"How I imagine the whole thing going down is: Emma and Lana had recently returned from exploring the surface of an alien planet. Emma at some point had stepped in an apparent puddle of slime but didn't think much about it. The slime has a strange property allowing it to grow in strength and size when exposed to oxygen or fluids and can control it's density on a molecular level. The slime seeps into Emma's suit and starts looking to get inside her to feed on her bodily fluids. Emma starts realizing the problem too late and struggles to get her helmet off. As the slime starts growing and dominating her, it's too much as they finish her off, leaving her suspended in the slime. Lana, trying in vain to help Emma is exposed to the slime and it starts to fill her suit as well, she doesn't want the slime to get out (unknowing of the slime's properties) so she tries to keep it contained in her suit until she realizes that she'll drown in it eventually. She tries to take off her helmet to avoid such a fate, but she can't get it off and drowns. Amanda and Riley having heard the radio comms, come over from another shuttle, only slightly prepared. The second team shoot at the slime, only for their shots to have no effect. The slime gets to them and they know they will meet the same fate."
-----------------------------------------
Just a larger version of a pic I've already posted to DA, plus an exclusive bonus image