With nearly 48 hours passed since Malaysia Airlines Flight 370 disappeared en route to Beijing, the Boeing 777 has yet to be discovered. As investigators from numerous countries work to piece together what happened, here is everything we still do not know.

1. The location of the plane

Authorities have been combing the South China sea and surrounding waters for over a day, but still have not found any concrete evidence of the plane's location.

On Sunday, Vietnam released the above photo of debris that it thinks might be from Flight 370. The country also announced that it thinks it has found parts of the plane's tail as well as fragments of an inner door, but that theory has yet to be confirmed.

Earlier on Sunday, a Singaporean search vessel came upon a yellow floating object, but it was determined to be unrelated to Flight 370. Per CNN, at least 40 aircraft and 12 vessels are currently looking for the plane, with Australia, China, Singapore and the United States among the countries assisting in the search.

On Saturday, Vietnam released a photo of what it believes to be miles-long oil slicks in the water off the country's southern coast, but no one has been able to determine the origin of the fuel, or if it even is fuel.

2. Why the plane vanished

While officials on the ground work to find the plane, others are trying to piece together exactly what happened in the air. As of now, authorities are still unsure when the pilots realized the plane was in trouble. An unnamed pilot spoke to a Singapore newspaper yesterday and said that he made contact with Flight 370 minutes after the plane's final communication with air traffic control. This came at the behest of Vietnamese authorities who had lost contact with Flight 370, but the pilot does not remember his brief contact with the plane being suspicious or distressed.

Meanwhile, an AP report cites unnamed Malaysian officials as stating that radar images show that the plane may have attempted to turn back before it finally disappeared from radar. But that report has not yet been corroborated.

Because officials have yet to find a debris field, Malaysian officials say they are investigating whether the plane disintegrated in mid-air.

3. If terrorism was a factor

Officials from a number of countries have confirmed that they are looking into the identities of two passengers who boarded the plane using stolen passports, though the Malaysian government is investigating if up to four people boarded the jet with false paperwork.

According to CNN, the two passengers in question — one of whom possessed a stolen Italian passport, the other a stolen Austrian passport — appear to have purchased their tickets together, using Thai currency through South China Airlines.

Still, there appears to be nothing remotely conclusive on this front yet. According to the New York Times, a preliminary Pentagon investigation of "flash" data did not detect any evidence of an explosion in the area where the plane is thought to have disappeared.

In response to the passport situation, an American official told the Times that "while the stolen passports are interesting, they don't necessarily say to us that this was a terrorism act."

[photo of mourners via AP]