WARNING: The following contains major spoilers for The Expanse Season 5, Episode 3, "Mother," available now on Amazon Prime Video.
Since Season 4, Marco Inaros' deadly plan has been clear: coat numerous asteroids in Martian stealth technology and slingshot them though space, bypass Earth's orbital asteroid-spotters and hit the human home world with at least one huge rock. The closing moments of The Expanse Season 5, Episode 3, "Mother," directed by Expanse alum, Thomas Jane, confirms the Belter terrorist's plan worked -- an asteroid has indeed hit Earth, and the impact is devastating.
During the build-up to the climactic event, both Crisjen Avasarala and UN Admiral Delgado, with the help of Doctor Alaoui, discovered Inaros was sending a concealed rock Earthward but it broke up while passing by Venus. However, they are certain that Inaros didn't settle for one attempt, so they get to work calculating the possible impact of such an asteroid. They conclude it would be a 1-4 megaton blast, with a radius of 13 kilometers, similar to a fusion warhead.
Avasarala asks Delgado try to get the Director of Intelligence to re-purpose Earth's "Watchtower" defense systems to scan for incoming stealth rocks, as they are the only systems that can identify stealth technology. Delgado explains that system is pointed at Mars and will likely stay that way, given Mars is the only force that has successfully harnessed stealth tech. Delgado and the wider Earth government have largely dismissed Avasarala's claim that Inaros has been buying that tech.
Throughout the episode, it's clear Earth isn't without its allies, tenuous as they may be. Camina Drummer finally finds Ashford's ship and uncovers a recording he made that confirms Inaros' intentions. She sends it on to Fred Johnson at Tycho Station, who subsequently sends it to Avasarala.
Avasarala has burnt all of her bridges, though, so information from her is being deemed conspiracy theory by Nancy Gao and her cabinet. As such, the intelligence that indicates Inaros intends to attack Earth is discredited, and Delgado informs her that the Watchtowers will not be reassigned, dooming Earth to a terrible fate. Avasarala tries to contact her husband, Arjun, without success before receiving Johnson's communication.
The first rock, having gathered speed through multiple orbital slingshots, flies past Earth's asteroid-spotting defense grid without raising a single alarm and barrels into the surface of Earth, the final thing a local fisherman ever witnesses. It's not immediately clear what part of Earth was hit, but information from The Expanse novel Nemesis Games identifies the location as Lagouat, Algiers. This isn't a coastal city, so it may be the show has taken some creative liberties regarding where the asteroid touched down.
An adaptation of the novel series of the same name by James S.A. Corey, The Expanse stars Steven Strait, Cas Anvar, Dominique Tipper, Wes Chatham, Shohreh Aghdashloo and Frankie Adams. New episodes of Season 5 premiere Wednesdays on Amazon Prime Video.