The Tenth Doctor, fearing his own mortality, travels alone between 2008-2010.
David James Tholen -LRB- born 1955 -RRB- is an American astronomer at the Institute for Astronomy of the University of Hawaii .. astronomer. astronomer. Institute for Astronomy. Institute for Astronomy. University of Hawaii. University of Hawaii. He holds a 1984 PhD from the University of Arizona , and specializes in planetary and Solar System astronomy .. University of Arizona. University of Arizona. planetary. planetary science. Solar System. Solar System. He is a discoverer of minor planets and known for the Tholen spectral classification scheme used on asteroids .. discoverer of minor planets. discoverer of minor planets. Tholen spectral classification. Tholen spectral classification