Newly discovered space rock loops the sun faster than any known asteroid

A recently discovered asteroid has the second shortest orbit known to us in the entire solar system, passed only by Mercury.

It’s called 2021 PH27, and it only takes 113 days to circle the Sun, in an unstable elliptical orbit that intersects the orbital paths of Venus and Mercury.

This means it gets extremely close to the Sun at its closest approach, or perihelion, grazing close enough to reach scorching temperatures of up to 480 degrees Celsius (900 Fahrenheit).

It also means that the asteroid’s time is limited: within a million years, it will either be thrown out of its current path, or it will be wiped out in a collision with one of the two planets or the Sun.

Although its lifespan – at least in its current orbit – is short, at least on cosmic time scales, 2021 PH27 and other objects in the inner solar system can reveal information about the evolution of our planetary system.

The orbital path of 2021 PH27. (Katherine Cain and Scott Sheppard / Carnegie Institution for Science)

That is, if we can figure out where it came from.

“Most likely 2021 PH27 has been dislodged from the main asteroid belt between Jupiter and Mars and the gravity of the inner planets has shaped its orbit in its current configuration,” said astronomer Scott Sheppard of the Carnegie Institution for Science.

“Although, based on its large tilt angle of 32 degrees, it is possible that 2021 PH27 was an extinct comet from the Outer Solar System that ventured too close to one of the planets as the trajectory of her journey brought her closer to the inner solar system. “

Spotting asteroids inside Earth’s orbit – known as Atira asteroids when their orbits are entirely contained within Earth’s – is usually very difficult to see, as they tend to be very close to the Sun. in the sky.

This means that the best time to spot them is just before sunrise or just after sunset – when the asteroid is illuminated by the Sun, but not eclipsed by it.

This is how astronomers Ian Dell’Antonio and Shenming Fu of Brown University photographed 2021 PH27 on August 13, 2021, using the National Science Foundation’s 4-meter Blanco telescope in Chile.

In their observations, taken just after sunset, Sheppard found the asteroid. David Tholen of the University of Hawaii, who frequently collaborates with Sheppard, then used these images to calculate where the asteroid would be the following evening.

“Because the object was already in the Sun’s glare and was heading more towards it, it was imperative that we determine the object’s orbit before it was lost behind our central star,” Tholen said. .

“I assumed that for an asteroid of this size to stay hidden for so long, it must have an orbit that keeps it so close to the Sun that it is difficult to detect from Earth’s position.”

This small moving point is 2021 PH27. (Ian Dell’Antonio and Shenming Fu / Brown University)

The data obtained over the next two nights allowed researchers to calculate an accurate orbit and learn a few things about 2021 PH27.

We know, for example, that its size is about 1 kilometer (0.62 mile) in diameter. We also know that, because it flies so close to the Sun, it is very strongly affected by the effects of its gravitational field as described by General Relativity – in particular, the rotation of its orbit, a phenomenon known as precession. apse.

Before the discovery of 2021 PH27, Mercury had the strongest apsidal precession in the solar system; but, although Mercury’s orbital period is shorter – only 88 days – its orbit is much rounder, meaning it does not approach as close to the Sun as the asteroid.

2021 PH27 is about to sway behind the Sun, which means we won’t be able to see it again until early next year. At this point, researchers hope to make more observations that will help refine its orbit even further, which in turn will reveal more details about the asteroid’s origin and what its future may hold.