That's not how plane crashes work. 

...It's also not accomplishing anything to sit here in the wet silty mud, getting wet and muddy, and mentally yelling at Reality that the situation she's apparently perceiving is physically impossible and doesn't make any sense. 

"Tsi-imbi," Merrin says to the quiet empty air, almost absentmindedly.

It's a strange kind of quiet. She can hear water moving, a quiet whispering from nearby and a louder rushing off in the distance, and that's the only sound. ...When she concentrates, she might also be able to hear a distant sighing that could be wind. She concentrates even harder, and can pick out very soft...clicking or popping noises? Coming from the sand around her, at irregular intervals. 

That's it. No other sound at all. 

...The tide seems to be on its way out, and the irregular popping-crackling might be the sound of the newly-exposed tidal flats literally freezing, because it's shockingly cold. Enough that Merrin's brain seems to be trying to reject it as some kind of bizarre sensory illusion, because it doesn't fit with anything else in her surroundings. The - ocean? - is apparently liquid. 

She stands up, to avoid getting any wetter, and looks around. 

Her Exception Handling wilderness survival and emergency medicine kit boxes are haphazardly scattered around her, some on rocks, some with their corners sunk into the wet silt. It's almost as though some capricious giant randomly dropped her, and them, out of the sky. 

NOTHING ABOUT THIS SITUATION MAKES ANY SENSE. 

...Also, if she just stands here repeatedly rejecting all of her sensory input as impossible and not making sense, then - well, she has no idea really, because she doesn't even have a hypothesis yet for what's actually happening, but if she's actually in an environment with ambient temperatures of at least -30º C, which is what it feels like, then she will DIE of HYPOTHERMIA with her emergency survival supplies right there. 

Merrin is going to provisionally give up on forming any coherent hypotheses for where she is, or how or why she ended up here, and instead focus on locating and unpacking the box with her power armor in it as fast as she possibly can. It's amphibious, with a built-in air supply, and rated to handle -50º C air temperatures, though operating in conditions that cold will drain the battery pretty fast. 

It's designed to be quick to put on with help, and possible to get into solo, but doing it solo is not as fast as she might hope, especially when she's starting out in comfortable clothing suitable for long-range air travel and now somewhat covered in wet mud and she needs to strip out of that first while her hands are already in the process of rapidly losing dexterity. By the time she has the armor on, her brain has stopped disbelieving the "cold" sensory signals in favor of FREAKING OUT about them and shivering uncontrollably. 

But the suit heating is on, and she should warm up from here without needing further actions from her. 

Merrin turns around on the spot to get a proper look at her surroundings. 

That doesn't look like anywhere. 

Merrin sits down, after a few moments, and stares stupidly at the horizon, which does not resemble any geographical location she's ever heard of. Why is everything purple. Why does the sky look wrong.

Why is she here, alone, with her survival kit and no sign of anything or anyone else, and not True Dead???? 

It takes Merrin what is in hindsight a really embarrassingly long time to piece together several disparate observations into a theory. 

The observations:

- This does not look like anywhere in dath ilan 

- She could gather more data by climbing to the top of the ridge and yet she's not doing that. She's sitting here on the tidal flats, which are rapidly frosting over, because she's tired. 

- She's really, really, really confused and failing to find traction on any of the pieces of her confusion

- She...has...a headache...? 

....This isn't dath ilan.

Therefore, it's a different planet. 

Merrin is having trouble thinking or doing things and has weird symptoms.

...And she's sitting here breathing the air normally, having not actually sealed the helmet fully out of some unthinking "not really liking how it restricts her peripheral vision" motivation, and also something on the suit panel is beeping an alarm, but Merrin puts it together in the second before she actually looks to see what the alarm is. 

There's no reason to assume that an entirely different planet, even one with air that initially seems breathable, has air with the same oxygen content. And so, by Merrin looks down and sees that the alarm is 'low oxygen detected', this is no longer particularly a surprise and she just feels very silly. 

She seals the helmet and the suit takes care of things from there. 

A minute or so later, she has less of a headache and feels a LOT more capable of being vertical. 

Wow. Merrin was aware that hypoxia can be hard to notice internally, because it impairs the metacognition that you need to notice you have a problem in the first place, but she has TRAINING for this and yet it took LIKE FIVE MINUTES for her to diagnose the problem and she was in fact completely tuning out the alarm trying to alert her of the problem and all of that is really quite embarrassing. She'll have to bring it up in the - 

- debrief.

That almost certainly isn't going to happen.

Because this isn't a training simulation, this is...something else. 

Put together the information she has. 

Her last memory is of a plane crashing. Merrin's understanding of the world confidently predicted that she would, at that point, cease having any experiences. 

Instead she's - apparently experiencing the actually-quite-recognizable fiction trope of finding herself on an exoplanet with various intriguing and plot-generating environmental hazards? With her Exception Handling gear all inexplicably along with her, which...is at least hopefully hinting at the version of the trope where the main character can, with great ingenuity, use the resources she has to survive? 

Merrin kind of still wants to yell at Reality that this is incredibly silly and doesn't make sense and should therefore not be happening. 

However, just because Reality is apparently insane, doesn't mean that Merrin would be making particularly sane choices if she reacted to all of this by closing her eyes and saying "tsi-imbi" repeatedly until someone rescued her. 

This appears to be the situation that exists to be interacted with. And...if she just rolls with the premise, it is in fact true that Merrin is rather unusually prepared for the "survival on an exoplanet" story trope. The reason it keeps feeling like a training scenario that she's going to get to debrief afterward is because it's totally one that Exception Handling would throw at her, if it were possible. 

Though even if it were physically within the capabilities of Civilization to arrange this for a training scenario, which Merrin really doesn't think it is, she doesn't think that Exception Handling would arrange to have her experience it without warning like this. It feels out of character. There are scenarios they might throw at her by surprise, where she's not necessarily prepared has to improvise with non-optimized equipment, but not 'surprise: you're on another planet'. If Exception Handling had access to instantaneous-travel to other planets with different atmospheres, Merrin is pretty sure she would get at least a briefing beforehand and a list of the situations in which she could expect them to call off the scenario and rescue her.

So she should not be expecting to be rescued, if she gets herself into something she can't handle. 

Okay. Time to focus, and stop wasting mental cycles on disbelieving that any of this is really happening, and instead use her entire brain toward surviving it if it is. 

