Astronomers have a hard time finding these interior asteroids because they are very often hidden by the glare of the Sun. When asteroids get so close to our nearest star, they experience a variety of stresses, such as thermal stresses from the Sun’s heat, and physical stresses from gravitational tidal forces. These stresses could cause some of the more fragile asteroids to break up.
“The fraction of asteroids interior to Earth and Venus compared to exterior will give us insights into the strength and make-up of these objects,” says Sheppard. If the population of asteroids on similar orbits to 2021 PH27 appears depleted, it could tell astronomers what fraction of near-Earth asteroids are piles of rubble that are loosely held together, as opposed to solid chunks of rock, which could have consequences for asteroids that might be on a collision course with Earth and how we might deflect them.
“Understanding the population of asteroids interior to Earth’s orbit is important to complete the census of asteroids near Earth, including some of the most likely Earth impactors that may approach Earth during daylight and that cannot easily be discovered in most surveys that are observing at night, away from the Sun,” says Sheppard. He adds that since 2021 PH27 approaches so close to the Sun, “…its surface temperature gets to almost 500 degrees C (around 900 degrees F) at closest approach, hot enough to melt lead.”
Because 2021 PH27 is so close to the Sun’s massive gravitational field, it experiences the largest general relativistic effects of any known Solar System object. This reveals itself as a slight angular deviation in the asteroid’s elliptical orbit over time, a movement called precession, which amounts to about one arcminute per century.
The asteroid is now entering solar conjunction when from our point of view it is seen to move behind the Sun. It is expected to return to visibility from Earth early in 2022, when new observations will be able to determine its orbit in more detail, allowing the asteroid to get an official name.
- The Local Volume Complete Cluster Survey (LoVoCCS) is an NSF’s NOIRLab survey program that is using DECam to measure the dark matter distribution and the galaxy population in 107 nearby galaxy clusters. These deep exposures will allow a clean comparison of faint variable objects when combined with data from Vera C. Rubin Observatory.
- 2021 PH27 is only one of around 20 known Atira asteroids that have their orbits completely interior to the Earth’s orbit.
- Observation of Mercury’s precession puzzled scientists until Einstein’s general theory of relativity explained its orbital adjustments over time. 2021 PH27’s precession is even faster than Mercury’s.
For more on this discovery, read Solar System’s Fastest-Orbiting Asteroid Discovered – Orbits the Sun in Just 113 Days.