47171 Lempo, or as a binary (47171) Lempo–Hiisi (also known as ), is a trans-Neptunian object and trinary system from the Kuiper belt, located in the outermost regions of the Solar System. It was discovered on 1 October 1999, by American astronomers Eric Rubenstein and Louis-Gregory Strolger during an observing run at Kitt Peak National Observatory in Arizona, United States. Rubenstein was searching images taken by Strolger as part of their Nearby Galaxies Supernova Search project. It is classified as a plutino with a 2:3 mean-motion resonance with Neptune and is among the brighter TNOs. It reached perihelion in July 2015. This minor planet was named after Lempo from Finnish mythology. The trinary system's other two components, Paha and Hiisi , were discovered in 2001 and 2007, respectively, and later named after Lempo's two demon cohorts, Paha and Hiisi. History Discovery The Lempo system was discovered on 1 October 1999 by American astronomers Eric Rubenstein and Louis-Gregory Strolger during an observing run for their Nearby Galaxies Supernova Search (NGSS) project at the Kitt Peak National Observatory in Arizona. Initiated in 1998 as part of Strolger's doctoral thesis, the NGSS project was a three-year-long CCD-based survey of galaxies along the celestial equator to search for nearby, low-redshift supernovae. The Kitt Peak Observatory's WIYN 0.9-meter telescope was used for wide-field imaging of this region, which coincided with the ecliptic plane where Kuiper belt objects (KBOs) including Lempo were likely to appear. Rubenstein identified Lempo as a relatively bright, slow-moving object in the constellation Cetus on images taken by Strolger on 1 October 1999. At an apparent magnitude of 20, its exceptional brightness for a suspected KBO warranted follow-up observations to confirm the object. Lempo was observed by Rubenstein and Strolger for three consecutive days after its discovery. The object was also found in images taken by Strolger on 30 September 1999, one day prior to its discovery. The discovery was then announced by the Minor Planet Center on 21 December 1999 and the object was given the provisional designation . The provisional designation indicates that Lempo was the 903rd minor planet discovered in the first half of October 1999. By 2002, additional observations have extended Lempo's observation arc to over two years, sufficient to determine an accurate orbit. Lempo was consequently given the permanent minor planet number 47171 by the Minor Planet Center on 21 September 2002. , more than 500 total