There's no particular reason to think that 'low oxygen atmosphere' and 'subzero temperatures' are the only life-threatening hazards. Merrin needs to orient, and form hypotheses about what sort of planet this is and what its properties are, and then test those hypotheses, and then make plans to survive both the immediate and the longer-term dangers. 

She accesses the wrist panel on her power armor to check what environmental parameters it's picking up. 

The basic suite is pretty straightforward. Ambient air temperature: -38.1º C. She was not wrong that it's really cold.

Ambient pressure: ...pretty normal. Slightly low for literal sea level, but not for, say, 1000m altitude, which would not give anyone altitude sicks. 

Atmospheric oxygen fraction, though: 13.5%. Eep. That's not quite low enough that she would have progressed to unconsciousness and seizures within minutes if the suit hadn't warned her, but...she's actually rather fortunate that it was so cold. If she'd arrived to a comfortable balmy temperature, she might have started exploring without first putting on the armor and switching it on for the heating, and she probably would have realized what was wrong before she collapsed, but...possibly not actually in time to fix it while already impaired. 

....Well, she's gotten as far as analyzing the hazards she already knows about and that's already enough to alert her to some very serious problems!

Namely: at these temperatures, her suit has maybe 18 hours of battery life. And less oxygen supply than that. And she's not predicting a rescue in the next 18 hours. 

Okay. What are her solutions. 

She has a field oxygen concentrator, in the extended medical kit. And one caniser of compressed oxygen, for use in conditions where for some reason she can't set up the oxygen concentrator. She can adapt the various components to refill her suit's tank from the canister, and then fill the canister from the oxygen concentrator, and that gives her mobility. If she doesn't need mobility, she can park herself next to the oxygen concentrator and pipe it directly into her suit; it produces slightly more than she'll need at rest, so she could even still accumulate some extra for storage. Or, given that she needs to figure out shelter anyway once the suit runs out of battery, she could just sit around with nasal cannula on her. The atmosphere isn't toxic, it just doesn't have quite enough oxygen for humans to stay healthy. 

The oxygen concentrator also needs power to run. 

She has batteries. At 15º C she could power it for a couple of days just off stored power. 

Merrin has no reason to think her situation will end in a rescue in two days. 

She has a portable kit with solar panels. The sky looks clear, so if she's lucky, and she can find a nice undisturbed place to set up camp, she can generate solar power to refill batteries during the day, use stored power at night, have some backup stored oxygen (as a backup for her backup, she does have three sodium chlorate candles which will generate 6h of oxygen each, but if she has to use them, they're gone.) 

...Great. Progress. She's broken it down to 'if she can find a place to camp, she can indefinitely keep breathing air with enough oxygen in it.' She also needs water, and food, but she has some of each with her - enough water for several days, enough food for a month - and she has a filter and purification tablets if she can find freshwater locally, and she doesn't have a pre-built kit to evaporate and distill seawater but she knows how they work and she has a lot of emergency medical equipment and supplies that she doesn't need and can instead repurpose for survival. ...She'll need a heat source, she can't evaporate enough water by the heat of the sun if it's winter - it has to be winter, if it were this cold all the time there wouldn't be liquid oceans -

- actually, no, she's confused.

It's -38º C. There should be icebergs. Not just frost on the ground and some delicate icing-over of the little river flowing down the center of its channel, surrounded on either side by hundreds of meters of silt and rocks. There should probably be snow??? A desert might be completely bare of snow even in the depths of winter, but deserts are usually in the continental interior, not coastal. She's standing right in the intertidal zone. There should be regular precipitation, here, and if it's this cold it should be coming down as snow, so where is the snow? 

...She checks the suit readout again. You know, just in case she hallucinated it the first time or something. 

Still -37.4º C. 

That's...about half a degree warmer, actually, which is maybe hopeful that the winter days are warmer than the winter nights. She arrived more or less right at dawn. She's been here for...twenty minutes? Huh, it feels like it must be less than that, or the sun would have covered more distance, it's still only a little ways above the horizon. 

Merrin navigates to see the temperature trend. 

It's definitely getting warmer! By about 0.6º C per ten minutes. Well, that's at least hopeful in terms of the peak afternoon temperature being less frigid. The coldest temperatures are usually going to be shortly before dawn, so if it warms up enough and takes long enough to cool fully overnight, then -40º C is probably the worst she has to deal with, and she might even be okay in just warm clothing for the warmest part of the afternoon. She'll absolutely need to figure out some kind of shelter by nightfall, that's still the next step, and by tomorrow she ideally needs a good place for solar panel setup...

The obvious constraint on where she can set up shelter is that it needs to be above the high tide line. So, next up: figure out where that is. 

She leaves the boxes where they are - she will need to haul them with her, she absolutely needs all of her gear to survive this - but for now she's just exploring. 

The silt is rapidly freezing over, and crunches under her feet. 

The exposed rocks are covered in some sort of purple biofilm, which seems to be resisting the frost, and incredibly slippery. There are also armored limpet-like organisms, some almost as large as her fist, with radial ridges that look razor-sharp. 

The exoplanet has multicellular animal life!!!!

 ...That was something Merrin probably had visual evidence of earlier - the weird little holes in the silty part of the tidal flats look like something left by burrowing invertebrates - but she hadn't quite fully and explicitly made the observation and inference, because at the point when she was paying attention, she also hadn't explicitly thought through the "being on another planet" part. 

The primary photosynthetic pigments in the local equivalent of...prokaryote algae?...are purple. Dark purple, a lot of it is closer to black with purple undertones, and iridescent blue-green from some angles when it catches the light. She...can probably infer things about the planet's sun, from that, once she has a chance to dredge up her not-strictly-human-medicine-related biology knowledge. 

The time for that is probably not right now. ...A lot of dark pigment might hint at high UV levels? Which is useful to know - and makes perfect sense, a lower-oxygen atmosphere would mean somewhat less ozone production and a thinner ozone layer - but if she's wearing the power armor for heating anyway, she's not going to get a sunburn. 

(There's no reason to assume the animal life is edible for her. Or the plant life, for that matter. It might all use completely different amino acids and undigestible sugars. ...Reasoning off fiction tropes rather than physics - which Merrin is making SO many mental faces about doing but this is SUCH a tropey situation to be experiencing - then it depends on the author's taste and the flavor of story they're going for, it might be the case that this biosphere is just mysteriously compatible with dath ilani life. Maybe given time she can figure out how to repurpose her field blood-test lab equipment to figure out the composition? ...Off the top of her head Merrin has no idea how to do that but if she uses her brain and doesn't DIE STUPIDLY then she might have time to figure something out...) 

