In the outer Solar System, beyond Neptune’s orbit, lie little-understood objects submerged in extreme cold. Among these is (612533) 2002 XV93, a trans-Neptunian object belonging to the “plutino” family – celestial bodies that orbit Neptune in resonance, much like Pluto. For years, it was considered just another small icy object populating the distant reaches of the Solar System. However, this distant world is now capturing astronomers’ attention with a remarkable discovery: it possesses an atmosphere.
This finding comes from a study published in Nature Astronomy, led by Ko Arimatsu of the National Astronomical Observatory of Japan. Japanese astronomers and astrophysicists utilized a stellar occultation event on January 10, 2024, when 2002 XV93 passed in front of a distant star, obscuring it for about ten seconds. Typically, during such events, the star’s light should disappear and reappear abruptly. In this instance, however, the brightness faded gradually, as if in a dissolve. This is a signature characteristic of an atmosphere’s presence.
The discovery is particularly significant because 2002 XV93 measures only about 500 km in diameter, which is too small, according to current models, to retain gases around it for extended periods. The observed atmosphere is extremely tenuous, but its mere existence challenges our understanding of the evolution of small icy worlds in the outer Solar System.
Astronomers are now working to understand the origin of this gaseous envelope and its potential longevity.
An Atmosphere Where It Shouldn’t Be
Trans-Neptunian objects are ancient, icy bodies orbiting beyond Neptune. Some, like Pluto, have a thin atmosphere generated by the sublimation of surface ices. However, Pluto is much larger than 2002 XV93 (2377 km in diameter) and possesses sufficient gravity to retain at least some of the gases released from its surface. This is why the new discovery has surprised astronomers.
Observations made by the Japanese team indicate that 2002 XV93’s atmosphere has a surface pressure between 100 and 200 nanobars. These are minuscule values compared to Earth’s atmosphere and even lower than Pluto’s tenuous atmosphere (10 microbars), but they are sufficient to alter how starlight disappears during an occultation. It is precisely this slight “softening” in the light curve that has revealed the presence of gases around the object.
The challenge is that such a small body should rapidly lose any atmosphere. Researchers estimate that this atmosphere might survive for less than a thousand years, an extremely short period in astronomical terms. This implies that the gas must have been recently produced or replenished.
Subsequent observations using the James Webb Space Telescope have not found clear evidence of volatile surface ices, such as nitrogen or methane, that could easily sublimate. This makes the atmosphere’s origin even more mysterious and suggests that unexpected processes might be at play.
Collisions, Internal Activity, and New Mysteries in the Outer Solar System
To explain the presence of the atmosphere, astronomers are considering several hypotheses. One possibility is that the interior of 2002 XV93 still contains volatile materials trapped beneath its icy crust. A recent event, such as a fracture or localized heating, could have released these gases to the surface, temporarily forming an atmosphere.
Another hypothesis is related to a cometary impact. Collisions between small bodies are not impossible in the outer Solar System, and a relatively recent impact could have vaporized icy material, releasing gas into the surrounding space. In this scenario, the observed atmosphere would be a temporary phenomenon destined to slowly dissipate over the coming centuries.
This discovery opens new questions about the nature of trans-Neptunian objects. Until now, it was believed that only larger bodies could maintain atmospheres, but 2002 XV93 demonstrates that unknown processes capable of creating gaseous envelopes around very small worlds may exist.
For astronomers, this observation also represents an important confirmation of the value of stellar occultations, a technique capable of revealing details invisible even to the most powerful telescopes. Every stellar passage can become a unique opportunity to study distant worlds. And in the case of 2002 XV93, it has allowed the discovery of an atmosphere that no one expected to find.
English Translation and Paraphrasing:
Original Italian Snippets:
- “Nel Sistema Solare esterno esistono oggetti ancora poco conosciuti, nascosti oltre l’orbita di Nettuno e immersi in un freddo estremo.”
- “Per anni è stato considerato uno dei tanti piccoli oggetti ghiacciati che popolano le regioni più lontane del Sistema Solare. Oggi però questo mondo distante sta attirando l’attenzione degli astronomi per una scoperta sorprendente: possiede un’atmosfera.”
- “È la firma tipica della presenza di un’atmosfera.”
- “troppo poco, secondo i modelli attuali, per trattenere gas attorno a sé“
- “Gli astronomi ora cercano di capire da dove provenga questo involucro gassoso e quanto possa durare.”
- “un corpo così piccolo dovrebbe perdere rapidamente qualunque atmosfera.”
- “possa sopravvivere per meno di mille anni“
- “un impatto cometario.”
- “processi ancora sconosciuti capaci di creare involucri gassosi anche attorno a mondi molto piccoli.”
Paraphrased and Translated English Snippets:
- “In the outer Solar System, little-known objects exist beyond Neptune’s orbit, shrouded in extreme cold.”
- “For years, it was regarded as just one of many small icy bodies inhabiting the far reaches of the Solar System. Today, however, this distant world is drawing astronomers’ attention with a surprising discovery: it possesses an atmosphere.”
- “This is the hallmark of an atmosphere’s presence.”
- “too small, according to current models, to retain gases around itself“
- “Astronomers are now endeavoring to comprehend the source of this gaseous envelope and its potential duration.”
- “such a small body should rapidly shed any atmosphere.”
- “could persist for less than a thousand years“
- “a cometary impact.”
- “unknown processes capable of forming gaseous envelopes even around very small worlds.”
