25143 Itokawa

25143 Itokawa, also called 1998 SF₃₆, is a small space rock that orbits close to Earth. It was found in 1998 by the LINEAR program and named after the Japanese rocket engineer Hideo Itokawa. This asteroid is shaped like a peanut and is about 330 meters, or 1,100 feet, wide. It spins around once every 12.1 hours and is made of many pieces of rock held together, like a pile of loose boulders.

Itokawa was very important because it was the first asteroid visited by a spacecraft that brought pieces of it back to Earth. The Japanese probe Hayabusa collected tiny pieces of dust from Itokawa’s surface in 2005. When the probe returned to Earth in 2010, scientists studied these pieces. This helped them learn more about our Solar System. Before the DART mission to Dimorphos in 2022, Itokawa was the smallest asteroid ever seen up close by a spacecraft.

Discovery and naming

Itokawa was found on 26 September 1998 by astronomers using the Lincoln Near-Earth Asteroid Research (LINEAR) program at Lincoln Laboratory's Experimental Test Site near Socorro, New Mexico, in the United States. It was given the provisional designation 1998 SF₃₆. The minor planet was named after Japanese rocket scientist Hideo Itokawa, who helped begin rocket science in Japan. The official naming was announced by the Minor Planet Center on 6 August 2003.

Orbit and classification

Itokawa is part of a group called the Apollo asteroids. These are special rocks that cross Earth’s path. Itokawa travels around the Sun at a distance between 0.95 and 1.70 times the distance from Earth to the Sun, or 0.95–1.70 AU. It completes one trip around the Sun every 18 months. Its path is slightly stretched out and tilts a little compared to Earth’s path. It sometimes comes very close to Earth.

Exploration

In 2000, Japan picked this asteroid for its Hayabusa mission. The spacecraft reached Itokawa on September 12, 2005. Because Itokawa’s gravity was too weak to keep the spacecraft in orbit, Hayabusa stayed in line with the Sun and the asteroid.

Hayabusa landed on Itokawa on November 20 for a short visit. It tried to collect soil samples but was not successful this time. A second landing was tried on November 25. The spacecraft returned its sample capsule to Earth, landing in Woomera, South Australia on June 13, 2010. Scientists later confirmed that the dust collected came from Itokawa.

Surface features

Scientists from the Hayabusa mission suggested names for the main features on Itokawa. These names were approved by experts from the International Astronomical Union. Smaller features still have temporary names for study. Below are tables showing the names of some geological features on the asteroid.

Craters

Ten impact craters on Itokawa received their names on February 18, 2009.

Regiones

Regiones are large areas on a planet or asteroid that look different from nearby areas because of brightness or color. Several regiones have been named on Itokawa.

Physical characteristics

Itokawa is a stony S-type asteroid. In 2001, pictures from Goldstone showed it looks like an ellipsoid. It is about 630 meters long and 250 meters wide.

The Hayabusa mission checked these facts and thought Itokawa might be made of two or more smaller asteroids stuck together. The mission showed Itokawa has a rough surface with big rocks and very few craters. Its density is too low to be solid rock, meaning it is made of loosely connected fragments.

Since 2001, many watching of Itokawa’s spin have been done. They showed it spins once every 12.132 hours and has a shape that is not round. Scientists also found two possible directions for its spin axis.

In 2011, scientists looked at dust collected by Hayabusa and found it matched a common type of meteorite. They also found the dark color on Itokawa’s surface came from tiny space particles scraping it.

In 2018, researchers found water in different particles from Itokawa. The water’s make-up matched that found in our solar system and on Earth.

In 2020, more studies showed water and organic materials in another particle from Itokawa.

In 2021, more studies supported the idea that some of Earth’s water may have come from hydrogen in space dust that landed on asteroids like Itokawa.

The asteroid also has areas where dust collects in dips, known as dust ponds. These were found in places called Sagamihara and Muses-Sea. The dust particles range in size from millimeters to less than a centimeter.