47171 Lempo

47171 Lempo, also known as (47171) Lempo–Hiisi, is a special object in space found beyond the planet Neptune. It is called a trans-Neptunian object and is located in a distant area of our Solar System called the Kuiper belt. This object was discovered on October 1, 1999, by American astronomers Eric Rubenstein and Louis-Gregory Strolger while they were using telescopes at the Kitt Peak National Observatory in Arizona, United States.

Lempo moves in a special pattern related to the planet Neptune, which helps scientists classify it as a plutino. This means it follows a path that repeats every two years for every three years Neptune takes to orbit the Sun. Lempo is one of the brighter objects of its kind and came closest to the Sun in July 2015.

The object got its name from Lempo, a figure in Finnish mythology. Later, scientists found two smaller objects moving together with Lempo. These were named Paha and Hiisi, after Lempo’s demon companions in the myths.

History

Discovery

The Lempo system was found on October 1, 1999, by American astronomers Eric Rubenstein and Louis-Gregory Strolger. They were working at the Kitt Peak National Observatory in Arizona as part of a project to study faraway stars. During this project, they noticed a bright object moving slowly across the sky. This object was later named Lempo.

After finding Lempo, Rubenstein and Strolger watched it for three more days to make sure it was real. They even found it in pictures taken the day before they first saw it. The discovery was shared with scientists around the world in December 1999. Lempo was given a special number, 1999 TC₃₆, to show when it was found. By 2002, they had watched Lempo long enough to figure out its path around the Sun, and it was given the permanent number 47171. By 2021, over 500 observations of Lempo had been recorded.

Name

Lempo is named after a character from Finnish mythology. In old stories, Lempo was first seen as a god but later as a tricky spirit after new beliefs came to Finland. The two smaller parts of the Lempo system are named after Lempo's friends, Hiisi and Paha. These names were picked by astronomer Bryan J. Holler, and the official name was announced in 2017. Hiisi is also the name of a faraway planet called HAT-P-38b.

Triple system

Lempo is a special group of three objects orbiting each other in space. It has a central pair called Lempo and Hiisi, which spin around each other. A smaller object named Paha goes around this central pair.

Lempo and Hiisi are almost the same size, while Paha is much smaller. Scientists discovered Paha in 2001 using a powerful telescope. This system is one of only a few known objects in space that has three parts orbiting together.

System dynamics

The way the Lempo system moves in space is very complicated and cannot be explained using simple science rules. Important details about how the pieces spin and their shapes are unknown, making it hard to understand their movement together. A study in 2018 showed that even with good guesses about these details, the orbits of the pieces still did not match what we see. Researchers think we need better measurements before we can make a more detailed model.

Origin

There are two main ideas about how this triple space object formed. One idea is that a big crash happened, and then the pieces came back together. Another idea is that a third object was pulled in by the gravity of two objects that were already together. The fact that Lempo and Hiisi are about the same size makes the second idea seem more likely.

Physical characteristics

Observations from space telescopes like the Spitzer Space Telescope, Herschel Space Telescope, and the Hubble Space Telescope help scientists guess the sizes and densities of objects like Lempo. The size of Lempo is about 393 kilometers across.

Studies show that Lempo has a very low density, meaning it is likely made of loosely connected pieces of rock and ice. Its surface appears red in visible light and has some signs of water ice. These details come from studying the light reflected from Lempo.

Exploration

The Lempo system is interesting for future space missions because of its special setup. Scientists have thought about sending a spacecraft called New Horizons 2 to visit Lempo, along with Jupiter, Uranus, and up to four other objects in the Kuiper belt.