19 gigajoules was the amount of energy which resulted from the terminal impact of the Deep Impact probe. But how many of us remember what a gigajoule is? Hearing this number reminded me of Doc Brown saying that the DeLorean needed 1.21 gigawatts of power in order to initiate time travel. As we all laughed at Doc Brown and his horrid pronunciation of gigawatt (he said “jig-o-watt”), most of us wanted to know just how much power that really was.
Well, I want to know just how much force was imparted upon Tempel 1 this morning. From computer science (or from studying ancient Greek), we know that giga is the term for a billion. So a gigajoule is a billion joules. And a joule is the work done to exert a force of one newton for a distance of one meter. OK. Now that we have that in our minds, let’s look for some common point of reference. According to the Online Unit Converter,
1 gigajoule = 737562149.3 foot pounds, or
1 gigajoule = 372.506136111 horsepower-hour
So the NASA impactor exerted the same amount of force as over 6700 horses could exert over the course of an hour. The pre-impact estimate was that this impact would result in a crater as big as a professional football stadium.
So why do we fling objects into space and aim them at unsuspecting comets? Well, we want to know whether these things are rocks or just dirty snowballs. We will learn that as the data is analyzed. But until thne, we have learned something very important. Tempel 1 is not shaped like a peanut. It’s more like a banana. 😉