(Life!!!! Alien life on another planet!!!!!!!! Merrin might not have chosen to be in this situation and might - pointlessly, she's aware of that - resent Reality enormously on multiple levels, but also, ALIEN LIFE ON ANOTHER PLANET is really superheated cool.) 

The tidal flats slope gradually upward for a while. Eventually Merrin reaches the edge of the (probably limestone? definitely some kind of sedimentary rock with visible strata) valley walls, and when she looks back, the boxes are definitely at least four or five meters lower than her current elevation, over maybe 300 meters of horizontal distance. 

The valley walls aren't cliffs. Fortunately, or it would be a lot harder to climb up. It seems like it was once a V-shaped valley - carved by a river, maybe, at some point in the past when the river was a lot larger, or maybe it is larger in non-winter seasons. The erosion pattern produces a step-like effect. The stone is also crusted with (much smaller) limpet-like molluscs, and more of the purple probably-algae-biofilm. Here, it's been exposed long enough that the surface has dried out to the texture of waxed leather, and is no longer particularly slippery, but when Merrin touches it, there's still a feeling of gelatinous squishiness underneath: there's water present under the waxy surface, and it's still liquid. 

That's really cool. It's probably full of antifreeze proteins or something! 

She starts hiking up the slope. 

...The gravity on this planet is not right. 

It was less noticeable on the flatter area; the power armor gives her some help, to avoid her exhausting herself just hauling around its weight, and it probably recalibrated automatically, and the default panel readout doesn't list local gravity because, like, why would it, the suit is not rated for space. She was falling down kind of a lot, but it was easy to blame it on the insanely slippery mucilaginous biofilm stuff all over the rocks. 

Merrin digs through suit readout menus and determines that the suit sure is estimating an effective gravity of 1.18G.

She eyes the sloping limestone. It's going to be even more annoying than she thought to haul eight entire boxes of gear to the top. She's really not going to want to carry them any further than necessary. And she doesn't know how close the tide was to fully out; if it's already turning, she doesn't have that long to work. 

She climbs. 

Eventually she's covered another ten meters of elevation, over maybe fifty meters of horizontal distance. 

There's less of the algal film - and what there is looks more thoroughly dessicated, it's firm rather than gelatinous - but the rocks are still crusted with limpet-like and barnacle-like molluscs. 

....She's still below the high tide line. 

Merrin looks down into the valley. There are her boxes of gear, near the bottom, looking small and sad, especially when she thinks about the fact that that's all she has. 

She turns and looks out toward the ocean. 

...It's further out. It's a lot further out. And still going out, judging by the smooth outflow rather than turbulence of rising-tide-against-river-current. 

Her suit clock thinks it's been about two hours since she put the suit on. It's not trivial to eyeball from here, but when she appeared she was just above the high tide line, sitting in mud that had been covered until recently enough that it hadn't yet frosted. The water could easily have dropped three or even four meters since then. 

Great! She's managed to figure out the next environmental hazard while it's still getting further away from her rather than closer to her! 

In dath ilan, most coastal areas have a tidal range of less than five meters. Based on what she knows right now, this planet has a tidal range of at least twenty meters. 

And she's in a river valley. Even with just, like, eight meters of tidal range, river valleys can act like a funnel, squeezing the incoming tide into a tidal bore wave of pretty significant height and force. 

She doesn't want to be anywhere near the bottom of the valley when the tide comes back in, and she doesn't know how long she has to work.

...How much higher than this does she need to get?

Looking up, she can see a couple of different debris lines; this planet doesn't seem to have trees, there's no driftwood, just shredded bits of what must be some kind of seaweed, dried onto the rock. Probably the most recent high tides line up with the lower debris lines, given how thoroughly dried-out the higher ones are, but she doesn't know that for sure. 

Time to scramble up faster and see what's at the top of the valley walls! 

Incidentally, the sun isn't actually all that high in the sky yet, but her suit thinks the ambient temperature is now up to -31º C. Still chilly, but a seven-degree increase. The suit power expenditure on heating is very slightly lower. 

Maybe by afternoon it won't be all that far below freezing! 

It takes Merrin another fifteen minutes to reach the top of the cliff. She checks the suit readout again; the temperature is up almost another degree. 

There...isn't much...on land, in terms of signs of life. It's basically just patches of lichen and more biofilm-like stuff. 

The rocks have very noticeable bleaching patterns on the areas that Merrin can predict would be sun-facing. There's also a lot of cracking, of the kind you might expect from repeated cycles of frigid temperatures - with water freezing and expanding in tiny cracks - followed by heat expansion of the rock itself. 

It sure does look like the photosynthetic life goes for purple pigment, and occasionally orange. 

...It does not look like a hospitable place to make camp. Merrin has gear for that, in one of the boxes, she's not stuck making her own shelter out of local materials – which is GOOD because this planet doesn't have WOOD – but she's not sure she has a great setup to anchor a tent into cracked and UV-damaged bare stone. She could improvise carrying slabs of broken rock to weight it down, but - it's so exposed, up here... 

She turns around and eyes the terrain upstream. 

There's a cave. 

...Which Merrin can't even slightly use for shelter because it's blatantly going to flood at high tide. Probably flood explosively when the tidal bore squeezes its way up the river channel. In fact, she wonders if the cave exists directly as the result of water erosion from the regular gigantic tides blasting their way into an obstacle in the river channel and finding a region of softer stone. This is a silly way to feel, but Merrin is almost mad at the cave, sitting there practically offending her with its tempting yet treacherous offer of protection from the elements.

Maybe at some later point she'll have time to explore. For now, she'd better get her gear out of the path of the GIANT TIDAL BORE before the tide starts turning. 

She starts scrambling back down, which does at least go faster than climbing up. 

Still, by the time she's at the bottom, the temperature is all the way up to -26º C. 

The sun still hasn't covered all that much of the sky, given that it's now been three hours since dawn. 

.....Merrin is starting to have. A little bit of a suspicion. 

She can't easily test it now. The valley floor, soon (hopefully not too soon) to be submerged, is not a good place to set up any kind of observation station. It'll have to wait until she's dragged herself back above the high-tide line again. 

She reviews her supply kit. 

Each of her boxes has an inset on the side where a laminated inventory card can be swapped in, and each card lists all the boxes, with color coding shown, before listing the full detailed inventory of the individual box. 

