"Interplanetary space" refers to the vast void or empty area between planets in our solar system. It is the space where there is no solid mass, like a planet or satellite. Full definition
[Full disclosure: I have a very small dog in this fight, having demonstrated some time ago that solar - emitted magnetic fields, projected into interplanetary space by the solar wind, modulate the intensity of cosmic rays striking the Earth's atmosphere; this is no longer a contentious, hot - topic issue. (americanthinker.com)
The effect of long - term travel in interplanetary space is unknown, but scientists estimate an added risk of between 1 % and 19 % (one estimate is 3.4 %) for men to die of cancer because of the radiation during the journey to Mars and back to Earth. (en.wikipedia.org)
Although it could take a few years to mature an X-ray navigation system practical for use on deep - space spacecraft, the fact that NASA engineers proved it could be done bodes well for future interplanetary space travel. (sciencedaily.com)