Pluto Atmosphere

My understanding is that the atmosphere only exists when the planet's orbit nears the sun. When at aphelion, the extreme cold has caused the atmosphere to freeze and collapse back to the surface.

It might depend on the core temperature of the planet. If it's core were radioactive and gravity was sufficient, in the absence of excessive solar wind, then the atmosphere could be higher than expected. But then, who would want to go near it?

"nears" is a highly subjective word in this case

That's true, but Pluto's orbit, being highly elliptical, experiences vast changes in its distance from the sun, it can vary by around 9 earth orbit radii, and in the 248 year orbit time, the atmosphere has plenty of opportunity to freeze and thaw.

Scientists believe that Pluto does have both wind and clouds, and that its atmosphere is partially lost when thawed due to low gravity.

It's hard to say how big an atmosphere is. There is no well defined top, it just gets thinner and thinner.

It's colder than hell out there, so the atmosphere doesn't boil off within several billion years.

Ok I'm calling it the same size as a planet on this technicality.

Can we all go back to calling it a planet now.

When Pluto is closer to the Sun in its orbit, the warmth from the Sun heats up the frozen ices of nitrogen, methane and carbon monoxide on Pluto's surface. These ices vaporize and form a temporary atmosphere. When Pluto moves farther from the Sun, the atmosphere freezes and falls back onto Pluto's surface.