💎 A unique diamond-made exoplanet?
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Named PSR J2322-2650b, this exoplanet presents an atmospheric composition dominated by carbon and helium, a unique combination never observed before. Its clouds resemble carbon soot, and under intense internal pressures, the carbon could transform into diamonds. With a mass similar to Jupiter's, its proximity to its host star, a neutron star, profoundly influences its structure.
This artist's illustration shows what the exoplanet PSR J2322-2650b (left) might look like orbiting a rapidly spinning neutron star, called a pulsar (right). The gravitational forces of the much more massive pulsar stretch this Jupiter-mass planet into a lemon shape.
Credit: NASA, ESA, CSA, Ralf Crawford (STScI)
The star around which this planet orbits is a pulsar, an ultra-dense stellar remnant that emits intense radiation at regular intervals. Its mass equals that of the Sun, but it is condensed into a volume the size of a city. This particular configuration allows scientists to study the planet without being hindered by the star's brightness, providing high-quality spectroscopic data. Consequently, researchers indicate that this situation makes the analysis more precise than for typical exoplanets.
Due to its very tight orbit, at just 1 million miles (1.6 million km), the planet completes one revolution in less than eight hours. Models indicate that the tidal forces exerted by the pulsar deform the planet, giving it an elongated appearance. This situation is reminiscent of 'black widow' systems, where a pulsar gradually consumes its companion. Nevertheless, in the present case, the object is officially classified as an exoplanet by the International Astronomical Union.
The formation of such an object remains enigmatic. Indeed, the usual mechanisms of planetary formation do not seem applicable, given the carbon-rich composition. Researchers suggest the hypothesis of carbon crystallizing into diamonds in the internal layers, but the dominant presence of carbon in the atmosphere challenges current theories. This study, accepted for publication in The Astrophysical Journal Letters, highlights the uniqueness of this discovery.
The James Webb Space Telescope played a major role in this advance. Its ability to observe in the infrared and its position far from Earth allow it to capture very faint signals without thermal interference. This observation thus opens the way to studying other extreme systems and could help better understand the diversity of planets in the galaxy. Subsequently, scientists eagerly anticipate new data to clarify this unique case.
Atypical Exoplanetary Atmospheres
Exoplanetary atmospheres show great diversity, but that of PSR J2322-2650b stands out due to its dominance of carbon and helium. Usually, planetary atmospheres contain elements like hydrogen, oxygen, or nitrogen, reflecting their formation from clouds of gas and dust rich in these compounds.
In this case, the abundance of carbon suggests a different origin, perhaps linked to nuclear processes or the evaporation of a companion star. Researchers believe the carbon could come from internal crystallization under high pressure, forming diamonds that rise to the surface.
Studying such atmospheres allows testing models of planetary chemistry under extreme conditions. It reveals how planets can survive in proximity to violent stellar objects, broadening our view of planetary diversity.