Japan quake effects felt in space



Japan quake effects felt in space London: The magnitude-9 earthquake in Japan two years ago was so big that its effects were even felt in space, the BBC reported Sunday.

Scientists say the March 11, 2011 tremor sent a ripple of sound through the atmosphere that was picked up by the Goce satellite.

The super-sensitive instrument was able to detect the disturbance as it passed through the thin wisps of air still present 255 km above the Earth.

The observation has been reported in the journal Geophysical Research Letters.

Major quakes generate very low-frequency acoustic waves, or infrasound, below those discernible to the human ear. But no spacecraft in orbit has had the capability to record them until now.

"We've looked for this signal before with other satellites and haven't seen it, and I think that's because you need an incredibly fine instrument," said Rune Floberghagen from the European Space Agency (ESA).

"Goce's accelerometers are about a hundred times more sensitive than any previous instrumentation and we detected the acoustic wave not once, but twice - passing through it over the Pacific and over Europe," the mission manager told BBC.

Goce's prime purpose is to map very subtle differences in the pull of gravity across the surface of the Earth caused by the uneven distribution of mass within the planet.

These variations produce almost imperceptible changes in the velocity of the satellite as it flies overhead.

The ESA spacecraft encountered the signal as it passed over the Pacific some 30 minutes after the onset of the quake, and then again 25 minutes later as it moved across Europe.

Scientists are now checking through the satellite's data to see if an infrasonic signal was also recorded when an asteroid entered the atmosphere over the Russian city of Chelyabinsk in February.

Goce, however, is running low on fuel and is nearing the end of its mission.

The ESA will lower its orbit in June to below 230 km to try to obtain even finer detail on Earth's gravity field. In November, the agency will command the satellite to fall back to Earth.

IANS