Project Amaze!

In Chapter 22, Ryland wonders to himself why the Hail Mary resembles “something out of a Heinlein novel” 22.189, with a smooth hull and sharp nose cone, despite the fact that this ship was never intended to interact with an atmosphere.

His conclusion: it was designed in this aerodynamic way not because of air resistance, but due to the interstellar medium. Ryland reminds himself: “There’s a teeny, tiny amount of hydrogen and helium wandering around out there in space. It’s on the order of one atom per cubic centimeter, but when you’re traveling near the speed of light, that adds up.” 22.190

We often think of the space between stars as being completely empty, but stars and planets must be born from something, and that something is the interstellar medium. This gas and dust, remnants of long dead stars and the raw materials for future stars yet to be born, lies scattered in the space between stars. Around 98% of the interstellar medium consists of hydrogen and helium, though there also exist heavier elements and molecules including ammonia, which we discussed in #86.

Studying the interstellar medium allows us to better understand many astrophysical processes including star formation, galaxy formation, and nucleosynthesis. Astronomers also observe the properties of the interstellar medium at the edge of our solar system to better understand how our Sun interacts with neighboring stars.

Ryland’s conclusion that this diffuse material is worth considering when designing an interstellar spacecraft is a valid one. Due to the high speeds and energies of such hypothetical future travel, these particles could greatly damage spacecraft. In fact, one calculation indicates that these interstellar particles could reach impact velocities of 20% of the speed of light. “Relativistic physics is weird” 22.190 indeed, Dr. Grace.