Written by OC Wanderer, author of Destiny Among the Stars, a LitRPG sci-fi series set in the real stellar neighborhood. Published September 9, 2026.
An Alcubierre drive still needs three things nobody has: negative energy, control from inside and an answer to loops in time. Destiny Among the Stars grants its crew the drive anyway, which opens a question I find much more fun to imagine: once you can travel between stars, where do you point the ship?
Destiny gave me the freedom to send the crew anywhere; the science helped me decide what kinds of worlds they should find when they arrived. I imagine a survey ship dropping out of its drive at a new star with a list of planets and time to visit only a few. Which world gets the first close look? The habitable zone offers a tempting answer, a ring around the star where surface water might survive. I would want that ring on the ship's chart, while leaving plenty of room for the planets to surprise me.
Drawing a promising ring around a star
The habitable zone is the range of distances from a star where liquid water could exist on a planet's surface.1 Its inner edge is where a planet gets warm enough to lose its oceans to space, and its outer edge is where even a thick blanket of carbon dioxide cannot keep water liquid. For the Sun, a widely used calculation puts the inner edge at 0.99 astronomical units (AU, the Earth-to-Sun distance) and the outer edge at 1.70 AU.2 Earth, at 1.0 AU, sits just past the inner edge. Seeing our own home so close to a modeled boundary makes that neat ring feel a little less comfortable.
Those numbers need only the star's temperature and brightness, which astronomers can measure from far away. We can sketch a promising neighborhood before seeing the world itself. The star's wobble gave astronomers Proxima b's orbit, enough to place it inside its star's zone while leaving its surface unknown. There is something wonderfully tantalizing about that: a possible destination appears on the chart long before we know what a visitor would find there.
Telescope time is scarce, so even that incomplete clue has value. Missions use the zone to select promising targets for follow-up study.3 Faced with more worlds than I could inspect, I would want a way to choose where to look next.
Destiny gives that choice a very practical incentive. In Book 1, Chapter 22, the habitable zone objective reads: "Investigate planetary bodies located within the habitable zones of the system's stars. Assess atmosphere, climate, surface gravity, magnetic shielding, and the presence of liquid water or breathable air." The chapter then gives the payouts for that analysis: "Five hundred million for a habitable world, two hundred more for a bio-compatible atmosphere." That is quite a reason to go exploring, with another two hundred million riding on what the crew finds in the air.
Clouds can move the boundary
The Sun's 0.99 to 1.70 AU comes from a model that leaves out clouds, and its authors say the real boundaries may extend further in both directions.4 Now imagine a planet circling a small, dim red dwarf so closely that the same face always points at the star, as the Moon's does at Earth. A permanently sunlit face sounds like a place where water might have a hard time hanging on. But climate models with an assumed atmosphere and water reveal a lovely complication: warm air rises on that face and builds thick water clouds, which reflect much of the light. Brighter starlight makes more cloud, helping the planet stay cooler as the light grows. In these models, such planets can be habitable at twice the starlight that earlier models allowed, which roughly doubles the expected number of habitable planets around red dwarfs.5
Clouds could give the planet a reflective parasol right where the sunlight is strongest. I love how an ingredient so familiar from our own skies can change where we might look for an alien world. For those modeled planets, the inner boundary moves much closer to the star. A survey crew following a rigid line could overlook exactly the unusual weather worth investigating; the classical zone remains a useful guide through a diversity of possible habitable worlds it cannot fully capture.6
What happens when you open the airlock?
Mars sits at 1.52 AU, inside the Sun's modeled zone, and its surface air pressure is roughly one 160th of Earth's.7 With air that thin, liquid water cannot last on the surface.8 It is an unsettling answer to the hopeful ring on our chart: a world can occupy the right orbit and still greet its visitors with a landscape where they need sealed suits.
Book 3 gives the crew the opposite problem. In Chapter 116, the briefing sends them to "Alpha Centauri A, fourth planet. Still in the habitable zone, still needs a survey according to our charter." By Chapter 118 they are in orbit around Alpha Centauri A d, named Midnight Veil. Its atmosphere is plentiful, at a pressure about one point two times Earth's, but its sensors read sulfur dioxide and hydrogen sulfide, and the chapter calls it "an actively corrosive and poisonous planet." Imagine arriving with that promising orbit already on the chart, then watching the atmospheric readings come in. I would be very interested in the view through the window and very careful about the airlock.
Where the survey begins
I would happily give a survey crew the habitable zone as its first guide. The excitement is in what comes after: a close look at a world whose clouds might move the expected boundary, or whose air turns a promising destination into a hazardous one. Mars brings me to the next part of that puzzle. Before I wonder what a visitor might breathe, I want to know what conditions a planet actually needs to hold on to its atmosphere long-term.
Endnotes
NASA Science, “The Habitable Zone”: “the distance from a star at which liquid water could exist on orbiting planets’ surfaces.” The description of the two edges follows Kopparapu et al. (note 2), whose limits are named the water-loss limit and the maximum greenhouse limit. ↩
Ravi Kumar Kopparapu et al., “Habitable Zones Around Main-Sequence Stars: New Estimates,” The Astrophysical Journal 765 (2013): 131, DOI, arXiv. For the Sun, the water-loss limit is 0.99 AU and the maximum greenhouse limit 1.70 AU, from a one-dimensional radiative-convective model for stars of 2600 to 7200 K. One AU is about 149.6 million km, or 150 million km rounded. ↩
Ramses M. Ramirez, “A More Comprehensive Habitable Zone for Finding Life on Other Planets,” Geosciences 8 (2018): 280, DOI, arXiv. The abstract: “Space missions employ the HZ to select promising targets for follow-up habitability assessment.” NASA’s planned Habitable Worlds Observatory works from a catalog of about 13,000 nearby bright stars (Tuchow, Stark and Mamajek, The Astronomical Journal 167 (2024): 139, DOI), validated against an expert list of the top 164 candidates suitable for exo-Earth imaging. ↩
Kopparapu et al. (2013), abstract, as in note 2: “Our model does not include the radiative effects of clouds; thus, the actual HZ boundaries may extend further in both directions than the estimates just given.” ↩
Jun Yang, Nicolas B. Cowan, and Dorian S. Abbot, “Stabilizing Cloud Feedback Dramatically Expands the Habitable Zone of Tidally Locked Planets,” The Astrophysical Journal Letters 771 (2013): L45, DOI, arXiv. The abstract: tidally locked planets “can be habitable at twice the stellar flux found by previous studies,” which “roughly doubles the frequency of habitable planets orbiting red dwarf stars.” The result comes from three-dimensional global climate models with an assumed atmosphere and water, where strong convection produces thick water clouds near the substellar point that raise the planet’s albedo. ↩
Ramirez (2018), as in note 3: “Although the classical HZ is an effective navigational tool, recent HZ formulations demonstrate that it cannot thoroughly capture the diversity of habitable exoplanets.” ↩
NASA Space Science Data Coordinated Archive, Mars Fact Sheet: semimajor axis 1.524 AU; surface pressure 6.36 mb at mean radius (4.0 to 8.7 mb by season), against about 1,013 mb for Earth at sea level. Author calculation: 1,013 / 6.36 = 159. That Mars sits inside the 0.99 to 1.70 AU interval is the author’s comparison of these figures with note 2. ↩
NASA Science, “Mars: Facts”: liquid water cannot persist on the present surface because the atmosphere is thin. ↩