The Milky Way is filled with strange planets, far beyond the variety seen in our solar system. NASA has confirmed over 6,000 exoplanets, some of which are truly bizarre, featuring multiple suns, molten iron rain, enormous ring systems, or extreme sizes and temperatures.

Planet oddities extend to their orbits. Mercury's year is only 88 Earth days, with one Mercurian day lasting twice as long as its year. Many exoplanets detected have very short years due to detection methods. The shortest known year belongs to an object orbiting a pulsar, completing an orbit in under 49 minutes. For a main sequence star, the shortest year is 4.31 hours for K2137b, which is slowly being pulled into its star. Conversely, some planetary mass objects have years lasting roughly a million Earth years.

While our solar system has one star, many planetary systems feature multiple stars orbiting each other. These systems are typically hierarchical to maintain stability. Planets can orbit individual stars or orbit multiple stars within the broader system. A hypothetical seven-star system demonstrates how a planet could orbit all seven stars, experiencing multiple 'suns', though their brightness would vary depending on distance and the planet's specific orbit. Initially, astronomers believed multi-star systems were common, but improved technology shows that most star systems, especially those with red dwarfs, contain only one star.

The first exoplanet discovered with more than one sun, Kepler 16b (the 'Tatooine planet'), is a gas giant. Imagine Earth with a second star: a small red dwarf would cause significant temperature increases, unpredictable seasons, and frequent, intense stellar flares. Larger secondary stars, like a blue supergiant, would make Earth uninhabitable due to extreme luminosity, radiation, and destructive stellar winds. If binary stars are far apart, planets can orbit one star and see the other as a bright object in the night sky. However, the lifespan of a supergiant is short, posing a threat of supernova radiation. A close second sun would also severely disrupt Earth's day and night cycles.

Rogue planets are planetary-sized objects not bound to any star. They may have been ejected from planetary systems or failed to accrue enough mass to become a star. Billions to trillions are expected in our galaxy, but they are difficult to detect as they emit no light. Gravitational microlensing is a key detection method, where a foreground rogue planet temporarily magnifies the light of a background star. This method can detect small, distant exoplanets. The upcoming Nancy Grace Roman Space Telescope will significantly improve detection rates, focusing on the galactic centre where stars are more numerous. Early observations have identified 22 rogue planet candidates, with one estimated to be Earth-mass. Rogue planets are incredibly dark and cold, but a hydrogen-rich atmosphere could retain enough internal heat for liquid water. Life would likely be chemosynthetic, relying on the planet's core.

WASP 76b, a massive gas giant orbiting very close to its star, experiences extreme temperatures. Its tidally locked nature means the day side reaches approximately 2,400°C, hot enough to vaporise metals. Strong winds transport vaporised iron to the cooler night side (around 1,500°C), where it condenses and falls as molten iron rain. Spectroscopic analysis of the planet's atmosphere during transit reveals the abundance of iron, confirming this bizarre weather phenomenon.

Kelt 9b orbits exceptionally close to its parent star, Kelt 9, which is nearly twice as hot as our sun. As a result, Kelt 9b's daytime temperature can reach 4,300°C, surpassing that of some red dwarf stars. Its hydrogen atmosphere is actively boiling off and being pulled back into the star. Eventually, Kelt 9b will lose its atmosphere, exposing its core, or be consumed entirely when Kelt 9 expands in 300 million years. The extreme heat on its surface breaks down molecules.

While stars are generally larger than planets, exceptions exist, particularly concerning volume rather than mass. Stars must have a minimum mass (0.08 solar masses) to sustain nuclear fusion; below this, they are brown dwarfs. Neutron stars, despite being 1-2 solar masses, can be only 30km across, making it possible for orbiting planets to be significantly larger in volume. White dwarfs, stellar remnants about the size of Earth, can also host larger planets that survived the star's red giant phase. WD1856b, an exoplanet orbiting a white dwarf, is an incredible example of such a system. Finding a planet larger than a main sequence star is more challenging but may occur around the smallest red dwarfs. VHS1256-1257b is a promising candidate, though its exact radius is uncertain, and it could potentially be a brown dwarf.

Defining the 'biggest' exoplanet is complex. GQ Loopy B, DH Tori B, and Rocs 42BB are contenders for the largest known exoplanets, with GQ Loopy B estimated to be three times the size of Jupiter, though exact physical characteristics remain uncertain due to direct imaging limitations.

J1407b is a visually stunning potential exoplanet known for its massive ring system, dwarfing Saturn's. Discovered through stellar occultation, the rings blocked an astonishing 95% of the star's light, indicating a system 40,000 times larger than Saturn's rings, the size of Venus’s orbit. Although no equivalent dimming events have been observed since the initial detection, leading to theories of it being a free-floating brown dwarf or having much thinner rings, the possibility of J1407b with its immense rings remains captivating.

The universe holds an immense variety of strange exoplanets, pushing the boundaries of our understanding. The channel encourages viewers to share their favourite bizarre exoplanets and supports the creation of more space-related content through Patreon.