Fastest orbiting asteroid in the solar system discovered

Asteroid 2021 PH27 takes only 113 Earth days to complete a circle around the Sun. The newly discovered asteroid orbits the Sun faster than any of its known relatives.

The space rock, known as 2021 PH27, makes one circle around our star every 113 Earth days, its discoverers found. It is the shortest orbital period of any known object in the solar system, with the exception of the planet Mercury, which takes only 88 days to circle the sun.

However, 2021 PH27 follows a much more elliptical path than Mercury and is therefore much closer to the Sun – about 12.4 million miles (20 million kilometers) at closest approach, compared to 29 million miles (47 million kilometers) for the innermost planet in the solar system.

During such close passages of the Sun, the surface of 2021 PH27 becomes hot enough to melt lead — about 900 degrees Fahrenheit (500 degrees Celsius), the research team estimates. These deep dips into the Sun’s gravitational well also mean that the asteroid is experiencing the largest general relativity effects of any known object in the solar system. Such effects manifest themselves as a slight wobble in the elliptical orbit of 2021 PH27 around the Sun, which the team observed.

This orbit, by the way, is not stable in the long term. 2021 PH27 is likely to collide with the Sun, Mercury or Venus in a few million years if it is not first thrown off its current path by gravitational interaction, team members say.

2021 PH27 was first spotted by astronomers Aug. 13 using the Dark Energy Camera (DEC), a powerful multipurpose instrument mounted on the Víctor M. Blanco 4-meter telescope at the Cerro Tololo Inter-American Observatory in Chile.

Over the next few days, the team was able to determine the asteroid’s exact orbit through further observations with the DEC and Magellanic telescopes at the Las Campanas Observatory in Chile, as well as smaller telescopes in Chile and South Africa operated by the Las Cumbres Observatory.

Sheppard and his colleagues estimate that 2021 PH27 is about 0.6 miles (1 km) wide. According to the researchers, the space rock may have originated in the main asteroid belt between Mars and Jupiter, and then been thrown into space by gravitational interaction with one or more planets.

However, the orbital path of 2021 PH27 is tilted by 32 degrees relative to the plane of the solar system. Such a large tilt suggests that it may be an extinct comet, which was born far outside the solar system, and then was transferred to a closer orbit after passing by Mars, Earth or another rocky planet.

Further observations may help solve this mystery, but Sheppard and other astronomers will have to wait a few months to gather more data. 2021 PH27 is now moving behind the Sun from our vantage point, and it won’t reappear until early 2022, members of the research team say.

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