By 2007, Prince had already established himself at the forefront of innovative music distribution. He had let fans order albums directly online; he’d sold digital downloads and streams; and he’d given superfans special bonus content for becoming members of his NPG Music Club.

But with his 32nd studio album, Planet Earth, Prince did something that truly shook the music industry: he gave it away for free with a newspaper, specifically the July 15, 2007 edition of the U.K.’s Mail on Sunday.

Usually, free newspaper giveaways were cobbled-together compilations or DVDs of dated films. To get a brand new album from a major artist was unheard of, and it caused a storm. Simon Fox, chief executive of HMV — the U.K.’s biggest music store at the time — said the move was "absolutely nuts."

But there was method to Prince’s madness. Prince explained his decision as "spreading my music and my word to as many people as possible. It's direct marketing, which proves I don't have to be in the speculation business of the record industry, which is going through tumultuous times right now."

In addition, releasing the album this way guaranteed him a great review from the widely-read newspaper, and helped his music reach people who wouldn’t have bought it in HMV anyway. More importantly, though, just two weeks after he put the album out, Prince would kick off 21 Nights in London: The Earth Tour. And Planet Earth’s free release was the ultimate advertisement.

Prince was really pushing the limits of the word "tour" in this case. The Earth Tour took place not just in one city, but also in one venue — London’s O2 Arena, with aftershows in the adjoining Indigo club. These concerts where a huge deal in the U.K., and part of the final performance was broadcast live on Sky News.

You only have to watch his Super Bowl halftime show — which took place earlier in 2007 — to see that Prince was at the absolute peak of his performing powers. And the O2 shows proved it 21 times over, to a total of more than 350,000 people. More than a decade later, no one has beaten Prince's record.

Prince played a different setlist every single night. And it wasn’t just small differences, either. The closing number one night could be near the beginning of the set on another.

Looking at the set lists — stuffed with greatest hits and fan favorites — you can barely tell that Prince had just released an album. A few Planet Earth songs made the cut, but really 21 Nights was all about the classics.

And the fans loved it. Every single show sold out and many people went to multiple shows. The reviews were universally positive — but the same can't be said for Planet Earth.

In the U.K., at least, Planet Earth had a specific purpose: to get people excited about Prince ahead of the O2 dates. But elsewhere on planet earth, you had to pay for Planet Earth. So was it worth the price of admission?

Critics gave the album a mixed reception, with many wheeling out the old "it doesn’t live up to his '80s work" staple. It’s unlikely Prince cared. A year earlier he told the Guardian, "All these non-singing, non-dancing, wish-I-had-me-some-clothes fools who tell me my albums suck. Why should I pay any attention to them?"

Obviously, Planet Earth isn’t '80s Prince, but that doesn’t mean there’s nothing to enjoy. Speaking to the Current in 2018, longtime NPG member Morris Hayes said the title track — a climate change anthem that sounds more urgent than ever today — is one of his favorite Prince songs. “Just what he's saying and then the rest of the record and some of the stuff that's in there was just really incredible,” he said.

"Guitar," too, is worth mentioning. The straight-ahead rocker slotted perfectly into Prince’s live repertoire, allowing him to declare his love for the instrument night after night. "Future Baby Mama," the smooth-as-butter R&B slow jam, won Prince his final Grammy in 2008. It's also notable that former collaborators Sheila E. and Wendy & Lisa perform on the album. Though sadly these are blink-and-you'll-miss-it cameos rather than full features.

Taken on its own, Planet Earth might have been disappointing. But the overall Prince-in-2007 package was so good it didn’t matter. His other album release of 2007, Indigo Nights, might be the better recording. Sold with his 21 Nights photobook, that disc captures the raw energy and pure joy of his O2 aftershows.

As for whether giving Planet Earth away for free turned out to be a good idea, Prince clearly thought it was. His next studio album, 2010’s 20Ten, would once again be handed out with newspapers as a free covermount in Europe. Sadly, for fans who got their hopes up, there would be no 21 More Nights in London.