CASE 1 (RED) - CRITICAL MEDICAL SUPPLIES 
20 kg
Trauma supplies: tourniquets, hemostatic gauze, chest seals, airway management, IV access, critical injectable medications (epinephrine, morphine, ketamine). 4L IV fluids. Oxygen concentrator, main battery pack (5 kWh), backup O₂ generators, pulse oximeter.

CASE 2 (GREEN) - WATER & FOOD
25 kg
15 days emergency rations (3500 kcal/day), 5L drinking water, water filter, purification tablets, UV sterilizer, collapsible containers, cooking gear, fuel canisters.

CASE 3 (BLUE) - SHELTER & THERMAL
15 kg
Tarp, sleeping bag, insulated pad, 100m paracord, emergency blankets, chemical heat packs. 

CASE 4 (ORANGE) - TOOLS/POWER
22 kg
Solar panels (100W), backup batteries, 50m climbing rope, harness, carabiners, knife, axe, multi-tool, sewing kit, tactical lights.

CASE 5 (PURPLE) - EXTENDED MEDICAL
30 kg
Antibiotics, oral medications, additional wound care, suture kits, surgical supplies, diagnostic equipment, decontamination supplies.

CASE 6 (GREY) - EXTENDED PROVISIONS
30 kg
30 additional days of emergency rations.

CASE 7 (GREY) - REDUNDANT MEDICAL
25 kg
Redundant medical supplies: extra IV fluids (6L), gauze, sutures, medications, gloves, emergency blankets, reference materials.

CASE 8 (BLACK) - POWER ARMOR 
80 kg (full)
(However, currently empty except for a 5kg spare power pack in a 4kg box) 

Okay. 

Merrin needs Case 1 because the atmosphere isn't breathable, that's non-negotiable. She needs power, or she dies after the battery power runs out for the oxygen concentrator; Case 4 is also non-negotiable. 

She needs shelter. She does not have the option of building one with local materials. 

She needs food. Ideally all of it, to buy more time to figure out which local lifeforms are edible with what processing. 

Honestly, the only boxes she doesn't really desperately need are Case 5 and Case 7, all the backup medical supplies. Except that, one, she might well end up injuring herself, and two, her trope-sense is tingling and insisting that it would be TOTALLY ON THEME for this stupid survival scenario to somehow also involve someone showing up with a medical emergency. Merrin does not THINK that's how any of this works, because it would be so incredibly silly, but given her spectacular levels of uncertainty around everything she thought she knew about Reality, she's not SUFFICIENTLY CONFIDENT in that to entirely discount it. 

Since transport would also be a significant issue in the survival scenario she had been expecting to need this gear for, the boxes lock together, and in theory she can lock together four of them and lock that onto a harness and the power armor would let her carry that many at once. 

In theory. In normal gravity, on reasonable terrain. Merrin is absolutely not going to risk it at 1.2G when needing to scramble up uneven, potentially slippery slopes. Too much risk that she would at some point slip and fall and tumble end-over-end all the way to the bottom of the valley again, which could injure her and might damage the power armor and would definitely set back the timeline. 

Two at a time, then, and she'll just have to keep an eye on the receding tide and do as much as she can. 

Even laden, it's a little faster; she has her route planned, and the terrain is steadily drying out; the mucilaginous rock films retain water remarkably well, but the surfaces eventually dry out to a waxy texture. They're surprisingly tough, too. Even with all the extra mass she's carrying, the treads of her boots don't shred them. 

Well, they have to go through a lot, what with the violent tides blasting up and down this riverbed on a twice-daily basis. 

It's now slightly less than five hours after dawn.

The sun is...higher. It doesn't look anywhere near the zenith of its arc through the sky. It's noticeably an angled arc – which makes sense, for winter at a temperate latitude – and it's a little hard to judge when Merrin keeps changing position and viewing it from different angles, but eyeballing it, the sun is maybe a third of the way up the arc its tracing. 

Eyeballing it isn't good enough for planning purposes. Merrin is going to pause for five minutes, despite the time pressure, and kludge together a sundial out of fragmented bits of shale and, when it doesn't want to hold together as sturdily as she prefers, a mouthful of water from the built-in drinking bladder in her power suit, mixed into one of the exposed patches of hard-baked dry clay to make it into, instead, sticky wet clay. 

She marks the sun's current shadow with an indelible marker - she has one of those in the small light front-pack clipped to her suit where it's not in the way. 

And then back down. ...Temperature check? 

It's now -17º C. 

That's a twenty-degree increase in five-ish hours.

If she's eyeballing it right, solar noon might not be for another ten hours, and the temperature will probably peak a little after that. 

...Merrin now has a hypothesis for why there aren't any icebergs. 

Again, it takes about an hour to scramble all the way back down and return to her remaining boxes. 

(The tide, so far as she could tell, was even further out when she was climbing down and had a good view. From her current angle she can no longer see ocean at all, just the river itself, still working on icing over but in another five hours that's going to start reversing course.)

Almost three hours per trip, once you take into account loading and unloading. She won't have to climb down on the last one, but that's still eight hours to get everything else and that's assuming she doesn't rest at all. 

She has longer than she feared. This ridiculous planet clearly has a longer day-night cycle than what she's used to, and the tidal cycle should be (approximately) (at least, assuming there's just one moon) tied to the length of the day. With high tides specifically twice a day, she thinks - yeah, she's remembering that right, the "tidal bulges" are on the side of the planet facing the moon and, symmetrically, on the opposite side, and rotate as the planet rotates under the moon. 

...She hasn't seen the moon, so the last high tide must have been the tidal bulge opposite the moon; otherwise, low tide would correspond to moonset, implying the moon had previously been visible the entire time. (She thinks "low tide is always moonset" holds? She doesn't know how long a full orbit of the moon would take - it depends how fast the moon is moving relative to the planet, on dath ilan the "lunar day" determining tides is almost an hour longer than the solar day as the planet "catches up" with a moving moon - oh, no, and she's also doing some approximation, she thinks moonrise-to-moonset isn't always exactly half of the lunar day period, it varies based on...stuff...that she knew some facts about once that she cannot retrieve right now and probably can't figure out on the fly for another planet anyway so it's irrelevant and she'll need to determine it empirically...) 

- approximation is better than nothing. Low tide is moonset or moonrise. She hasn't seen a moon yet, ergo, it's not yet low tide, the tide is still going out. Once she sees the moon, she'll know its on its way back in. 

