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An Australian military aircraft has spotted four orange objects at sea, more than two metres in size, which will be analysed by the Australian co-ordination centre for missing flight MH370.
Clear skies and a search zone closer to land had meant greater visibility and a cluster of object sightings for the Australian P-3 Orion crew captained by Flight Lieutenant Russell Adams on Sunday.
"We were able to detect many objects in the water today," Flight Lieutenant Adams said, speaking on the tarmac at RAAF Pearce base overnight, after an 11-hour mission.
"We were able to rule a few out as fishing buoys and fishing nets, however, of interest today we did encounter an area within approximately five nautical miles which included at least four orange coloured objects greater than approximately two metres in size each.
Adams said the origins of the objects was still unknown, but the co-ordinates and images had been passed on to the rescue co-ordination centre and a GPS buoy dropped in the area.
"It's for the rescue co ordination centre to analyse these and send investigators to investigate as they see appropriate, however, for my crew, from our perspective this was the best visibility we had of any objects in the water and gave us the most promising leads," he said.
Because the Orion had stayed in the same area for most of its mission on Sunday it had fuel to burn and was able to stay at sea an extra hour.
"We really wanted to investigate those objects to give ourselves the best chance of identifying them before we came home," Flight Lieutenant Adams said.
SEABED SEARCH ZONE
Three kilometres under the sea where satellites and planes were looking for debris from the missing jet, the ocean floor is cold, dark, covered in a squishy muck of dead plankton and - in a potential break for the search - mostly flat.
The troubling exception is a steep, rocky drop ending in a deep trench.
The seafloor in this swath of the Indian Ocean is dominated by a substantial underwater plateau known as Broken Ridge, where the geography would probably not hinder efforts to find the main body of the jet.
The search zone is huge: about 319,000 sq km, roughly the size of Poland or New Mexico. But it is closer to land than the previous search zone, its weather is much more hospitable - and Broken Ridge sounds a lot craggier than it really is.
And the deepest part was believed to be 5,800 metres, within the range of American black box ping locators on an Australian ship that left on Sunday for the area and were expected to arrive in three or four days.
Like snow, the layer of microscopic plankton shells tends to smooth out any rises or falls in the underlying rock. In places, the layer is up to 1km deep.
But if the fuselage of the Boeing 777 did fall on to Broken Ridge, it would not sink much into the muck.
"The surface would be soft, it would squeeze between your toes, but it's not so soft that you would disappear like snow," Sager said. "Something big like pieces of an airplane, it's going to be sitting on the surface."
Searchers will be hoping that if the latest area turns out to be where the plane crashed, the fuselage did not go down on the southern edge of Broken Ridge.
That's where the ocean floor drops precipitously - more than 4km in places, according to Robin Beaman, a marine geologist at Australia's James Cook University.
It's not a sheer cliff, more like a very steep hill that a car would struggle to drive up. At the bottom of this escarpment is the narrow Diamantina trench, which measurements put as deep at 5,800m, though no one is sure of its greatest depth because it has never been precisely mapped.
"Let's hope the wreck debris has not landed over this escarpment - it's a long way to the bottom," Beaman said.
- Fairfax and AP