Mercury is the first of them to be. The first planet, they mean- their polestar neighbor was first of all, flickering to life before the rest of them formed.
The other planets- their neighbors/siblings/rivals- they're bigger than Mercury, all keeping such great distances from each other. All made of soft gas and gentle ice and calm waters; things that spread them out large but thin. That's something that's survivable that far out in the Solar System, where the danger is comets and rogue moons; things that they can fight, not just hunch their surface against and try to endure. Mercury is the only one who had to form from heavy metals, iron smoke and silicate dust, the only things that could withstand the heat so close to their neighbor.
They hadn't always been the closest to them- the memories are there, dimly, of others like them drifting ever closer to their neighbor until they suddenly weren't, anymore.
(The Sun never mentions them, and neither does Mercury.)
Mercury was tough, then. Even when not even they had believed it, they were tough.
Their neighbor's upper atmosphere, according to those few planets who've seen it (the planets who never. stop. talking.), glows pale pink and flutters like ribbons.
It shines too dimly for most to see, compared to the glare of the rest of their neighbor. It's the part of them that can only be seen at those rare eclipses, when a planet or moon stands in shadow and catches a glimpse of the light's silhouette. Sometimes, Mercury thinks it'd be nice to have someone between them and their neighbor for once.
A corona, says Earth, quiet for a moment in the temporary dark. It's rare to see them humble, and Mercury tries to remember the moment. A crown.
Mercury has never seen it themself- there is no one closer to their neighbor than them, no one to block the glow. They don't need to; they understand their neighbor far better than Earth or Venus or Mars ever will.
The Sun's atmosphere is an endless, twisting glade of teeth; it shines as it burns, tearing through Venus's storms, Earth's machines, Mars's oceans.
It eats, and Mercury wishes that it was out of malice. It'd be so much simpler.
Mercury races in their orbit, trying to outrun the heat.
The tether they circle (have always circled) follows them with their soot-soft gaze, tells them anything they think Mercury would find interesting. Their neighbor understands movement and not travel and can't (or. won't.) believe that Mercury's story will end in darkness.
Mercury runs, and feels the tail burning away behind them, stretching and curling as their orbit shifts, twists. It's horrifying in a way that's instinctual. Orbits aren't supposed to move, to breath like that; they're as central to a planet as their heartbeat.
They do what they always do: Mercury endures by focusing on what's in front them.
And what's in front of them still stings, because that's their surface that's burning away, atom by atom, oxygen and sodium and hydrogen. They're wearing away, little by little, and they can't stop themself from snapping when Earth asks how someone so small can keep shrinking.
They look hurt when Mercury tells them that if they want to find out why even their moon can't stand to be around them, all they need to do is take one of their fancy pictures of themself right then. It wipes the smug curl of their stratosphere away, but somehow it doesn't quite feel like a victory.
Especially when their twin notices.
(You look, Venus tells them, close enough that Mercury can see faint bands in their seething cloud cover and feel the quiet rage radiating off them, just like a comet.
Pretty in pieces.)
It's not something they like to bring up, to Venus's barbs or Earth's callousness or especially Mars's hesitant pity. (The large cold planets, they speak to only rarely. They're family by the metals that flow in their cores, nothing else.) Like most of their wounds, Mercury keeps their worry and weakness near to their heart, gnawing at it like a bone when they can. Like most of their wounds, they end up sharing it with their neighbor.
The Sun listens as best they can through the static that surrounds them, gaze wide and unblinking while their surface flickers and boils. They're hard to read at the best of times; their atmosphere is too big and too violent to look to for clues, and their surface is constantly shifting from one set of features to another as easy as breathing. They are not a planet, and Mercury envies Earth for ever being able to mistake them for one.
"So I'm... I'm kind of worried, Sun. That it'll spread to my surface and I'll-"
They stop, feeling the steady heat around them intensify as they drift towards perihelion, quicker and quicker. It's like an avalanche gaining speed, and there's always the same fear that one day they won't be able to turn away in time.
"You'll be burned?" their neighbor suggests curiously, their voice the distant roar of flames. It's surprising pleasant to listen to them talk, if Mercury ignores the way their words hiss and pops at the edge of their hearing, like a badly transmitted radio signal, a harshness so faint that they wonder if it's even there at all.
Mercury takes a deep breath, tenses as the solar wind strengthens suddenly, punching through their magnetic field as if it were tissue paper. It sandblasts them, ripping off layers of their surface and dragging them into the lengthening tail behind them. (It had hurt more, in the beginning, when there had been parts of them that hadn't been worn down to hardness; they'd had an actual mantel like a normal planet with normal neighbors, once. Even Venus doesn't talk about what happened to that.) Their neighbor, hissing in irritation as they shake off the impact of a comet, doesn't seem to notice.
"Whoops. Sorry about that." Their neighbor returns their focus to Mercury as the small (for them, which is to say dozens of times larger than Mercury) flare dies down. The comet's orbit had been decaying for centuries, spiraling in towards their neighbor with helpless desperation.
Mercury recognizes the scene- slight pain, a casual flash from an explosive temper, an abashed return to calm. It isn't even voluntary; it's instinctive to their neighbor the same way breathing is.
Over the years, they've come to recognize the elements, even if they can't remember the names. After a point, it stops being a tragedy and just becomes a pattern. Comets that drift too near. Asteroids that miscalculate. Planets that don't realize that their neighbor is nothing that can be challenged, that try to go nearer than even Mercury dares.
In the end they all sound the same, the harsh crackle as their surfaces crack and tear away, as the Sun's gravity drags them closer and they scream. The photosphere always cut them short. Mercury prefers to think that they stop on their own, rather than that the sounds aren't strong enough to escape from the gravity well.
"I think you'll be alright, Mercury. You're pretty tough; tougher than me, a lot of the time!" their neighbor says encouragingly, granules on their surface boiling and fading. (Does it hurt, burning like that? They've never thought to ask.) Mercury feels the weight of gravity on them, the pressure of an unblinking, guileless gaze. They can almost feel the edges of millions of teeth gently run over their surface, as close to a planet's comforting pat on the atmosphere as their neighbor can imitate. It's almost sweet.
For (someone?) something so terrifying, Mercury thinks, the Sun is very hard to hate.
“You know... whatever happens, Mercury... You’ll always be my friend.” The Sun seems to flicker, spots of dark trailing across them as they speak. Mercury tries to blink, unsure if the spots are the darkness of solar storms, or of their eyes burning while their neighbor watches. Either way, weakness isn't something they can show.
“Yeah,” they say, gold imprinted behind their eyes. “I know.”