In the new alternate timeline Star Trek movie, the icy M class planet Delta Vega is so close to Vulcan that the latter planet has an angular diameter that is comparable to Earth's moon when seen from the former. It is in fact close enough for an escape pod to reach it from the vicinity of Vulcan.

The Question:

In this case, should not Vulcan's catalogue name be Gamma Vega? Would this make Vulcan the third planet orbiting the star Vega? This star is 25 light years from Earth. Yet the Vulcan system is said to be 16 light years from Earth, which is widely believed to be the same as the real star system 40 Eridani A (though never canonically confirmed).

Also, why is a habitable planet so close to Vulcan not heavily colonized by Vulcans?

  • 2
    Never forget Star Trek's motto: We hate continuity. Feb 23, 2012 at 20:38
  • 7
    "Delta Vega" doesn't follow a standard astronomical naming convention. In real life, Vega is the name of a star also known as Alpha Lyrae, so called because it's the brightest star in the constellation Lyra. Planets are sometimes referred to by the name of the star followed by a number; for example Earth is Sol III. More recent practice appends a lower case letter. The name "Delta Vega" would imply that it's the 4th-brightest star in the nonexistent constellation Vega. Feb 23, 2012 at 21:33
  • I'm sure that "Delta Vega" is merely the closest English approximation of the name of the planet in Vulcan, similar to how we use "Kronos" for "Qo'noS". Feb 23, 2012 at 21:54
  • @KeithThompson - I can't believe I didn't notice that myself. Wish I could upvote it twice.
    – Plutor
    Feb 24, 2012 at 13:02
  • @KeithThompson An alternative interpretation (which admittedly relies on the recent practice changing slightly in the next 200 years, perhaps to accommodate other spacefaring civilizations) might be that Vulcan orbits Alpha Lyrae, and Delta Vega is the 4th planet/planetoid. (Also except, of course, that Vulcan orbits 40 Eridani..)
    – Izkata
    May 16, 2014 at 0:36

3 Answers 3


There's not a lot of in-universe information, although Memory-Alpha does say (without citation) that "Its orbit carried it near enough to Vulcan that the other planet could be seen from Delta Vega's surface." Perhaps Delta Vega had a very eccentric orbit. Although that's purely speculation, and it wouldn't explain Vulcan being in orbit around Vega.

From a real-world perspective, Roberto Orci talked about naming the planet after one from the TOS episode "Where No Man Has Gone Before":

"We moved the planet to suit our purposes. The familiarity of the name seemed more important as an Easter egg, than a new name with no importance."

And he also touched on motivation behind the scene in question in an online Q&A thread (comment 464):

"I prefer to think of Delta Vega as being in close orbit (although it could be a moon), but nonetheless, we like to think of that sequence as impressionistic for a general audience. In other words, Nero could’ve beamed Spock prime down to Delta Vega with a telescope or some other type of measuring device to allow Spock to experience the pain of perceiving the destruction of his home world, but that simply isn’t very cinematic."

So unfortunately, you probably just have to chalk it down to "poetic license".

  • @KeithThompson's comment on the question answers the part about nomenclature.
    – HNL
    Feb 24, 2012 at 4:54
  • Upon viewing the trailer of Star Trek: Into Darkness, I am convinced that the "Easter Egg" mentioned above is far more than just a shout-out to fans. Delta Vega was the planet where Gary Mitchell was marooned and buried. Dec 8, 2012 at 4:51

It can't. Twice over, it can't.

First of all: Delta Vega was established in "Where No Man Has Gone Before" as being close enough to the galactic rim as to be reachable at sub-light speeds after Enterprise bounced of off the barrier (itself a mistake, since hardly anything ought to be reachable in a matter of days at sub-light speeds). The same story makes it fairly clear that Enterprise, the galactic rim, and Delta Vega, are all a long, long way away from the usual Starfleet stomping grounds.

Second of all: there's no way Vulcan would appear so large in the sky of another body orbiting Vulcan's sun, unless it was a satellite or twin planet of Vulcan. Canonically ("The Man Trap"), Vulcan has no moon (despite an artist's mistake in Star Trek: The Motion Picture).

In short, the 2009 movie made a monumental error that cannot be rationalized in any way.

