Warning: SPOILERS for Star Trek: Discovery Season 3, Episode 6 - "Scavengers"
Star Trek: Discovery's Captain Saru (Doug Jones) is in need of a new First Officer, but who will it be? Saru demoted Commander Michael Burnham (Sonequa Martin-Green) as punishment for her going rogue against his direct orders in Star Trek: Discovery season 3, episode 6, "Scavengers". Although Burnham and Emperor Philippa Georgiou's (Michelle Yeoh) unsanctioned mission to rescue Cleveland "Book" Booker (David Ajala) and retrieve a pre-Burn black box from the Emerald Chain was a success, Saru still had to break his XO for her insubordination.
Unfortunately, neither Saru nor Star Trek: Discovery's fans were surprised by Michael's actions and, truthfully, Commander Burnham as Discovery's Number One was a big mistake, as Captain Saru was sad to realize. Michael is still sorting out the drastic personal changes she has undergone after arriving in the 32nd century one year before the U.S.S. Discovery did. For that year, Michael feared she would never see her friends again, but she was also free of the Starfleet duties that defined and structured her adult life, and the freedom Burnham tasted as she searched the galaxy for answers about The Burn left her reluctant to even return to the Discovery when she found them again. When she reunited with her crewmates, Michael immediately withdrew her candidacy for Discovery's Captaincy, yet she reluctantly accepted Saru's offer to become his First Officer, even though Michael knew deep down it was a mistake.
Michael's demotion to Chief Science Officer means that Discovery needs a new Number One, which is vital since the starship has a crucial new mission as Admiral Charles Vance's (Oded Fehr) Starfleet rapid responder. This is also, unfortunately, a familiar situation for the time-tossed starship, which cycled through several different Captains in Star Trek: Discovery seasons 1 and 2 before Acting Captain Saru finally got his well-deserved promotion to call the shots aboard Discovery.
Given Discovery's bad luck with commanding officers, it wouldn't be a surprise if Michael's quick flame out as XO kicks off a new game of musical chairs until someone proves themselves as the permanent First Officer. However, even though Commander Nhan (Rachel Ancheril), who would have been next in line after Burnham, left the ship, there are worthy candidates aboard Discovery's senior staff. This could also be a great opportunity for Star Trek: Discovery to shine a greater spotlight on the ship's bridge crew, which season 3 has been making a noticeable effort of doing. So, now that Commander Burnham is out, here are the best candidates to take her place as Discovery's new Number One.
Ensign Sylvia Tilly
Despite only being an Ensign, Sylvia Tilly (Mary Wiseman) has the inside-track because she is Captain Saru's protégé. The Kelpien has clearly taken a shine to and favors the brilliant Tilly, and he was her sponsor in Starfleet's Command Training Program. Tilly's dream is to become a starship captain one day and a promotion to First Officer instantly would take her out of Engineering and place her only one step away from the big chair.
However, Tilly is still very inexperienced and she doesn't project command authority. She is also just an Ensign and there are officers ahead of her in line who are more qualified for command. Captain Saru could solve one issue by promoting Tilly to Lieutenant so that she could take the XO position but he may find that if he did so, it would be making the same mistake he made with Michael by choosing someone out of fondness instead of who is best qualified, all things considered. Tilly will likely make a fine commanding officer one day but she may not be the best-suited candidate for Number One at this point in time.
Lt. Joann Owosekun
Lt. Joann Owosekun (Oyin Oladejo) is Discovery's operations officer, which is high up on the bridge crew's command chain and carries numerous responsibilities for the overall functions of the starship. For reference, Lt. Commander Data (Brent Spiner) was the operations officer aboard the U.S.S. Enterprise-D and he was third in command after Captain Jean-Luc Picard (Patrick Stewart) and Commander Will Riker (Jonathan Frakes).
As a key member of the senior staff on the command track, Owosekun sits at the forward conn position on the bridge opposite the helmsman, Lt. Keyla Detmer (Emily Coutts). Owosekun is well-liked and respected by the bridge crew and she's often a calming influence, which are skills and traits that would be valuable as Captain Saru's new First Officer.
Lt. Nilsson
Star Trek: Discovery fans don't know much about Lt. Nilsson (Sara Mitich) - including what her first name is - but she is nonetheless a candidate for First Officer. Nilsson left Engineering and replaced the late Lt. Airiam on the bridge as the new spore drive operations officer. As such, Nilsson interacts with Lt. Paul Stamets (Anthony Rapp), who is the spore drive's human navigator, and she programs the Black Alerts and Discovery's jumps across the mycelial network.
Tellingly, Nilsson is one of the officers whom Captain Saru or Commander Burnham give the conn to, which leaves her in charge when they depart the bridge. This indicates Lt. Nilsson is part of the command track, which would place her in line for First Officer. As of now, Nilsson is a bit of a mystery due to her lack of screen time but she appears to be highly competent and is well-liked by the crew. Lt. Nilsson could make a fine First Officer.
Lt. Gen Rhys
Lt. Gen Rhys (Patrick Kwok-Choon) is Discovery's Chief Tactical Officer, which also makes him a potential First Officer. Rhys is responsible for activating Red Alerts and executing the captain's orders during combat, including firing Discovery's weapons like phasers and photon torpedoes. Rhys is on the command track and he's also an officer who is often given the conn when the Captain and XO leave the bridge. Captain Saru could pick Lt. Rhys as his new Number One.
Someone New From Starfleet
Despite the qualified candidates aboard Discovery's crew, Admiral Vance may opt to place one of his Starfleet Officers as Saru's new Number One. The Commander-in-Chief of Starfleet has a lot of urgent business on his plate but, in the scant few weeks the Discovery has been around, he's already dealt with and watched Michael Burnham's failure as First Officer. It would be understandable if Vance chooses to take a hands-on approach with his all-important rapid responder.
Admiral Vance could decide that the best way to get Discovery up to specs and also keep Captain Saru, who he is still uncertain about, in check would be to install one of his own loyal subordinates as Discovery's second-in-command. While this would be a fish-out-of-water scenario for a 32nd-century Starfleet commander to help oversee a thousand-year-old starship full of time travelers, it would be an interesting and logical move if Admiral Vance chooses to do it.
Commander Michael Burnham
The final possible replacement for Michael Burnham is... Michael Burnham. Despite her personal issues, there's no denying Commander Burnham is a brilliant and gifted Starfleet Officer when she applies herself to her duties. Michael is in a state of flux right now but she could still straighten herself out, recommit to Starfleet, and regain her position as Number One.
However, the inconvenient truth about Commander Burnham is that her record as First Officer is appalling. After seven years as the XO aboard the U.S.S. Shenzhou, Michael became Starfleet's firsr mutineer, got her Captain, Philippa Georgiou, killed, and she instigated the Klingon War of 2256-2257, which she went to prison for. Michael's second tenure as First Officer to Captain Saru ended in near-record time with another breach of trust, although Burnham betrayed her Captain to mount a successful rescue mission. Michael could still find the excellent Starfleet Officer within herself and prove worthy of being First Officer in Star Trek: Discovery season 3, but it's also possible that she's simply out of chances.