Level 1 — Absolute Beginner
Far past the planet Neptune, there are many small icy worlds. Pluto is the most famous one. People used to think only Pluto had air around it.
Now scientists have found something new. A very small world named 2002 XV93 also has a little air. It is much smaller than Pluto.
The scientists used a telescope in Japan. They watched the small world pass in front of a far star. The star light went down slowly, not all at once. That slow change showed there is air.
The air is very thin. But it should not be there at all. The world is too small. Now scientists must learn why.
- planet
- a large round body that goes around a star
- icy
- made of ice or very cold
- world
- a planet or large object in space
- air
- the gas around a planet that we can breathe on Earth
- telescope
- a tool that makes far things look closer
- star
- a bright, hot ball of gas in the sky
- thin
- not thick or strong
- scientist
- a person who studies the world to learn new things
Level 2 — Elementary
Astronomers have spotted a thin atmosphere around a small world far beyond Neptune. The object is called (612533) 2002 XV93, and it lies in the Kuiper Belt — a region of icy bodies beyond the main planets.
Until now, Pluto was the only trans-Neptunian object known to have an atmosphere. The new find, published in the journal Nature Astronomy, is a real surprise because 2002 XV93 is only about 500 kilometres across, while Pluto is almost five times bigger.
The discovery was made using the Kiso Schmidt telescope in Nagano, Japan. On January 10, 2024, the small world passed in front of a distant star. Instead of the star vanishing in an instant, it dimmed slowly over up to 1.5 seconds.
That gentle fade is the fingerprint of an atmosphere bending starlight as it disappears behind the object. The new atmosphere is calculated to be about five to ten million times thinner than Earth's air, but it should not exist on a body this small. Scientists are now trying to work out where it comes from.
- astronomer
- a scientist who studies stars, planets and space
- atmosphere
- the layer of gases around a planet or moon
- Kuiper Belt
- a region of icy bodies beyond the planet Neptune
- trans-Neptunian object
- a small body that orbits the Sun beyond Neptune
- occultation
- when one object in space passes in front of another
- telescope
- a tool that makes distant objects appear closer
- fingerprint
- a unique pattern that points to a particular cause
- calculate
- to work something out using numbers
Level 3 — Intermediate
An international team of astronomers reports in the journal Nature Astronomy that they have detected a thin atmosphere around a tiny trans-Neptunian object called (612533) 2002 XV93 — only the second such body, after Pluto itself, ever found to possess one.
The detection was made on January 10, 2024, when 2002 XV93 passed in front of a background star. Observers using the Kiso Schmidt telescope in Nagano, Japan, watched the star fade gradually for up to 1.5 seconds rather than blink off abruptly. That gentle gradient in starlight is the classic signature of an atmosphere refracting and absorbing light along the limb of the body.
Cross-checks with several other observatories confirmed the same gradual fade. From the shape of the light curve, the team estimates that the atmosphere is around five to ten million times thinner than Earth's at sea level — vanishingly faint, but unambiguously present.
What makes the result striking is the body's size. Pluto, the only previous trans-Neptunian object with a confirmed atmosphere, is about 2,377 km wide. 2002 XV93 spans just 500 km. Models suggest a body that small should not have enough gravity or heat to hold gases for long, raising new questions about how surface ices can sustain even a wisp of atmosphere far from the Sun.
- trans-Neptunian object
- an icy body that orbits the Sun beyond Neptune
- occultation
- the passage of one celestial body in front of another
- gradient
- a gradual change from one value to another
- refract
- to bend light as it passes from one medium to another
- limb
- the outer edge of a planetary body as seen from far away
- light curve
- a graph showing how an object's brightness changes over time
- vanishingly
- to a degree so small it almost disappears
- wisp
- a small, thin strand or trace of something
Level 4 — Advanced
An international observing campaign led by Japanese astronomers has reported in Nature Astronomy the unexpected detection of a tenuous but unmistakable atmosphere encasing the Kuiper-belt body (612533) 2002 XV93 — only the second trans-Neptunian object after Pluto for which an envelope of gas has ever been confirmed and, by an order of magnitude, the smallest world known to host one.
The signature was teased out from a stellar occultation observed on 10 January 2024, when 2002 XV93 transited in front of an unrelated background star as seen from Earth. Multi-station photometry from the Kiso Schmidt telescope in Nagano, Japan, and several auxiliary sites recorded a starlight extinction profile that decayed gradually over intervals of up to 1.5 seconds rather than dropping with the sharp, near-instantaneous edge expected from a vacuum-bounded body.
That smooth decay is the canonical fingerprint of refraction and absorption by neutral gas along the limb. Modelling of the light curve suggests an atmospheric pressure roughly five to ten million times lower than Earth's surface pressure — exquisitely thin, yet sustained enough to imprint itself coherently across multiple observing stations and statistical re-reductions.
The result is theoretically uncomfortable. With a diameter of only about 500 kilometres, 2002 XV93 is several times smaller than Pluto and lies on the very edge of the size domain in which thermophysical models permit a stable, even ephemeral atmosphere. Possible explanations now under active discussion include episodic sublimation of nitrogen or methane ices, dust-driven outgassing, and exotic seasonal effects tied to the body's orbital geometry, each carrying significant implications for how planetary scientists understand volatile retention in the cold, faint reaches of the outer Solar System.
- tenuous
- very thin or weak
- envelope
- an outer layer that surrounds something
- occultation
- an event in which one celestial body passes in front of another
- photometry
- the precise measurement of how bright objects are
- extinction profile
- a graph of how starlight is dimmed over time during an occultation
- sublimation
- the change of a substance directly from solid to gas
- outgassing
- the release of gases trapped in a solid material
- volatile retention
- the ability of a body to hold on to easily evaporated chemicals
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