In fact, this hoax isn't even a new one. Slate's Phil Plait was able to recycle a debunking post he wrote at the beginning of 2014 on the subject.
This "science news" comes from a "satire" site that doesn't even bother with actual satire -- it just makes stuff up to get clicks. If you look closely enough, you can see disclaimers around the site warning you that the stories are just "satirical" nonsense.
So as a general reminder, check your news sources to make sure they at least try not to make things up before you hit the share button -- especially when the claims therein are so utterly ridiculous.
But hey, we're not all planetary science experts here, and maybe this one sounded plausible to you. That's okay! Let's learn some planetary science:
The hoax claims that when Pluto passes directly behind Jupiter (in relation to the Earth's position), the "rare alignment" of the two planets will combine their gravitational force and counteract the gravity of our own planet. From Slate:
First of all, the gravitational forces of the other planets in the solar system have essentially zero effect on you personally.
And we’re done. Full stop.
OK, fine, I’ll give some brief details. The planets are big objects with lots of gravity, but that only affects you if you’re close to them. Space, however, is big—that’s why we call it space—and planets are far away. This weakens their gravity on you hugely, reducing it to less than the impact of the flutter of a butterfly’s wing.
According to Plait's calculations, the Earth pulls some 200 trillion times harder on you than poor little Pluto ever will. Oh, and that nonsense about the two planets "aligning"? They're not even going to be close to being in alignment -- not that it makes any difference.
The original source of this silliness was a real physicist's April Fools' Day prank. He announced that the phenomenon would occur, and people reported feeling its effects -- but they were obviously just anticipating a feeling of weightlessness, and got a little excited when they felt an extra spring in their steps.
Alas, the forces of Pluto and Jupiter will not act to make your holiday pounds melt away on Sunday -- not even momentarily.