2021 PH27 manages to make a full orbit in just 113 of our days, either moving away from the Sun further than Venus, then converging closer to Mercury.
Asteroid 2021 PH27 has a fairly ordinary size - about a kilometer across - but an extremely unusual orbit. Its orbit is closer to the Sun than any other known asteroid. 2021 PH27 makes a full revolution along it in just 113 days and converges with the star at a distance of 20 million kilometers, closer to Mercury. This is stated in the message of the Laboratory of Optical and Infrared Astronomy (NOIRLab) of the US National Science Foundation (NSF).
The find was made on August 13 this year. Carnegie Institution astrophysicist Scott Sheppard and colleagues used a 570-megapixel DECam camera mounted on the four-meter Víctor M. Blanco telescope at CTIO in Chile. The observations were carried out at dusk - this is the optimal time to study Venus, Mercury and asteroids closer to the Earth than the Sun. Such asteroids are called atyrs; only about 20 of them are known.
Noticing 2021 PH27, scientists quickly calculated its trajectory and predicted where the asteroid would be a day later. On August 14, the observations were successfully repeated using not only DECam, but also telescopes in other observatories in the world. On the 15th, astronomers collected more accurate data using ESA's network of telescopes located in Chile and South Africa. The orbit of 2021 PH27 has been shown to be elliptical, with a semi-major axis (largest radius) of only 70 million kilometers.
The asteroid makes a full revolution along it in 113 days, crossing the orbits of both Venus and Mercury on the way. This is the fastest movement of all known asteroids, with a higher frequency only Mercury turns around the Sun - in 88 days. And, of course, both heat up due to the proximity of the star: according to scientists, the surface of 2021 PH27 is capable of heating above 480 ° C. In addition, calculations show that the orbit of 2021 PH27 may be unstable and in the next few million years it will either fall on the Sun, Mercury or Venus, or be thrown back into more distant regions.
Most likely, this celestial body was formed far from them, in the asteroid belt between Mars and Jupiter, but was thrown into the innermost regions of the solar system by a random play of gravity. On the other hand, its orbit is distinguished by a large inclination (relative to the plane of the solar system) - 32 °. This may indicate that 2021 PH27 flew in from the outermost periphery and is a degenerate comet nucleus that has lost its volatiles and is no longer able to form a bright coma and tail. Perhaps the answer will be given by new observations.