Japan megaquake shifted satellite orbit

[questionmark]

The Tōhoku earthquake that rattled Japan on 11 March changed Earth's gravitational field enough to affect the orbits of satellites. The satellites' altered courses suggest that the earthquake was stronger and deeper than instruments on Earth indicated.

These weren't just any satellites: they are the twin spacecraft of the Gravity Recovery and Climate Experiment (GRACE), which fly 220 kilometres apart in a polar orbit about 500 kilometres above Earth.

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[Karlis]

Actually -- these results are "good news", rather than "bad news". What I mean is that these specific satelites are designed to do exactly what happened; for changes in Earth's gravitational field (caused by an earthquake) "to affect the orbits of [these two] satellites".

Concluding remarks from the article:

New mission

The leftover signal showed that the rate at which the distance between the two GRACE satellites changed – the so-called range rate – was twice as high in the month after the earthquake as in the month prior to the event.

The researchers then built models of the earthquake using data from seismographs and surface GPS instruments, and estimated what the satellites' range rate would be in these models. They found that a model in which the earthquake was of magnitude 9.1 and occurred in Earth's lower crust came closest to the true range rate. By contrast, conventional estimates have put the Tōhoku earthquake's strength at 9.0 and located it in the upper crust.

NASA and DLR, the German space agency, which are joint partners in GRACE, are planning a new mission to measure with greater precision how Earth's gravity field changes. This would allow the satellites to monitor earthquakes with magnitudes as low as 7.5, which occur nearly every month somewhere on Earth.

[questionmark]

Actually -- these results are "good news", rather than "bad news". What I mean is that these specific satelites are designed to do exactly what happened; for changes in Earth's gravitational field (caused by an earthquake) "to affect the orbits of [these two] satellites".

Concluding remarks from the article:

New mission

The leftover signal showed that the rate at which the distance between the two GRACE satellites changed – the so-called range rate – was twice as high in the month after the earthquake as in the month prior to the event.

The researchers then built models of the earthquake using data from seismographs and surface GPS instruments, and estimated what the satellites' range rate would be in these models. They found that a model in which the earthquake was of magnitude 9.1 and occurred in Earth's lower crust came closest to the true range rate. By contrast, conventional estimates have put the Tōhoku earthquake's strength at 9.0 and located it in the upper crust.

NASA and DLR, the German space agency, which are joint partners in GRACE, are planning a new mission to measure with greater precision how Earth's gravity field changes. This would allow the satellites to monitor earthquakes with magnitudes as low as 7.5, which occur nearly every month somewhere on Earth.

Oh, I did not post it because it was "bad" news, I posted it for the wider picture: Our theories about gravitation are pretty accurate.