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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?

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  • $\begingroup$ You have to be careful with how you interpret 'collapse'. In nature not all collapse or evacuation processes are 'total' in any sense of the word. Plutos atmosphere expanded for example between 1988 and 2012 from 6 to 18 nbar. So maybe you would think that 6 nbar in 1988 is a collapsed atmosphere, somebody else might not. However Eris' distance to the sun varies by a factor 3, so it is hard to imagine the same ratios of min/max pressures apply. $\endgroup$ – AtmosphericPrisonEscape Feb 11 at 19:08
  • $\begingroup$ @AtmosphericPrisonEscape The 6 nbar you're referring to: do you mean on Pluto or on Eris? $\endgroup$ – user30007 Feb 11 at 19:11
  • $\begingroup$ Pluto. Have you read the paragraph about pressure in the article about Plutos atmosphere? $\endgroup$ – AtmosphericPrisonEscape Feb 11 at 19:30
  • $\begingroup$ @AtmosphericPrisonEscape It writes that Pluto's air pressure was 0.4 pa (4000 nbar) in 1988. That is a thousand times higher than the maximum value on Io's surface, so it is far from a "collapsed" atmosphere. Is your value for Eris? $\endgroup$ – user30007 Feb 11 at 19:45
  • $\begingroup$ I might have misrembered the units, but that's the data for Pluto. You should define what you mean with collapsed then. You seem to be aware of Io's collapsing atmosphere, so I am not sure what you're asking. $\endgroup$ – AtmosphericPrisonEscape Feb 11 at 19:54
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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 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 AU, can be significant. The nitrogen-ice temperatures are < 30 K and vapor pressures are < 10 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.

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    $\begingroup$ Note: this limit on Eris's atmospheric pressure of 1 nanobar is 10,000x smaller than the Pluto atmospheric pressure at the time of the occultation. $\endgroup$ – astrosnapper Feb 12 at 0:24
  • $\begingroup$ Will the Webb telescope be able to give us more information on Eris' atmosphere? $\endgroup$ – user30007 Feb 12 at 6:18
  • $\begingroup$ @user30007 - I suspect that might be a good topic for a new question... :-) $\endgroup$ – antispinwards Feb 12 at 8:55

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