Don Yeomans; Paul Chodas & Steve Chesley (28 December 2007). "Mars Impact Probability Increases to 4 Percent". NASA/JPL Near-Earth Object Program Office. Archived from the original on 29 December 2007. Retrieved 28 December 2007.
Steve Chesley; Paul Chodas & Don Yeomans (8 January 2008). "Mars Impact Seems Less Likely". NASA/JPL Near-Earth Object Program Office. Archived from the original on 12 January 2008. Retrieved 8 January 2008.
Don Yeomans; Paul Chodas & Steve Chesley (28 December 2007). "Mars Impact Probability Increases to 4 Percent". NASA/JPL Near-Earth Object Program Office. Archived from the original on 29 December 2007. Retrieved 28 December 2007.
Steve Chesley; Paul Chodas & Don Yeomans (8 January 2008). "Mars Impact Seems Less Likely". NASA/JPL Near-Earth Object Program Office. Archived from the original on 12 January 2008. Retrieved 8 January 2008.