NASA's New Horizons data hint at hidden ocean beneath the surface of Pluto

It's been nearly a decade since NASA's New Horizons spacecraft made its historic flyby of Pluto, but the enigmatic dwarf planet is still yielding remarkable secrets. Scientists poring over the spacecraft's data have uncovered evidence of a potentially recent cryovolcanic eruption, a phenomenon never before observed in our solar system.

The intriguing discovery centers around a peculiar crater nestled in the heart-shaped region known as Sputnik Planitia on Pluto. Researchers believe they may have stumbled upon what could be a supervolcano that erupted just a few million years ago – a cosmic blink of an eye when you consider the solar system's age of more than 4.5 billion years.

This is not your typical volcanic eruption, where molten rock spews from the Earth's crust. Instead, the 44-kilometer-wide Kiladze crater seems to have unleashed ice lava, a phenomenon called cryovolcanism, onto Pluto's icy surface. This process, also observed on the moons of gas giants in our solar system, is believed to have transported water from Pluto's hidden subsurface ocean to reshape the dwarf planet over millions of years.

The presence of such a cryovolcano raises questions about the heat sources lurking within Pluto. Traditional volcanoes on Earth rely on molten rock, and their activity is a testament to our planet's internal heat. So, the recent cryovolcanic activity on Pluto hints at a previously underestimated heat reservoir beneath its icy exterior.

The findings emerged from a comprehensive analysis of images captured by New Horizons, focusing on the Kiladze crater situated northeast of Sputnik Planitia. Initially, scientists believed it resembled the aftermath of meteorite impacts, but they noticed distinct characteristics. The absence of a central peak, a typical feature of meteorite impact craters, and its elongated shape suggested tectonic forces at play within Pluto, as outlined in a new study, pending peer review.

Pluto's surface is predominantly covered with methane and nitrogen ice, making Kiladze's unique attributes stand out. Dale Cruikshank, the lead author of the study and a professor at the University of Central Florida, explains, "The water ice stands out clearly from the methane ice that covers much of the planet's surface."

Pluto's unusual climate dynamics further underscore the mystery. Its extreme axial tilt of 120 degrees means it spins nearly on its side, leading to dramatic shifts in climate as it orbits the sun. This causes methane ice to sublime into hydrocarbon haze within Pluto's atmosphere, with some particles settling back onto its surface as snow.

Over the course of Pluto's 4.6-billion-year existence, scientists estimate that this methane ice layer could have grown to be at least 14 meters (46 feet) thick. Even a thin layer of this organic smog could obscure the spectral signature of the water ice, making Kiladze's differentiating features even more intriguing. This led Cruikshank and his team to conclude that Kiladze must have been "alive" just a few million years ago.

The conundrum deepens as scientists grapple with the source of the heat driving cryovolcanic activity on Pluto. Given the planet's diminutive size, it should have lost its heat long ago. One theory posits that Pluto once contained radioactive elements in its core that released heat as they decayed, but previous research suggested that these elements might be insufficient to fuel such eruptions.

Cruikshank offers an alternative hypothesis, stating, "As the planet cooled, it is plausible that pockets of liquid water were left behind, and perhaps our eruptions of water onto the surface tap into those pockets." However, he concedes, "We don't know."

This revelation opens a new chapter in the ongoing exploration of Pluto, hinting at an active and dynamic world far from the icy, desolate image often associated with it. As our understanding of Pluto's geological history deepens, researchers are left eagerly anticipating future missions that may unlock the planet's many mysteries.