Exoarchaeology is a little-known discipline: It can be defined as the archaeology of outer space. Lacking opportunities to conduct digs for artifacts on other planets, those interested in this field have had to rely mostly on the observations of astronomers and the thoughts of conspiracy theorists who think the U.S. government is trying to hide evidence of alien life.
In 1877 Giovanni Virginio Schiaparelli, an Italian astronomer, peered through his small telescope and, soon after, announced to the world that he had seen channels on Mars. "Channels" was erroneously translated into English as "Canals", and it was assumed that Schiaparelli was referring to canals constructed as public works projects by Martians. After this theory came out, Percival Lowell, an amateur astronomist, investigated these "canals" through his telescope and concluded that they were indeed made by aliens. He also claimed to have seen some vegetation, which of course, if true, would indicate life on Mars in general: The canals, if indeed there, would prove there were actual beings on Mars capable of cooperation, civil engineering, and implementing a plan with a specific goal in mind. These qualities, if they could be proven to exist among the alleged Martian beings, would indicate intelligence. Of course, nothing could be proved at all.
By 1976, satellite imagery made it clear (to most)that Mars did not, in fact, have any artificially made canals. NASA made the mistake (or produced a clever PR piece to draw attention to its work) of implying to the general public that there was a region covered with what could be mountains - which they said looked suspiciously like human heads complete with all the requisite facial features.
On his website "Bad Astronomy", astronomer Phil Plait, who researched in the mainstream of the field for ten years, talks about various "pseudo-scientists" like Richard Hoagland. Hoagland is a modern-day astronomer on the very fringes of the field. He has been featured many times on "Coast to Coast A.M.", a radio show which he claims has a fairly decent amount of listeners. Hoagland has basically based his career on the notion that one of the "human heads" on Mars is actually a city, complete with large pyramids, all surrounding an enormous statue of some kind. Plait says that he has been invited on several occasions to debate Hoagland, but that to try to refute such ridiculous theories would be a waste of time, and merely help Hoagland build a larger following and to perhaps profit from the increased attention.
Three scientists; Carl Sagan, I.S. Shklovskii and Hermann Oberth, are said to have studied the theory of ancient alien astronauts, which has captivated the imaginations of various peoples for millennia. Some cultures have stipulated, through the ages, that humans are so intelligent, so different from animals, that they must be descendants of an alien race that visited earth at some point in the distant past. The theory often points to various religions and myths and stipulates that many of the gods worshiped by ancient peoples were actually originally real, live alien visitors. These visitors, it is proposed, passed valuable knowledge to the human race, contributing to various unexplained leaps in development, knowledge and wisdom throughout the ages, and in turn spurring the creation of many great civilizations.
If scientists like Stephen Hawking have their way, people will, over the next 500 years or so, be setting up colonies on the Moon and on Mars. If this happens, the exoarchaeologists will finally have something concrete to study - the artifacts humans will inevitably be leaving behind after several generations of habitation. Like most people who are touted as geniuses and yet seem to teeter on the edge of insanity, Hawking jokes that there is no intelligent life anywhere in space, including earth. But then he seriously adds that the world should devote 0.25% of its Gross Domestic Product to the colonization of outer space. What benefits could people possibly reap from this? The answer is a frightening one, and seems to come straight out of a science fiction novel. As the earth is ravaged by pollution and climate change, and depleted of valuable minerals and other resources, scientists are suggesting that we look to the skies for a new home, where we can continue to mine and pillage the natural resources as much as needed. It's the newest incarnation of imperialism.
Exoarchaeology is a pseudoscience that only exists, even in theory, as a footnote in the study of astronomy and, for the time being, an embarrassing one at that.