I think that a Protoform is their Cybertronian form but transformed into the comet that used for long distance travel Because Cybertronian for is just that. But when it needs to travel, it becomes a protoform. Just my theory.
For shape changers, protoform usually means the original form when they are not copying an object. To travel in space, it seems that the robots have to transform into comet form thereby losing their scanned form. After reaching earth, they need to scan for new forms.
It's a base form upon which the different modes are built. The liquid metal flows into the designs needed to adopt the trans-scanned form. They also apparently have the ability to extract metals from the ground and other sources to replenish their on-board supplies.
Due to the multiple continuities of TF fiction, it is hard to pinpoint just what a Protoform is. Most continuities label it almost like a "baby", a TF that has no Spark or memory codes yet and also has yet to adopt an alt-mode. In the live-action movie story however, TFs can choose to revert BACK to the Protoform body yet retain their memories and sparks. This Protoform body is what Transforms into the comets for re-entry into another atmosphere. This mode, however, is not what they use all the time on Cybertron, they have a seperate mode for getting around, doing tasks, and fighting.
So we have a general idea on what these protoforms are. How do they propel themselves out of each planets gravity if they are not able to fly? I mean we see how starscream did it but what about the bots who dont have this ability? Do they launch from a ship? If every transformer has the ability to travel from planet to planet why would they not be able to fly on each planet? To many questions but I have always been confused on the whole "flying" thing. I know, were talking about fictional alien robots, but still curious.
