Webb Telescope Reveals Why Inflated Exoplanet WASP-107 b is So Puffy

May 20, 2024 - Deep in the cosmos, roughly 200 light-years from Earth, lies a planetary oddity – WASP-107 b. This "warm Neptune" exoplanet boasts a size comparable to Jupiter, yet holds a density akin to a marshmallow. For years, this enigmatic world has puzzled astronomers, its inflated nature defying conventional theories of planetary formation. However, the arrival of the James Webb Space Telescope (Webb) has ushered in a new era of exoplanet exploration, and WASP-107 b is now revealing its secrets.

A Giant Enigma: Unveiling the Mystery of WASP-107 b

Imagine a celestial body with a radius exceeding three-quarters that of Jupiter, yet harboring a mass less than one-tenth of our giant gas giant. This is the peculiar reality of WASP-107 b. Classified as a "warm Neptune," it falls within a category of exoplanets possessing a mass similar to Neptune but boasting a significantly larger size. This immense discrepancy in size and density is what makes WASP-107 b so intriguing. Standard models of planetary formation suggest a planet of this size should hold a much greater mass, primarily composed of hydrogen and helium gas surrounding a relatively small, rocky core.

Prior to Webb's observations, astronomers believed WASP-107 b adhered to this traditional model. The prevailing theory depicted a scenario where the planet possessed a minuscule, rocky core shrouded in a vast atmosphere brimming with hydrogen and helium. However, this model struggled to explain how such a diminutive core could retain such a substantial amount of gas. The question of WASP-107 b's inflated state remained a perplexing mystery.

Webb's Keen Eye: Unmasking the Truth Within

The James Webb Space Telescope, heralded as the most powerful space telescope ever built, boasts unparalleled capabilities for studying exoplanets. Armed with these revolutionary instruments, researchers embarked on a mission to unravel the enigma of WASP-107 b. Webb's exquisite sensitivity allowed them to conduct a meticulous analysis of the exoplanet's atmosphere, revealing a crucial piece of the puzzle.

The analysis yielded a surprising result: an unexpected dearth of methane (CH4) within WASP-107 b's atmosphere. This observation held immense significance. Methane, a molecule commonly found in gas giants, is known to be relatively stable at cooler temperatures. However, its stability diminishes significantly in scorching environments. The scarcity of methane in WASP-107 b's atmosphere hinted at a far hotter interior than previously anticipated.

The Culprit Revealed: Tidal Heating and a Redefined Core

The newfound knowledge about WASP-107 b's internal temperature prompted researchers to re-evaluate the planet's structure. Here, another crucial factor emerged – the exoplanet's peculiar orbit. Unlike planets with near-circular orbits, WASP-107 b follows a slightly elliptical path around its host star. This eccentricity plays a vital role in shaping the planet's internal dynamics.

The varying distance between WASP-107 b and its star throughout its 5.7-day orbit triggers a phenomenon known as tidal heating. As the planet traverses its elliptical path, the gravitational pull exerted by the star fluctuates. During its closest approach, the star's gravitational influence stretches the planet, generating significant internal friction. This friction translates into heat, effectively warming WASP-107 b's core to much higher temperatures than previously assumed.

The revelation of tidal heating as the source of WASP-107 b's internal heat provided a missing piece of the puzzle. With the newfound knowledge about the planet's scorching interior, researchers could re-examine its structure based on the observed lack of methane. The data pointed towards a significantly larger and more massive core than originally estimated. This substantial core, coupled with the inflated atmosphere, explained WASP-107 b's overall puffy appearance.

A Paradigm Shift: Redefining Puffy Exoplanets

The groundbreaking observations of WASP-107 b by Webb hold immense significance for our understanding of exoplanets, particularly those categorized as "puffy." Traditionally, astronomers have attributed the inflated nature of these exoplanets to unorthodox formation processes. However, WASP-107 b presents a compelling alternative. It suggests that these puffy worlds could, in fact, be "hot Neptunes" harboring substantial cores, their inflated state a consequence of tidal heating.

This discovery opens a new chapter in exoplanetary science. It underscores the crucial role of tidal heating in shaping the internal dynamics of exoplanets, particularly those with non-circular orbits.

Source - NASA