Strange New Worlds

"Space, the final frontier. These are the voyages of the Starship Enterprise. Its continuing mission: to explore strange new worlds, to seek out new life and new civilisations, to boldly go where no one has gone before."

The existence of planets beyond our Solar System - extrasolar planets or just exoplanets - is so fundamental to the premise of the science fiction franchise Star Trek that it is encapsulated in the opening narration that so famously defines the series. First broadcast in 1966, existing through multiple generations of television and feature film series, and still being made today, Star Trek is one of the most influential science fictions of all time. But how does it represent exoplanets, and how has that changed as our scientific understanding has evolved?

Earth Twins

“Enjoy yourself, Captain. It's an interesting planet. You'll find it quite pleasant. Very much like your Earth.”
- Mr Spock, episode “Shore Leave” (1966)

Most of the worlds visited by the various starships of the Star Trek universe (Enterprises, Voyager, Defiant, Cerritos and others) appear, at first sight, very familiar. With atmosphere, gravity, temperature and other subtler characteristics since as colour of sunlight close to that we are familiar with, they can be characterised as Earth Twins - comfortable worlds where humans (and similar aliens) can exist without significant protection or life support equipment.

The reason for this is perhaps obvious - scenes must be filmed on Earth, and typically feature human crews. Complications in the environment would be both challenging and expensive to film, and might detract from more character or plot driven scenarios as time would need to be spent exploring, explaining and negating the environment. There is even a good in-universe reason to believe that the ships would visit these worlds disproportionately often: with predominantly human crews, complemented by aliens from similar planets, the ships in question might naturally be assigned missions predominantly on relevant planets, leaving other duties for differently crewed vessels.

However it is still interesting to ask whether the number of Earth Twins seen in Star Trek is realistic. When Star Trek was first created, through the initial run of movies, and even at the start of Star Trek: The Next Generation, the existence of exoplanets was purely theoretical. The only known planets were those in our own Solar System. Since the first planet orbiting another normal star was first seen in 1995 and reported a couple of years later. Confirming this world, and finding others, was an intense effort. By the time Star Trek Enterprise finished in 2004 we knew of 187 planets, most of them hot gas giants very different in character to Earth. We now know of over 6000 (as of October 2025), of which a substantial fraction are rocky worlds. To date, none of them are very similar in size and orbit to Earth, and orbiting around a Sun-like star. However this is largely an observational selection effect: with our current equipment, finding such worlds would be extremely unlikely. Instead, the worlds we do see - some slightly larger, some slightly closer to their host stars, give us confidence that large numbers Earth-sized, Earth-orbit worlds (perhaps as many as one per star on average) almost certainly do exist in their sun’s habitable zones.

Of course, that does not necessarily mean those worlds are Earth-like.

Desert Worlds

“How can it be so cold when the sun is shining?”

“It’s not much of a sun, and this isn’t much of a planet.”

- Quark and Odo, ST:DS9 “The Ascent” (1996)

The concept of a habitable zone is simple. A planet a certain distance from its star will intecept a certain amount of heat. It will also radiate a certain amount of heat into space. Over time these effects balance, so that the planet will end up at a charactistic temperature. If that temperature lies between the freezing and boiling points of water, the planet is said to be in a habitable zone. Of course this doesn’t mean that it will be straightforwardly habitable or teeming with life. If the planet doesn’t have an atmosphere then any water would boil away. It may not have had any water to begin with, instead having different atmospheres to ours. And even with the right atmosphere, if the planet doesn’t have the right balance of land and ocean, climate may not operate as it does on Earth. Even on Earth itself, there are regions of desert (both hot and cold) which are uninhabitable, and a combination of solar and climate cycles means that the planet’s habitability has changed over time (being lower at times when the Sun was more active, or during ice ages).

However, broadly speaking, a planet towards the inner edge of its habitable zone will be hotter, while one at the outer edge will be cooler. In our own Solar System, Venus and Mars occupy these positions. Both are planet-wide deserts, lacking liquid water, although in the case of Venus its huge atmospheric loading of carbon dioxide has raised the surface temperature enormously.

Desert planets have featured throughout Star Trek’s history [1]. The most prominent example is Vulcan, which is shown in the series as having some small bodies of liquid water, and an atmosphere and temperature in which water can exist, but is nonetheless extremely arid, with vast expanses of desert and life adapted for limited water availability. The deserts of Vulcan are hot, suggesting it lies close to the inner edge of its habitable zone, with the desert known as Vulcan’s Forge lying at the borders of habitable to life even on the planet.

Other desert dominated planets in Star Trek include Tyree (where a Prophet was located in Star Trek: Deep Space Nine episode “Image in the Sand”, 1998), while a number of other worlds are shown to be of marginal habitability (in Star Trek in-universe parlance a habitable world is Class M, while planets with marginal habitability are class L). Many of these would be considered deserts.

