The latest spectra from New Horizons Ralph instrument reveal an abundance of methane ice, but with striking differences from place to place across the frozen surface of Pluto. Photo / NASA
A Kiwi astronomer says stunning new images of Pluto and its largest moon reveal surprising glimpses of activity on the planet and its satellite.
Auckland's Stardome Observatory and Planetarium astronomer Grant Christie said he was surprised by the newly released images, which reveal icy mountains on the dwarf planet's surface.
Nasa's New Horizons probe beamed back the high-resolution images, which show 3.35km high mountains on the planet's surface, earlier today.
The photos come after the probe made its closest pass of the dwarf planet overnight. Their resolution is 10 times that of the previous best pictures send back.
Nasa spokesman Dwayne Brown told CNN today: "Yesterday, America's space programme took another historic leap for humankind. Today, the New Horizons team is bringing what was previously a blurred point of light into focus."
Images of Pluto's moon Charon also revealed a "surprisingly youthful and varied terrain", the space agency said.
Nasa said "a swath of cliffs and troughs stretches about 1000km from left to right, suggesting widespread fracturing of Charon's crust, likely a result of internal processes".
Mr Christie said he was surprised at how young Pluto and Charon's surfaces were.
"That's the first thing that really strikes you. Yesterday it was surprising to see only a small number of impact craters, and astronomers basically can estimate the age of planetary surfaces in the solar system by how many impact craters there are per square kilometre.
"Pluto would come up pretty short in that measure - in other words the surface has to be fairly young. It must have been hit by things - four billion years sitting out there it has been hit by lots of things. There should be more impact craters, so something is erasing the impact craters."
Mountains on Pluto and Charon's surface showed there was some kind of activity on both the planet and its moon, Mr Christie said.
"There are great big, what look like geologic structures, long canyons and rifts in the surface. Something is active on both Pluto and Charon.
"The question will be for the experts to figure out what is the actual energy source. Inside the earth it is very hot ... so we understand that that drives the plate tectonics.
"But what is it inside Pluto that causes those tectonics events essentially on the surface?"
Some of the mountains in the images were 3500m high - which was roughly the size of Aoraki-Mt Cook, Mr Christie said.
This was also the equivalent of 10-and-a-half Sky Towers, if they were stacked on top of one another.
"Planet Earth is six times the diameter of Pluto, so for something that high to be on Pluto is surprising."
He said the bedrock of Pluto had been described as being made up of water ice, and it could be possible that the make-up of Pluto was similar to that of Saturn's moon Titan.
Mr Christie said in very cold temperatures, water ice was so hard it behaved like rock, and some substances like methane played the part of water.
"The parallel there is that similar processes take place on Titan that cause lakes, rivers, rain where instead of water it's methane, and the water actually behaves like the rock.
"That is what you get with a very cold world - it's quite possible that there is something like that going on on Pluto."
Mr Christie said Pluto was probably the last large piece of major real estate scientists would be able to reach for a while.
He said it was likely attention would now turn to Triton, the moon of Neptune.
"That could be a target in the future. My guess is that in terms of a similarity to Pluto, Triton the large moon of Saturn will be an interesting place to visit."
He said no decision had been made yet as to what direction New Horizons would be steered to after its Pluto mission.
"There is a number of other objects out in the Kuiper Belt region of the solar system that they are considering, and it's possible to direct New Horizons to do a fly-by of one of those objects.
"After that, whether we keep talking to it will depend on budget - it costs money to keep talking to these things over time."
Alan Gilmore, from the University of Canterbury's Mt John Observatory in the South Island, said most people expected to see a surface which was covered in a lot more craters, rather like the surfaces of asteroids Ceres and Vesta, which travelled in the asteroid belt between Mars and Jupiter.
"What's noticeable about Pluto and its moon is a lot fewer craters than were excepted."
Processes over time were erasing craters by one means or another, Mr Gilmore said.
"The surface is what they call 'being renewed', in much the way the Earth's surface gets renewed by plate tectonics and weathering and all that sort of stuff.
"It will be up to the geologists and planetary scientists to work out just what is going on with that."
Mr Gilmore said the existence of high mountains would imply long-term activity on the planet's surface.
"We are talking here about time intervals of tens of millions of years, so it's not like it is something going on very quickly.
