Hiʻiaka (moon)

HiÊ»iaka was the first satellite discovered around Haumea. It was discovered on 26 January 2005 by Michael E. Brown and the W. M. Keck Observatory adaptive optics team at Mauna Kea, Hawaii.^[2][1] The discovery of Haumea had not been made public at the time,^[11][12] so the discovery of HiÊ»iaka was announced later on 29 July 2005.^[2] When HiÊ»iaka was announced, it given the temporary provisional designation S/2005 (2003 EL₆₁) 1, which indicates it is the first moon of Haumea (then known as 2003 EL₆₁) discovered in 2005.^[2] At the time, Brown had been nicknaming Haumea "Santa," so he nicknamed HiÊ»iaka "Rudolph," after one of Santa Claus's reindeer.^[11][12]

Haumea, Hiʻiaka, and Namaka were all officially named after Hawaiian deities by the International Astronomical Union (IAU) on 17 September 2008.^[13] In Hawaiian mythology, Hiʻiaka is the patron goddess of hula and is the daughter of the fertility goddess Haumea.^[13] These names were proposed to the IAU by Brown's team in September 2006, who wanted to pay tribute to the location where they discovered the moons of Haumea.^[14]

Namaka and Hiʻiaka are widely believed to be fragments of Haumea that were ejected in the aftermath of a giant impact 4.4 billion years ago (77–82 million years after the formation of the Solar System), when Neptune was migrating outward and gravitationally scattering objects in the Kuiper belt.^{[21]: 1–2, 14 } This impact event is hypothesized to involve two large Kuiper belt objects of similar size, which obliquely collided with each other and merged into a single, rapidly rotating body that eventually deformed into an ellipsoidal body, becoming Haumea today.^{[21]: 2 } While this hypothesis explains Haumea's rapid rotation and high bulk density, it fails to explain the existence of Haumea's moons and family of icy KBOs on similar orbits, because such an energetic impact would have ejected fragments at speeds several times Haumea's escape velocity.^{[21]: 2 }

Rather than having formed directly from a giant impact, Haumea's family and moons are instead believed to have been ejected via rotational fissioning of Haumea roughly 80 million years after the impact (147–162 million years after the Solar System's formation).^{[5]: 15 [21]: 1, 14 } A 2022 study led by Jessica Noviello and collaborators proposed that Haumea continued differentiating and growing its rocky core after the giant impact, which led to a gradual speed-up of Haumea's rotation rate as a consequence of angular momentum conservation.^[21] Centrifugal forces on Haumea's equator eventually grew so great that icy surface material began ejecting into orbit around Haumea, forming a disk of material that eventually coalesced into moons.^{[21]: 2–3 } About 3% of Haumea's initial mass and 14% of its initial angular momentum were lost via rotational fissioning.^{[21]: 1 }

• Namaka – the smaller moon of Haumea
• Haumea family – a population of water-ice rich Kuiper belt objects that were ejected from Haumea 4.4 billion years ago
  • 2002 TX300 – one of the largest Haumea family KBOs, with a diameter similar to HiÊ»iaka