The countdown has begun for a mission to discover whether life might exist on Jupiter's moon Europa.
US space agency Nasa has announced what instruments the Europa probe will carry to the mysterious ice-covered water world, setting the clock ticking for the mission's launch in the 2020s.
Scientists believe a thick layer of ice covers a global salty ocean on Europa that may provide conditions suitable for life. The nine instruments chosen by Nasa from a short-list of 33 include cameras and spectrometers to produce detailed images of the moon's surface and determine its composition, and ice-penetrating radar to measure the thickness of its icy shell.
The spacecraft will also carry a magnetometer to investigate Europa's magnetic field, which will allow scientists to work out the depth and salt content of the ocean.
A thermal instrument will scour Europa's frozen surface in search of recent eruptions of warmer water. Additional instruments will search for evidence of water and tiny particles in the moon's thin atmosphere.
Nasa's Hubble Space Telescope observed water vapour above the south polar region of Europa in 2012, providing the first evidence of watery eruptions from beneath the ice.
Dr Curt Niebur, Europa programme scientist at Nasa headquarters in Washington DC, said: "This is a giant step in our search for oases that could support life in our celestial backyard. We're confident that this versatile set of science instruments will produce exciting discoveries on a much-anticipated mission."
He added: "The big question this mission needs to answer is: is Europa habitable? The instruments could find indications of life, but they are not life detectors."
Nasa's 2016 budget request includes 30 million US dollars (£19.55 million) to formulate a mission to Europa which will send a solar-powered spacecraft to perform repeated close fly-bys of the moon over a three-year period.
In total the probe will perform 45 fly-bys at altitudes ranging from 16 to 1,700 miles.
Nasa's Galileo spacecraft, which explored Jupiter and its moons for eight years from 1995, revealed strong evidence of a subterranean ocean on Europa.
Scientists now think the ocean could contain more than twice as much water as exists on Earth, despite Europa only being about the size of Earth's moon.
Powerful tidal forces caused by the tug of Jupiter's gravity are believed to keep the ocean warm and unfrozen.
Dr John Grunsfeld, associate administrator for Nasa's Science Mission Directorate in Washington DC, said: "Europa has tantalised us with its enigmatic icy surface and evidence of a vast ocean, following the amazing data from 11 fly-bys of the Galileo spacecraft over a decade ago and recent Hubble observations suggesting plumes of water shooting out from the moon.
"We're excited about the potential of this new mission and these instruments to unravel the mysteries of Europa in our quest to find evidence of life beyond Earth."