Prof. Bhardwaj initiated the research in planetary science at SPL and contributed to the development of planetary science program in ISRO/Department of Space, and planning of planetary missions of India. He was the Principal Investigator (PI) of SARA experiment on the first Indian Lunar mission Chandrayaan-1, which has revolutionized our understanding on the interaction of solar wind with the Moon through several new findings. He was the PI of MENCA experiment on the Indian Mars Orbiter Mission (MOM). He and his team have PI-lead experiments on Chandrayaan-2 Orbiter, and Chandrayaan-3 Lander and Rover missions, as well as solar mission Aditya-L1.

He has been an observer on Chandra and XMM-Newton X-ray Observatories, Hubble Space Telescope, and Giant Meterwave Radio Telescope (GMRT).

His primary research field is planetary and space sciences, and solar system exploration. He has made outstanding contributions in the field of solar system X-ray astronomy, including discovery of X-rays from the rings of Saturn and X-ray flares from Jupiter and Saturn, and theoretical modelling of aurora and airglow emissions and photochemistry in planetary upper atmospheres and ionospheres and comets. His research findings have led to several Press Releases by NASA and European Space Agency, ISRO Story of the Week and Cover pages of American and European journals, and Journal Highlights.