541132 Leleākūhonua

• 1. Introduction

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  Leleākūhonua has a visual magnitude of 24.64, placing it in roughly the same faint range as Pluto's smaller moons. Three American astronomers found it on the 13th of October 2015. The letters in its provisional designation, combined with a discovery timing close to Halloween, prompted the team to call it informally "The Goblin." Students in a Hawaiian-language program would eventually propose the official name, chosen for what it evokes about the object's long wandering path through the deep Solar System. Its orbit ranks among the most elongated ever documented for a solar system body. Most of its existence unfolds at distances few frames of reference can capture. Only two sednoids, the rare class of objects this one belongs to, had ever been catalogued before.

• 2. Hunting the Outer Edge

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  David Tholen, Chad Trujillo, and Scott Sheppard were the American astronomers behind the search. Their survey targeted the region past the Kuiper Cliff, the outermost boundary of the Kuiper Belt. For Northern-hemisphere coverage, the team used the 8.2-meter Subaru Telescope at Mauna Kea Observatories in Hawaii. Its Hyper Suprime Camera was designed for wide-field imaging, suited to scanning large areas of sky for faint objects. Southern-hemisphere coverage came from the 4-meter Blanco Telescope at the Cerro Tololo Inter-American Observatory in Chile, using its Dark Energy Camera. Once a candidate appeared on those images, the Magellan and Lowell Discovery telescopes handled the follow-up tracking needed to calculate an orbit.

  The 1st of October 2018 marked the formal public announcement of the discovery. Years of orbital confirmation had preceded the release. The orbital data assembled for Leleākūhonua would reveal one of the most extreme trajectories yet catalogued in our Solar System.

• 3. An Extreme Path

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  At its closest, Leleākūhonua comes within 65 astronomical units of the Sun, a distance still well beyond Neptune's orbit. At its farthest, it swings to roughly 2,800 astronomical units. A single orbit takes approximately 55,000 years to complete. The semi-major axis, a measure of the orbit's average radius, sits at around 1,450 AU.

  The orbital eccentricity reaches 0.955, one of the highest values documented for any solar system body. An eccentricity of zero would describe a perfect circle; Leleākūhonua's value describes a path stretched almost to a line. Its orbit is also inclined approximately 12 degrees to the ecliptic, the plane the planets share.

  At the time its orbit was being studied, Leleākūhonua was on its inbound journey, approximately 78 AU from the Sun. That placed it about two and a half times farther out than Pluto's current position. Its next perihelion, its closest approach to the Sun, will come in 2078. The sednoid Sedna follows the same principle. Had either object been on its outbound leg when astronomers looked, neither would have been visible to the instruments available. The implication is that many similar objects exist but currently lie too far out to detect.

• 4. Planet Nine's Shadow

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  The orbit of Leleākūhonua does not stand alone. Sheppard and colleagues found that its trajectory clusters with those of several other distant trans-Neptunian objects. All share a broadly similar orbital orientation. That clustering is consistent with a large, undiscovered planet shaping those orbits from the outer Solar System. This hypothetical body, known as Planet Nine, has not been directly observed. The orbital evidence is considered suggestive, not conclusive.

  Sheppard's team also worked out what Leleākūhonua's discovery implies about the broader population. They estimated that the inner Oort cloud likely contains around 2 million objects larger than 40 kilometers in diameter. Their combined mass would be approximately equal to that of Pluto. Pluto is itself a fraction of Earth's moon in mass, but several times heavier than the asteroid belt. The Minor Planet Center formally numbered Leleākūhonua on the 10th of October 2019, opening the path toward a permanent name.

• 5. The Kolea's Migration

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  On the 3rd of June 2020, the International Astronomical Union formally named this object Leleākūhonua. The name was proposed by students enrolled in A Hua He Inoa, a Hawaiian-language naming program. The word breaks into four components: lele, meaning "to fly"; ā, meaning "until"; kū, meaning "to appear"; and honua, meaning "land." Together they translate as "it flies until land appears."

  The students drew a parallel between Leleākūhonua's orbit and the seasonal migrations of the kolea, the Pacific golden plover. That bird travels between Alaska and Hawaii each year. The object, tracing its vast ellipse around the Sun, reminded them of that journey. The official English description of the name captures this directly. It says the name "compares the orbit to the flight of migratory birds and evokes a yearning to be near Earth." A Hawaiian phrase accompanied the formal naming. It describes the object as like a bird on a path circling the sun, forever seeking a leeward wind back toward home.

  The name offered a cultural and scientific context; the physical measurements required different methods.

• 6. A World Measured by Starlight

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  The size of Leleākūhonua depends on how much sunlight its surface reflects, a property called albedo. An object with a lower albedo is darker and would need to be larger to produce the same apparent brightness. Assuming an albedo of 0.15, early estimates put the diameter at roughly 300 kilometers.

  On the 20th of October 2018, Leleākūhonua passed in front of a background star as seen from Earth, producing a brief stellar occultation. Observers at Penticton, Canada, recorded a single-chord crossing of that event. The data from that observation suggested a smaller diameter of about 220 kilometers, consistent with a higher albedo of 0.21. A single-chord measurement captures only one line across an object's profile, leaving the full shape and precise size uncertain. The 220-kilometer estimate stands as the best available figure, not a fully confirmed value. Leleākūhonua's long orbit means that opportunities to improve this measurement through another occultation will not come frequently.