Fuel-air mixtures are pretty badass, and we've seen the Mythbusters do it with wood chips, sawdust, and coffee creamer. Flour is certainly plausible. The difficulty is in rapidly mixing the fuel and the air. The Mythbusters used a very large blast of high pressure air. Modern fuel-air bombs use a series of two explosive charges - one to disperse the fuel, and a second one to detonate it.How powerful is an explosive based on flour mixed with air? In my WIP, a beseiged castle uses flour barrels as an improvised defense. The intended result is the destruction of incoming seige equipment and the first couple of lines of the enemy army. The more traditional route of oil vats + fire isn't really an option in this scenario.
This is true for the signalling part.You can have Neutrinos or Radio as beacon. Ordinary Radioactivity won't work.
andabout half an hour. On average, Jupiter is 5.2 AU from the sun and Earth is 1 AU from the sun, So its about 4 AU from Earth to Jupiter on the average. Light crosses 1 AU in about 8 minutes - so maybe 32 minutes.
Right now, about 35-40 minutes, give or take. But that changes every second, because Jupiter is now moving away from Earth.