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    Unless for some reason the Vulcans added a moon to their planet in the alternate time line that they, or Star Fleet, named Delta Vega for some reason. But still +1.
    – Xantec
    May 19, 2014 at 18:40
  • The hill spheres of close in bodies can be surprisingly small.
    – aramis
    May 20, 2014 at 6:47
  • Some of the novels described Vulcan's moon / sister planet. I think it was called T'Khut, I'm only certain of the T' part. May 20, 2014 at 18:27
  • Yes, and I almost mentioned that...but it isn't canon, while, "Vulcan has no moon," is a direct quote from a TV episode, spoken by someone we generally consider to be reliable :-) (And "T'Khut" is correct, by the way; I think it's first referenced by that name in Spock's World by Diane Duane) May 27, 2014 at 19:25
  • @UncleMikey I agree, that Vulcan has no moon is a canonical quote, but wasn't Tuvok born on the Vulcan Lunar Colony?? He spills out random stuff about himself in order to prevent being taken over by the collective during the infiltration mission in Unimatrix Zero, IIRC.
    – BMWurm
    Dec 6, 2014 at 16:35

Since there is little to no canonical information about the Vulcan system, other than "Vulcan has no moon" from the TOS Episode, The Man Trap, there is room for speculation.

Stuff we can figure about Vulcan

It can be implied that Vulcan is higher gravity than Earth; in the extended universe, it's routinely listed as 1.4 G's. (As exemplified in Decipher's Worlds for the Star Trek Roleplaying Game.) Likewise, it's extensively assumed in the extended universe that it is indeed orbiting 40 Eridani. (0.86 solar masses, 0.46 sols luminosity.) It needs to be slightly brighter apparent luminosity, call it 1.05. So it needs to appear about 2.3x the brightness of Sol... and that means we need to figure it's about 0.23 AU orbit.

Vulcan is thus about 2.7 earth masses.

Delta Vega

The gravity looks Earthlike. So, let's assume it's a fairly earthlike body. It's cool - I'll examine that later. It's got a lot of water.

There are several possibilities as to what Delta Vega could be.

  • Double Planet
  • LaGrange Point co-orbital body
  • "horseshoe orbit" co-orbital body
  • eccentric orbit.
  • Vulcan's parent Planet. ("Vulcan has no moon, it is a moon!")

So, let's first see if it's plausible that it is a planet.

For our purposes, it needs to orbit no closer than the sum of the hill spheres.


Assuming similar density, that puts it at about 18,000 km diameter.

Given the appearance on screen, it appears to be about 4x the size of our moon. Our moon is about 1736 km diameter; for simplicity, I'll use 1700. (Earth is about 12742 km.) the moon is roughly 1/7th earth's diameter, or about 1/10 the diameter of Vulcan. So, were it at lunar distance, it should appear about 10x the size of the moon; this implies it's 4x further, or about 1.2 million KM. Normally, this would be a problem...

Hill Sphere:

Simplified greatly, a hill sphere is the radius at which a body captures other bodies in its region.

For reference, Earth's Hill Sphere is about 1.471 million km. Hence the problem. Anything within that radius should end up orbiting Earth, and nothing should orbit within 2x that, because it would be unstable.

Vulcan's Hill Sphere, however, isn't nearly so big; 0.499 million km based upon the above assumptions.

Placing Delta Vega

Assuming the same excentricity as Earth for both worlds, we know that it has to have a perehelion no further than Vulcan's Perehelion plus about 1.2 million km.

But it really doesn't need to be even that far. Because of their relative proximity to the star, their hill spheres are pretty small. Vulcan's is 499,000 km and Delta Vega's around 369,000 km. So... a close approach of 1.2 million km is probably a safe orbit, especially if, at that point, Vulcan is approaching apohelion and Delta Vega is approaching perihelion.

So, using 3.49E+07 km for Vulcan's semi-major, and 3.610E+07 km for Delta Vega's, we get about 0.95 (40 Eridani)s Luminosity from Vulcan. This should be plenty warm for liquid water. Increasing the eccentricity and semi-major axis of Delta Vega would potentially explain the glaciation better.

Bottom Line: Delta Vega could be another body orbiting 40 Eridani from Vulcan.

  • 40 (Omicron) Eridani and Epsilon Eridani are two separate stars, neither of which are actually canonically established as being Vulcan's sun. May 19, 2014 at 18:31
  • @UncleMikey 40 Eridani A has gotten about as close as possible without actually appearing onscreen, given that Roddenberry endorsed it as such
    – Izkata
    May 19, 2014 at 23:31
  • @Izkata Perhaps, but as Disney has just recently reminded us as regards one of the largest, most entrenched Expanded Universes in existence, if it ain't on screen, it ain't canon. May 20, 2014 at 15:02

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