A newly discovered asteroid is approaching our Sun – and getting much closer to it than planet Earth itself.
Called 2021 PH27, the asteroid completes an orbit around the Sun every 113 days and comes within 20 million kilometers of our star.
This gives this space rock the distinction of having the shortest known orbital period for an asteroid – and only the second shortest orbit around the Sun after Mercury, which takes 88 days to complete its orbital journey around the star.
Scott Sheppard, an astronomer at the Carnegie Institution for Science, discovered the celestial body after observations made in the twilight of August 13 by astronomers Ian Dell’Antonio and Shenming Fu, both at Brown University.
Dell’Antonio, a physics professor, and Fu, a doctoral student, took the images using the Dark Energy Camera mounted on the four-meter Víctor M. Blanco telescope, installed at the Inter-American Observatory of Cerro Tololo, in Chile.
Several aspects of the asteroid surprised Sheppard, starting with its size: it measures a kilometer and “very few asteroids of this size present in the inner solar system are still unknown”, commented the astronomer. The inner planets include Mercury, Venus, Earth and Mars.
“2021 PH27 is so close to the sun that its surface can reach 482 degrees Celsius, which is hot enough to melt lead. Because of these extreme temperatures, 2021 PH27 is unlikely to be composed of any volatile material. Most likely it has a rocky composition with the presence of some metal such as iron”, evaluated Sheppard.
The asteroid describes an unstable trajectory that crosses the orbits of Mercury and Venus around the Sun. Within a few million years, the asteroid’s orbit tracing is likely to cause its destruction by colliding with Mercury or Venus, or with the Sun itself.
The asteroid is so close to the Sun’s enormous gravitational field that it suffers effects in its orbit, Sheppard said. He is just one of about 20 Atira asteroids that are completely within the Earth’s orbit around the Sun.
There are other celestial bodies on the approach to the Sun, but they all have much longer orbits than 2021 PH27.
“Some of these asteroids have dust in their orbits, suggesting that they are slowly fragmenting or cracking due to the extreme thermal stresses they experience,” explained Sheppard.
A notable example is Phaethon, the comet-like asteroid that creates Geminid meteor showers in our sky every December.
tracking an asteroid
But where did this space rock come from? This is one of the questions Sheppard wants to investigate from preliminary observations.
It is likely that the object was dislodged from the main asteroid belt located between Mars and Jupiter, but the astronomer has not ruled out the possibility that 2021 PH27 is actually an extinct comet.
“This is a possibility, as comets are known to come from outside the Solar System in elongated orbits and gravitationally interact with the inner planets, so they can get shorter period and circular orbits to stay in the inner solar system for long periods of time,” detailed Sheppard. When this happens, some of the elements evaporate and the comet is reduced to remnant fragments.
Sheppard normally searches for objects very far away in the Solar System and beyond. However, it is also crucial to understand the population of asteroids close to Earth’s orbit. Celestial bodies near Earth have a chance of impact in the future, but some of them are incredibly difficult to observe because they approach our planet during the day.
“The inner space of Earth’s orbit remains relatively unexplored to this day,” said Sheppard. “It is difficult to observe the region towards the Sun because of the extreme brightness of the Sun”.
But the Dark Energy Camera has a large field of view, making it a powerful tool for looking for objects like the 2021 PH27 that would otherwise be elusive – especially when the sun goes down and just before sunrise.
After Sheppard’s discovery, astronomer David Tholen of the University of Hawaii measured the asteroid’s position and predicted where it might be observed the following night. This allowed several telescopes from Chile and South Africa to see the asteroid at 14 and 15
of August. They postponed their own research to make the observation and thus learn more about the asteroid.
“Although telescope time is very precious, the love of the unknown makes astronomers very willing to follow interesting new discoveries like this one,” said Sheppard. “We are very grateful to all our employees who allowed us to act quickly on this discovery.”
Soon, the asteroid will pass behind the Sun and will not be observable until early 2022. Sheppard is eager to learn more about the asteroid’s composition and origin.
“Where do these internal asteroids come from? Some have recently been displaced from the Main Asteroid Belt, others may be extinct comets, but there may be another source population, such as the Vulcanoids, which are a hypothetical population of asteroids,” Sheppard listed.
(Translated text. Click here to read the original in English).