Science & Environment

Juno probe captures movie of Earth-Moon 'dance'

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Media captionThe dance between Earth and the Moon, seen from a unique perspective

The US space agency (Nasa) has released an extraordinary new movie of Earth and the Moon moving through space together.

The images that make up the sequence were acquired by the Jupiter-bound Juno satellite when it passed by our home planet in October.

Earth is observed spinning on its axis with the Moon passing in front and heading off to the right of the scene.

Juno's chief scientist Scott Bolton says the images should make people think about our place in the Universe.

"Humans can see the Earth and the Moon in motion, doing their cosmic dance. And I think it puts everything into perspective," he told BBC News.

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Media captionScott Bolton: "We fell into this opportunity quite by accident"

"You may remember some years ago that Carl Sagan took a picture he called the Pale Blue Dot, and made a lot of very important points about the fact that everything we know is on this little dot. And I think our movie does the same thing but with a moving image rather than just a still one."

Dr Bolton was speaking in San Francisco at the American Geophysical Union (AGU) Fall Meeting, the largest annual gathering of Earth and planetary scientists.

There have been other sequences that capture the Earth-Moon system in motion, but not quite from the distance seen in the Juno production.

The flyby movie is available on YouTube. The accompanying music is scored by the renowned film composer Vangelis.

Juno was launched from the Kennedy Space Center in Florida on 5 August 2011.

The trajectory chosen to send it out to Jupiter required the spacecraft to fly back around the Earth on 9 October this year.

This gave the satellite a gravitational boost that will hurl it towards the gas giant with a rendezvous set for 2016.

But the mission scientists realised that the Earth flyby could also provide a unique photo opportunity.

Image caption The Earth flyby gave Juno the kick it needed to get out to Jupiter in 2016

They programmed a camera system on Juno to compile a series of images during the approach.

This was not the main camera system onboard, but rather the equipment normally employed to track stars for navigation purposes.

But it had the advantage, says the team, of having a low-enough resolution that only a manageable volume of data would be produced to make the movie.

The result is slightly surreal, but unquestionably familiar.

Earth and the Moon enter the field of view at left, when Juno is about 1,000,000km away - about three times the Earth-Moon separation.

Then, with the Moon gradually drifting off to the right, the Earth comes closer and closer as Juno prepares to swing around for its slingshot.

"The big trick for a low-light camera like this was to tune it in a way that we were able to get images of a very bright object," explained participating scientist John Jorgensen of the Danish Technical University, near Copenhagen.

Image caption Jupiter's Great Red Spot: A persistent storm located just south of the planet's equator

"The camera was designed for operating at the Jupiter system where light is a hundred times fainter than what we can see in this movie."

Juno's mission once it gets to Jupiter will be to explain the Solar System by investigating the origin and evolution of its biggest planetary member.

The spacecraft's remote sensing instruments will look down into the giant through its many layers and measure their composition, temperature, motion and other properties.

This should yield some remarkable new insights into the coloured bands that wrap around the planet, and give us a new perspective on the famous Great Red Spot - the colossal storm that has raged on Jupiter for hundreds of years. Juno will tell us how deep its roots go.

A key quest is to measure the abundance of water in the atmosphere - an indicator of how much oxygen was present in Jupiter's region of the Solar System when it formed.

The probe will also try to settle old arguments over whether the planet hosts a rocky core or whether its gases go all the way down to the centre in an ever more compressed state.

All this information bears down strongly on the competing theories for how the eight worlds we now call planets came into being.

Image caption The Juno spacecraft has a long journey to make it out to the Jupiter system and follow me on Twitter: @BBCAmos

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