Namaka (moon)
Inner, smaller moon of dwarf planet Haumea.
Namaka, officially designated (136108) Haumea II, is the smaller and closer of the two moons orbiting the dwarf planet Haumea, which lies beyond Neptune. It was spotted in the autumn of 2005 by Michael E. Brown and the adaptive optics team at the Keck Observatory, using high-resolution images taken on 1 March, 28 May, and 30 June of that year. The moon was initially missed because it is much fainter and sits nearer to Haumea than its brighter sibling, Hiʻiaka, which had been found earlier in January 2005. The discovery was announced on 1 December 2005 by the Central Bureau of Astronomical Telegrams, and the moon was given the temporary designation S/2005 (2003 EL61) 2. Brown nicknamed it "Blitzen," after one of Santa’s reindeer, continuing a Christmas-themed naming scheme for the Haumea system. On 17 September 2008, the International Astronomical Union officially named it after Nāmaka, a water spirit and daughter of the Hawaiian fertility goddess Haumea—a name proposed by Brown’s team in September 2006 to honor the Hawaiian location of the discovery.
Namaka orbits Haumea every 18.3 days at an average distance of 25,500 km (15,800 mi). Its path is highly elliptical, with an eccentricity of about 0.22, and tilted roughly 13° relative to both Haumea’s equator and Hiʻiaka’s orbital plane. This orbit is strongly disturbed by the gravity of the larger outer moon Hiʻiaka and by the uneven gravitational pull from Haumea’s elongated shape, causing Namaka’s eccentricity and inclination to change over time, along with precession of its orbital nodes and apsides. The ratio of Namaka’s orbital period to Hiʻiaka’s is 2.689±0.004, suggesting they may be in or near an 8:3 mean-motion resonance—where Hiʻiaka completes three orbits for every eight of Namaka’s. Whether this resonance still holds is uncertain, but simulations indicate it likely played a key role in shaping the moons’ current orbits, allowing Hiʻiaka to transfer its initial eccentricity and inclination to Namaka over hundreds of millions of years. How long ago this resonance began and how long it lasted remain unknown.
Namaka’s gravity exerts a small torque on Haumea, causing the dwarf planet’s rotation axis to precess slowly by less than one degree. The period of this axial precession matches the nodal precession period of Namaka’s orbit, which spans several decades. Namaka’s influence on Haumea’s ring is min
- discovered
- Fall 2005
- discoverer
- Michael E. Brown and the Keck Observatory adaptive optics team
- diameter
- ~150 km (93 mi)
- orbital period
- ~18.3 days
- average orbital distance
- 25,500 km (15,800 mi)
- mass
- ~1×10^18 kg
- named after
- Nāmaka, Hawaiian water spirit
Lore & Background
Namaka was discovered in high-resolution images of Haumea taken by the Keck II telescope on 1 March, 28 May, and 30 June 2005. It was not recognized earlier because it was much fainter and closer to Haumea than its brighter sibling moon Hiʻiaka, discovered in January 2005. The discovery was announced by the Central Bureau of Astronomical Telegrams on 1 December 2005, with the provisional designation S/2005 (2003 EL61) 2. Brown nicknamed the moon 'Blitzen,' after one of Santa Claus's reindeer. Haumea, Hiʻiaka, and Namaka were officially named after Hawaiian deities by the IAU on 17 September 2008.
Namaka follows a highly tilted elliptical orbit with an eccentricity of about 0.22 and an inclination of roughly 13° with respect to Haumea's equator. Its orbit is heavily perturbed by Hiʻiaka and Haumea's elongated shape, resulting in time-varying eccentricity and inclination. The ratio of Namaka's and Hiʻiaka's orbital periods is 2.689±0.004, suggesting they may be in or close to an 8:3 mean-motion orbital resonance. Simulations show this resonance likely played a major role in producing the moons' present-day orbits.
Namaka has a diameter around 150 km, an irregular shape, and a chaotic rotation. Its surface is made of fresh water ice, similar to Haumea and Hiʻiaka. Its low bulk density of 0.650 g/cm³ suggests a highly porous interior. Namaka is believed to be a fragment of Haumea ejected via rotational fissioning roughly 80 million years after a giant impact 4.4 billion years ago.
Reader's Guide
Namaka is significant as the inner moon of Haumea, providing key insights into the dynamics of the Haumea system. Its highly perturbed orbit, influenced by both Hiʻiaka and Haumea's irregular shape, makes it a valuable case study for orbital mechanics in complex gravitational environments. The potential 8:3 orbital resonance with Hiʻiaka helps explain the evolution of the moons' orbits over hundreds of millions of years. Namaka's composition of fresh water ice and its likely origin as a fragment from a giant impact support the hypothesis that Haumea and its moons formed from a catastrophic collision early in Solar System history. Its chaotic rotation, predicted by simulations, parallels that of Saturn's moon Hyperion, offering a rare example of such rotational behavior. Observations of Namaka, including a stellar occultation in March 2025, continue to refine our understanding of its size, shape, and orbit. The moon's discovery and naming also highlight the cultural connection to Hawaiian mythology, as the moons were named after deities to honor the location of their discovery at Mauna Kea, Hawaii.
Did You Know?
- Namaka is about 67 times fainter than Haumea and 3.7 times fainter than Hiʻiaka when viewed from Earth.
- Namaka's orbit is highly tilted by roughly 13 degrees with respect to Haumea's equator.
- Only one stellar occultation by Namaka has been observed, on 16 March 2025.
- Namaka was nicknamed 'Blitzen' by discoverer Michael E. Brown after one of Santa Claus's reindeer.
More in Discoveries by Michael E. Brown 1-24
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