Skeptophilia (skep-to-fil-i-a) (n.) - the love of logical thought, skepticism, and thinking critically. Being an exploration of the applications of skeptical thinking to the world at large, with periodic excursions into linguistics, music, politics, cryptozoology, and why people keep seeing the face of Jesus on grilled cheese sandwiches.

Wednesday, September 9, 2020

A planetary Tilt-o-Whirl

A long-standing unsolved puzzle in physics is the three-body problem, which despite its name is not about a ménage-à-trois.  It has to do with calculating the trajectory of orbits of three objects around a common center of mass, and despite many years of study, the equations it generates seem to have no general solution.

There are specific solutions for objects of a particular mass starting out with a particular set of coordinates and velocities, and lots of them result in highly unstable orbits.  Take, for example, this one, which involves three objects of equal masses, starting out with zero velocity and sitting at the vertices of a scalene triangle:

[Animation licensed under the Creative Commons Dnttllthmmnm, Three-body Problem Animation with COM, CC BY-SA 4.0]

It's a problem that has application to our understanding of double and triple star systems, which seem to be quite common out there in the cosmos.  For people like me, who are fascinated with the possibility of extraterrestrial life, it's especially important -- because if the majority of planets in orbit around a double star (or worse, a triple star) follow unstable trajectories, that would represent a considerable impediment to the evolution of life.  Such planets would have wildly fluctuating climates, a possibility that resulted in a plot twist on the generally abysmal 1960s science fiction show Lost in Space, even though when it came up (1) the writers evidently didn't know the difference between a planet's rotation and its revolution, with the result that the blazing heat wave and freezing cold only lasted a few hours each, and (2) in subsequent episodes they conveniently forgot all about it, and it was never mentioned again.

Be that as it may, now that we have a vastly-improved ability to detect extrasolar planets and determine their orbits around their host star(s), it's given us more information about what kinds of trajectories these complex systems can take.  For example, consider the system GW Orionis, which was the subject of a paper last week in Science.

GW Orionis is a trio of young stars, two of which are quite close together, and the third further away.  The two closer ones are whirling around pretty quickly, and the third making long swoopy dives in toward (and then away from) the others.

Complicated enough, but add to that a set of proto-planetary rings.  Three of them, in fact.  And unlike our own rather sedate star system, where all the planets except for Pluto are orbiting within under seven degrees' tilt with respect to a flat plane -- even Pluto's orbit is only tilted by fifteen degrees -- this system is kind of all over the place.

Here's an artist's conception of what GW Orionis looks like, based on the measurements and observations we have:

[Image courtesy of L. Calçada/ESO, S. Kraus et al., University of Exeter]

Pretty cool-looking.  Given our lack of knowledge of (in this case) six-body problems -- the three stars and the three planetary rings -- no one knows for sure if this is going to be a long-lasting, stable system, or if it will eventually collapse or fly apart.  It seems likely that the system would be a planetary Tilt-o-Whirl, and any orbits formed would be as chaotic as the animation I included above, but honestly, that's just a guess.

However, it's entertaining to think of what life would be like on a planet with three suns in the sky.  One more even than Tatooine:

The more we scan the skies, the more awe-inspiring things we find.  I'm glad to live in a time when our ability to study the stars has improved to the point that we're able to consider not just systems like our own, but the vast array of possibilities that are out there.  One thing's for certain: if you are into astronomy, you'll never be bored.


Humans have always looked up to the skies.  Art from millennia ago record the positions of the stars and planets -- and one-off astronomical events like comets, eclipses, and supernovas.

And our livelihoods were once tied to those observations.  Calendars based on star positions gave the ancient Egyptians the knowledge of when to expect the Nile River to flood, allowing them to prepare to utilize every drop of that precious water in a climate where rain was rare indeed.  When to plant, when to harvest, when to start storing food -- all were directed from above.

As Carl Sagan so evocatively put it, "It is no wonder that our ancestors worshiped the stars.  For we are their children."

In her new book The Human Cosmos: Civilization and the Stars, scientist and author Jo Marchant looks at this connection through history, from the time of the Lascaux Cave Paintings to the building of Stonehenge to the medieval attempts to impose a "perfect" mathematics on the movement of heavenly objects to today's cutting edge astronomy and astrophysics.  In a journey through history and prehistory, she tells the very human story of our attempts to comprehend what is happening in the skies over our heads -- and how our mechanized lives today have disconnected us from this deep and fundamental understanding.

[Note: if you purchase this book using the image/link below, part of the proceeds goes to support Skeptophilia!]

1 comment:

  1. Love your animation!

    What generally happens is that multiple star systems eventually (say, in a few million years) fly apart except for hierarchical pairings that are relatively close enough to behave like single stars.

    For example, with Tatooine, you've got a planet orbiting a close pair. That's stable. But to add a third star, it must be far enough away from the first two that they're effectively a single point. That'll make it far enough that it doesn't show a disk, although it may still be bright enough to light up the night brighter than a normal office conference room.

    Add a fourth star, and it either needs to closely orbit #3 or else be way, way far out there.

    So the upshot is that for most stories, you shouldn't have more than one or two stellar disks in the sky.