The team searching for missing Malaysia Airlines flight MH370 has released detailed images of the seabed.
The new images reveal features such as extinct volcanoes and 1,400-metre depressions for the first time.
The collection of data from one of the most secret parts of the world is a by-product of the search.
Until now there were better maps of Mars than of this bit of the sea floor.
The Malaysia Airlines plane vanished without trace on March 8, 2014, with 239 people on board.
Twenty-six countries have helped look for the Boeing 777, but nothing has ever been found.
The aircraft was flying from the Malaysian capital, Kuala Lumpur, to Beijing.
The team at the Australian Transport Safety Bureau (ATSB), which is leading the hunt for the plane, is using sonar to map the new “priority” search area, at the bottom of the Southern Indian Ocean.
After that they will deploy two or three deep sea vehicles to begin the painstaking, inch-by-inch seabed search for wreckage.
The “priority” area is based on the only piece of hard evidence investigators have, which is a series of brief, electronic “hellos” between the Boeing and a satellite.
It is the equivalent of your mobile phone buzzing next to a loud speaker because it is checking in with a ground station, even when you are not making a call.
However, those “hellos” don’t give an exact location, just a very rough idea, so the smaller, “priority” area is still 23,200 square miles – an area roughly the size of Croatia.
Making sonar maps is vital to ensure the team does not crash its deep-water vehicles into ridges and volcanoes. The equipment is pulled along just above the sea floor by a 10km-long armored cable.
Snagging that cable could damage the kit, or even cut it free, so the maps help them avoid any obstructions.
The deep sea search vehicles have sonar that can pick out odd lumps, cameras that can double check if that lump is wreckage or just a rock and an electronic nose that can smell aviation fuel in the water, even if it is heavily diluted.
The operation to find flight MH370 is the most complex search in history.