Orphans Far From Stars

When God spoke to Abram of many descendants, his reference was astronomical:

Look up at the sky and count the stars, if you can. Just so, shall your descendants be. (Gen 15:5b)

Count the planets, if you can: that would have been more impressive, though a bit mystifying to the patriarch.

Modern astronomy continues to turn expectations on their ears. Universe Today reports on a New Zealand-Japanese study that found a handful of Jupiter-sized planets wandering in deep interstellar space.

The Greek word πλανήτης (planetes) means “wanderer.” These newly-found bodies certainly are. While most known planets (531 at today’s count) orbit their star in a very orderly way), these others are unattached to any star, wandering freely–and coldly–through deep space in between the stars. There is one of two possible mechanisms for that.

Door number one: an interstellar cloud might not have had enough material to coalesce into a star. So there was just enough material for a large planet, a body too small to ignite the hydrogen fusion that powers a star.

Door number two: a planet was formed in orbit around a star, but was ejected by the gravitational influence of a larger planet. Does this really happen? The mechanism happens early in a solar system’s development: giant planets experience a “braking” from the gas and debris surrounding a star. They slow down, which means they very gradually spiral in toward the star. Any smaller planet in the way, will either be nudged to plummet into the star or ejected into the outer system or beyond.

How could we tell which one happened in a particular case? It would hard without on-the-scene examination. An orphan planet with moons was more likely to be born in deep space. The ejection from a star system will possibly scatter any moons involved in such a cosmic near miss. The smaller the planet, the more likely it was ejected.

I was reading of a theory that some of the early large moons of Jupiter and Saturn also experienced a similar fate. Perhaps even two or three generations of them.

So not only are there giant planets born in deep space, and planets of various sizes hurtling through the universe, but also moon-sized bodies completely divorced from home planet or star. It could be that such bodies are ten to thirty times more abundant than the stars themselves.

Image (it’s an artist’s depiction, not an actual planet) credit: NASA/JPL-Caltech

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About catholicsensibility

Todd and his family live in Ames, Iowa. He serves a Catholic parish of both Iowa State students and town residents.
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