A team of Japanese astronomers has discovered a thin atmosphere surrounding the trans-Neptunian object (612533) 2002 XV93, which has an approximate diameter of 500 km. This celestial body is too small and cold to retain a substantial atmosphere.
Artist’s conception of trans-Neptunian object 2002 XV93. Image by: National Astronomical Observatory of Japan
“The cold regions of the outer solar system host thousands of small bodies known as trans-Neptunian objects (TNOs) because they orbit outside Neptune.” according to Dr. Ko Arimatsu from Ishigakijima Observatory.
“While Pluto, the most well-known TNO, has been observed with a thin atmosphere, studies of other TNOs generally yield negative results.”
“Most TNOs are extremely cold and possess weak surface gravity, making it unlikely for them to maintain an atmosphere.”
Astronomers utilized stellar occultation to study trans-Neptunian object 2002 XV93, measuring its light fluctuations as background stars passed behind it.
“With a diameter of around 500 km, 2002 XV93 is significantly smaller than Pluto, which has a diameter of 2,377 km,” they noted.
“On January 10, 2024, 2002 XV93’s orbit caused it to briefly obscure a background star.”
“As the star gradually dimmed while being obscured by 2002 XV93, it indicated the possibility of light attenuation due to the thin atmosphere, or a sudden disappearance as it moved behind the solid surface of the TNO.”
The researchers concluded that the observed behavior best supports the existence of a thin atmosphere around 2002 XV93.
They estimate that this atmosphere could vanish in approximately 1,000 years unless it is replenished in some manner.
This suggests that the atmosphere must have formed or been replenished relatively recently.
“Observations with the NASA/ESA/CSA James Webb Space Telescope reveal no indications of frozen gas that could sublimate to create an atmosphere on 2002 XV93,” the authors stated.
“One hypothesis is that deep internal processes brought frozen or liquid gas to the surface of the TNO.”
“Alternatively, a comet may have collided with 2002 XV93, releasing gas and forming a temporary atmosphere.”
“Further investigations are essential to clarify these possibilities.”
“This finding sheds light on the potential for even smaller TNOs to temporarily harbor atmospheres, challenging conventional volatile retention models,” the researchers concluded.
“Our results imply that some distant icy bodies could be sustained by ongoing cryovolcanism or exhibit atmospheres formed by recent impacts from small icy objects.”
The team’s research paper was published in the journal Nature Astronomy.
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Kazuya Arimatsu et al.. Discovery of the atmosphere surrounding a trans-Neptunian object beyond Pluto. Nat Astron, published online on May 4, 2026. doi: 10.1038/s41550-026-02846-1
Pluto's surface is dominated by Sputnik Planitia, a giant pear-shaped basin. Although it appears to be of impact origin, modeling has not yet accounted for its unique shape. Planetary scientists at the University of Bern have proposed an impact mechanism that would both recreate the topography of the basin and explain the alignment around the Pluto-Charon axis. According to their research, Sputnik Planum was created by a collision between Pluto and a planet about 700 km (435 miles) in diameter.
This mosaic of Pluto was created from the New Horizons LORRI image taken on July 14, 2015 from a distance of 49,700 miles (80,000 km). This view is projected from 1,118 miles (1,800 km) above Pluto's equator, from northeast over the dark, cratered Cthulhu region to a bright, smooth, icy plain called Sputnik Planum. I am. Pluto's north pole is off the left side of the image. This mosaic was created using panchromatic imagery from the New Horizons LORRI camera, with color overlaid from New Horizons' built-in Ralph color mapper. Image credit: SA Stern other.
In 2015, NASA's New Horizons spacecraft revealed that Pluto's surface is geologically complex.
The region is dominated by a 1,200 x 2,000 km (746 x 1,243 mi) nitrogen ice-filled basin called Sputnik Planitia.
Sputnik Planitia is located in the western part of Pluto's Tombow region, a famous heart-shaped structure.
This basin is 3 to 4 km (1.9 to 2.5 miles) lower in elevation than most of the dwarf planet's surface.
“Sputnik Planitia's bright appearance is due to the fact that it is filled with mainly white nitrogen ice, which moves and convects to constantly smooth the surface,” said Dr. Harry Ballantyne, a planetary scientist at the University of Bern. Ta.
“Due to the low altitude, this nitrogen likely accumulated quickly after the impact.”
“The eastern part of the 'heart' is also covered with a similar but much thinner layer of nitrogen ice, the origin of which is not yet clear to scientists, but is probably related to Sputnik Planum.”
“The elongated shape of Sputnik Planitia strongly suggests that the impact was an oblique impact rather than a direct head-on impact,” said Dr. Martin Jutzi, a planetary scientist at the University of Bern.
This high-resolution image of Pluto was taken by New Horizons on July 14. Pluto's surface boasts an astonishing range of subtle colors, highlighted in this view by a rainbow of pale blues, yellows, oranges, and deep reds. Many landforms have unique colors that tell complex geological and climatological stories that scientists are only beginning to decipher. Image credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute.
The authors used smoothed particle hydrodynamics (SPH) simulation software to digitally recreate such collisions while varying both the composition of Pluto and its impactors, as well as the speed and angle of the impactors. did.
These simulations confirmed our suspicions about the oblique angle of the impact and determined the configuration of the impactor.
“Pluto's core is so cold that the rocks remain very hard and do not melt despite the heat of the impact, and the angle and low speed of the impact prevents the impactor's core from sinking into Pluto's core, leaving it intact. “It's like a splatter,” Dr. Ballantyne said.
Dr. Eric Asfaug, a planetary scientist at the University of Arizona, added: “Somewhere beneath Sputnik are the remains of the core of another giant object that Pluto was not able to fully digest.”
“The strength and relatively low velocity of this core were the keys to the success of these simulations. At low strengths, the highly symmetrical remnants look nothing like the teardrop shape observed on New Horizons. surface features are obtained.
“We're used to thinking of planetary collisions as incredibly violent events, and we can ignore the details except for things like energy, momentum, and density.”
“But in distant solar systems the velocities are very slow and the solid ice is strong, so the calculations need to be more accurate. That's where the fun begins.”
The research team's findings also shed new light on Pluto's internal structure.
“In fact, a giant impact like the one simulated is much more likely to have occurred very early in Pluto's history,” the researchers said.
“But this poses a problem: giant depressions like Sputnik Planitia are expected by the laws of physics to move slowly towards the dwarf planet's poles over time because of the lack of mass. ” But paradoxically, it is close to the equator. ”
“A previous theoretical explanation was that Pluto, like several other planetary bodies in the outer solar system, has an ocean of liquid water underground.”
“Previous explanations suggest that Pluto's icy crust thins in the Sputnik Planum region, where the oceans swell and liquid water is denser than ice, creating a mass surplus that triggers a shift toward the equator. It will be.”
“But new research offers a different perspective.”
“In our simulations, all of Pluto's primordial mantle is excavated by the collisions, and as the impactor's nuclear material splatters into Pluto's core, it creates a localized overmass that causes the absence of a subsurface ocean. Or, at best, it could be explained as moving toward the equator without the ocean being present, “very thin,'' Dr. Yutzi said.
“This novel and original origin of Pluto's heart-shaped feature may lead to a deeper understanding of Pluto's origins,” said Dr. Adeen Denton, a planetary scientist at the University of Arizona.
of result It was published in the magazine natural astronomy.
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HA Ballantine other. Sputnik Planum as an impact debris showing an ancient rocky mascon on oceanless Pluto. Nat Astron, published online on April 15, 2024. doi: 10.1038/s41550-024-02248-1
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