It was tall and conical, but looked like nothing I'd seen in the movies. Not smooth, or shiny. It was lumpy and irregular, with fans and vents and heatsinks exposed and visible. Things which looked like cameras and things which looked like ladders. It looked like the Lunar Lander plus a few hundred years. It wasn't even particularly streamlined. Bits were shiny, bits were matt black. Bits stuck out at odd angles. In short, it looked like a spaceship. Not a spaceship designed with the purpose of looking cool or intimidating or mysterious, but a spaceship designed with the purpose of travelling through space.
And when they climbed out, after only a few minutes, they didn't unfold a ramp of steps and walk down out of brilliant shining light within. There wasn't room for a ramp. They popped open a relatively small hatch and climbed out. Like astronauts.
There were three of them. They were like big caterpillars - short, fat, segmented cylinders about two feet long and one foot in diameter - but with four jointed legs nearly five feet long. They had manipulators on the front, along with a cluster of sensors around what I decided to call the head. They weren't used to such high gravity, and wore robotic exoskeletons which they didn't take off for the whole time they were here. Perhaps they had some sense of modesty as well.
The first one that had come out made its way to the kitchen door where I was watching, and waved its manipulator at me in a friendly manner. It emitted a strange series of shrieks and shrills, occasionally slipping into the ultrasonic. Before it had finished, a speaker on the front of its exosuit began talking to me in plain English. "Hi," it said. "We come in peace and all that jazz."
"Uh. Uh, that's... good..." I reply. There's an awkward pause. "Cup of coffee?"
"I'm afraid we'll have to politely decline on that score," said the alien. "In all probability it's completely incompatible with our metabolism, besides which our suits don't have suitable orifices. But thanks for the offer. Look, we're not staying long, we just wanted to ask you a few questions. Does your species have a religion or religions?"
"Um, sure. Lots. All different kinds. Including atheism."
"Any of them monotheistic?"
"I can name three. Listen, what are you so interested in our religions for, are you intergalactic Jehovah's Witnesses or something? Are you about to enslave us and force us to adopt your beliefs instead?"
There was a pause. "My translator doesn't seem to understand the phrase 'Jehovah's Witnesses'. But please be assured we do not intend to impose any kind of doctrine on you or your people. As a matter of fact there aren't actually any formal plans for our species to contact yours yet, but my colleagues and I felt that this matter was more important than maintaining our distance and observing you.
"Do any of your monotheistic religions refer to God begetting some sort of offspring on your planet?"
"Yeah. Christianity. Maybe others. Not sure."
"And what happened to the offspring?"
"I thought you'd be more interested in our language, the way we reproduce, stuff like that..."
"Yes, we are, but for reasons that will become apparent, this is far more important. What happened to the offspring of God after he/she/it came to your planet? Do you have holy writings of some kind which record what he did?"
"The Bible. He was called Jesus. He wandered around, preaching and doing miracles, then he died, was resurrected after three days, was taken into heaven along with - quote - the sins of anyone who believes in him. So it goes, at least."
"And when did this happen?"
"Two thousand years ago, almost exactly."
This seemed to get a reaction from the other two creatures. The one to the left of the one who had spoken to me began to chitter. "Two thousand! Incredible!" And the one to the right said "Do you think it will really happen?"
"What is this about?" I asked them.
The creatures stopped talking. They suddenly seemed to become incredibly solemn. I don't know why I got that impression. They were aliens. Solemnity doesn't cross species like that. Or does it? Maybe keeping quiet and paying attention means the same thing on every planet.
"The exact same thing happened on our world," said their leader. "Our God, whose name is untranslatable, sent a child, whose name is also untranslatable. The child became an adult, and began doing things that nobody could explain, except as miracles. And then he died for our sins, and rose again, and disappeared. This is how it is recorded."
"This is true? You have the exact same religion?"
"Yes. It is particularly well-documented in our case. The man you call Jesus came. And it happens on other planets too. God created the whole universe, after all. He cares for all of us."
It feels like I haven't taken a breath in about a minute. "Oh my God," I gasp.
"Just thought you might like to know," said the leader as they returned to their ship. "It's been a great comfort to us, and we hope it will be to you too. We'll be back in a few years to do all this properly. In the meantime, stay cool, yeah?"
On the flip side is the possibility that the aliens would turn out not to have any religion at all; or a dozen of them, none of them resembling Earth religions. That, if it happened, could be catastrophic for organized religion worldwide.
Christianity was chosen pseudo-randomly; any religion would've made the point.