In other examples, such as in the opening story of Star Trek Discovery (episode “The Vulcan Hello”, 2017) it is challenging to tell whether the entire planet is a desert, or simply whether the crews are visiting a desert biome within the planet’s more varied ecosystem. However another undeniably desert world in Star Trek is Mars, home of the Utopia Planetia shipyards. In the later series of the Star Trek canon this world is described as being partially terraformed. In Picard, for example, it is clear that humans still need support to live on the planet but far less so that astronauts today would require. It is thus a cold desert, arid and dusty but frigid.

Ocean Worlds

“Akkalla is of great scientific interest because of its unusual ecology. It’s one of only a handful of worlds with a surface almost completely covered by water yet also having developed a normal variety of flora and fauna, including intelligent humanoid life.”
- Captain Kirk’s log, novel “Deep Domain” (1987)

The opposite problem (from the perspective of human life) can be found in a different form of planet: ocean worlds have a surface dominated, or even entirely covered, by water. While this can lead (in theory) to abundant ocean life, it might lead to challenges in evolving large land based forms.

Ocean worlds are relatively rare in the Star Trek universe, although examples include Kaminar (Star Trek Discovery) which hosts two sentient species, one primarily aquatic, and Argo (Star Trek: The Animated Series, episode “The Ambergris Element”, 1973) in which previous land masses somehow sank under the sea during earlier seismic upheaval (not possible given Earth-like plate tectonics!). The extended Star Trek universe also features water worlds, such as Akkalla in the 1987 novel Deep Domain by Howard Weinstein, described in the quotation above.

Given that humanoid life evolved on Earth to adapt from swinging through trees to making best use of sub-desert savannah, it is unclear what survival benefit such a form would provide in an aquatic environment [2]. In an ocean environment streamlining and/or bulk for thermal regulation tend to be prioritised. Indeed, all warm blooded life on Earth (including whales and dolphins) originally evolved on land. It is unclear what ratio between land and sea environments might lead to selection pressures for humanoid life, although the adaptability and flexibility of the human form appears to have led to both our colonisation of a range of environments and to the development of intelligence.

Water worlds may in fact be relatively common. By combining two observing techniques (transits, which give a planet radius, and radial velocities, which give its mass) we are starting to be able to constrain the densities of some rocky planets - or in other words, to find out if they’re made of iron-rich rock, gas clouds or something in between. A number are now falling between the extremes, suggesting that they may have substantial amounts of water, or perhaps water-ice in their composition.

An interesting subset of these are the so-called Hycean worlds; planets which have been interpreted as having thick layers of ocean, with hydrogen (rather than nitrogen, oxygen or carbon dioxide) dominated atmospheres. While these would not be habitable to surface life as we know it, sub-ocean life would remain a possibility.

Circumbinary and Twin Worlds

“I remain optimistic. It's hard not to be in the face of such beauty - in this case, a binary star system. Around these two suns, ice, dust, and gasses collide to form planets future generations will call home. A humbling reminder that all life is born from chaos and destruction.”
- Michael Burnham, Star Trek Discovery episode “The Vulcan Hello”

Our Solar System has just one dominant source of power, the Sun, and amongst the major planets only Earth has a companion anywhere near its own size (the Moon has a mass a hundredth of Earth’s, compared to less than a ten thousandth for most other satellites). However other arrangements are likely to be not just possible but common.

About one in five stars similar in mass to the Sun have a companion - they form part of a stellar binary. Depending on the size, type and separation of the binary stars, new opportunities for habitability arise. Some worlds may orbit one of the stars in a wide binary (known as a P-type orbit), with the distant second star having relatively minor impacts (either on heat or illumination). Alternatively, some planets may sit in an (S-type) orbit which circles both stars of a close-in binary. These systems are sometimes considered true circumbinary planets, and will see both stars remain close together in the sky, rising and setting a little apart. Examples from the Star Trek universe include the holiday world of Risa (Star Trek: The Next Generation, Deep Space Nine, Enterprise) and Talos IV (Star Trek: The Original Series).

We now know of several circumbinary planet systems, some with planets in their circumbinary habitable zones, although most of these involve gas giant rather than earth-like planets. The first of these was the Kepler-47 system - nicknamed Tatooine in the press after the circumbinary world in Star Wars. However circumbinary systems may be less stable over long timescales than single star systems - eccentric or inclined orbits are likely to interact with the binary stars’ motion, while the stars must be luminous enough for their shared habitable zone to lie well outside the binary stars’ tight orbit.

Of course, not only stars can have twins. While Earth and the Moon are sufficiently different in size that they orbit a point within Earth’s bulk, the dwarf planets Pluto and Charon are so similar in size that they orbit a point that lies between them. Twin planets are another common theme in science fiction [3] and are seen in Star Trek, notably in the form of Vulcan’s sister world T’Khut.

