Hori, the New Horizons space probe, wakes up on his way to Pluto. As he checks in with mission control, the Dawn space probe, entering orbit around the dwarf planet Ceres, greets him by telling the story of Rip Van Winkle. Rose, the European Space Agency's Rosetta probe, joins the conversation as Hori learns things have changed during his nine-year-long sleep.
Dawn informs Hori he is on his way to a dwarf planet, as is she. Rose identifies her destination as the comet Churyumov-Gerasimenko. Dawn provides a quick survey of the terrestrial planets: Mercury, Venus, Earth, and Mars. She says she is just beyond Mars in the asteroid belt, then continues with a survey of the Jovian planets: Jupiter, Saturn, Uranus, and Neptune.
Hori protests that Dawn has forgotten his destination, Pluto, but she reminds him Pluto is a dwarf planet. As Hori complains that his destination is only a dwarf planet, Dawn informs him her destination, Ceres, is also a dwarf planet. Hori argues that Ceres is an asteroid, which leads to a discussion of the discovery of asteroids in the first days of the Nineteenth Century.
Dawn goes on to describe her earlier encounter with the asteroid Vesta, revealing its mountains, craters, and snowman.
Rose notes that asteroids are rocky, but comets like her destination are made of frozen gases. She explains the parts of comets and describes findings from Stardust, which collected specks of comet dust and returned them to Earth for analysis, and the Deep Impact mission that blasted a crater in the surface of comet Temple1.
When Hori asks what Rose has seen at her comet, she shows images of Churyumov-Gerasimenko becoming active as it nears the sun. When Hori asks about her discoveries, Rose discusses the theory that Earth's water came from comets and how her observations suggest the theory is incorrect.
The program ends as Dawn tells Hori that he is about to become the first probe to return information about the small worlds at the edge of the solar system.