...The tide seems to have been draining out at a rate of somewhere between one and four meters per hour depending how far she trusts her eyeballing. In theory, knowing that the "lunar day" is closeish to the solar day should, once she has a sundial measurement to sanity check her sun-eyeballing, let Merrin estimate the duration between high tides and, given the per-hour rate of water dropping, get an estimate of the total tidal range that way. Ish.

Merrin is really hoping it's closer to 1-2m, because 4m and a day that might be 30 hours long - a winter day! in addition to her first uninformed wild guess that it surely can't be -40ºC in summer or she would be in a glacier right now, the sun's trajectory is compatible with winter-at-temperate-latitudes, though she has no way to estimate her actual latitude without knowing the planet's axial tilt - anyway, if a winter day is 30 hours, then who knows maybe the night is 50 hours and an 80-hour solar day divided by four is twenty and twenty times four meters an hour would mean EIGHTY METER TIDES and that's pessimistic wildly-approximate-math, it's probably more like her 95%-confidence-interval for maximum tidal range than her 50%-confidence-interval, but it sure is a terrifying 95%-confidence-interval upper bound to be assigning. 

For now: there's still no moon in the sky. Not low tide yet. She should focus on hauling boxes. 

Two hours later - seven hours after dawn - and she's dropping off more boxes at the top of the slope and making a mark on her sundial. It's not an accurate enough sundial to be certain yet but it does, in fact, look compatible with "sunrise to sunset will take about 30 hours". 

...Check on ambient temperature trends? 

-9 º C. 

The ocean is....just, barely, visible, as a strip of glimmering purple-maroon that might be a whole ten kilometers away. 

STILL NO MOON. Not that Merrin wants a moon, because she doesn't want it to be low tide yet, but it's still mildly driving her nuts not knowing.

She mostly hasn't been itching too much about the lack of prediction markets - she's done a whole run of training sims recently with only low-bandwidth voice-on-radio backup, specifically to practice decisionmaking under stress without all the smartest people in the world feeding her advice via prediction markets, and she managed to successfully discount it as not worth being mad about - but right now Merrin would REALLY LOVE if the twelve most excited astrophysicists in dath ilan were eagerly debating every single data point available and narrowing down probabilities. She's pretty sure she could be doing more with observations she could make if she knew to make them, and it's just that she's not a superheated expert in tides, or in any of the several thousand fields of expertise that are not specifically emergency medicine but would be A LOT MORE HELPFUL right now. 

...At least Merrin is unusually well-prepared for one element here, which is repeatedly hauling very heavy storage crates of life-critical emergency supplies up a giant limestone slope, while under the effects of 1.2G, and also keeping the suit power-assist as low as she can cope with to save on battery life, and resisting the temptation to bump her air up to 25% oxygen for the stamina boost because she doesn't know how many problems she'll have with solar generation, and doing all of that for what's going to end up being nearly twelve hours straight. 

It really feels like the universe is trolling her.

Cases 1, 2, 3, and 4 are now at the top of the slope!!!! Merrin has oxygen, power for the oxygen, the makings of a shelter, and 15 days of food! 

Merrin scrambles down as fast as she can. She's definitely going to have time to grab Extended Provisions and Extended Medical. Whether she has time for the box her armor came in - light, since she's wearing the others, but unwieldy enough that she doesn't want to attempt to paracord-tie it on top of two other crates - or for the Redundant Medical Supplies, depends on when she sees a moon and how scary the incoming tide looks. 

Tidal bores are unpredictable, is the thing. You don't get a steady flow, you get a small incoming tide – because most of it is getting hung up in the narrowing river-mouth inlet - and then you get a wave bringing tens of meters of tide all at once. She thiiiinks she read one time that you can get tidal bore waves nearly as high as the total tidal range in a region, though that takes very specific conditions and geography and she's probably not that unlucky. Unless the universe is trolling her. 

Anyway: there's a discontinuity, turning a smooth water-level graph into a step-function, and there might be physics to determine when the step happens but Merrin doesn't know it and it would rely on measurements she has no way to take. She suspects it means that the point where her stuff is will be flooded sooner than it would otherwise, because it's at least ten meters below high tide and at least ten above low tide and so, approximation, it's exactly in the middle, and probably the step-function jumps from "tide is below what the naive math predicts" to "tide is above that" across the middle of the tide graph?

...Or possibly Merrin is incredibly confused because she's trying to visualize hypothetical graphs of water levels in her head while hauling stuff up a hill. 

She's halfway up the limestone slope - moving a bit more slowly, now, she's starting to risk fatigue - when she sees the moon. 

It is a superheated enormous moon. ...Well, strictly speaking Merrin has no way of knowing if it's larger than dath ilan's moon or just closer, just that the angular diameter as seen from the planet's surface is a lot larger. (There's probably some sort of astrophysics where one is related to the other but she doesn't know it and cannot rederive it from basic principles on the spot in her head while hauling crates up a hill.) 

That...would in fact explain the enormous tides, wouldn't it. 

Top of the hill. An hour later, according to her suit clock, and it's now been ten hours in total since dawn. 

The temperature is now 0.2° C. Positive 0.2° C. The ice is about to start melting. 

The sundial, and also Merrin's eyeballs, think the sun is about two-thirds of the way to its zenith. More likely to be a bit more than that than a bit less, but...call it a 30-hour day.

Merrin should try to estimate how close in angular degrees the zenith is to "directly overhead", once the sun is there, that'll let her do some math and figure out roughly how much longer the night is than the day? ...Is that true, or would it need to be stupid guesswork math because she can't untangle "different axial tilt" from "exact latitude" or "exact season relative to winter solstice and nearest equinox"? - no, she thinks if she can get a sense of where the sun rises and where the sun sets and estimate that as a fraction of the total...horizon circumference? there's got to be a better term than that? - but if she knows how "small a bite" of the sun's arc happened above the horizon, relative to if it were passing directly overhead at a 90 degree angle and the day and night were exactly equal, she can figure out how much of the circle is left "under" the horizon and thus the relative durations of day and night?

This is definitely math she needs writing materials for, it's been a while since she had any reason to do math like this. Fortunately, her gear includes a reasonable quantity of (tough, waterproof) paper, plus writing utensils for it. She'll run out food before she runs out of notebook space. 

...And low tide was an hour ago. 

She can almost certainly make it down and back. The ocean still looks very far away and she still can't see or hear the roar of a wave surging up the inlet. It seems likely that the interval between low tide and high tide is, like, fifteen hours or something, and ten hours ago her nearby spot was already above water, so it's probably more than halfway up in terms of elevation. She doesn't have another ten hours, because of the tidal bore effect, but it would be really quite baffling if she had less than two hours. The tide looks like it's gone out past the eroded cliffs at the mouth of the river inlet, so initially it's going to be rising normally without encountering obstacles to concentrate the forces. 