Observationally, most twin worlds would lie beyond current limits of technology, but some early examples a handful of times larger than Jupiter (known as Jupiter Mass Binary Objects or JuMBOs) have now been discovered in a nearby dense stellar region.

Gas Giants and Exomoons

“Siren calls. That's what we called them when I was a kid. My dad would put them through the speakers whenever we flew by a gas giant. It gave me nightmares sometimes.”
- Travis Mayweather, Enterprise episode “Sleeping Dogs”

In our own Solar System, the number of gas or ice giants is equal to the number of rocky worlds (4 of each). In the observed sample of known planets, hot and giant planets are massively over-represented. The reason for this is simple: big planets are much easier to find than small ones, particularly if the planet is orbiting close to its sun. While giant planets in orbits similar to our own Saturn or Jupiter are harder to find (simply because their orbits take many years), it seems likely that most solar systems will host one or more of these worlds. 

Star Trek has explored relatively few gas giants over the years - at least partly due to the same bias that has led to Starfleet’s ships exploring so many terrestrial worlds. If there’s no surface to land on or beam down to, it’s harder to construct a story or imagine a life form that might have evolved in the atmosphere. Other science fictions have imagined whale-like creatures; in Star Trek: The Next Generation, at least one gas giant (Marijn VII) was home to creatures which existed as subspace distortions (episode “Interface”, 1993).

A handful of gas giants have nonetheless been featured in Star Trek episodes, although often as settings rather than subjects. The Star Trek: The Next Generation episode “A Ship in a Bottle” (1993) notably showed two such worlds colliding and triggering the birth of a (presumably very short-lived) star. Even this extremely unlikely event (planets will very seldom collide!) is no more than the background for a story centred on the ship’s holodeck. In the Enterprise episode “Sleeping Dogs” (2002), by contrast, the crew undertake a scientific investigation of a gas giant, only to find a crippled Klingon vessel trapped there. It’s interesting that Ensign Travis Mayweather comments on the radio frequency emission associated with the strong magnetic fields on such worlds, as in the quote above.

While these strong signals are described in the episode as coming from a rare class of giant planets, we are now able to study the aurorae (energetic emission powered by the interaction of solar wind with a magnetic field) on Jupiter, and sensitive radio observations have confirmed that similar effects exist on at least some of the known gas giant exoworlds.

Perhaps the most interesting possibility centering on gas giants, where habitability for human-like life is concerned, is the abundance of large moons expected to orbit such worlds. In our own Solar System, Jupiter’s moon Ganymede is larger than the planet Mercury, while Titan is the only known solar system object other than the major planets to hold onto a thick (hydrogen and carbon-dioxide dominated) atmosphere.

A large number of studies have suggested that gas giants in habitable zones may potentially host habitable exomoons, and surveys for these are ongoing, with some candidates located (although none, as yet, confirmed). Star Trek too has explored this possibility. The Star Trek: The Next Generation episode “Power Play” (1992) was set on a “Class M” (i.e. habitable) world which was a moon of the gas giant Mab-bu VI. Unfortunately this proves to be a penal colony for non-corporeal entities. Star Trek Enterprise raised the stakes by revealing that one of the major homeworlds of the Federation, Andoria, is in fact an exomoon of a large ringed planet (episode “The Aenar”, 2005). This moon is cold and icy, but with more temperate regions near the equator.

Into the Future

Over its six decades of history, the Star Trek universe has depicted a vast range of worlds, from Earth itself to free floating planets which lack suns entirely (e.g. Enterprise, “Rogue Planet”, 2002). In “The Balance of Terror” (1966), Doctor Leonard McCoy asserted that:

“In this galaxy, there’s a mathematical probability of three million Earth-type planets. And in all of the Universe, three million, million galaxies like this. And in all of that, and perhaps more, only one of each of us.”

In fact, this now looks likely to be a massive underestimate. From the 6000 known planets, astronomers currently extrapolate more than a hundred billion in our Milky Way alone. If even one tenth of one percent of those is in the habitable zone of their star, perhaps a hundred million planets in our galaxy could host life - assuming life ever got started anywhere other than Earth.

Over the next few years a range of planet-finding telescopes will be deployed, notably including the ESA’s PLATO mission, which will target Earth-like planets around bright stars [4]. New technologies and new techniques will push our observational limits ever further into habitable zone territory.

Since its first broadcast, exoplanet science has vindicated the faith of Star Trek’s creators in the potential for theoretically-habitable exoworlds. Whether life will ever by found on them remains to be seen. These strange new worlds are nonetheless out there, ready and waiting for those with the patience and skills to explore.