Article history: Received 7 December 2007 Received in revised form 29 May 2008 Accepted 31 May 2008

Article history: Received 3 December 2007 Received in revised form 6 September 2008 Accepted 29 September 2008

Article history: Received 29 December 2007 Received in revised form 5 May 2008 Accepted 26 October 2008

Article history: Received 30 August 2008 Received in revised form 29 December 2008 Accepted 28 January 2009

Article history: Received 29 July 2008 Received in revised form 15 December 2009 Accepted 17 December 2009 Available online xxxx JEL classification: D81 Q42

Article history: A central target in Earth s Received 22 July 2008 Received in revised form 27 October 2008 Accepted 29 October 2008 Available online 6 December 2008 Editor: R.D. van der Hilst

Article history: This paper reports the deve Received 5 October 2007 Received in revised form 29 September 2008 Accepted 24 December 2008 Available online 9 January 2009