The new Michael Jackson single, “This Is It,” debuted online at midnight today, with some instantly speculating that the heartstring-tugging song could become one of the late pop star’s best-selling singles of all time. The spare, mid-tempo love ballad, which was reportedly recorded during the sessions for his 1991 “Dangerous” album, finds Jackson in classic voice, singing in his clear falsetto along to finger snapping, a subtle jazzy piano and swelling strings, as his brothers, the Jacksons, provide ethereal backing vocals. The new song is currently streaming on the singer’s official site, and it will play over the credits of the documentary of the same name, which hits theaters October 28 for a limited two-week run. The track will appear twice on the two-disc soundtrack to “This Is It,” as both the vocal version and an instrumental take. The soundtrack, with a handful of previously unreleased versions of some of Jackson’s classic hits, will go on sale October 27. “This Is It” may be the first of many previously unreleased Jackson songs that will be issued in the wake of the singer’s death, with reports that there are 100 or more tunes in the vault that fans have not heard. Michael Jackson’s website via mtv