of them carry small craters from impacts with other objects which gets back to june shue -- jeanne schumacher's hail of bullets which he called the universe in terms of what's going on out there but the point is come in all shapes and sizes and they vary enormously. as you say it buries according to which one you are talking about in the answer is we don't know enough. that's why that mission if you years ago worked and the japanese did the same thing but to get as much information as possible about our neighbors. >> host: said that means if we see one coming it is the first thing we have to do is send a mission to it to find out what it's like before we send a mission to move that? >> guest: that depends on how close it is. if it's 11:00, no. then you save earth anyway you can but if it's very far away yes that would be the smart thing to do. find out what it is and in addition to everything else the science builds up. you learn things about them and that's what's important. again it's a matter of how close it is. >> host: right. so hit how big and how close to something up to be when the only