The Egg-Shaped Planet: WASP-12b Quiz

Tidal stretching occurs because the planet is located extremely close to its host star, being roughly 44 times closer to its sun than Mercury is to ours. The star's gravity pulls much more strongly on the side of the planet facing the star than on the opposite side. This intense gravitational tug-of-war physically distorts the gas giant, stretching it into an elongated shape known as a prolate spheroid, which resembles a giant cosmic egg.

In our solar system, the Moon is moving away from Earth, but WASP-12b is experiencing the opposite effect. Due to tidal interactions and a loss of orbital energy, the planet’s orbit is actually shrinking. It is spiraling inward toward its host star in a process called orbital decay, which will eventually lead to the planet being completely consumed or shredded by the star's gravity.

WASP-12b has a surprisingly low albedo, meaning it reflects almost no light. It is described as being "darker than fresh asphalt" because it absorbs nearly 94% of the starlight that hits its surface. Rather than reflecting light, the atmosphere traps the energy and converts it into heat, contributing to the planet's extreme temperatures and making it appear nearly pitch black to the human eye.

As the star's gravity pulls material away from the planet, the stolen hydrogen and helium gas does not disappear immediately. Instead, the material falls toward the star and begins to orbit it, creating a swirling accretion disk. This disk of superheated gas acts as a bridge between the planet and the star, slowly siphoning the planet's mass away until the planet eventually vanishes.

The planet's heat is driven by three main factors: its extreme proximity to the star, its low albedo which causes it to absorb almost all radiation, and tidal heating. Tidal heating occurs as the star’s gravity constantly squeezes and stretches the planet, creating internal friction that generates massive amounts of thermal energy from within the planet's core and atmosphere.

While Earth takes 365 days to complete one orbit around the Sun, WASP-12b is so close to its star that it completes a full orbit in just 1.1 Earth days. To stay in orbit at such a close distance without falling in immediately, the planet must travel at incredible speeds, making its "year" shorter than a standard weekend on our home planet.

Scientific observations show that WASP-12b is a carbon-rich world. While most stars and planets have more oxygen than carbon, this planet has a ratio where carbon is more abundant. This suggests that the chemistry of the planet is very different from Earth, potentially allowing for the formation of exotic materials like graphite or even a mantle made primarily of diamond.

Astronomers estimate the planet only has about 3 million years left before it is destroyed. While this sounds like a long time to humans, it is a tiny fraction of the billions of years that stars and planets usually exist. Because the orbit is decaying so rapidly, we are essentially witnessing the final moments of this planet’s life in a cosmic sense.

It is classified as a Hot Jupiter because it shares physical characteristics with our Jupiter, such as being a massive gas giant composed of hydrogen and helium. However, unlike our Jupiter which is cold and distant, this planet orbits so close to its sun that it is seared by heat, giving it the "hot" prefix used by astronomers.

Because the planet is tidally locked, the same side always faces the star. This means the opposite side is in a state of total darkness forever. While heat is moved around the planet by powerful winds, no light from the host star ever reaches the night side, so you would never see a sunrise or any direct light from its sun.

Unlike Earth, which is a terrestrial planet with a solid surface, WASP-12b is a gas giant. This means it is composed almost entirely of hydrogen and helium gas and does not have a solid place to stand. The extreme heat on the planet keeps these elements in a gaseous state, though deep in the interior, the pressure may turn them into liquid.

Although WASP-12b is a very famous exoplanet, it is located about 600 light-years away in the constellation Auriga. The closest known exoplanet to Earth is actually Proxima Centauri b, which is only about 4.2 light-years away. WASP-12b is much further into deep space, making it a target for large space telescopes rather than direct exploration.

On Earth, hydrogen usually exists as molecules made of two atoms (H2). However, the temperature on the day-side of WASP-12b is so high that these molecules are ripped apart into individual atoms. This atomic hydrogen creates a unique atmospheric chemistry that is very different from the gas giants in our own solar system, which are much cooler and keep their molecules intact.

The star's gravitational pull is the primary force at work. Because the planet is so close, the star’s gravity is stronger than the planet’s own gravity at its outer edges. This allows the star to physically pull the gas away from the planet's atmosphere. The star is essentially "eating" the planet's outer layers, a process that happens continuously as the planet orbits.

The Hubble Space Telescope was the key instrument used to determine that WASP-12b is pitch black. By using a technique called spectroscopy to measure how much light the planet reflected back into space, astronomers were surprised to find that it absorbed nearly all visible light. This discovery changed our understanding of how Hot Jupiters interact with stellar radiation.

WASP-12b is a "laboratory" for extreme physics. It allows astronomers to observe orbital decay in real-time, see how tidal forces can reshape a whole world, and study carbon-rich chemistry. It is not a place to look for liquid water, as the extreme heat makes water in liquid form impossible; instead, it helps us understand the violent end-stages of planetary systems.

The host star, WASP-12, is actually a bit larger and more massive than our Sun. It is classified as a yellow-white dwarf star. Because it is slightly hotter than the Sun, it emits even more radiation, which contributes to the rapid destruction and extreme temperatures seen on the planet. It is roughly 1.4 times the mass of our own Sun.

The day side of the planet reaches a staggering 4,000°F (2,200°C). This is hot enough to melt steel and most other metals found on Earth. This extreme heat is caused by the planet’s proximity to its sun and its dark color, which ensures that it traps almost every bit of energy that reaches its atmosphere from the star.

Orbital decay is the scientific term for an orbit that is slowly collapsing. As the planet loses energy through tidal friction and gravity, it can no longer maintain its distance from the star. This causes the planet to spiral closer and closer to the star’s surface, a process that will eventually end with the planet falling into the star.

The planet was found using the Transit Method. This involves pointing a telescope at a star and waiting for the star's light to dim slightly. That "dip" in brightness indicates that a planet is passing in front of the star. Because WASP-12b is so large and its orbit is so fast, it was an ideal candidate for discovery using this specific detection technique.