Looking at the past submissions it seems to be weighted by how fast it accumulates those up votes. It's already at 10 when I wrote this reply and likely more when I click 'reply'.
I've often suspected that there are many voting rings on here, another time a Youtube video downloader hit the front page.
I did inform the mods about the issue but they said that there wasn't any suspicious voting on that topic, though I do find that conclusion somewhat questionable since it's easy to create loads of accounts on here.