Why are there two possible arcs for the path of MH370?

[txsl]

In all of the reports and images of where MH370 could be (based on Inmarsat data) eg http://www.bbc.co.uk/news/world-asia-26503141, they show two possible (and opposite in direction) arcs where MH370 could be. How come this is the case? Must be something to do with which regions and areas different satellites collect data from?

[graeham]

The arcs are from a single 'ping' from a single satellite. The satellite knows where it is, and with the 'ping' it was able to determine the distance from the satellite to the aircraft. The satellite is the distance of this arc, the radius is the known distance between the satellite and aircraft. By having the last known radar location near Malaysia, approximate flight speed, and time between radar contact and satellite contact, an approximate distance is predicted along the circle defined by the centre (satellite) and radius/arc.

[sp332]

Yes, according to the chart on the page you linked. The satellite that it used to communicate its last info only gets information from that arc of the globe. So it must have been in there somewhere when it sent its last broadcast. That doesn't mean it was travelling along that path the whole time though. It could have turned after that transmission.