It's worth a tiny risk, for the benefit of backup medical supplies that could mitigate other risks later. And it would be really nice to have a way to store her armor securely where it can't get damaged by the elements.

Merrin isn't certain, though, and so it's going to be an intensely nervewracking last trip. 

The trip down is rapidly becoming noticeably more difficult than the previous three trips were.  

The thing is that the ground was previously frozen, and froze within seconds to minutes of being exposed by the tide. Which created its own hazards, of course, but the black-ice tidepools were visible and possible to avoid, and much of the rest ended up freezing with a sandpaper texture that did not create additional slipping hazards. 

Now the little pockets of trapped water are melting. They'll almost certainly dry out the rest of the way under the bright, increasingly hot sun, but in the meantime, it takes Merrin 50% longer to safely make it down. 

By the time she's back at her stuff, the air temperature is still only up to 4° C, but the surface level of the frozen tidal silt is absorbing the sunlight and melting. It's quickly becoming very squishy. 

Merrin - somewhat unusually for her social group - has spent enough time near oceans to have an intuitive-level prediction about how long it would take for the silt-mud to bake in the sun and dry out a bit and have less of a tendency to try to eat her boots. 

...Longer than she expects she has. 

Well, nothing for it but to load up again and trek back. 

Merrin plus power armor weighs around 130kg. (It's not the kind of armor that would deflect high-energy projectiles; it's designed to make her able to carry more with less fatigue and to safely operate underwater and survive being banged around a bit, but it's also optimized to be lightweight and have as long a battery life as possible, for scenarios where she's a long, long way from Civilization and a reliable power supply. The armor itself still weighs more than she does, but only slightly more.) 

Another 35kg of boxes is "just" a 27% increase in mass. But it's mass in a location that shifts her center of gravity, and the thawing ground is trying even harder to eat her feet.

...Merrin might, perhaps, have prioritized suboptimally here, though admittedly there's also an element of poor luck. 

She could have done this ten hours ago, no problem. She would be having a somewhat easier time now if she had EATEN MORE CALORIES, which she hasn't, because she would have to unseal the suit helmet to eat a meal bar and she didn't prioritize taking half an hour to set up the oxygen concentrator, partly because she was worried about leaving it exposed to the frigid cold and draining its battery life, but she could have caught onto the trend like SIX HOURS AGO if she had been PAYING ATTENTION and guessed that there would be a window of totally innocuous temperatures. 

Anyway. She's had maybe 800 calories worth of meal replacement liquid, by dint of just pouring it directly into the drinking bladder built into her suit, which she can do without removing the suit though she's perhaps going to regret it when she has to clean it later, normally she sticks to electrolyte powder in there.

(She can, fortunately, pee in the suit, and it doesn't even involve having to catheterize herself, there's a pad of super-absorbent material that wicks the moisture away. She'll have to dry it out later and reuse it, she only has one spare.) 

She does have a couple of meal bars in her front pouch but the problem remains that she would have to unseal the helmet, and either breathe low-oxygen air or, like, override the "open helmet" alarm and waste a lot of the air supply blasting oxygen out the front of her open helmet. And stopping to eat won't actually fix the whole problem. Her body doesn't just need a meal in her stomach; her muscles need rest. 

And she can't afford to stop here, because it's POSSIBLE that she has only ONE OR TWO HOURS until an enormous wavefront that could be up to 25 meters high and will be moving at 50 km/h bears down on her. 

(She probably has longer than that, and it might not be quite that high; tidal range varies. But if Merrin makes a habit of taking risks because it's 95% likely to be fine this one time, then all those 5% risks of disaster will RAPIDLY COMPOUND. She has no backup, here.) 

...Can she manage without the boxes, or has she just thoroughly misjudged her endurance and doomed herself here? 

She can manage a lot more easily without the boxes! It's still an intense workout, keeping her balance while the silty mud tries to swallow her boots, but she can do it. 

Okay. 

Merrin does not think she can afford to risk another laden trip up the slope.

(For one, if she gets caught in the wave, she...will have a significantly better chance of surfing it upstream and surviving the adventure if her suit has the hydrodynamics she's used to. She's never actually done a training that involved challenging water conditions with several boxes of gear strapped to her suit and completely ruining its streamlined profile, let alone what more or less amounts to attempting to surf a tsunami. 'Getting caught in the tidal bore' is still a huge risk, to be clear, her challenging-water-training took place in the open ocean and not in a river channel full of dangerous obstacles, but she might be able to manage it if she can trust her power armor's water functions to be at top performance.) 

...She's genuinely pretty upset at the prospect of losing the last two boxes. The backup medical supplies aren't just useful for emergency medicine; she could turn the gauze into textiles for clothing, use the sute needles as...fishhooks? does this planet have actual fish or just simple invertebrates?...she hasn't thought through everything that could be improvised into something, but eight boxes of gear is all she has and it's viscerally painful to think about losing it. And her armor box is, in addition to a safe place to keep her precious and essential armor suit, an insulated, waterproof, and highly durable storage location for arbitrary objects. She doesn't have the manufacturing ability to make any more. 

The boxes might wash upstream and be findable later? If she's willing to spend the next several months looking? They're really durable; Exception Handling toughened wilderness gear is dath ilani manufacturing at its finest. The contents might pick up some damage if exposed to extreme g-forces, but the medical supplies in particular are not very fragile and are packed in a way where they ought to survive being literally airdropped from 5,000 meters without a parachute.

The main cost is that she would have to scour every meter of riverbank, and meanwhile they would move with every tide, and...yeah, she might find them before she dies here, or she might not. 

...Can she somehow wedge them in a place where they'll still be there once the tide drops? Put them somewhere where the incoming tidal bore will just push them harder against the wedging surface, and hope that the speed and turbulence of the current from the outgoing tide is less intense and they stay put? 

Well. She's actually pretty much right beside the river channel. And the very bottom of that channel, already submerged, is going to be the place least disturbed by the violently incoming tidal waters. And she is wearing a suit that's designed for underwater operations, and taking a break from the gravity might actually count as a bit of a rest. 

She slips down into the water. 

(It doesn't feel cold. It must be frigid - the suit will have a record to peruse later - but the armor takes care of heating.) 

....It's beautiful. It's really, really pretty. 

