What is the biggest planet in the universe? Hint: Its not Jupiter

ROXs 42Bb is about nine times more massive than Jupiter
The illustration shows different planets. — Freepik
The illustration shows different planets. — Freepik

Alright, so picture this: the universe, massive beyond comprehension, and our little blue planet, Earth, it's like a speck of dust in the grand scheme of things. Think about it, even in our own solar neighborhood, Earth is nothing compared to those big gas giants like Jupiter. But here's the thing that gets me wondering: are there planets out there that make Jupiter look like a marble in comparison? I mean, what's the biggest planet we've found so far?

Well, buckle up because the answer's a bit tricky. You see, it depends on how you define a planet. But let me tell you about a top contender for the heavyweight champ of planets. There's this one called ROXs 42Bb, chilling out there, orbiting a star roughly 460 light-years from our little rock. This bad boy is about nine times more massive than Jupiter and has a radius that's around 2.5 times larger than Jupiter itself.

Now, here's where it gets interesting. Thayne Currie, a cool professor of physics and astronomy at the University of Texas — San Antonio, doesn't believe this planet's the biggest fish in the cosmic pond. He thinks there might be others out there that are even larger. Currie spotted ROXs 42Bb back in 2013, using data from the Keck Space Telescope. But hey, there are these "protoplanets" hanging around a star called PDS 70, roughly 370 light-years away, and they might be contenders too. These protoplanets are still in the making, and they could be anywhere between two to four times the size of our buddy Jupiter.

Now, why all this uncertainty, you ask? Well, it's because scientists measure these planets in different ways. Some, like ROXs 42Bb, are directly imaged thanks to nifty telescopes. But others are detected when they pass in front of their host stars, causing a little dimming of starlight. And you know what? That's just the beginning of the planet-size detective work.

To add to the mystery, there's this gray area called "brown dwarfs." They're bigger than planets but not quite stars. Scientists are still arguing about how to tell them apart. Some say it's all about mass, setting a limit of 13 Jupiter masses. But recent studies suggest this line might be blurrier than we thought. It seems the universe might have a different opinion on what's what.

Currie's even got this wild theory about how ROXs 42Bb formed, suggesting it might've taken shape in a totally different way compared to regular planets like Jupiter. And that's where things get fuzzy because our current definitions don't cover these oddballs too well.

In the end, while this whole debate might sound like a nerdy argument, it's actually mind-boggling when you think about it. It's like, our solar system is just one tiny possibility among countless others out there.