Habitable Zones | The Institute for Creation Research
Habitable Zones

When speculating about life in the universe, scientists need to be more realistic than Hollywood. In Star Trek, no matter where the actors land, they can walk around and breathe the air. That may be easier on directors, but for a surface to be habitable, there are physical requirements.

Astrobiologists limit their searches to regions around stars where liquid water can exist. Because liquid water is bounded by its freezing and boiling points, a "Goldilocks" zone neither too hot nor too cold must be found at particular distances from a star. Extending the inner and outer radii in the orbital plane produces a ring-shaped region called the Continuously Habitable Zone, or CHZ. Under-surface oceans may exist on some planets or moons, but surface life must be in the zone.

A paper in Icarus last August added a complication to the CHZ concept. Earlier estimates overlooked the hazards of ultraviolet light. Highly-ionizing UV radiation rapidly destroys organic molecules. Many massive stars output prodigious amounts of UV. This cuts down on the number of candidate stars. Of twenty-one extrasolar planets studied, only five had an overlap between the UV-safe zone and the CHZ, where life could exist.

Smaller stars have a different problem: a much narrower CHZ. The zone is also closer in, meaning that any planet lucky enough to fit in the zone would become gravitationally locked to the star, with one hemisphere always facing the star, overheating, and the other hemisphere facing away, forever freezing. It is unlikely life could survive except along a very thin longitude near the terminator (the boundary between light and darkness). This means that life is highly improbable except around sun-like stars, a mere 5% of all stars.

Further complications arise when considering a star's host galaxy. Conditions too close to the center are exposed to hazardous radiation levels; too far out lack the heavy elements required for life. This means there is also a Galactic Habitable Zone (GHZ) to consider. Having a zone defined, of course, does not mean an earth-like planet will be present.

Astronomers continue to find extra-solar planets at an accelerating clip. Upcoming missions like the Terrestrial Planet Finder (TPF), Kepler, and Space Interferometry Mission (SIM) may one day succeed in finding an earthlike planet around another sun-like star. Spectral analysis may even be able to infer the possible presence of life from certain "biosignatures" such as gas ratios unexpected from geological or atmospheric processes alone. Given the vastness of space and the number of stars in the "cosmic lottery," astrobiologists are not discouraged at the prospects for life, even with few suitable zones.

What does this mean for Biblical creationists? The Bible does not specifically rule out some kind of life on other worlds. Many Christian thinkers have speculated about it. In the eighteenth century, in fact, the majority thought it foolish to deny it. Now that we have the means, searching for data to replace speculation is a good thing that Christians should welcome. A day of evidence is worth a millennium of conjecture.

*David F. Coppedge works in the Cassini program at the Jet Propulsion Laboratory.

Cite this article: Coppedge, D. 2007. Habitable Zones. Acts & Facts. 36 (4).

The Latest
Does Oddball Platypus Genome Reveal Its Origins?
How in the world did a creature as odd as the duck-billed platypus originate? This creature lays eggs like a reptile, has venom like a reptile, spurs like...

Is Evolution ‘Fake Science’?
The organization BioLogos, which advocates that Christians accept secular evolutionary claims, recently published an online essay entitled “How to...

Cambrian Explosion Alive and Well
A new editorial in GSA Today is claiming that secular scientists should cease using the term “Cambrian Explosion.”1 It’s not...

Abraham Ate Bananas?
Since the word banana does not occur in Scripture, any evidence of bananas in ancient Middle Eastern diets would have to come from the ground. New research...

3-D Human Genome Radically Different from Chimp
All plant and animal genomes studied so far exhibit complex and distinct three-dimensional (3-D) structures in their chromosome configurations depending...

Amazonian Artwork and the Post-Flood Ice Age
An extensive series of South American Ice Age artwork may be of interest to biblical creationists. In 2017 and 2018, scientists discovered a nearly eight-mile-long...

Creation Kids: Dinosaurs
You’re never too young to be a creation scientist! Kids, discover fun facts about God’s creation with ICR’s special Creation Kids learning...

Inside January 2021 Acts & Facts
How is ICR winning science and scientists back to Christ? What is the significance of fossil bone collagen discoveries? Did pterosaurs have feathers?...

Savvy Sons of Light
Many Christians grow uncomfortable when their pastor teaches about money. If it’s any consolation, I know many pastors who feel the same way....

Did God Make Harmful Parasites in the Beginning?
Parasites are a unique form of life in today’s world. These invertebrates come in all shapes and sizes, from single-cell animals (e.g., Plasmodium...