retrograde

 On occasion I write poetry!

I'm fascinated by the fact that just because our Solar System looks a certain way right now, doesn't mean things were the same all throughout its history. It's also amazing how in the past few decades of space science, researchers have noticed peculiar little incongruities about our planetary neighborhood, and from them have begun to tease out pieces of an incredible story--tales of wild planetary migrations, moon systems built from the rubble of an earlier satellite catastrophe, and episodes of intense bolide bombardment. It makes our present-day Solar System seem completely tame in comparison. I'm excited to see what other stories we can uncover as we learn more about our little spot of space.

Neptune's moon Triton is a definite oddball in its system. It's the largest Neptunian moon by far, looks completely unlike the others, and has a really unusual retrograde orbit. From this and other bits of evidence, most scientists have reached the consensus that Triton is probably a Kuiper Belt object that was gravitationally captured by Neptune when that planet moved outward during aforementioned planetary migration episode. However, in order for this to work, Triton would have had to have originally been part of a binary system, and the capturing interaction would have to involve its companion being flung away to who-knows-where. 

It's a rather poignant story when you think about it--somewhere out there is a missing twin, wandering the void alone after an unfortunate encounter with a big blue bully. Is there any way to figure out if a given object is Triton's missing companion? Makes you wonder if we'll ever happen upon it someday.

If we do, we should tell Triton.

retrograde

Triton had a twin once. 

(The name “Triton” seems to effortlessly attach itself to the planetesimal

As if it were the name Triton had all along.

In contrast she never had an Earth-christening—

Her name is the spray of her nitrogen geysers

And the etched-out scrawls of countless freezings and thawings

And the way sunlight spills into her craters at dawn.

But she will never receive a human title

At least not until telescopes become strong enough

And she will likely just be a string of numbers and letters

Assuming she’s still around to be catalogued.) 

They spun together in the beginning,

Aggregated from hot clumps of raw element

That coalesced, cooled, concentrated.

They faced each other, their gazes 

Eternally locked on the barycenter they shared

A point between them they felt out and clung to

As they careened past other shapes in the smothering fog

That Triton only dimly remembers now and does not know if they survived.

The dust dispersed.

The clouds faded into the dim light of a hydrogen-helium day 

Whose photons took hours to reach the sibling worlds.

And they spun on,

Circling their distant mother sun

For ages neither of them felt 

Except that their mantles became slowly more solid

And their crusts hoary with nitrogen frost

That would shimmer as their atmospheres in the summer

And then fall back to become their regoliths’ winter coats 

As the two huddled close for warmth at periapsis.

Things as they were for eons.

But planetesimals trembled with gravity echoes

And spoke of disturbance deeper in.

The giant planets, those titanic orbs 

Who had gorged themselves on gas so that they might first lay claim

To a swept-clear orbit and a satellite family of their own

Were restless.

Reaching adolescence, craving elbow room

They edged away from their close-knit planetary family

To carve their own niches, and shoved askew

Those who stood in their path.

The small ones, Triton and its twin among them

Skittish and scared, scattered into wider orbits 

To accommodate these imperious new settlers of the outer reaches

And peer meekly inward from the safe fringes of the gravity well.

And most of them escaped

But some were not so blessed.

Triton still remembers that deep-blue leviathan

Ploughing its angry way through the aether

Its azure cloud decks pockmarked bruise-brown

By the dead remnants of those 

Who dared deny it passage.

And the two of them can do nothing but watch the behemoth blot out the sun.

Neptune sweeps past and drags them along to join its entourage

Tearing them away from the orbit they’d meticulously traced a million times.

At first Triton fears that their fate is to be slammed into those cloudy depths

But in an adroit maneuver Neptune pulls the strings of its own gravity

And grasps Triton in its orbital clutches

While at the same time discarding the twin, 

Flinging her further into the void

In a haphazard revolution that may see her ejected from the system completely.

Triton watches as she becomes a smaller and smaller pale disc

And then stops being a disc altogether

As it strains against the influences of its new lord

And she is lost forever.

And so it has been. 

Long, long ages pass; 

Neptune is a tempestuous commander

But a benevolent one, keeping its moons

In neat little rows and protecting them from further disturbance.

Triton’s thoughts turn ever outward

And it watches the starry backdrop

Hoping to see the faintest blip in parallax.

Neptune is on the very edge of cold outer vastness

And this gives Triton the hope 

That someday they will chance upon her again.

A probe from Earth comes to call.

It passes by Triton and aims its cameras

A gawking tourist on a one-way cosmic vacation.

All Triton can do at that point is orbit contrariwise

To show that it will never fully conform.