If text in two cells exist, this creates a unique number

I am working with an excel file where I need a unique number created if the text in two cells are present: example

Text 1     Text 2       Value
star       comet        100
star       asteroid     101
asteroid   nova         102
nova       star         103
asteroid   nova         102
star       comet        100
nova       star         103

I assume its something to do with the IF function but I'm now completely snowblind. Any help?

Thanks