"Morning," Uchenna said as she entered the rabbitat, munching a breakfast burrito. "Day eighteen, can you believe it?"

Lira narrowed her eyes at the burrito. "I asked you not to eat in here."

Uchenna looked sheepishly at it, then stuffed the rest into her cheek in a single bite like a hamster. Around the bolus, she said, "Sorry." A few crumbs puffed out and landed on the artificial turf. One of the rabbits, a sable-coated lop named Scout, hopped over and gave a sniff, then wandered away. Uchenna bent down and picked the crumbs out of the fake grass. "It's fine, they don't want breakfast sausage."

Lira turned back to her work, annoyance rising in her gorge.

Yes, it had been eighteen days since the Exodus initiated the acceleration burn that put them on their trajectory toward Mars. Eighteen days of working with Uchenna… and working on the first ulcer of her life.

Everything that happened on launch day was explainable by the unique and extreme stress of the circumstances. Dr. Bello was a life scientist, not an astronaut, same as Lira. Strapping themselves to a rocket and allowing themselves to be shot into outer space was not natural for either of them so it was to be expected that they wouldn't quite be themselves at that time.

The stuff that came after… the apparent split personality that had been giving Lira whiplash for three weeks now… Well, they were on a massive spaceship with strangers, eating rehydrated food and sleeping in narrow, stiff bunks. The Exodus was well-appointed with creature comforts to counteract the confinement and the recycled air and the abject lack of fresh produce… but it was a lot to adjust to. It was understandable if it took a few weeks for Uchenna to get her proverbial sea legs – space legs – and focus on the research that VossCorp was paying her to do.

A few mood swings would be understandable too.

But it wasn't just how late she slept, or how often she could be found lingering in the galley, looking for crew members to chat with. It wasn't the fact that she rarely shared her work with Lira, choosing to type away in silence instead.

Uchenna barely seemed interested in the rabbits, and they were her life’s work, both here and back on Earth. She dutifully stuck to the schedule the two of them had devised for playtimes and mealtimes and health checks, but beside that, she seemed to want nothing to do with them. Before launch, she'd had ideas for growing fresh microgreens so they would have something better than the dried greens during the six-month journey. She'd been coming up with different strategies in case growing greens in this environment proved challenging.

Lira had practically had to beg her to start trying, and when the seeds refused to sprout, Uchenna had lost interest and pointed out that the dried greens were nutritionally sufficient. 

"That's not the point, though," Lira had said, frustrated tears rising in her throat. "How would you like to spend six months only eating dried food?"

"I am spending six months only eating dried food," Uchenna had pointed out before she made yet another excuse to leave.

And now here she was, thirty minutes late for her shift, stuffing her face with reconstituted sausage and contaminating the module after Lira had asked her repeatedly not to bring human food in here. 

What kind of scientist did that?

Lira felt for her, if all this was just various manifestations of depression. Going to Mars was a bigger adjustment than any of them had anticipated. Lira missed her own mother so much it hurt sometimes, and lying in her bunk at night, she often wondered what had possibly compelled her to take this job and the attendant possibility of never seeing her face-to-face again.

Never getting another bear hug from her.

Never eating her chicken adobo again.

But they were here now. There was no going back, and the mission had to take precedent or it was all for nothing. Uchenna had to snap out of it.

That was, if depression truly was the problem.

Lira had been working on a theory the past few days. It was insane and it made zero sense, but neither did half of Uchenna's actions since launch day. 

Watching the rabbits sniff around the sausage grease stain on the turf, Lira steeled herself to test her theory. "Hey, Uchenna, can I get your opinion on something?"

"What's up?"

"I was thinking about that paper you wrote a couple years ago," Lira said. "The one about gut microbiome adaptation in high-oxygen environments."

She watched Uchenna finish masticating her breakfast and swallow hard. "Mm-hmm?"

"I've noticed Zen and a few of the others are producing cecotropes faster than they did on Earth," Lira said. "They're getting a highly regulated mix of oxygen and nitrogen here. Do you think that could be why?"

Uchenna tapped her chin, her attention on the rabbits in their cages rather than looking at Lira.

"Could be," she said slowly. "In fact, I think you may be onto something with that. I'll do some research of my own, maybe reach out to some colleagues Earthside and see what they think."

Lira opened her mouth to respond, but Uchenna lifted her arm to look at her smartwatch, which she’d gotten from Bart when she finally fessed up about her broken implant.

"Shoot, I asked Natalia if I could pick her brain about my microgreens not sprouting and she's waiting for me in her lab right now. Be back in a while," she said, then did an abrupt about-face and walked out of the room.

Lira did let the tears flow then. They were hot on her cheeks, and they beaded up on the artificial turf when they fell off her chin. Scout made her way over and headbutted Lira's ankle, so she fished a little square of dried carrot out of her jumpsuit pocket and bent down to give it to her.

The rabbits had been living in the same mix of oxygen and nitrogen since the day they were born. Everything about their lives had been highly regulated to remove every possible variable and give them the highest chance of survival on the Exodus and on Mars. Uchenna Bello knew that – the geneticists back on Earth had consulted with her extensively about their environment before they bred this forty-eight. She'd set the parameters of many of those variables herself.

If she didn't know that now…

Well, there was only one possibility Lira could think of, as improbable as it was. 

Lira had applied for this mission after she lost her practice, when it felt like she had no future on Earth. She'd left her family to come here, to devote herself to these rabbits, and to the ones that would hopefully come in future generations on Mars. 

Uchenna Bello was the most qualified exobiologist on Earth and she was here for the exact same reason. Except it was like she'd had a personality transplant on launch day. No, an entire brain transplant. Like she was a different person who only gave enough of a crap about the mission as she absolutely had to to get by, and just wanted to dodge Lira and go off cavorting with the other crew members every chance she got.

She had Uchenna's face, but she knew nothing that Uchenna should know.

She cared nothing for the things Uchenna cared for.

It didn’t seem possible, but Lira could think of no other explanation.