Pluto: What have we learned so far?

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image copyrightNASA/JHUAPL/SWRI
image captionOn Tuesday, the US space agency released the most detailed view of Pluto yet

Now that the New Horizons probe has successfully flown past Pluto and confirmed to Nasa that it is all in one piece, researchers can look forward to a "waterfall" of images and data from the strange, distant world over the next 16 months. But even though just a couple of pictures from the dwarf planet have been released so far, scientists are learning more from these than they have in years of attempted observations by telescope.

What is Pluto's heart made from?

For 60 years scientists have known that there was a bright mass on Pluto, but it was only through the increased resolution provided by the cameras on board New Horizons that detailed its distinctive heart shape.

The shape, instantly beloved on social media, is believed to have been caused by an impact at some point in history. One side of the heart is smoother than the other. Researchers believe the crater is filled with frozen gases from the atmosphere - namely nitrogen, methane and carbon dioxide.

However a false coloured photo from Pluto released by Nasa indicates that the heart is actually broken in two. The colours show different chemical signatures in the image. On the left it is a type of beige while on the right is a mosaic of blue, these indicate that the two parts had different geologic or tectonic origins.

image copyrightNASA/JHU-APL/SWRI
image captionTwo stretched-colour images, of Pluto (L) and Charon (R); the stretching amplifies surface differences

Is Pluto another red planet?

The initial image released by Nasa had a reddish hue, something that scientists have long known. It's very different from the other red planet, Mars, in that the colour of the more distant, tiny world is likely caused by hydrocarbon molecules called tholins, that are formed when solar ultraviolet light and cosmic rays interact with methane in Pluto's atmosphere and on its surface.

image copyrightNASA
image captionMars, the red planet, may not be the only one

"Pluto's reddening process occurs even on the night side where there's no sunlight, and in the depths of winter when the sun remains below the horizon for decades at a time," according to New Horizons co-investigator Michael Summers.

Does Pluto's size matter?

New Horizons has provided more accurate information on the size and scope of Pluto. It's a little bigger than expected, about 80km wider than previous predictions, making it around two thirds the size of our moon.

The increased dimensions mean that Pluto is likely to be made of less rock and more ice beneath its surface according to members of the mission team.

The reclassification means that Pluto is now officially bigger than Eris, one of hundreds of thousands of mini-planets and comet-like objects circling beyond Neptune in a region called the Kuiper Belt.

Is Pluto geologically active?

The relative lack of impact craters on Pluto suggested by the first image could be an indication that the surface of the dwarf planet is renewing, either by geological or atmospheric activity, such as erosion.

Mission chief Alan Stern says there is evidence of "surface activity" on Pluto, a tantalising hint of earth-like tectonics "in its past or even its present".

Nasa have dubbed one of the strange, darker regions of Pluto the "whale".

Researchers say it is unusual to have contrasting bright and dark surfaces on objects in our Solar System, reflecting the fact that Pluto is far more complex than previously thought.

What's the weather like?

Surface temperatures on Pluto are extremely cold, ranging from -172 to -238 degrees C depending on where it is on its 248 year orbit of the Sun.

Since it passed the closest point to our star back in 1989, experts assumed that after that the dwarf planet started cooling.

Some computer models even predicted that the atmosphere would have fallen as snow and disappeared.

That hasn't happened. But the New Horizons Principal Investigator agrees that snow does likely fall on the distant body.

"Pluto has strong atmospheric cycles, it snows on the surface, the snows sublimate and go back into the atmosphere each 248 year orbit," said Alan Stern.

What about the five moons?

Little light has so far been shed on the moons of Pluto but the coloured image released yesterday indicates that Charon, the biggest, is covered with red material around its pole.

Scientists believe that this stuff may be tholins that have escaped from Pluto's atmosphere.

Experts believe that the mottled colours at lower latitudes point to a diversity of terrains on Charon.

So far little detail has emerged about the other moons of Pluto except more accurate measurements of their size.

How are the images and data being transmitted to Earth?

image copyrightNASA/Bill Ingalls
image captionScientists celebrate the closest approach of New Horizons to Pluto

Very slowly indeed. At a distance of 5bn kilometres from Earth and with a radio transmitter that can only output 12 watts, that means New Horizons is signalling across the Solar System with the equivalent power of a small LED bulb.

The transfer rate is achingly slow, around 1kb per second - if things go really well it can reach a dizzying 4kb. That's slow even by 1980s standards.

All this means that a black and white picture of Pluto would take over three hours to transmit. Even if massively compressed it would still take around 20 minutes.

As Nasa is handling communications to several other missions at one time, it means that New Horizons has to wait in the queue for access to the Deep Space Network, the radio telescopes that communicate with distant probes.

Getting all the data from the brief flypast of Pluto will take almost 16 months.

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