A recently identified exoplanet has claimed the distinction of being the most peculiar celestial body ever detected within our Milky Way galaxy.
Designated PSR J2322-2650b, its characteristics are utterly astonishing. This gas giant, akin to Jupiter, orbits a millisecond pulsar, its form grotesquely distorted into a lemon-like shape due to the immense gravitational pull of its stellar companion. The atmosphere comprises carbon vapor and potentially a helium-rich interior, with the entire atmospheric shell rotating at an astonishing velocity, in the contrary direction to the planet’s axial spin.
“This discovery was entirely unexpected,” stated astronomer Peter Gao from the Carnegie Earth and Planets Laboratory. “I recall that after we received the data, our collective utterance was, ‘What on Earth is this?'”
Undeniably, the cosmos possesses a profound capacity for generating extraordinary worlds, encompassing phenomena from atmospheres resembling cotton candy to clouds composed of metallic elements, precipitation of corundum, and hyper-dense ‘bullet’ exoplanets.
While these celestial bodies frequently push the boundaries of perceived possibility, the attributes and behaviors of the majority can be elucidated. PSR J2322-2650b eludes straightforward interpretation; its characteristics do not align with any established evolutionary trajectory for planetary formation.
“It is exceedingly difficult to conceptualize how such an exceptionally carbon-enriched composition is achieved,” observed astronomer Michael Zhang of the University of Chicago. “It appears to invalidate all recognized formation mechanisms.”
Let us dissect this phenomenon, commencing with the stellar entity, PSR J2322-2650 (identical to the exoplanet but without the trailing “b”), situated approximately 2,055 light-years distant. This is a degenerate star classified as a millisecond pulsar – a neutron star endowed with additional characteristics.
A solitary neutron star is already an extreme entity, originating from the hyper-dense collapsed core of a massive star that underwent a supernova demise. These remnants can possess a mass up to 2.3 times that of our Sun, compressed into a sphere merely 20 kilometers (12 miles) in diameter.
Neutron stars achieve the status of millisecond pulsars when they attain rotational speeds measured in milliseconds – a mere 3.46 milliseconds for PSR J2322-2650 – concurrently emitting potent beams of radio and gamma radiation from their poles at precise intervals.
This phenomenon was instrumental in the initial detection of PSR J2322-2650b in 2017. Astronomers noted a slight deviation from the expected temporal precision in the radio pulses emitted by the host star. Upon meticulous examination of the timings, the perturbation was attributed to an undetected planetary-mass companion, possessing roughly 80 percent of Jupiter’s mass, traversing its orbit around the pulsar in a mere 7.8 hours.
This constituted the extent of our comprehension until the James Webb Space Telescope (JWST) conducted a more in-depth investigation of the system. As the space observatory captures celestial imagery in infrared wavelengths, while simultaneously being unaffected by the blazing radio and gamma rays emanating from the star, it offers an unobstructed vista of the exoplanet, presenting an exceptional observational opportunity.
“This system is singular in that we can observe the planet illuminated by its host star, yet remain entirely blind to the host star itself,” explained astronomer Maya Beleznay from Stanford University. “Consequently, we obtain a remarkably pure spectrum, allowing for a more detailed study of this system than is typically possible with conventional exoplanets.”
This facilitated a comprehensive series of observations pertaining to the world’s atmospheric conditions, encompassing wind velocity and direction, temperature profiles, and its chemical composition.
Planetary scientists, drawing upon prior studies of exoplanetary atmospheres and fundamental chemical principles, possess a general understanding of what an exoplanet’s atmosphere should conventionally resemble. It was plausible that PSR J2322-2650b, as the inaugural pulsar world whose atmosphere has undergone analysis, might exhibit certain anomalies; however, the revelations provided by the JWST observations far exceeded any expectations.
Firstly, due to the exoplanet’s extreme proximity to its star, its atmosphere is subjected to gravitational forces that elongate it into an ovoid shape, reminiscent of a football. This atmosphere is assailed by gamma radiation, elevating its temperature to approximately 1,900 Kelvin (1,630 degrees Celsius, or 2,960 degrees Fahrenheit) – significantly exceeding the 1,300 Kelvin it would attain if solely heated by stellar light.
Furthermore, the atmosphere circulates around the exoplanet in a westward trajectory, directly opposing the planet’s eastward rotation, which is synchronized with its orbital path around the pulsar.
The planetary composition represents the pinnacle of its peculiarity, characterized by vast quantities of carbon that may crystallize into diamond precipitation at reduced altitudes.
“This represents an entirely novel category of planetary atmosphere, unprecedented in prior observations,” affirmed Zhang. “Rather than detecting the standard molecular constituents we anticipate on an exoplanet – such as water, methane, and carbon dioxide – we identified elemental carbon in molecular form, specifically C3 and C2.”
Certain explanatory insights may be derived from contemplating the query: How does a planet endure the core-collapse supernova event that engendered the neutron star? Actually, a highly plausible answer exists for this. It does not, at least in the case of PSR J2322-2650b.
Based on its observed properties, Zhang and his colleagues posit that the exoplanet may not have originated as a planet at all – but rather commenced its existence as a helium star.
Pulsars recognized as “black widows” are observed within binary systems alongside other stars, which they gradually consume, akin to a black widow spider devouring its mate. This erosive process can account for the ‘exoplanet’s’ helium-rich interior and even the presence of carbon within its atmosphere.
Nevertheless, certain enigmas persist.
“As the companion cools, the internal mixture of carbon and oxygen begins to crystallize,” commented astrophysicist Roger Romani of Stanford University and the Kavli Institute for Particle Astrophysics and Cosmology. “Pure carbon crystals ascend to the upper layers and become intermingled with the helium, which is what we observe. However, a subsequent process must occur to sequester the oxygen and nitrogen. This is the locus of considerable debate.”
Given that the companion star no longer possesses sufficient mass to sustain nuclear fusion within its core, it can no longer be classified as a star, or even a brown dwarf – which introduces yet another piece of evidence that blurs the distinctions between planets and stars.
Anticipated future observations may contribute to resolving the profound strangeness of a system heretofore unparalleled in our cosmic observations.
“It is gratifying to acknowledge that not everything is understood,” concluded Romani. “I eagerly anticipate acquiring further knowledge regarding the peculiar nature of this atmosphere. It is immensely rewarding to have such a compelling puzzle to investigate.”
