Summary

How big is our solar system? This question became real rather than fanciful when NASA's Voyager I rocket flew into deep space in 2012. News reports that the vehicle had reached the edge of the solar system and was barreling into interstellar space made the question about size of the solar system timely and relevant. By most "reasonable measures," Randall asserts, the Oort cloud alone extends to 50,000 times the distance between the sun and and earth—and possibly twice that distance.

At the time of writing this book, Voyager will not enter the Oort cloud for another 300 years and may not emerge for another 30,000 years. One way of estimating this passage beyond the edge of the solar system is by measuring the increase in high-energy particles that hit the spaceship, as was the case in 2012. Simultaneously, there was...