Planet Moons:
This one is simple, just type how many moons a planet in our solar system has.
For example, How many moons orbit Earth? The correct answer is 1.

Planet Distances:
How many light years is planet x from the sun? Type your answer.

Moon Locations:
The challenger is given a grid of 9 by 3. The columns (usually letters) are the names of planets. Each planet column has 3 rows.
Four to 8 moons are placed in random positions on the top row. The user must move the moons to their respective planet. Not every column will have values, sometimes the puzzle gives multiple moons of the same planet.
For example, the challenger might have 2 moons from Jupiter, 0 from Earth, 1 from Neptune, etc.
Just because a planet has moons doesn't mean they will be on the grid. Of course each planet could have up to 3 moons, but with 4 to 8 selected that is extremely unlikely.

Planet Composition:
This one might be too close to colored buttons and too easy since it is the same outcome every time.
View the list of planets with 1 through 9 and press control plus a number to change the matter state between rocky and gaseous.
Unlike colored buttons of course it doesn't change the neighbors, and it would be more interesting to randomize the order of planets.

Wouldn't it be easier to put all the different challenges into one topic? I have noticed recently that if people have 3 ideas they become 3 topics when they should be one, game suggestions is another example.

We already have a lot of questions on Moons, planets etc.

This is unique though we can impliment. We have to check if it would be easy for developers to code. after all the complexity of the code and time for developers to write this challenges is deiding factor.

Wouldn't it be easier to put all the different challenges into one topic?

I considered for a second but decided against it. People would just make their own suggestion topics anyway, and if this giant topic did get barried then it would be hard for the developer to uncover any of the suggestions.
Using separate topics makes it easier for people including the developer to reply to specific challenges and gives a better indication of what people are interested in.
Plus a user can't write two replies in a row, they would have to edit a previous reply if they came up with new ideas. And topics don't get bumped for edits alone, so some new ideas would go unnoticed.

We have to check if it would be easy for developers to code. after all the complexity of the code and time for developers to write this challenges is deiding factor.

The first 2 are simple number row answers as the mental math one.
The fourth one is very similar to colored buttons, the developer can just put a new variable in the code to specify if the neighbors should be flipped as well. I'm sure each time that action is performed it runs a unique callback.
The third is a grid system which has already recently been implemented for these challenges. The only code the developer would have to make is the list of moons, and ensure that the moons don't need to be in a specific row, only planet column. Meaning if a user puts a moon on the second and third rows, it would count it correct instead of requiring them to put it on the first and second. I'm sure he already has code for that situation but if not then it would only take a few lines of simple code.

Numbers of moons have also changed over the years. Jupiter and Saturn have changed at least 3 times over the life cycle of Quiz party.

Hmm ok I didn't know that. Thanks for bringing it to attention, what a shame though.

Hello,

Planet moons:
YNWA has already pointed out potential problems for your first idea. Whatever the topic or almost, you always must have in mind that the answer can change as science is progressing.
IF I add a challenge of that type, whatever the topic, it has to be directly connected to Quiz Party, or we must create a separate database of questions, which have to be managed with the same care.
I have already had such kind of challenge in mind, not necessarily in astronomy topic though, but without going further with it. So it might well come up at some point.

Planet distance:
I don't think it's useful to have a specific challenge for this one, if we already introduce a challenge where you have to answer questions with a number.

Moon location:
We are entering the bind matching elements kind of challenge, and for this kind of challenge, there is probably much better and more efficient ways to present it than a grid. With a grid, I feel it would be too complicated. This has to be thought again.

Planet composition:
As you have said, this is a kind of poorer version of colored buttons where the answer is always the same, so I don't think it's very interesting.

I suppose for the third challenge it gives you one moon at a time and you use the number row for each answer. That could work.

If you want a space challenge then try something like planets in order or by size as I am sure they don't change. Having said Pluto was a planet when I was at school.

Moons change as they include moons that are the size of a football. Many of the new ones are yet to be named, may be they should name one YNWA, lol.

Moons are changing because they class objects even the size of a football as a moon now...

Rearranging the planets in order would be a copy paste of quick sort, that's why it wasn't listed. I tried to think of a way that I could do such a challenge differently, but could not brainstorm anything.