That's a meaty question that brings out emotional responses from anyone you ask.
For decades, researchers have claimed that strange objects have been seen on or above the moon -- things that shouldn't be there. From mysterious pyramid shapes to unusual moving lights to tall towerlike objects to geometrically oriented buildings and huge glasslike dome structures, stories and pictures abound claiming that Earth's next-door neighbor is loaded with extraterrestrial artifacts.
Hoagland, a former NASA consultant and curator of astronomy and space science at the Springfield Science Museum in Springfield, Mass., was also a consultant to CBS News during the Apollo moon missions. He has spent decades looking into what he asserts is the truth about the numerous unmanned spacecraft missions as well as the manned Apollo voyages to the moon 40 years ago.
"The orbital photographs show us the scale of ancient ruins on the moon. And surface photography by the astronauts have shown remarkable, specific examples of anomalies that could only be explained through there being ancient remnants of some extraordinarily advanced technology," he says.
In his book, "Dark Mission: The Secret History of NASA" (Feral House), co-written with Mike Bara, Hoagland alleges there are huge glass towers and domes on the moon that have produced repeated prismatic or rainbow effects on Apollo astronaut photographs available on NASA websites. He also claims numerous geometric ground features are evidence of ancient structures.
One section of the report says: "While face-to-face meetings with it [extraterrestrial intelligence] will not occur within the next 20 years (unless its technology is more advanced than ours, qualifying it to visit Earth), artifacts left at some point in time by these life forms might possibly be discovered through our space activities on the moon, Mars or Venus."
Hoagland believes that NASA did indeed uncover evidence on the moon of an extraterrestrial civilization, but decided the public wasn't ready to accept such information.
But what about the astronauts who went to the moon? Wouldn't they have spoken up if they had encountered any evidence of an ET presence there? Cover-up theorists would say the astronauts were either ordered not to talk about this subject or they somehow, conveniently, forgot critical things about their trips to the moon.
Capt. (USN, Ret.) Edgar Mitchell, the sixth man to walk on the moon, was the Apollo 14 lunar module pilot in 1971.
According to Hoagland's computer analysis of an image of Mitchell standing on the lunar surface, an ancient glass dome can be seen in the background. Did Mitchell spot this?
"It's just nonsense! But this isn't to say that aliens haven't used the moon or Mars. I'm not saying that. I'm saying that what Hoagland is pointing out doesn't make any sense," Mitchell says.
He also says he knows of no cover-up by astronauts. He isn't convinced by images Hoagland points to as evidence of an alien presence.
"Most of what I have seen is either so fuzzy, out of focus or nebulous that it would stretch the imagination to be what it's claimed to be. I haven't seen anything that really definitively fits as a structure on the moon. I haven't seen any credible evidence for it."
But while Mitchell himself hasn't seen evidence of an alien presence on the moon, he's open to the possibility.
"There could very well be alien utilization of the moon. Those guys have to be in space out there somewhere. They may keep themselves concealed behind the moon."
Mitchell, author of "The Way of the Explorer" (New Page Books), has doubts about claims of alien artifacts on the moon, but he definitely believes ETs are close by.
"Well, for me, it's just a matter of the evidence, and the evidence, as far as I'm concerned, is overwhelming. Not only are they here, they've been here for quite a long time, and the more I've investigated, the more I realize it's been much longer than any of us really thought," he says.
Mitchell grew up near Roswell, N.M., home of the legendary Roswell UFO crash, where, in 1947, an alien spaceship allegedly crashed, killing its otherworldly crew. Mitchell believes the Roswell alien crash was "a real event and it was strongly covered up by the military."
The former astronaut, member of the U.S. military and founder of the Institute of Noetic Sciences thinks the amount of evidence going back many decades points to more than one group of ETs involved.
"It's the preponderance of evidence that counts here. There seems to be far more than one species of visitors here, from all the evidence that I know, and several of them are investigating our people in their own way.
"Their motivations are somewhat different, depending upon what species we're talking about. Some seem to be here to help us and to be saying, 'Hey, you're about to destroy yourselves and your civilization with your way of doing things,' and what others are doing -- maybe they're just looking at us."
The recent news of vast quantities of water -- and other compounds, including mercury, silver and gold -- on the moon raised many more interesting questions about our rocky satellite in space. But Peter H. Schultz, one of the scientists on the team analyzing lunar water data, doesn't think the aliens-on-the-moon theory holds water.
"In the past, we've seen impact flashes, and we may have had eruptions on the moon, but everything we've seen so far indicates that this is a very quiet place, except for a few punctuated events," the Brown University geological sciences professor told AOL News.
"Look, I've seen all the photographs from the moon, and that's just untrue stuff. And it's too bad because you'll have students who hear this on the news and believe that this is real."
Schultz isn't rejecting the notion that there could be some form of life out there somewhere.
"When you do research, exploration and discovery, it's easy to be wrong. This is why we do this. If we knew everything, we might as well stay in our houses. The fact is, we go out to explore to find out -- you've got to find the evidence for it. Within the realm of possibilities, within the galaxy, sure that's possible. But next door? I think this gets hard to fathom."