This often happens, and it's why the committee distinguishes between splitting and sharing the prize. The first physics split by separate citations was 1903 Be

This often happens, and it's why the committee distinguishes between splitting and sharing the prize. The first physics split by separate citations was 1903 Becquerel / Curie+Sklodowska-Curie, though their citation explicitly mentions how it's related to Becquerel's work. But as early as 1961 Hofstadter and Mössbauer split the prize for two separate things that can be grouped together as "well... nuclear physics" in the same way as these prizes are "... SPACE!". It's happened a lot in the past. Often the split allows them to cover two things that are only really related on a superficial level. Just going through the list: 1963: Wigner (symmetry) / Goeppert-Meyer + Jensen (nuclear shells) 1970: Alfvén (MHD) / Néel (anti/ferromagnetism in solid state) 1973: Esaki + Giaever (semi/superconductors) / Josephson (Josephson effect) 1978: Kapitsa (low T) / Penzias+Wilson (CMB) 1983: Chandrasekhar (stellar evolution) / Fowler (nuclear abundances) 1986: Ruska (electron microscope) / Binnig+Rohrer (scanning-tunneling microscope) 1989: Ramsey (masers) / Dehmelt+Paul (ion traps) 1994: Brokhouse (neutron spectroscopy) / Shull (neutron diffraction). This one is weird because they also get a joint citation for using neutrons to study materials. 2000: Alferov+Kroemer (heterostructures) / Kilby (integrated circuit) 2002: Davis Jr.+Koshiba (cosmic neutrinos) / Giacconi (cosmic x-rays) 2005: Glauber (coherent states) / Hall+Hänsch (laser spectroscopy) 2008: Kobayashi+Maskawa (CKM matrix) / Nambu (spontaneous symmetry breaking). I think most physicists I know agree that this one should really have been two prizes, one shared K+M+Cabibbo (C in CKM) and one shared Nambu+Goldstone. 2009: Kao (fiber optics) / Boyle+Smith (CCDs) 2018: Askin (optical tweezers) / Mourou+Strickland (chirped pulse amplification)