H.G. Wells’ Martians certainly screwed up on that.
They probably evolved from the same DNA precursor that we did. A meteor hit whatever planet in this system life first evolved on and splashed the soup on all the local celestial bodies. The Jovian swimmers probably have the same ACGT building blocks that we do as well.
I’d hope first contact would be peaceful.
My favorite such story is “Custom Fitting”, by James White. First contact is made in London, with the insterstellar ambassador being presented to the court of St. James. But first he needs clothes, so a tailor is secretly contacted to make formal wear for a being that rather resembles a centaur out of Terran mythology.
They would have to be accreddited to have diplo plates, can you imagine them in the DMV.
There is no such thing as an unarmed spaceship. Whatever they’re using to get into space, if you point it in the wrong direction, will make a quite effective weapon. And if they can make gentle landings with their ship, then they can make not-so-gentle landings with big rocks.
The aliens might or might not choose to use their spaceship as a weapon. We have no clue as to xenopsychology, and hence can’t even begin to answer that question. But the technology, yes, they absolutely certainly have that.
The aliens wipe out all our technology, which they gave us in the first place. Lacking our devices, we are all totally helpless and become their slaves.
Alternately; “Bah! These bloodless petaQs—and intruder barges in and lands on their boss’ lawn, and they don’t even take a token potshot at it? What a bunch of service, plant-eating serfs.”
Trump opens fire, without negotiations.
We are conquered.
Trump says he wanted to be conquered, & declares it a YYYUUUUGE victory.
If they come it’s either to give an ultimatum like Klaatu did or they want our resources so they need to persuade Washington to guarantee control of the people. This they will do easily by promising them tech and to stay in power. Then, when the idiots in charge are no longer needed, they will be discarded. You know how easy it is for an adult to manipulate the mind of a child, that’s how they will manage us. They are ahead of us in every way, and using psychology instead of blasters is how an advanced life form is going to take over. Just like politicians, they will have the people drooling over what they say they can do for them. Those who believe them will get milked first, for their glandular secretions.