Harvard researchers have calculated that unusual speedup and movement of Oumuamua indicate that it could be solar sail. It might weigh only 100 to 300 kilograms instead of a solid comet-like material. If it was comet material it would weigh one million to ten million tons. If it is a solar sail it would be evidence of a civilization of technologically capable aliens that sent out a solar sail probe millions of years ago. We have only just had a few smaller solar sail probes.