Cryptids

[Anomalocaris]

if we look at all our space movies like alien, avatar, startrek, Prometheus, id4, district 9, etc, they all have one thing in common. All their vehicles are whoppers!
Motherships! why? Because if you're going to travel a long way, you need a lot more than a cut sandwich and a can of coke.
You need stasis bays, sick bays, cargo bays, enough supplies to last the return journey, weapons systems, fuel, propulsion systems (voyager's warp core alone is how many stories tall, 7?)
plus a myriad of other logistical issues which need to be taken care of. My point is if anybody is ever going to come here, we most miss them!
99% of the dodgy photos of ufo's are the small garden variety type and therefore unfeasible to make the journey.
Also, out of curiosity, if life was to evolve on another planet, what is the smallest size planet which can exist and still have enough gravity to support an atmosphere?
Assuming life needs an atmosphere ... you know the little 6 inch alien controlling the human looking robot in MIB11?, or 111?, could they evolve that size AND be intelligent with such a small cranial capacity. This is why I also don't believe in the little Roswell ufo myth? It also suffers from the same issues as stated above.

How big a planet needs to be to hold an atmosphere depends on how hot is the surface temperature. For something with fairly warm at about ~300 degrees kelvin, which is similar to earth and where liquid water can exist, it needs to be about mars sized (half the diameter of earth and 10% of earth mass) hold a substantial atmosphere over geological time scale of several billion years.

For something with surface temperature of about 150 degrees kelvin, which is somewhat warmer the saturn's moon Titan, it only needs to be about moon sized (quarter the diameter of earth, 1% of earth mass ) to hold a substantial atmosphere over geological time scale.

For something with surface temperature of about 50 degrees kelvin, a bit warmer than Pluto, it can be one sixth the diameter of earth and 0.1% mass of earth and still retain an atmosphere over geological time scale.

If the life evolved in a subterranean and subaqueous environment, the planet it evolved on needn't have any substantial atmosphere.

Also, if intelligence is based on some kind of neural network where each cell functions as some sort of a binary gate, then it is reasonable to suppose there is a minimum number of neural cells that must be present for a creature to even be theoretically capable of intelligence. Add on top of that a minimum number of other cells to make up the organs to keep the nerve cells alive, allow it to receive input from the environment, and put its thoughts into action, we can probably arrive at some absolute minimum number of cells a plausible creatures must have to have intelligence, to say nothing of evolving intelligence.

We know we humans are not a very efficient bag of biological tricks. We have all sorts of structures and organs that are the present size because of the baggage of its evolutionary history. We can be made much smaller with fewer cells and more streamlined if we were designed from the ground up without baggage of evolutionary history. I don't know how small. But let's say we can be made with 1/10 as many cells as we have and still carry on all of our functions.

But the trick is the size of the biological cell on earth varies greatly. We humans have giant big cells. Our smallest cells are still huge in the scheme of cells on earth. Many bacteria cells are 1% the size of our smallest cells. Biologists have suggested it is biochemically possible for cells 1% the size of any bacteria to be fully functional. This implies the smallest viable cell would be 1 ten thousandth the size the smallest human cell.

Put this together, a creature with 10% as many cells as we have and each cell 1 ten thousandth the size of corresponding human cells, we arrive at a intelligent creature can be 1 one hundred thousandth the mass of a human.

Such a creature would weigh between 0.5-1 gram. It would weigh about as much as 15 drops of water, somewhat more than a bee.

There probably can't be any intelligent microbes, at least not if it's intelligence is based on similar neuralogical principle as ours. But it seems to me it is quite possible for intelligent creatures the size of a mouse or cat to develop.