Astronomers Detect 'Pluto-Like' Trans-Neptunian Object With Thin Atmosphere

Hyderabad: Astronomers have detected an extremely thin atmosphere around the Trans-Neptunian object or TNO (612533) 2002 XV93. According to the National Astronomical Observatory of Japan (NAOJ)’s report, the discovery will deepen human understanding of small solar system bodies. The study was led by Ko Arimatsu, a lecturer from NAOJ. TNO 2002 XV63’s discovery is significant, as it is the first time researchers have found a TNO, apart from Pluto, with an atmosphere, as they usually do not have one.

What are TNOs, and why don’t they have an atmosphere?

TNOs are small, distant icy objects that orbit the Sun beyond Neptune, the most distant planet in our Solar System. Weak Gravity and extreme cold are the primary two reasons why TNOs do not have an atmosphere. Compared to planets in our solar system, TNOs are relatively small and composed of low-density materials like ice and rock. Gravity works directly proportionally to an object’s mass, meaning if an object has less mass, then it will have a weaker gravitational pull.

The other reason for TNOs not having an atmosphere is their extreme cold temperature. They can have an extremely low surface temperature of below minus 220-degrees Celsius.

What is TNO 2002 XV93, and how was it found?

NAOJ’s report mentions that the TNO 2002 XV93 is a small object, roughly one-fifth the diameter of Pluto. It also highlights that the critical observation took place on January 10, 2024 (UTC), when 2002 XV93 passed directly in front of a background star in what is known as a stellar occultation. The findings were subsequently published in the journal Nature Astronomy.

The observations were carried out from multiple sites across Japan. Gradual changes in starlight were recorded at two key locations — Nagano Prefecture and Fukushima Prefecture — providing the data necessary to confirm atmospheric refraction around the object.

Rather than using direct imaging, the team measured the brightness of a background star as 2002 XV93 passed in front of it. If no atmosphere had been present, the starlight would have disappeared and reappeared sharply. Instead, the brightness faded and returned gradually over approximately 1.5 seconds at both observation points — a pattern consistent with an atmosphere bending, or refracting, incoming light. Analysis of these brightness curves confirmed the presence of a thin but measurable atmosphere.

Given 2002 XV93's weak surface gravity, scientists estimate the atmosphere would dissipate within approximately 1,000 years without a replenishing source. Its origin is believed to lie either in continuous gas release from within the body or in the aftermath of a recent collision with another object.