Comet Hartley 2, designated as 103P/Hartley by the Minor Planet Center, is a small periodic comet with an orbital period of 6.48 years. It was discovered
to permit a flyby. Instead, the team decided to send Deep Impact to comet 103P/Hartley requiring an extra two years. NASA approved the additional funding
elsewhere". Comments in Astrophysics. 7 (4): 103–119. Bibcode:1978ComAp...7..103P. Handel, P. H.; Chung, A. L. (1993). Noise in Physical Systems and 1/"f"