Peer-reviewed research citation proving this speculation or please just stop insisting that aliens exist.
I don't need peer-review because I have physical evidence.
"It has been my sad observation that by mid-career there are very few professionals left truly working for the advancement of science, as opposed to the advancement of self. And given enough people with strong enough interests, professional peer pressure takes over from there. Peer pressure in science, as elsewhere in society, consists of alternately attacking and ignoring the people who advocate a contrary idea, and discrediting their motives and/or competence, in order to achieve conformity." -- Tom Van Flandern, astronomer, 1993
Peer-review this:
"The case in point is the origin of the human race. By either Von Daniken's approach or by Sitchin's, Occam's Razor argues that the single hypothesis of earlier alien contact with extraterrestrials to explain the wonders of the ancient world and the remarkable agreement among ancient texts in speaking of visitation by "the gods" should be prefered to the multitude of separate and ad hoc explanations others have offered. If mainstream science were not so preoccupied with avoiding extraordinary hypotheses, it would surely be agreed by most parties that the evidence, severely lacking though it is, mildly favors the extraterrestrial visitation hypothesis over most others. However, it cannot be argued that the evidence is anything approaching compelling, especially since it is all indirect (i.e., no definite extraterrestrial artifacts have been found). And since the hypothesis is certainly extraordinary, science prefers to reject it until and unless some extraordinary proof comes along. But what if the hypothesis were true, but most of the evidence has been destroyed?" -- Tom Van Flandern, astronomer, 1993
"... in a universe in which life is also possible at many levels in an infinite range of scale too, life elsewhere becomes a certainty. It is therefore of interest to speculate about why we are not in obvious communication with extraterrestrials, rather than about whether or not such beings exist." -- Tom Van Flandern, astronomer, 1993
"To me the most exciting speculation is the idea that extraterrestrials have indeed visited this planet in the past, which is what deductive logic would dictate." -- Tom Van Flandern, astronomer, 1995