THE SATELLITE IMAGES:
Australian defense force experts assessed images taken by a commercial satellite of two main objects: one 24 meters (almost 80 feet) long and the other 5 meters (16 feet) long. The objects are south of the area where searchers have been focusing in recent days.
The location is about 2,500 kilometers (1,550 miles) southwest of Perth in remote waters that often are stormy. Searchers caution the objects could be shipping debris or something else unrelated to the plane.
John Young, the manager of the Australia Maritime Safety Authority's emergency response division, said the images were relatively indistinct but credible sightings nonetheless. He said he thinks the objects are of a reasonable size and probably awash with water.
Peter Marosszéky, an aviation expert at the University of New South Wales in Sydney, said the objects could be some of the thousands of shipping containers that litter the ocean.
Australian authorities have redirected other commercial satellites to take higher resolution images, which might provide more clues.
THE PLANES:
Four search planes and one transport plane from three countries flew to the site. Young said visibility was poor, which would hamper efforts. AMSA said clouds and rains obscured the view for at least one of its flights Thursday.
The search area is also far from land, so search coordinators have taken the approach of staggering the arrival of the planes.
Two Australian P-3 Orions and a New Zealand Orion made eight-hour round trips, allowing them only two hours to search before they had to return. They will resume searching on Friday.
Made by Lockheed Martin, the Orion was once used as a submarine finder but these days is more often used for maritime patrol. They were used to help in Hurricane Katrina and the BP Horizon oil rig disaster. Their sensors can detect objects at or below the water's surface.
The U.S. Navy sent a P-8 Poseidon airplane. It is adapted from a Boeing 737 commercial jet and is designed for long-range anti-submarine warfare as well as reconnaissance.
India is sending a P8i long-range maritime patrol with electro-optics and infrared pods and a C-130J Hercules aircraft to search an area up to 5,000 nautical miles south of Jakarta, Indonesia, on Friday.
Australia's Air Force has also sent a C-130 Hercules, a Lockheed military transport plane, to drop marker buoys in the area.
THE SHIPS:
A Norwegian merchant ship that responded Monday to a request for help arrived in the search area Thursday evening and was expected to scan the area with radar overnight then start a visual search during the day Friday. A second merchant ship was also heading to the area, AMSA said.
The Australian Navy has sent its own ship, the HMAS Success. The Success is the largest ship built for the navy and is large enough to recover any plane debris from the ocean if needed and transport it back. The naval ship is several days from the location.
Launched in 1984, the Success is 157 meters (515 feet) long with a displacement of 18,000 metric tons. It has a crew of 220 and comes complete with its own bakery and medical operating theater.
THE BUOYS:
The Hercules transport plane will drop marker buoys that float and drift with sea currents, theoretically mimicking the drift of any debris. Searchers then can track the buoys, which will be crucial if weather or other factors delay the search.
Marosszéky said the satellite images were cause for some hope in the search effort.
"But you've got to be careful," he said. "The ocean is full of debris."