"Pluto is a very tiny world - you would need five Plutos to make the moon. It's only about 2400km across, so you expect a tiny world like that not to have any internal heat, but there are other factors.
"It has a big moon Charon. You get what is called tidal heating - that is tides caused by the gravity pull of Charon being quite big. The same thing will be going on the opposite way around.
"We know for instance the moons of Jupiter are heated inside by tidal forces caused by Jupiter. So although they're relatively small - they're about the same size as our moon, which is cold inside - the inner big moons of Jupiter are kept hot by tidal forces.
"It may be there is some process like that going on. I'm sure more expert comment will come out in the next few days."
Mr Gilmore said he understood they would now tweak New Horizon's track so it could pass more objects in the Kuiper Belt.
Images sent back from Pluto marked a significant step in space exploration, Mr Gilmore said.
"It's the usual story of you don't know what you're going to find until you go out and look. I think people are a bit surprised with what they have found so far.
"Much more detailed stuff is going to come back over the next many months because it takes a long long time to send that data back ... it's like an old fashioned modem basically.
"I think it is just technologically amazing just to see a picture, any picture, from Pluto."
There will be a lot of expert discussion about the significance of what has been seen on Pluto, Mr Gilmore said.
"These pictures are going to feed into the whole study of the origin of the solar system."
Pluto was discovered by Clyde Tombaugh on February 18, 1930, and some of his ashes are on board the New Horizons probe.
Mr Gilmore said this had been done before.
The ashes of Eugene Shoemaker, a planetary scientist who studied lunar craters, had some of his ashes placed on board a lunar spacecraft that circled the moon, and eventually crashed on to the moon's surface, Mr Gilmore said.
"I think it's rather nice that a little bit of Clyde Tombaugh actually went past Pluto - Clyde himself didn't live long enough to actually see these pictures."
Director of Otago Museum and astronomer Ian Griffin explains why receiving photos and data from Pluto is an amazing technological achievement.
What technology was used to transmit the photos?
It was basically digital cameras on board. There are bunch of instruments on board the ship and they digitise the data and send it back. A lot of it is stored on hard drives, and is going to be sent back via radio over the next few weeks and months because there is so much of it.
Why do the images and data take so long to return to Earth?
The information comes back at the speed of light, which is the speed that radio waves travel. That's 300,000 km per second. The space probe is so far away that it takes light just over four hours to get here. It's all to do with the distance of the space probe and it just shows how incredibly far away from us it is. The reason it is taking so long to get the data back is because they're so far away and there is only so much information you can send at any one time. These images are all very very large images, they're all stored on board, and they are just going to be sent back as fast as the information can travel.
So it will be transmitted back using radio waves?
Basically yes. It is kind of complicated, but the further you are away from the Earth, the lower the speed of the data you can send back. So when the spaceship flew past Pluto it took huge amounts of data. Cameras were pointing at it and taking lots of pictures and recording lots of information. That was all stored on board, and that is going to be effectively replayed back to us over the next few weeks and months.
How do radio waves work?
It's the same way when you watch television. When you watch television in your home, it comes down from a satellite but it's transmitted up from a station on the ground... what's happening is that a radio transmitter on board the spaceship is sending transmissions towards the Earth, and on Earth, Nasa have got these big dishes around the planet picking signals up.
How would you describe the quality of the data?
It's extraordinary. We've actually already seen stuff from Pluto that we weren't expecting to see. For example one of the most fascinating things about the picture that came back this morning, is before hand you would expect Pluto to be covered in craters. The fact that it is not means that there is some kind of dynamic process, some weathering, or geological thing going on that gets rid of the craters... as one of the scientists from Nasa said this morning, literally they are re-writing the book on Pluto with every image that comes back. That's exciting stuff.
How much remaining data do you expect there is to come back?
Lots... when the probe flew past it had all those cameras and instruments photographing and recording data and all of that has been stored on board, and that it all going to be replayed over the next few weeks and months and sent back to Earth.
Do you consider this to be a technological achievement?
This is phenomenal. We are looking at pictures of an object in the outer part of the solar system. If you are an astronaut standing on Pluto you are so far from the sun it looks just like a bright star in the sky. You're in the outer reach of the solar system, it's dark, it's cold and we've managed to spend a space craft to photograph this amazing object. I think it is an amazing technological achievement.
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