Nicholas Kang
Tutorial Publisher
BBC: Methane ice dunes found on Pluto
Scientists say they have found evidence of dunes of frozen methane on Pluto.
The research, which is published in the journal Science, suggests that the distant world is more dynamic than previously thought.
Pluto's atmosphere was believed to be too thin to create the features familiar in deserts on Earth.
The findings come from analysis of the startling images sent back by Nasa's New Horizons mission, which flew close to Pluto in July 2015.
In their study, the researchers explain how they studied pictures of a plain known as Sputnik Planitia, parts of which are covered with what look like fields of dunes.
They are lying close to a range of mountains of water ice 5km high.
The scientists conclude that the dunes are 0.4-1km apart and that they are made up of particles of methane ice between 200-300 micrometers in diameter - roughly the size of grains of sand.
Dunes can be seen in the bottom half of this picture of Pluto's Sputnik Planitia region
Credits: NASA / JHUAPL / SWRI
The paper's lead author is Dr Matt Telfer, a physical geographer at the University of Plymouth. He told BBC News: "We can't see individual grains but what we are able to identify dunes, and characterise their basic physical parameters, and the density of the atmosphere that they've been formed under.
"And we can measure some basic things like how far apart they are spaced, and have an estimate at least of the wind speeds that are forming them.
"We can feed all that back into a physical model and from that deduce what the size of the grains must be."
To be able to form, dunes need an atmosphere dense enough to make wind transport possible, a supply of dry particles, and a mechanism that lifts particles off the ground.
At first sight, none of those conditions seem to be met on Pluto.
But Dr Telfer and his colleagues calculate that the dunes may be in one of the windiest areas of the Pluto with wind speeds reaching up to 10m/sec - enough to keep particles moving.
Pluto's strange "snakeskin terrain" may represent not dunes, but blades of ice
Credits: NASA / JHUAPL / SWRI
The wind is generated as air flows downhill from the neighbouring mountains and also as frozen material sublimates - or turns directly into gas.
They believe that the dunes are composed of grains of methane, and maybe of nitrogen as well, and that a "reservoir" of methane may exist in the snowpack of the mountains.
As for the process of "lofting" the grains off the ground, the paper suggests that the driver could be a slight warming from the distant Sun, raising the temperature above the frost point of nitrogen: -230C.
With that warming of the ice below the surface, methane crystals should enable nitrogen ice to sublimate - and that would allow the methane crystals to be wafted into the atmosphere.
Dr Telfer says the analysis provides a new insight to Pluto and also changes our view of it.
"It's really exciting just to be able to look at this world and recognise that it's not just a frozen icy blob in the outer reaches of the Solar System but really we're seeing a dynamic world still changing, still forming today," he said.
That sentiment is echoed in an article accompanying the Science paper by Prof Alexander Hayes, an astronomer at Cornell University in Ithaca, US.
He quotes the late Sir Patrick Moore, the famous BBC Sky at Night presenter, describing Pluto in 1955 as "…plunged in everlasting dusk, silent, barren, and touched with the chill of death…" and says that that perspective has to shift.
Prof Hayes says we now know Pluto to be "a geologically diverse and dynamic world driven by internal heat, extreme seasons and sublimating ices".
He adds that it's not the frontier of the Solar System as Patrick Moore suggested, but the "gateway" to the unexplored realm of the Kuiper Belt.
And it may be that dunes themselves are emerging as a fascinating new feature of space exploration.
Pluto now joins Earth, Mars, Venus, Saturn's moon Titan and even the comet 67P - which a European Space Agency (Esa) mission landed on - as homes to dunes.
Scientists say they have found evidence of dunes of frozen methane on Pluto.
The research, which is published in the journal Science, suggests that the distant world is more dynamic than previously thought.
Pluto's atmosphere was believed to be too thin to create the features familiar in deserts on Earth.
The findings come from analysis of the startling images sent back by Nasa's New Horizons mission, which flew close to Pluto in July 2015.
In their study, the researchers explain how they studied pictures of a plain known as Sputnik Planitia, parts of which are covered with what look like fields of dunes.
They are lying close to a range of mountains of water ice 5km high.
The scientists conclude that the dunes are 0.4-1km apart and that they are made up of particles of methane ice between 200-300 micrometers in diameter - roughly the size of grains of sand.
Dunes can be seen in the bottom half of this picture of Pluto's Sputnik Planitia region
Credits: NASA / JHUAPL / SWRI
The paper's lead author is Dr Matt Telfer, a physical geographer at the University of Plymouth. He told BBC News: "We can't see individual grains but what we are able to identify dunes, and characterise their basic physical parameters, and the density of the atmosphere that they've been formed under.
"And we can measure some basic things like how far apart they are spaced, and have an estimate at least of the wind speeds that are forming them.
"We can feed all that back into a physical model and from that deduce what the size of the grains must be."
To be able to form, dunes need an atmosphere dense enough to make wind transport possible, a supply of dry particles, and a mechanism that lifts particles off the ground.
At first sight, none of those conditions seem to be met on Pluto.
But Dr Telfer and his colleagues calculate that the dunes may be in one of the windiest areas of the Pluto with wind speeds reaching up to 10m/sec - enough to keep particles moving.
Pluto's strange "snakeskin terrain" may represent not dunes, but blades of ice
Credits: NASA / JHUAPL / SWRI
The wind is generated as air flows downhill from the neighbouring mountains and also as frozen material sublimates - or turns directly into gas.
They believe that the dunes are composed of grains of methane, and maybe of nitrogen as well, and that a "reservoir" of methane may exist in the snowpack of the mountains.
As for the process of "lofting" the grains off the ground, the paper suggests that the driver could be a slight warming from the distant Sun, raising the temperature above the frost point of nitrogen: -230C.
With that warming of the ice below the surface, methane crystals should enable nitrogen ice to sublimate - and that would allow the methane crystals to be wafted into the atmosphere.
Dr Telfer says the analysis provides a new insight to Pluto and also changes our view of it.
"It's really exciting just to be able to look at this world and recognise that it's not just a frozen icy blob in the outer reaches of the Solar System but really we're seeing a dynamic world still changing, still forming today," he said.
That sentiment is echoed in an article accompanying the Science paper by Prof Alexander Hayes, an astronomer at Cornell University in Ithaca, US.
He quotes the late Sir Patrick Moore, the famous BBC Sky at Night presenter, describing Pluto in 1955 as "…plunged in everlasting dusk, silent, barren, and touched with the chill of death…" and says that that perspective has to shift.
Prof Hayes says we now know Pluto to be "a geologically diverse and dynamic world driven by internal heat, extreme seasons and sublimating ices".
He adds that it's not the frontier of the Solar System as Patrick Moore suggested, but the "gateway" to the unexplored realm of the Kuiper Belt.
And it may be that dunes themselves are emerging as a fascinating new feature of space exploration.
Pluto now joins Earth, Mars, Venus, Saturn's moon Titan and even the comet 67P - which a European Space Agency (Esa) mission landed on - as homes to dunes.
