Pluto has been revealed to be a true icy world of wonders in the latest images from New Horizons, with new discoveries including flowing ice on the dwarf planet’s surface and a surprising extended haze enveloping its globe.
Seven hours after its close approach, which saw New Horizons get 7,800 miles (12,500 kilometres) above Pluto’s surface, the spacecraft looked back with its Long Range Reconnaissance Imager (LORRI) camera and captured sunlight filtering through the world’s atmosphere. Hazes as high as 130 kilometres (80 miles) soon became apparent and of which appears to be split into two layers. The New Horizons team speculate that one layer of haze is about 80 kilometres (50 miles) above the surface whilst the other is at an altitude of about 50 kilometres (30 miles).
“My jaw was on the ground when I saw this first image of an alien atmosphere in the Kuiper Belt,” says New Horizon’s principal investigator Alan Stern, who is based at the Southwest Research Institute (SwRI) in Boulder, Colorado. “It reminds us that exploration brings us more than just incredible discoveries – it brings incredible beauty.”
Getting a closer look at Pluto’s atmosphere will also open up a deluge of information relating to what’s happening on the surface under it. “The hazes detected in this image are a key element in creating the complex hydrocarbon compounds that give Pluto its reddish hue,” explains Michael Summers, New Horizons co-investigator at George Mason University in Fairfax, Virginia.
It’s thought that the haze is made when ultraviolet light from the Sun breaks up the methane gas particles – a simple hydrocarbon found in Pluto’s atmosphere. This breakdown of methane then triggers a build-up of hydrocarbon gases, such as ethylene and acetylene, which have also been uncovered by New Horizons. As these hydrocarbons fall to the lower and cooler parts of the atmosphere, they turn into ice particles before creating the ‘fog’. Ultraviolet sunlight is thought to then convert the haze into tholins – the dark hydrocarbons that give the dwarf planet its colour.
However, with the spacecraft’s team calculating that temperatures would be too warm for hazes to form at altitudes higher than 30 kilometres (20 miles) above Pluto’s surface, Summers states: “we’re going to need some new ideas to figure out what’s going on.”
The latest images from the New Horizons mission have also revealed evidence for exotic ices flowing across Pluto’s surface as well as signs of recent geological activity. Fascinating details within a Texas-sized plain, informally known as Sputnik Planum and found within the western half of Pluto’s heart-shaped feature, have additionally been pinpointed by the keen spacecraft: LORRI has detected sheets of ice that clearly appear to have been flowing – or may still be flowing – in a way similar to the glaciers on our own planet. “We’ve only seen surfaces like this on active worlds like Earth and Mars,” says John Spencer of SwRI, also a co-investigator of New Horizons. “I’m really smiling.”
And that’s not all that has been uncovered. Compositional data from the spacecraft’s Ralph instrument indicates that the centre of Sputnik Planum is rich – not just nitrogen – but also carbon monoxide and methane ices. “At Pluto’s temperatures of -234 degrees Celsius (-390 degrees Fahrenheit) these ices can flow like a glacier,” explains Bill McKinnon, deputy leader of the New Horizons Geology, Geophysics and Imaging team at Washington University in St. Louis. “In the southernmost region of the heart, adjacent to the dark equatorial region, it appears that ancient, heavily-cratered terrain has been invaded by much newer icy deposits.”