UNS Arboghast was a United Nations science vessel.
The Arbogahst was a civilian research/science (survey) vessel, commandeered by the United Nations Navy and refitted with sensors and probes.
Following the Eros Incident, the UN needed to send a research team to Venus to study the aftermath of Eros impacting its surface. The UN sent the Arboghast under the command of Colonel Janus, head of UN Science Committee. Accompanying his crew was Doctor Michael Iturbi, a scientist and confidante of Assistant Undersecretary Chrisjen Avasarala Books • TV.
Upon arriving at Venus, they found that Mars had also dispatched a ship to study the Eros Crater. The Martian Congressional Republic Navy ship was broadcasting a warning to all ships nearby to avoid them. The Arboghast attempted to get detailed scans with its complement of six probes on board. The first four probes disappeared before they were able to transmit any telemetry. The crew then tried again by lowering their altitude and launching their fifth probe, which was loaded with extra protective plating cannibalized from the sixth to help it survive the descent. Although this one was successful in its attempts at reaching the crater, it only broadcast video and telemetry of protomolecule structures for a few moments before dying. 
Knowing that the crater was active, Janus and Iturbi discussed what to do and decided to descend the ship into Venus's atmosphere to get a closer look. The crew prepared for the descent and deployed the ship's ballutes for atmospheric entry. Their sensors started to malfunction mid-descent before spotting that the crater itself appeared to be moving. The Martian vessel, which had been observing the Arboghast's efforts, followed the UN ship into the atmosphere, descending faster and passing very close to the Arboghast. However, it disappeared from sensors soon after.Next, the Arboghast came to an abrupt stop in mid-air, not yet having reached the surface. The crew spotted floating blue particles from the protomolecule moving about the ship moments before the vessel was completely dis-aggregated. All hands on board were lost.
Doctor Michael-Jon de Uturbé, head of the UN Science Committee, had been aggregating telemetry data received from the Arboghast and sending it to Avasarala. When the ship was disassembled by the Protomolecule, telescopes on Luna captured a video recording of the event. Uturbé's analysis of the activity from the Eros crash site provided evidence to the Earth scientists that the activities were synchronized throughout the Sol system in a way that didn't suffer time lag constraints of electromagnetic communication.
Notes and trivia
- The character Michael-Jon de Uturbé was split into two characters for the television adaptation, likely to better dramatize the opposite views of analysts.
- Michael-Jon de Uturbé is the head of the UN Science Committee in the books but Colonel Janus is the head of the UN Science Committee in the TV adaptation.
- Michael-Jon de Uturbé was responsible for making the science understandable to Avasarala but, in the TV adaptation, Colonel Janus attempted to fill that role for the politicians in the UN.
- Michael-Jon de Uturbé is the confidante of Avasarala while Michael Iturbi is her confidante in the TV adaptation. These two send Avasarala the observations and analysis from Venus data.
- Michael-Jon de Uturbé was never aboard the Arboghast. Consequently, when the ship was taken apart by the protomolecule in the book Caliban's War, Uturbé is unharmed and survives. However, he does not play any role after this in the books.
- Michael Iturbi and Colonel Janus are aboard the TV adaptation's Arboghast. It is apparent that the TV characters aboard the Arboghast probably perished in the season 2 finale episode, "Caliban's War". There is, however, some room for speculation that the producers allowed them to survive through some unknown means, though there is no evidence in the books that this is likely.
- The ship is probably named after the mathematician Louis François Antoine Arbogast (1759–1803) or the more contemporary mathematician, Todd Arbogast (PhD 1987), an expert in subsurface modeling.
- It appears than, as it was seen in the eyes of the Hybrid Katoa Merton (TV) , after the ship was disaggregated, the mechanical parts of the Arboghast were absorbed by the Protomolecule, who learned enough about human ships to later infect quickly the Agatha King (TV).