It's an ACTUAL EXOPLANET with ALIEN LIFE!!!!!!!! Merrin has not had a huge amount of time to think about the positives of her extremely ridiculous current situation, but it continues to be really cool!!!!!!!!

There are more, and larger, mollusc-like organisms down here. Some of the shells - a little like clamshells or oystershells in shape, but remarkably dense and heavy and thick - are slightly open, with delicate fronds waving, but if Merrin's shadow passes over them they immediately snap shut with rather a lot of force. You could lose a finger that way. If Merrin tries tugging on them, she'll find them glued to the rock with a very impressive stubbornness; it would take a sharp knife, or possibly underwater explosives, to dislodge them from their anchors.

There are algae biofilms plastered flat against the stone everywhere, and in a wider range of colors – not just the deep maroon-purple-black, but vivid crimson reds and even deep rosy pinks, the photosynthetic pigment present with less of the melanin-analogues for UV absorption. 

There are...tubeworms? Short, segmented, heavily armored bases, with long delicate tendrils waving in the water that, again, instantly curl up and vanish inside the armored tube when Merrin's shadow passes over them. 

There aren't all that many mobile fishlike organisms. A few semi-translucent wormy things, no larger than Merrin's pinky finger, that stick close to the rock surfaces and corkscrew into crevices when her movement disturbs the water near them. She sees one larger organism – a segmented-worm body with bilateral rows of flat paddle-like limbs, like a bizarre combination of a fish and a centipede. It's about twenty centimeters long and swims slowly, radial mouthparts opening and closing in the algae-hazy water. 

Cooooooooool!!

(This planet is...probably a lot earlier in the history of complex multicellular life, Merrin thinks? It would make sense of the lower oxygen, if there just hasn't been enough photosynthesizing biomass for long enough to complete the shift from a low-oxygen to a high-oxygen atmosphere. The centipedefish is the only organism she's seen that looks like it has a genuine nervous system, and probably not much of one.)

There are also larger, thicker mounds that, on closer examination, seem to be some kind of sea sponge. They're flattened, not structured like coral on dath ilan, but they're hardened - calcium-like deposits, or some kind of very tough hard keratin-like protein, or both, or something else entirely, Merrin has no way to determine the exact chemical composition. 

There's also seaweed! It's the most complex and structured plant life she's seen by far. It's sort of kelp-like, with a root-system anchor and fronds that extend into the water column. No sign of air bladders for buoyancy, though, and the fronds mostly hang downward from rock overhangs into the current, though they're anchored in ways where it doesn't look like it would risk dislodging them if the incoming tidal current were to tug them the other way.

Unsurprisingly given the forces they're regularly subjected to, the root-anchors are huge and extensive. If Merrin swims up close and paddles against the gentle river current to stay there for a while, and uses her headlamp, she can see that the roots aren't just stuck to the rock, but at dozens or hundreds of points seem to have eaten into it. This particular patch has an anchored-root-system base a good two meters across, securing a bundle of fronds less than four meters long. 

They're very secure. Merrin can grip a frond and plant both feet and use the suit power as well as her own muscle strength to pull as hard as she can, and it doesn't budge at all. 

Hmmmmmmmmmmmmmm. 

...Merrin is going to swim downstream a bit and check out some of the other seaweed patches. 

Here's one where the root system is anchored on the floor of a shallow erosion-depression, not quite an underwater cave yet but on its way there. There appear to be several of the plants, with root systems overlapping and reinforcing each other. The fronds are particularly long, maybe as much as five meters, undulating in the current; if the current switches, they'll be plastered against the arch of the would-be cave. 

Hmmmmmmmmmmmmmmmm. 

.....The straplike fronds are flexible enough to tie into knots. And the root system has points where one could slide a loop of paracord under a particularly thick route and secure additional ropes. 

Yeah. Merrin thinks she has a scheme for where to attempt to secure her last two crates. Though she had really better hurry. 

When she re-emerges, she still can't see any ocean, and she doesn't hear the roar of an approaching tidal bore wave, though of course at the point when she did hear one it would be at most minutes away. 

....Merrin has an unforeseen problem, which she could have foreseen if she had thought about it for ten entire seconds. 

The full box of redundant medical supplies is neutral-to-negative buoyancy. Merrin won't have any trouble swimming down to 10m of depth with it and holding it against the current while she ties it into place with the 10m of paracord she has in her front pouch. (Because she was being dumb and did not think through the fact that she might want to secure anything at the bottom of the river channel, and she has a lot more paracord than that but it's at the top of the riverbank, which right now might as well be the Moon.) 

The empty power armor crate is sealed full of air. And thus rather buoyant. She does not think she can easily haul it deep underwater, and its buoyancy will strain the attachment points even when there's no current. 

...She'll swim down with the first box and secure that and use the time to think of solutions. 

The seaweed frond material is really remarkably tough. Merrin tries dissecting one down the middle to split it into two halves, so she can knot it in more places without using paracord, and her small multitool knife is having a lot of trouble with it. (She has sharper knives, and a lightweight hatchet, but both are in the toolbox at the top of the hill.) 

She gives up on that plan and just knots what she has; it's a thick, flattened, slightly twisted ribbon, as wide as her wrist and almost a centimeter thick at the center, leathery rather than woody, and she thinks there's silica incorporated too. The edges of the ribbon are sharp and it's a very good thing her suit gloves are sturdy. 

....And then she's going to saw through one frond at the base, to try to take with her. Because this planet might not have any trees, but this ultrasturdy seaweed might have real promise as a building material. She'll want to see what it's like when it dries. 

By the time she makes it back to her last remaining crate, her suit clock thinks it's been 13 hours and 20 minutes since dawn. Eyeballing it from this angle, it looks like the sun is nearly at its zenith. 

The temperature is up to almost 18° C. The tidal flats must be getting even hotter; some areas are steaming as water rapidly evaporates. 

The moon is still a long way behind the sun, in terms of making its arc across the sky. It does look like a depressed arc, not one that will pass directly overhead. Not a spring tide. She still can't see or hear the ocean. 

Okay. 

She has two options: 

- Try to carry the crate up the hill - it's not heavy - and, if she hears the roar of ocean approaching, ditch it for streamlining in case she doesn't make it and has to surf 

- Load it up with rocks???? 

...There is, unfortunately, a complete lack of nicely sized stackable rocks, down here. Some of the "exposed rock" might belong to large boulders embedded in sediment, rather than being directly attached to the bedrock, but she doesn't know which ones to try to dig up, and they might all be too big to even fit in the crate. Any small rocks have clearly been thrown around by the tide until they were eroded down to pebbles and grit. 

