Twitter index: Doctor Who’s Sarah Jane Smith dies, global warming bigger threat than Terminator’s Skynet

English actor "Elisabeth Sladen," who famously played the role of "Sarah Jane" Smith in the Doctor Who series, has lost her battle with cancer.

"What terribly sad news about Elisabeth Sladen - her Sarah Jane was part of my childhood. Deepest sympathy to her family," tweeted English actor Stephen Fry.

The Twitter account of Gallifrey One, a science fiction convention based on the British television series, added "We are absolutely devastated to note the passing today of the extraordinary Elisabeth Sladen. Our deepest sympathies to her family."

"Skynet was supposed to go operational tonight. Instead of machines taking over, we have the very real threat of global warming," tweeted James Cameron (@JimCameron) in response to the large numbers of tweets referencing "Skynet," the artificial intelligent computer network from the Terminator series that comes to life and revolts against its creators on the evening of April 19.

Lexus is promoting its "Lexus CT Hybrid" electric vehicle on Twitter on the morning of April 20, informing microbloggers that the car is one of the top 10 green cars for 2011.

"#yallneedtobreakup," "#snoop420" and "#twittercrush" fill the next three places in Twitter's most talked about topics.

The name of Indonesian actor and journalist "Christian Sugiono" is in eighth place and "Mike Chang," a character from the TV series Glee, is in ninth place.

If "Adolf Hitler" were still alive today, he would celebrate his birthday on April 20, say Twitterers, but his name is also appearing in Twitter's top topics as microbloggers post that Kate Middleton and Prince William will share their wedding anniversary with Adolf Hitler and Eva Braun.

The top 10 most talked about topics on Twitter on April 20 at 7:30 AM GMT are:

1. Lexus CT Hybrid (promoted)

2. #yallneedtobreakup (new)

3. #snoop420 (new)

4. #twittercrush (new)

5. Elisabeth Sladen (new)

6. Sarah Jane (new)

7. Skynet (new)

8. CHRISTIAN SUGIONO (new)

9. Mike Chang (new)

10. Adolf Hitler (new)