Question

### Origin of Titan's Atmospheric Nitrogen

Titan, Saturn’s largest moon, has a dense, nitrogen-rich atmosphere. Scientists debate the origin of this atmospheric molecular nitrogen ($N_2$).

Hypothesis 1
Titan formed in a warm region of the Saturnian subnebula where molecular nitrogen gas could not condense. Instead, Titan accreted nitrogen primarily in the form of ammonia ($NH_3$) ice. Over time, internal heating caused the ammonia to outgas into the early atmosphere. Solar ultraviolet (UV) radiation then photolyzed the atmospheric ammonia, splitting it into nitrogen gas ($N_2$) and hydrogen gas ($H_2$). The lighter hydrogen escaped into space, leaving behind a thick layer of $N_2$. Thus, Titan’s atmospheric nitrogen is a secondary product of chemical reactions.

Hypothesis 2
Titan accreted in a much colder region of the Saturnian subnebula, allowing molecular nitrogen ($N_2$) gas to be directly trapped as clathrate hydrates (icy cages) within Titan's silicate and water-ice core during formation. As Titan heated up internally due to radioactive decay, this primordial $N_2$ gas was released directly from the interior into the atmosphere through cryovolcanism. Under this hypothesis, Titan’s atmospheric nitrogen is primordial, having undergone no major chemical conversion from ammonia.

According to Hypothesis 1, which of the following processes was directly responsible for producing the molecular nitrogen ($N_2$) now found in Titan's atmosphere?