(Filling it with water - with pure water of neutral pH - might not irreversibly degrade the lining, but it's not really meant to be totally waterproof from the inside. She has lots of collapsible-waterproof-container water storage; she wasn't supposed to need to adapt the boxes as cisterns. And, of course, she hasn't had a chance to fully analyze the seawater; the suit has sensors for pH and osmolality, once she gets around to digging around in the menu, but it was not designed to give her a full analysis and readout of the chemical composition of seawater on ANOTHER PLANET. Also, if she wanted to weigh down the box by filling it with water, she would have to remove the spare suit battery and rig something to carry that, if she wants to use it; it's water-resistant, dropping it briefly in a puddle wouldn't destroy it, but it's really not specced to survive sitting around in mineral-filled seawater for days.) 

...Okay. Merrin's climbing-relevant muscles do actually feel somewhat rested, after taking a break from the gravity and using different muscles.

Harnessing the empty box to her back and going as fast as she can, that's what the plan will be. (And the seaweed frond she cut is wrapped a few times through the harness webbing to secure it along with the box.)

It takes significantly longer. Before, when the ground was frozen and she wasn't so exhausted, she'd been able to make it from her landing spot to her box cache at the top of the bank in about 100 minutes. Exhaustion alone would probably have brought it to two hours. 

This time, three and a half hours pass - it's now been 16 hours since dawn, the sun is clearly trending back down in the sky, and her suit has flipped over to cooling mode because the outside temperature is up to 28° C - and she's still not up to the highest debris line, let alone all the way back to her cache. The stone is dry, here, it's no longer slippery, and she would be making faster progress, but it took her more than two hours just to cross the silty tidal flats, and she's very close to exhaustion.

And now she can hear a roar in the distance, and feel the vibration of it conveyed through the rock and into her bones. 

Perhaps Merrin is not quite on the edge of exhaustion after all! The adrenaline produced by sheer terror for her life can eke out a bit more speed! 

(She's really close to what she thinks is the true high-tide line, and she might already be above the current high-tide line, if she's right that this isn't the highest the tides will get. It doesn't quite seem worth ditching the box, especially since it's not really slowing her that much at this point, on stable rocky ground, and she would really like to have the spare suit battery for tonight.) 

She makes it, with - probably minutes and not literal seconds to spare, but still - and she flops down beside her haphazard pile of boxes, and she watches the tidal bore wavefront roll in. 

[AUTHOR'S NOTE: please ignore all the ways in which this image is not quite physically plausible, this is attempt #6.] 

....Eeeeeeeep.

Merrin is very, very glad that she knows enough about a hundred kinds of basic planet-related science to have predicted that the tempting cave is, in fact, a DANGER CAVE.

It's actually pretty majestic and epic and awesome to watch, and all that. Given that she survived it. 

(Merrin spends a little while wondering whether having just barely made it is evidence that the Literary Tropes Theory is applicable to her situation and the universe is, in fact, trolling her, before she concludes that it's stupid to be wasting mental cycles on that right now.) 

The wave settles. It's not yet high tide; the water level is more than halfway up the limestone banks and still rising, with the incoming tidal current completely overwhelming the underlying river current flowing the opposite way. 

Her suit temperature sensor picked up a peak of 29.3° C – and coinciding with almost 60% humidity, from the giant evaporating tidal-flats surface, meaning the calculated dry-heat-equivalent for predicting heat stress without the suit was 37° C. But the sun is sliding down the sky, and the inrushing water brought some cooler wind with it, and the temperature is now past its peak, down to 26.6° C and will, presumably, continue to drop.

Merrin missed her chance to mark solar noon on her sundial - or measure the exact highest angle of the sun - but at a guess, noon was a bit over two hours ago, so about 14 hours after dawn, and sunset will be in 12 hours. And then there will be a long winter night of unknown duration, and the temperature will drop, and drop, and probably reach a low of around -40° C just before dawn. 

...Which means that the 24h average temperature would be below freezing. 

Why is that relevant? Because seawater should (slowly) approach the average seasonal air temperature.

Merrin does have some other guesses now about what explains the lack of visible giant icebergs; the tidal turbulence would dash them to pieces, and fragmented sea ice would both be difficult to see in the distance and also much faster to melt in the heat of the day. (The lack of snow on the ground is no longer confusing. For all she knows, it did snow a week ago, but if the temperature spikes to a high 30° C each day cycle, snow on the ground wouldn't even last a single day; it would melt into water, flow away into cracks and hide out there contributing to rock weathering, and mostly end up right back in the ocean.) 

...But another thing about seawater, especially when the shallower and deeper layers are undergoing such thorough mixing, is that it lags behind the seasonal temperature. If the planet had no axial tilt and this latitude was always its current "season" - which, Merrin is realizing, is not in principle impossible, a zero-degree axial tilt and a high polar latitude could result in the sun-angle she's observing? - but if that were the case, the sea ought to reach an equilibrium at around -5° C. 

And she can confirm, with her suit data, that it's not that cold and somehow liquid anyway. She was getting readings between 1° and 3° C. 

One very obvious explanation is that this is winter, as opposed to summer, and that in summer the average temperature is significantly higher, and right now the ocean with its enormous heat capacity is still slowly cooling after last summer's heat, and won't quite get down to a below-zero average before it's spring and the temperatures are rising. 

....Which, if true, is a fact that predicts very serious problems for Merrin in...some fairly large but unknown number of planetary days (she doesn't know how long the year is.) 

The problem is that right now, the average daily temperature is below zero - unless the rate of heat loss is really nonlinear, Merrin was admittedly doing Stupid Approximate Math and should instead, like, get a full day and night trend and then graph it and get the actual area-under-the-curve - anyway, the low is further below zero than the high is above zero, and the high is still hot enough that, without her suit, she would not be able to do any serious physical labor without risking heatstroke. 

The peak summer temperatures on this planet could easily be another twenty or even thirty degrees higher, and that's flat-out not survivable even for a few hours a day. 

...But, of course, today Merrin's most immediate-term survival threat is the winter night and the cold.

Which means she cannot afford to waste any more time resting. She'll have at least thirty hours of night to rest, later. Right now, she needs to be frantically using the remaining hours of sunlight to generate power, and erecting an insulated shelter soon so it's starting out full of warm air and will cool more slowly than the ambient temperature...