Could Eris have a permanent atmosphere? In Wikipedia they write that Eris has an atmosphere when around perihelion (close to the Sun) which collapses when Eris moves away from the Sun. So it behaves similar to a comet's tail. However, they thought the same of Pluto's atmosphere, and the information on Wikipedia is from prior to the New Horizons Pluto flyby which proved that Pluto has a permanent atmosphere.

Could they be wrong on Eris too or does Eris really go far enough from the Sun so that its atmosphere collapses? It is possible that they are right with Eris for its aphelion is about twice as far as Pluto's, but are we sure about its atmosphere?
As far as I'm aware, there's no direct evidence of an atmosphere at the current time. The abstract of Sicardy et al. (2011) "A Pluto-like radius and a high albedo for the dwarf planet Eris from an occultation" gives a limit of ~1&nbsp;nanobar on the presence of methane, argon or nitrogen atmospheres during the stellar occultation observed in November 2010.

Hofgartner et al. (2019) "Ongoing resurfacing of KBO Eris by volatile transport in local, collisional, sublimation atmosphere regime" argue that at aphelion there would be a local atmosphere over the warmest region, which they state is a similar situation to the atmosphere of Io. They predict that this local atmosphere could still have significant effects on the volatile distribution on Eris:


  The model results indicate that volatile transport (VT) on Eris, even at
  its aphelion distance of nearly 100&nbsp;AU, can be significant. The nitrogen-ice
  temperatures are &lt;&nbsp;30&nbsp;K and vapor pressures are &lt;&nbsp;10&nbsp;nbar but the significant pressure gradients in the local atmosphere regime result in transport of
  nitrogen mass, that integrated over the long timescales associated with such
  a distant orbit, can be significant as compared to the column mass of the
  atmospheres of Triton and Pluto.


So depending on where you are on Eris, the atmosphere (if there is one) may or may not last for the entire orbit. It will take a long time to confirm this, though.