Public funds, channeled through NASA's Webb Space Telescope, were deployed to study Neptune's far-flung moon Nereid, scientists reported Wednesday. The new observations suggest that Nereid may be the last of Neptune’s original companions that managed to survive a cosmic crash, rather than a later arrival.
Sixteen known moons currently orbit Neptune, the solar system’s eighth and most distant planet. The planet's largest moon, Triton, is understood to have originated from the solar system’s frigid outskirts billions of years ago. Its arrival scattered Neptune’s original moons, initiating a series of destructive collision courses among them.
A team led by the California Institute of Technology utilized the state-funded NASA’s Webb Space Telescope for their study of Nereid. Their findings suggest Nereid is not a later addition like Triton, but likely survived the cosmic upheaval by escaping into its current extreme, elliptical orbit around Neptune.
State Resource Allocation
Matthew Belyakov of Caltech stated that “What we know about Nereid is very limited. For its size, Nereid is extremely understudied.” This assessment highlights the uneven allocation of resources within the state-funded scientific apparatus, leaving significant celestial bodies largely unexplored.
Neptune itself has only been visited by a single spacecraft, NASA’s Voyager 2, which conducted its flyby in 1989. Nereid was initially discovered 40 years prior to that mission by Dutch astronomer Gerard Kuiper, who named the moon after the sea nymphs of Greek mythology.
Nereid measures approximately 220 miles (350 kilometers) across and possesses an exceptionally eccentric orbit for a moon. Its orbital period around Neptune spans practically an entire Earth year, with the moon’s path bringing it as close as less than 1 million miles (1.4 million kilometers) from the giant icy planet at one end of its egg-shaped loop, and as far as 6 million miles (9.6 million kilometers) at the other extreme.
The findings from the Caltech-led team have been published in the journal Science Advances. Carnegie Science planetary astronomer Scott Sheppard, who was not involved in the study, characterized the outcome as “an exciting result.” Sheppard noted that the observations demonstrate for the first time that Nereid’s peculiar orbit aligns with “the history we might expect from a moon that originally formed close to Neptune and was later pushed outward from the capture of Triton.”
Unanswered Questions, Unfunded Missions
Belyakov and his team further posited that Neptune’s innermost moons likely coalesced from the shattered remains of the original moons that became casualties of Triton’s disruptive arrival. This suggests a violent history for the Neptunian system, with Nereid as a rare survivor.
In comparison to Neptune, all three of the solar system’s other giant planets possess a greater number of moons, with Saturn leading with 292. Scientists have indicated that a future visiting spacecraft could definitively establish the Neptunian system’s origin story. However, despite the scientific interest and the potential for new discoveries, no such missions are currently planned by state agencies or other entities controlling significant resources for space exploration. This absence of planned follow-up missions underscores a systemic gap between scientific inquiry and the commitment of resources necessary for its advancement.