Image caption Planck made its observations far from Earth on the planet's nightside

The process of disposing of the Planck space telescope has begun.

The satellite, which mapped the "oldest light" in the Universe in unprecedented detail, has completed its mission and will be turned off in two weeks' time.

It is currently some 1.6 million km from Earth, where it is undergoing some final engineering tests.

European Space Agency controllers will initiate a big burn on Planck's thrusters on Wednesday, pushing it away from the planet into a separate orbit.

The best may be yet to come; the amazing possibility of probing the Universe less than a billionth of a billionth of a billionth of a second after it began Prof Mark McCaughrean, Esa's senior scientific advisor

A second burn on 21 October will run the satellite's propellant supply to exhaustion.

"We drain everything so there's no possibility of having an exploding tank in the future," explained Steve Foley, Esa's spacecraft operations manager for Planck.

"We'll disconnect the batteries and switch off the transmitters, patching the software so they can never be re-activated. Final contact is scheduled for 23 October, and that will be it - Planck will just drift off," he told BBC News.

The 600m-euro (£515m) telescope will end its days making a slow turn around the Sun. It will not come anywhere near the Earth again for another 13-14 years; and even then, the closest it will get will be about 10 million km.

Planck has returned an extraordinary treasure trove of information, picking out thousands of objects in the sky not previously recognised. It has even mapped the sum of all the matter in space.

But its main quest was to survey the Cosmic Microwave Background (CMB) - the "first light" to sweep out across space once a post-Big-Bang Universe had cooled sufficiently to permit the formation of hydrogen atoms.

Before that time, scientists say, the cosmos would have been so hot that matter and radiation would have been "coupled" - the Universe would have been opaque.

Planck's cosmic numbers Image caption Planck was launched in May 2009 The telescope's observations produced a new contents list for the Universe:

4.9% normal matter - atoms, the stuff from which we are all made

26.8% dark matter - the unseen material holding galaxies together

68.3% dark energy - the mysterious component accelerating cosmic expansion

Planck's number for dark energy is lower than previously estimated

It has also measured the expansion rate of the Universe

This is described by a value that scientists refer to as the Hubble Constant

It is found to be 67.2 km per second, per megaparsec (or per 3.2 million light-years)

This suggests the Universe came into existence about 13.8 billion years old

Today, the CMB pervades the entire sky, and scientists can measure tiny temperature variations in it to glean information about the shape, age and contents of the cosmos.

Planck scanned the full microwave background five times before its High Frequency Instrument ran out of helium coolant in January 2012.

The Low Frequency Instrument has continued operations, surveying the complete sky a further three times. This additional data will be used to help clean the telescope's final CMB map of any obscuring light sources, principally from our own galaxy.

Scientists presented their first take on Planck's view of the cosmos in March, but promise an update in summer 2014.

Of key interest will be whether the telescope has detected a particular type of polarisation in the ancient light known as the B-Mode.

Theory holds that the Universe experienced a faster-than-light expansion in the first moments of its existence, and that this superluminal event is imprinted on the polarisation of the CMB.

If Planck can resolve this very subtle "twist" in the directional quality of the light, it would open up a completely new way to probe the physics of the Big Bang.

Commentators say such a discovery would likely also draw the attention of the Royal Swedish Academy of Sciences, which annually selects the Nobel Prizes.

Prof Mark McCaughrean, Esa's senior scientific advisor, told BBC News: "Planck has done a fantastic job and has lasted considerably longer than expected. Any sadness about it being turned off is completely outweighed by the scientific results it has already delivered, namely the most precise assessment of the composition, structure, and early evolution of the Universe ever made.

"And the best may be yet to come; the amazing possibility of probing the Universe less than a billionth of a billionth of a billionth of a second after it began."

CMB - The 'oldest light' in the Universe Theory says 380,000 years after the Big Bang, matter and light "decoupled"

Matter went on to form stars and galaxies; the light spread out and cooled

The light - the CMB - now washes over the Earth at microwave frequencies

Tiny deviations from this average glow appear as mottling in the map (above)

These fluctuations reflect density differences in the early distribution of matter

Their pattern betrays the age, shape and contents of the Universe, and more

Jonathan.Amos-INTERNET@bbc.co.uk and follow me on Twitter: @BBCAmos