INTERNATIONAL - Chinese astronaut, Yang Liwei, said she heard a sound like a knock when making its maiden voyage in space in 2003.
In a recent interview, he recalled that someone knocked on the fuselage outer space just like knocking a metal bucket with a wooden mallet.
"It comes not from the inside or outside of the aircraft."
Obviously she became worried and peered into the hole, but still could not find an explanation regarding the strange sound.
He could not decide while still in space and after returning to Earth.
Yang Liwei had tried, but failed, to re-create the sound so that the experts can help identify them.
Not surprising that the story of the mysterious sound in outer space to invite the attention of various parties.
What or who is knocking spacecraft Yang while he alone away from Earth?
The silence of infinite?
Outer space is estimated silent because there is no middleman so that the voice can move.
"The movement of sound requires an intermediary - whether it's the element of air, water molecules, metal or solid atoms," says Professor Goh Cher Hiang, outer space experts from the National University of Singapore, told the BBC.
A simple example of this is the thunder, the sound moves through the air, underwater sonar, or solid musical instrument.
"If there was a knock, the possibility of an object 'hit' spacecraft carrying astronauts," he said. However, he stressed, this thinking imaginary.
His colleague, Wee-Seng Soh, gives a different view of this possibility by saying that "the result of expansion or contraction of air, especially because the temperature outside can greatly change in orbit".
Its days as a human space are long gone, but the Chinese media expressed the voice also be heard next Chinese astronaut on the mission in 2005 and 2008.
Who told them not surprised and worried. Although yet to be explained, he now declare it as a "classic symptoms".
Sounds outer space
In fact, it is not unusual to hear sounds in space, and also a common thing found no explanation will be related to the sound.
When a test flight in 1969 Moon landing mission, at the farthest orbit where there is no radio contact with Earth, the astronauts heard a strange sound that can not be explained.
The whistling sound they describe as the music space, but recently the confidential information disclosed recently.
The new sound recording is heard people earlier this year.
NASA stated, this possibility is radio interference, not extraterrestrials.
The next space mission also noted a similar sound and NASA has issued a recording space explorer Juno when orbiting Jupiter.