Was the first science fiction book I ever read, back in 72 when I checked it out of the Valencia Park branch of the San Diego Public Library. I was in 2nd grade going to 3rd, and I remember going to the Websters dictionary in the living room to the point where I just snuck it into the bedroom and kept it there for a month. A much different perspective on space travel and life than now in the 2020's. We were still landing on the Moon in manned flights and everything seemed possible to an 8 year old. The protagonist was a young adult in the story, but he seemed more like a teenager. I think he was 16, but I only read the book when I was 8 so I'm doing well to remember that much.The book was written in 55, and it showed in how women were portrayed in the book. They definitely took a back seat to men, but that was the case throughout the 'golden age' of science fiction.
The Earth humans were abandoning Mars, a barely habitable world with its intact but incomprehensible technology left by a 'unknown' race. The protagonist was coming back to Mars to join his father, who was part of a group of observers that were staying on Mars to try to solve some of the mysteries that had cropped up over the years of Earth occupation of Mars. The protagonist finds out that someone broke into the cabin he was travelling to Mar inside and left a handprint with only fingers on the mirror.
There are a lot of twists to the story, including the moons of Mars not being moons and there not really being 'Martians', but it was entertaining for a preteen who was tired of the Hardy Boys, The Three Investigators, Charlie Brown and The Archie's. I'm 60 now, but I remember seeing that lurid book cover on the hardback and just having to open it. Over 50 years , but I smile at the memories