three coexisting space planets

Orbiting a orange-yellow main sequence star are three large terrestrial planets. They are all in the habitable zone, and they are all home to carbon-based, protein-water life forms.

The innermost planet is Hocampe. It has 1.8 gees of surface gravity, plenty of water, and a thick atmosphere at 13 Earth atmospheres. It is home to the Hoxins, more commonly known as the Birdmen. It is gradually warming up as the Hoxins pollute their atmosphere and introduce dangerous levels of greenhouse gasses. There is a potential for a runaway greenhouse effect within only a couple hundred Hoyears. Hocampe can be seen from space as a white/purple marble, the purple coming from red/purple photosynthetic pigments in the planet life. The planet is largely swampland, with occasional rain forests. The powerful winds (13 times more powerful than Earth winds) are awful for tall buildings, so most structures are underground or short and strong.

The next planet is Irph. It has 0.92 gees of surface gravity, a decent amount of water, and a middle-of-the-road atmosphere of 1.3 atmospheres. It is home to the Humans, more commonly known as the Apemen. While the climate is generally stable, there is an inkling of climate change which could cause a rise in sea levels and melting ice caps. The planet is essentially Earth in every imaginable way, except for the continental arrangement. In fact, that's the whole point of this particular planet.

The final planet is Rydra. Rydra is a small planet with only 0.53 gees of surface gravity, and sparse water. It is largely a desert planet, and it is loosing surface water due to a dwindling atmosphere at 0.23 atmospheres and a gradually colder climate, depositing more and more water ice into the ice caps. It is inhabited by the Rebers, more commonly known as the Wolfmen.

The first planet to create the radio technology was Hocampe. For thirty Hoyears they happily used the radio technology for themselves. Just around the same time they had realized it would be a fun idea to put on serialized radio stories to listen to, radio telescope operators on the northeastern continent heard a strangely ordered signal coming from Irph. At first it was just faint beeping at a constant pitch, but after about a year some more, faint radio transmissions were decoded into the audio of an ape's babbling.

No one on Hocampe really knew what to do. It seemed to be obvious that the far-fetched hypothesis that the planet Irph could harbor life wasn't so far-fetched after all. After much discussion and squawking by world leaders, it was decided that Hocampe send a message to the radio transmissions of Irph. The message would consist of a list of the first hundred prime numbers in Base 2, followed by a spoken repetition of the apelike babbling, and a sample of normal Hoxinian spoken speech.

On Irph, the inventor of the radio was freaking out about this "discovery". This would mean fame, fortune, women, all the good stuff.

Rydra, meanwhile, was too busy fighting over remaining farmland and water reserves to pay attention to this radio-based conversation.