scientists think it did in the distant past. We don't know whether there are still occasional surface water flows. We don't know if it's sterile, if it used to harbor life, or if it harbors life now.
The only way to solve all the mysteries of Mars is to go there. NASA these days talks a good game, and their Orion capsule and Space Launch System may be useful pieces of a Mars expedition, but we're not really doing significant work on long-term habitats for humans or on landers that could carry astronauts. In other words, they're dreaming about a landing in the next two decades, unless they want to start or at least plan real work on the missing pieces.
Still, someone, someday, will go. I volunteer.