Triceratops

The chances of anything coming from Mars are a million to one.

DCG2U

I'd say hysterical. And like TJadams said, it would shake (if not, destroy organized religion). I would be very curious but also cautious. The reation of individuals over intelligent alien species will vary to an individual to another. However, I think the governments of Humanity as a whole would tend to be extremely cooperative.

Hostile. Do you really think an interstellar specie that has travelled billions of kilometers just come here by accident to greet us? They are looking ofr something, ressources, slaves?, technologie, a new home. There is a small possibility that they may be friendly but I don't think that would be the case.

Unlikely. If they are, humans will see it as a weekness and will try to exploit their "kindness".

One day or another, when humanity will have grown strong enough, we will backstab them.

They will.

Annahilated. What use will they make out of us? We are a technologically inferior specie (compared to them because they are able to achieve interstellar travel) so they can't salvage anything useful/interesting from our technology.

You mean if organic life looks the same in the universe? Probably not but there will be some features that we will recognize (ex: eye(s), mouth(s), limb(s)).

Mangas Coloradas

I think that if we ever get visitors, it will be trouble for us. The universe functions by a universal set of rules, competition in many forms is one of those rules. If they come here it will be for a good reason, most likely for what we have up to and including this world.
They will have won their battle for existence, and they didn't do this by being nice to the competition. Considering our own behavior in the past and present I don't buy the highly advanced and enlightened theory put forth by Carl Sagan and company. I'll go with L-Ron Hubbard and Battlefield Earth type scenario. I do think a peaceful scenario is entirely possible but if a race had advanced so far as to free themselves from the need to compete why would they even want to come way out here?

I think we should just shut up and hide.

Mangas Coloradas

Maybe it will be these guys, they'll find us fun to run down and tasty to boot.

gregorian

How I would visit another solar system...
I think it would be quite doable. It would be an unmanned vehicle of course. Just too costly and difficult in all sorts of ways to send an actual human.
So you have a small smart module, with some extremely large nuclear explosives behind it. As it is leaving the Solar System, you give it a series of precisely controlled ka-blams, getting it up to some significant percentage of the speed of light... 25% perhaps? At that speed it might take a decade or two to get to the nearest star. Not unreasonable for a robot. And then some breaking explosions to slow it down again. That might freak out any intelligence at the other star. Mysterious nuclear explosions in the sky.

And then that small intelligent robot calculates the best path to pass the most planets, doing all sorts of reading and imaging and beaming it back to Earth. Obviously the robot itself would never physically return.

I think it would be quite practical if you were willing to play a long 20 year game.

SomeGuy

You've never seen "They Live"?

Greatest Scenes In Film: They Live - Sunglasses - YouTube

Greatest Scenes In Film: They Live - Sunglasses - YouTube

Eumenes

I like the Strugatsky brothers take on it from Roadside Picnic. An alien visitation of some sort took place and resulted in devastation and anomalies in six locations across the world. They also left behind various artificats ranging from a wish granting orb, a deathray, and batteries that provide endless power. This leaves humanity asking what was the purposes, with the answers ranging from hostile invasion to an attempt to communicate and help humanity advance.

The foremost expert in the story voices the opinion that most explanations being offered are colored by human vanity. He suggests that the aliens were vaguely aware of humanity (in the same way were are aware of insects) that they had no motive or plan concerning us. He describes the first visitation as such:

Brisieis

If we migrated from Mars there would be evidence of such. For a start, how would we migrate from another planet - on a space ship - with modern technologies, yet have to start from scratch all over again? There is a reason there is no evidence, because the theory is absurd imo.

As for the OP, considering the circle of life, the way humans and animals and even bacteria acts. And also how chaotic and dangerous the universe is in general. I would consider them hostile.

The Cell

Here's another theory, I know it sounds a bit "Scifi" but imagine this for a moment...

Life on Mars is failing due to the planets age and in a desperate effort to Save Man Kind(or should I say Martian Kind) a massive spacecraft is constructed and is launched on a mission to Earth, the closest planet to Mars, with every living creature upon it (literary like Noah's Ark) in the hopes of establishing life there... But, halfway one its journey to earth, something goes wrong and this massive spacecraft ends up crash landing on earth. As the years go by, the Micro-organisms(carried by the Martians from their planet) begin decomposing the remains of everything that was on this spacecraft... The plant life that might of been carried on this craft begins to spread... the Micro-organisms also begin to spread... and we all know the story after that...

Brisieis

Nice theory.

But I cannot agree with it.

I do think that life may have been possible on Mars at some point in the far away past, who knows what we may find in the future?