According to researchers, Pluto computer simulations indicate that an object around 730 kilometers wide, slightly surpassing the size of the asteroid Vesta, could have collided with the dwarf planet eons ago. This collision likely formed the renowned Sputnik Planitia and left behind a rocky residue. This report was published on April 15 in Nature Astronomy.
Pluto
Sputnik Planitia was initially observed in images captured by NASA’s New Horizons spacecraft during its flyby of Pluto in 2015. The heart-shaped expanse, comparable in size to the Democratic Republic of Congo, lies three to four kilometers beneath the rest of Pluto’s surface and is filled with frozen nitrogen.
“We believe it’s an impact basin because that’s the simplest way to create a large depression,” explains planetary scientist Adeene Denton of the University of Arizona in Tucson.
However, the position of the basin, spanning Pluto’s equator, poses a puzzle. Creating such a significant cavity on one side of a rotating celestial body, like a dwarf planet or moon, would induce unstable wobbles that alter the body’s orientation over millions of years. This phenomenon explains why the massive Aitken basin on the moon is currently located near its south pole.
Some scientists suggest that the impact responsible for Pluto’s heart also generated a dense, underground ocean of liquid water, which has anchored Sputnik Planitia at the equator. Yet, explaining how this hypothesized ocean could endure over geological epochs presents challenges. Pluto’s surface temperature is a bone-chilling -230°C, and even the base of Sputnik Planitia likely remains well below the freezing point of water.
“What if Pluto didn’t harbor an ocean at all?” ponders Denton.
In pursuit of this question, Denton and her team employed computer simulations to examine the consequences of various-sized rocky objects colliding with Pluto. An object approximately 730 kilometers in diameter would possess a dense, solid core enveloped by lighter materials. When such an object simulatedly struck Pluto, its outer layers vaporized, leaving behind its hefty core. This core then settled beneath Sputnik Planitia’s surface, possibly stabilizing the heart’s position.
“This concept is crucial for our further investigation,” notes Carver Bierson, a planetary scientist at Arizona State University in Tempe, who was not involved in the study. Considering doubts raised by some researchers regarding Pluto’s ability to harbor a cold, small ocean, Bierson welcomes an alternative model capable of elucidating Sputnik Planitia’s characteristics.
According to Denton, definitively resolving this debate will likely necessitate deploying an orbiter around Pluto equipped to measure the dwarf planet’s gravitational field. While such a mission has been proposed, achieving its objectives would require decades.
