Artist's interpretation of the dwarf planet. Photo / Nasa
Artist's interpretation of the dwarf planet. Photo / Nasa
For the scientists who have spent nine years waiting for Nasa's New Horizons space probe to reach Pluto, the mission has been a labour of love.
And it appears that the dwarf planet has returned their affection - the closest image ever taken shows a giant heart-shaped pattern on its surface.
The photograph was taken on Tuesday, when the spacecraft was just under 8 million kilometres from Pluto, and is the first to be received since a July 4 anomaly sent the spacecraft into a non-communicating "safe" mode.
The bright heart-shaped area is about 2000km across and scientists are puzzled about what it might be.
But all could be revealed on Tuesday when New Horizons makes a far closer fly-by.
The next time we see this part of Pluto at closest approach, a portion of this region will be imaged at about 500 times better resolution than we see today. It will be incredible.
Next week, the probe, carrying the ashes of Clyde Tombaugh, who discovered Pluto, will arrive alongside the dwarf planet.
The mission is hoping to answer fundamental questions about the ninth rock from the Sun and will send back the first intimate pictures of our elusive neighbour.
It could even help explain the origin of life on Earth.
Tombaugh died on January 17, 1997, nine years and two days before New Horizons' launch. One of his final requests was for his ashes to be sent into space.
A small container carrying his remains is affixed to the inside of the probe's upper deck, and bears the inscription: "Interned herein are remains of American Clyde W. Tombaugh, discoverer of Pluto and the solar system's 'third zone'."
Since Tombaugh discovered Pluto it has been of the most contentious bodies in the solar system with astronomers divided as to whether it is a planet, a dwarf planet, an escaped moon of Neptune or even a comet.
When New Horizons set off in 2006, carrying Tombaugh's ashes, Pluto was still considered a planet.
But a few months later it was downgraded to a dwarf planet or "plutoid" and is now known unceremoniously as "asteroid number 134340".
Scientists say the US$700 million ($1 billion) mission is "incredibly important".
New Horizons started photographing Pluto and its giant moon Charon on January 15 and has been moving closer ever since.
On Tuesday it will begin sampling the solar wind, magnetic field, dust and atmospheric conditions. Its seven-instrument science payload includes advanced imaging infrared and ultraviolet spectrometers, a compact multicolour camera, a high-resolution telescopic camera, two particle spectrometers and a space-dust detector.
Pluto as seen this week from the New Horizon space probe. Photo / Nasa
The big picture
After almost a decade of speeding through space to get to Pluto, the New Horizons spacecraft is going to keep zipping right on past it. But why not try getting into its orbit for a closer, longer look?
It all comes down to fuel: New Horizons - which is about the size of a baby grand piano - had to carry more than 7.5 billion km worth of fuel to get into the same neighbourhood as Pluto. That's already a lot of fuel, and fuel is heavy. The more fuel you carry, the more difficult and expensive it is to get your spacecraft off the Earth. Plus that extra weight slows you down, and nine years is already a long time to wait for data
Pluto - which is smaller than our moon - has low gravity, which means it would be tough to get it to grab on to a spacecraft and pull it into orbit. Right now New Horizons isn't even on course to be in the right spot for Pluto to grab it. To get New Horizons into orbit, the spacecraft would have to carry a second rocket that it could use to slow itself down and move it into Pluto's reach. But Nasa expects to find out a tonne of stuff during that brief fly-by. Even if the mission only completes its top-tier objectives, we're going to get detailed maps of Pluto and its largest moon, figure out what they're made of, and get a good idea of what Pluto's atmosphere is made of, too.
Will that be it?
Possibly not. Pluto may be at the very outer edge of our familiar solar system, but it's on the inner edge of the Kuiper Belt, which is full of objects that are mostly mysterious to us. With any luck, New Horizons will stay in good health and Nasa will extend the mission, allowing scientists to observe other, less familiar objects further away than Pluto.
