Proof that aliens might have visited earth

Once, a few years ago, I was lying in my backyard star-gazing. At some point in time I noticed a speck of light moving across the sky. If it hadn't been moving, it would have looked like a star millions of light years away, yet this speck was moving across the sky, and it was moving fast.

It seemed far too high for an airplane, and I thought maybe it was a satellite, the space station, even the space shuttle. Yet, none of those explanations made sense. Then, I figured it was probably some kind of advanced military technology that could not only fly very high - perhaps even into suborbital space - but could move extremely fast.

For the first few seconds, the speck followed a steady trajectory, then I suddenly lost it. After a second or two, I saw what appeared to be the same speck, yet it had covered a huge amount of space, instantly, then slowed back to a steady trajectory. This even happened a few times, and then it was gone.

Does this prove that aliens exist? 

Not by a long shot, but there have been numerous events throughout recent history that scientists have not yet been able to explain away. Yet, almost always, these astrophysicists and cosmologists will scoff at the suggestion of UFOs and aliens.

The science, they say, doesn't prove it.

Yet, recently, scientists have heard a new sound coming from space, and they have NO idea what it is.

The science, I say, proves that scientists are far from knowing everything, and open-minded should be a bigger part of their methodology.

Still, does that prove aliens are real?

No. And, one can only imagine that if UFOs and aliens are real, that their technology and science are far more advanced than our science on Earth.

Rate the possibility of aliens having visited earth. Are scientists overly and falsely pessimistic?