So, the overall theme for this episode is The X-Files. The cover is more generically 90s weird fiction than the standard promo shot of Mulder and Scully, but it's spelled out in the first line of dialogue of the issue: "The Truth is in here", which is followed up a few pages later with the Four's weapon being retrieved from a downed craft referred to as an abduction vessel, and a reference to cattle and people - UFOlogists frequently point to unexplained cattle mutilation as the work of aliens experimenting on terran life. And, of course human abduction has been part of alien conspiracy theories for decades. Similarly, the Antarctic research facility could be a direct reference to the final setpiece in the 90's movie, and the creatures in the tubes being Süskind and Dowling's children has parallels to the hybrid plotline in the X-Files specifically, but it's a common enough trope in SF beyond that.
The professor in the wheelchair could be any number of characters, but he's likely a reference to Charles Xavier and/or Niles Caulder
The stick that turns into a hammer is, of course a direct reference to Mjolnir as seen in Marvel comics. Like many deconstructions of superhero tropes in Planetary the glib line about surviving the weapon's transformation by being superhumanly resistant to damage is a reflection back onto the story from whence the trope originates, in this case Thor's own abilities.
Similarly, Kim Süskind's goggles are a pseudoscientific explanation for a common question around her originator's powers. There's no explanation given for why the goggles can absorb and reflect light while invisible, but Süskind's eyes can't. But still.
Beyond all this, we have the second explanation of a flashback from issues 11 and 12, another important moment. If issue 13 was the birth of Planetary, this issue is the temporary end thereof. It's the start of Snow's 4-year exile, and we don't know if the Planetary Journal was published for those years. These two issues, side by side are almost bookends for all the work Snow did in the intervening 70 years.
It's also interesting to see Snow's relationship with his colleagues in this issue. He's curt with the Professor, but is on a first name basis. Clearly he and Snow are friends, and he recognises Snow is somewhat effected by the gravity of their discovery. Also, Snow's "Let's ride" line before transitioning to the dead world shows he's still got a wry sense of humour even in a serious moment. He and Jakita are much the same, but The Drummer is far more reverential, calling him "Mr. Snow" and far more professional sounding than he is in the present.
It's worth noting that, as @Chris notes Planetary is a bigger concern to the Four than Dowling lets on. Snow's orders just before the Four's flying fucking saucer shows up suggests that he's intending this to be a precise decapitation strike, defeating the entire Four in a single battle. Three pages before, Süskind is saying "I don't know how they got this good, but this is beyond the pale".
It's the same thing Snow did in issue 12, or in being prepared to defeat and kill Dracula in issue 13. He knows more than his opponents assume he does, and he holds onto that information until he needs to use it to his advantage. It's just bad luck that The Four had one more ace in the hole than he did. Dowling definitely sees Snow as a bigger threat than he lets on, but Dowling is something of an egomaniac and has good reason to see himself as ruler of the world. Why would he admit that Snow came damned close to beating him?
The end of the issue is very much a case of Ellis' abrupt endings working for a change. Snow's last words to his team are powerful, even knowing after the fact that Jakita and The Drummer disobeyed his explicit orders.