Billboard is reporting that Katy Perry's "E.T." will top Thursday's Hot 100 chart, narrowly beating out Britney Spears' "Til' the World Ends,"  which has soared back up the chart on the back of a star-studded remix.  "E.T.," featuring Kanye West, is also sitting atop the Digital Songs Chart for a sixth straight week, with 300,000 downloads.  The song beat out Adele's "Rolling In the Deep" by just 500 downloads, the slimmest margin between the chart's top 2 entries since Christmas week, 2005.