Alien Planet
Alien Planet starts out with an interstellar spacecraft named Von Braun, leaving Earth's orbit. Traveling at 20% the speed of light (37,000 miles/s), it reaches Darwin IV in 42 years. Upon reaching orbit, it deploys the Darwin Reconnaissance Orbiter, which looks for potential landing sites for the probes. The first probe, Balboa, explodes along with its lifting body transport during entry, because one of its wings failed to unfold. Two backup probes, Leonardo da Vinci (nicknamed Leo) and Isaac Newton (nicknamed Ike), successfully land on the planet, and learn much about its bizarre indigenous lifeforms, including an apparently sapient species.
The robotic probes sent out to research on Darwin IV are called Horus Probes. Each Horus probe consists of an 8-foot (2.4 m) high, 40-foot (12 m) long inflatable, hydrogen-filled balloon, which is covered with solar receptors, a computer 'brain', a 'head' covered with sensors, and several smaller robots that could be sent to places more dangerous for the probes themselves. The probes had a limited degree of artificial intelligence, very similar to the 'processing power' of a 4-year-old. All the real thinking was done by a supercomputer in the orbiting Von Braun. The probes were programmed with different personalities; Ike was more cowardly and skittish, while Leo was the risk-taker. The two probes are also equipped with a holographic message that will be sent to any sentient life found on Darwin.
After the two probes inflate their gas-bags, they encounter a voracious Arrowtongue and watch it pursue a Gyrosprinter. Later that night, the twins find the wreckage of Balboa and are forced to split up, Ike studying the unique plant life and Leo going after big game. Ike's voyage takes him to one of Darwin IV's pocket forests, where he encounters a flock of Trunk Suckers and their predator, the ruthless Daggerwrist. Before his research is finished, a massive hurricane-like storm hits and Ike must take to the sky, launching weather balloons. Leo goes to the mountain ranges and finds a herd of Unths, engaged in rutting-like behavior.
Afterwards, Leo finds a pair of strange Bladderhorns enganging in combat. He tries to communicate with one, but fails and is knocked out by a mysterious creature. Ike ventures to the meadows and gullies of Darwin IV, only to encounter a massive herd of Grovebacks and Littoralopes. It is here that he also encounters a pair of Skewers.
Leo gets destroyed by a mysterious and evasive unknown creature, and Ike, ordered by the Von Braun to search for Leo's attacker, hopes to find a new sentient species. Ike's route takes him across perilous terrain, and across the Amoebic Sea in his quest for Leo. As he embarks on his journey, one of the Grovebacks seen earlier falls victim to a swarm of Beach Quills. Ike then finds a pack of Prongheads hunting a Gyrosprinter, and then crosses the Amoebic Sea (which attempted to attack Ike) and encounters a herd of Sea Striders.
Ike manages to make contact after a harrowing experience with a Skewer, but the newly discovered Eosapien disables Ike after it interpreted Ike's launch of its camera disk as an attack.
