JWST Finds CO₂ in HR 8799 System

The star HR 8799 is a young, energetic star, only about 30 to 42 million years old, which is a fraction of our sun's 4.6 billion years. It is roughly 1.4 times the mass of the Sun and about 5 times as luminous. This youthfulness means the planets are still hot from their formation, emitting enough infrared light to be directly imaged, a rarity among the thousands of exoplanets discovered. First discovered in 2008 using the Keck and Gemini telescopes in Hawaii, the HR 8799 system was the first multi-planet system to be directly imaged. Initially, three planets were identified, with a fourth, innermost planet discovered in 2010. Interestingly, after the initial discovery, researchers found that the Hubble Space Telescope had already captured images of the planets in 1998, but they were only revealed after new image-processing techniques were applied. The four gas giants are significantly more massive than our own, ranging from about 7 to 10 times the mass of Jupiter. Their orbits are also much wider than those in our solar system; the innermost planet, HR 8799e, orbits at a distance comparable to Saturn's, while the outermost, HR 8799b, is about twice as far as Neptune from the Sun. Consequently, their orbital periods are incredibly long, ranging from about 45 to 460 Earth years. The detection of carbon dioxide is significant as it points to the "metal enrichment" of the planets' atmospheres, meaning they contain a good amount of elements heavier than hydrogen and helium. This, along with the presence of hydrogen sulfide, supports the theory that these planets formed through core accretion. This process, which also formed Jupiter, involves the slow buildup of a solid core that then gravitationally attracts a massive gaseous envelope from the surrounding protoplanetary disk. The alternative planet formation theory, gravitational instability, suggests that planets form rapidly from the collapse of dense clumps in a protoplanetary disk. This model is less favored for the HR 8799 system, as the ordered 1:2:4:8 orbital resonance of the planets is a strong indicator of the more gradual and orderly process of core accretion. In addition to the planets, the HR 8799 system hosts two prominent debris disks, similar to our solar system's asteroid and Kuiper belts. One disk of warm dust exists inside the orbit of the innermost planet, while a broader, colder dust belt orbits beyond the outermost planet. This architecture further strengthens the comparison to our own solar system's layout, albeit on a much larger scale.