Why Do Comets Have Tails?

A comet's tail can stretch for millions of kilometers, even though its solid nucleus is only a few kilometers across. We explain how sunlight and the solar wind peel gas and dust off an icy body, why there are usually two tails, why those tails point away from the Sun rather than "behind" the comet, and what missions such as Giotto and Rosetta saw up close.This episode includes AI-generated content.

Earth's Moon is unusually large for a rocky planet, and the leading explanation is a giant impact about 4.5 billion years ago. We explain the Theia hypothesis, what Apollo samples revealed about the Moon's composition, why older ideas such as capture or fission fall short, and which details scientists are still debating.This episode includes AI-generated content.

Uranus is tilted by about 98 degrees, so it spins on its side and has seasons that can last two decades. We explain what that tilt does to its rings, moons, and weather, why a giant impact early in the solar system is the leading explanation, and what Voyager 2's 1986 flyby revealed about this still little-visited ice giant.This episode includes AI-generated content.

The asteroid belt between Mars and Jupiter is not the crowded rock field movies suggest. We explain what is actually in it, why its total mass is so small, how Ceres and Vesta fit the story, and why Jupiter's gravity likely kept those leftovers from becoming a planet. We also cover the Kirkwood gaps and what missions such as Dawn have shown.This episode includes AI-generated content.

Mars is called the Red Planet because iron oxide dust stains its surface, but the more surprising story is water. We explain why Mars looks red, what its thin carbon dioxide atmosphere is like today, and the evidence from orbiters and rovers that rivers and lakes once existed there — including Curiosity's ancient lake in Gale Crater and Perseverance's work at Jezero. We also cover polar and underground ice, why liquid water is unstable on the surface now, and why no life has been confirmed.This episode includes AI-generated content.

Jupiter's Great Red Spot is a storm bigger than Earth that astronomers have watched for well over a century. We explain what it is, how big it is, why it is red, how long it has lasted, why it has been shrinking, and what spacecraft like Juno have learned about how deep it goes.This episode includes AI-generated content.

Saturn's rings are one of the most stunning sights in the solar system, but where did they come from, and will they last? We look at what the rings are made of, how thin they are, how Galileo first saw them, what the Cassini mission revealed, the debate over whether the rings are young or ancient, and why every giant planet has rings but only Saturn's shine so brightly.This episode includes AI-generated content.

Mercury is closer to the Sun, but Venus is the hottest planet, at about 465°C (870°F) everywhere on its surface. We explain how its thick carbon dioxide atmosphere causes a runaway greenhouse effect, why Earth's "twin" turned out so differently, and some of its strangest features: it spins backward, and its day is longer than its year. We also cover the Venera landers and the missions planned next.This episode includes AI-generated content.

For 76 years, Pluto was the ninth planet. We trace its 1930 discovery, the Kuiper Belt, the discovery of Eris, and the 2006 vote that made Pluto a dwarf planet, along with the debate that still continues. Then we follow New Horizons' 2015 flyby, which showed a far more surprising world than anyone expected.This episode includes AI-generated content.

It's a Small Solar System - Allan Howard.This episode includes AI-generated content.