Futures | Published:

Uninhabitable zone

Nature volume 524, page 260 (13 August 2015) | Download Citation


Approach with extreme caution.

The primary gleamed benignly against a background dusted with stars. From the inner system it would have blazed angrily in the sky, but this planet was sufficiently distant to be safe.

Image: Illustration by Jacey

“Perfect!” Unit-Peripheral declaimed. “I find it hard to believe that such a beautiful, balmy world can be lifeless — yet it is! I will authorize colonization immediately.”

“The world is currently lifeless,” Plug-in-43 pointed out. “The sondage team suspects that living creatures were once present here. They left ... traces. Indicative of bipedality.”

“Garbage! Nothing can locomote on two appendages! The arrangement is unstable. The marks were made by a meteoroid impact.”

“Perhaps. The sondage team has formulated an alternative hypothesis. It is ... strange.”

“It would have to be. What is it?”


Unit-Peripheral paused to recompute and got the same result. “Nonsense. Extremophiles occupy extreme habitats.”

“Extremism is relative, Unit-Peripheral. These beings made a brief visit, decided this world was not to their liking, and departed.”

“Where to?”

“The sondage team suspects ... absurd, I know, but they take their duty to be open-minded terribly seriously ... that the extremophiles departed for the inner system.”

Unit-Peripheral expressed indicatory signals in the direction of the severely overheated local star. “Into that?”

Plug-in-43 said nothing, but q-mailed an image: two parallel linear series of depressions, melted into the rock.

“The inference of warmlife is highly improbable,” Unit-Peripheral stated. “This system's gas and ice giants are far too close to the star to be habitable. The cryonic zone starts with the ice dwarves, of which this is the innermost. Where does the sondage team imagine these extremophiles reside? On a comet?”

Plug-in-43 q-mailed another image. “Barrenworld-3. It resembles Fumarole in our own system.”

“Where rocks run molten, forming magma oceans.”

“As they do on Barrenworld-3. The sondage team suspects this system has evolved extremophiles that can inhabit such worlds. In fact, they suggest these organisms might largely consist of molten rock.” Noticing Unit-Peripheral's thunderous mode-expression, Plug-in-43 hastened to expand. “Held in ... a hugh multitude of ... tiny cocoons ... able to stand the searing tempera —”

Clusterglitch! Even extremophiles can't be that extreme! The radiation alone —”

“Barrenworld-3 has a protective magnetic field.”

Unit-Peripheral came to a reluctant decision. “Protocol requires me to act as if I take these insane conjectures seriously. Dispatch six-by-six hardened probes.”

The crew descended to the planet's orange and brown surface for a refreshing sunbath, and waited. Eventually one heavily damaged probe struggled back. Its report was disturbing. Not only a gaseous atmosphere, but —


“Six-plus-one six-by-sixths by volume.”

“And the cyanic areas truly are liquid rock?”

“Molten dihydrogen monoxide, Unit-Peripheral.”

“Despite vast amounts of atmospheric dioxygen carbide, indicative of past carbidation events on a huge scale, there remains free oxygen? Why did such a corrosive substance not combine with other elements long ago?”

“It did. It still does. But the poison is regenerated.”

Unit-Peripheral emitted a warning flash. “This smacks of theory-saving! How?”

“By extremophiles.”

The flash shorted out, destroying a food-booth. “Whenever something impossible is proposed, it is justified by invoking extremophiles! I've had enough of this nonsense. I cannot accept that intelligent space-traversing creatures can regenerate poison gas.”

“Apologies. I was unclear. The poison is regenerated by a different extremophile.”

Unit-Peripheral vibrated in a mix of anger and terror. “There's more than one of them?”

“Millions of formats, all multiple upgrades.”

“Even with a magnetic field, these creatures must live underground.”

“No, they lie around the edge of the magma and ... sunbathe. Like us.”

“At least they have the sense to stay out of the liquid rock.”

“No, they periodically immerse themselves in it. To — uh — I know no other way to say this, Unit-Peripheral. To keep cool.”

Cool? The probe is suffering from an overactive imagination. Oxygen is one of the most corrosive gases known to cryokind! How do these creatures avoid reacting with it?”

“They don't. They use it as an energy source.”

“But surely the organisms themselves would oxidize!”

Plug-in-43 abased its bias currents as a submission gesture. This one would not be well received. “Sometimes they do. The probe saw localized conflagrations in which thousands of extremophiles died.”

“The bipedal ones?”

“No. Sessile colonies. The team names them 'fire-forests'. They cannot reproduce unless there is a conflagration.”

They have babies by setting themselves on fire?

“Only some of the sessile formats. Other formats use different methods — all bizarre.”

“They don't flake off circuit copies like we do?”

“No, they ... never mind, you wouldn't believe it if I told you.”

“Do the bipeds set themselves on fire?”

“No, not deliberately. However, they do derive their energy from millions of diminutive internal fires —”

Enough! Another word and you will be demoted to long-term storage! I am stacked up to the back slots with this arrant nonsense! Put out a general order.”

“We are depositing a colony as planned? The conditions here are ideal for our superconductive brains, and —”

“No! We are departing forthwith. We will report that this system has no habitable worlds. Which is true. For if any of us were to live here for more than a few cycles, the mere thought of those things cavorting in magma would drive us mad!”

Unit-Peripheral's sensorium swivelled back to the q-mailed image: a multicoloured globe with ugly patterns of toxic cyan, sickly green patches, deathly brown scars, all overlain with ghastly albescent tendrils. It paused to purge its processors, and uttered its final words on the topic, dripping with scorn. “Why couldn't they have been normal, like us?”


Author information


  1. Ian Stewart, emeritus professor at the University of Warwick, writes popular science books and science fiction.

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