(via darksands dot com)

So Barnard's Star does have a planet after all!

Behind that paywall, i would know more than its period (233 days) & mass (3.2 times Earth's), but using Hipparchos' visual magnitude 9.54 & parallax 0".54901, & 0.144 times solar mass (i had always thought around 0.15) & other info like stellar temperature (M4) 3134 K from Wikipedia...i get a visual luminosity of 1/4126 & (BC -2.10 [they seem to be using a bit higher]) bolometric of 1/596. Which makes this planet orbit just at 36.1 million miles (albeit varying 11.55 either way-- this orbit is eccentric), for a blackbody temperature of a little less than 91 K. That's cold. Ammonia would be frozen, even.

What kind of world is this, rocky, gaseous, or some unheard-of middle thing? I will just hazard that it is not as low density as Neptune (making it 2.2 times the size of Earth), & not as dense as a regular terrestrial planet of that mass (which would give it a radius of 1.4); the Galileans, with some 60% Earth's density, suggest a radius around 1.75, thence a gravity pretty close to Earth normal (1.05). At their albedo (50%), the graybody temperature is 76.4 K, & if there's a bit of a greenhouse effect (40, from methane), then one might reasonably expect a surface temperature of some -157 C. It's beginning to look a lot like Titan.

Not sure if the eccentricity means methane would be sometimes liquid, sometimes frozen & sometimes gaseous, but that's not a ridiculous scenario. It wouldn't be tidally locked (tidal effect is actually LESS than Earth: 0.954), & with a shrunken red sun providing about the same illumination (1/622) as our own sun does to an orbit midway between Uranus & Neptune, dark. If there were anything to Bode-Titius, this could be the fifth planet. Inhabitants, call them "dubars from Izdubar" & their culture "dubaric." Their 8-month-long "year" would have a pretty serious (even by local standards) "winter" portion. I can see them hibernating like bears.

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Revising the albedo to a Titan-ish 0.2, i get: -129 C at periastron (0.264120329 AU) & -159 C at apastron (0.512704168 AU). The sun just about doubles in apparent size (0.27 to 0.53). The lower temperature is comfortably above methane's freezing point of -182 C, while at the higher one, a pressure of 8.25 atmospheres is necessary to keep the seas (or lakes) from boiling.

A pdf of the original paper--surprisingly uninformative. But there's a new article, too. Comments at Centauri Dreams (including Drew Ex Machina).