How Do Planets Form? | #AskAbby Homeschool Edition | The Mars Generation | Season 3 | Episode 10

Season 3, Episode 10, #AskAbby Space and Science Show: Homeschool Edition

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How Are Planets Formed?

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In this episode, host and aspiring astronaut Abby “Astronaut Abby” Harrison discusses planets! From how planets are formed to when they were formed, Abby will break down some of your biggest questions about planets. She will also discuss how astronomers know what they know about planets millions and even billions of miles away!

In the 9th Episode of the #AskAbby Space and Science Show: Homeschool Edition, host Abby Harrison answers a question submitted by Christine Graham’s 6th grade science class in Cockrill Middle School in Mckinney, Texas including: What is the temperature in space at the distance from the sun that the Earth is? What is the oldest planet? How were the planets formed? Why are all planets round? Is Neptune a water planet? How do you measure the distance between planets?

Transcription of How Are Planets Formed?


Hi everyone and welcome to #AskAbby: Homeschool Edition! This is a new series of Ask Abby intended to provide resources, as well as some space jokes and puns, to students who are now doing distance learning during the COVID-19 pandemic. Each episode will feature questions submitted by students from around the world. 

This episode is focused on planets in our solar system, with questions submitted by 6th grade students from Cockrill Middle School in Texas. For this episode we actually received so many questions that we just weren’t able to fit them all into this one video. But I do want to say thank you to those students, and to let you all know that we loved seeing your questions and that they were all fantastic.

Question Number One
Ella would like to know: What is the temperature in space at the distance from the sun that Earth is at?

While space is normally super cold, that doesn’t necessarily mean that the space around Earth is always cold.

When Earth is in direct sunlight, the space around it is roughly 50.3° degrees Fahrenheit or 10.17° Celsius. 

Question Number Two
Isabel would like to know: What is the oldest planet?

The oldest planet in our solar system is Jupiter at 4.503 billion years old! And just for reference, that’s about 2-3 million years older than Earth.

But the oldest planet in the universe? The oldest planet that we currently know about is PSR B12620-26 B…oof, say that name three times fast.

PSR B126 2… *sighs* …PSR B1 R2D…

Alright, you know what, from now on, PSR B12620-26 B shall be known to us as Planet Bob.

“You can’t call a planet Bob”


Planet Bob is a “Hot Jupiter” type planet that is about 2.5 times bigger than Jupiter. It’s 5,600 light years away in the globular star cluster M4 in the Scorpius constellation of the Milky Way Galaxy. 

Another cool fact about Planet Bob is that it orbits around both a white dwarf and a pulsar. That makes it a circumbinary planet, or a planet that orbits around two stars instead of one!

Question Number Three
David would like to know: How were the planets formed?

Planets form through a process called accretion. Our whole Solar System actually started out as a big nebula of gas and dust particles. And the first thing that was formed out of that nebula was the central star, or our Sun. After that star is formed, the rest of the gas and dust particles continue to orbit around the star in something that’s now called the protoplanetary disk. And as those particles orbit around the star, sometimes they bump into each other. You can think about it like roller skaters on a crowded roller rink. Collisions are bound to happen. 

So in this protoplanetary disk when you have very small pieces of material, just grains of dust or gas particles, bumping into each other. In some of those collisions, they actually end up melding together, and they start to form larger and larger objects that eventually get big enough that one of them becomes a planet, or multiple of them become planets.

And eventually after this process of bits and pieces of space debris in the protoplanetary disk bumping into one another or colliding, and then merging together happens enough times, they start to get large enough that they can actually exert gravitational pull. And this is really important to a planet forming, because one of the three central defining features of a planet is actually that it has to be large enough and have enough mass to clear its orbit around the sun of space debris through gravitational attraction.

Question Number Four
Jenna would like to know: Why are all planets round?

Jenna you’re completely right. Planets are all spherical, or at least, nearly spherical. Sadly you can’t have any cubic or trapezoidal or even…hmm…even any dinosaur-shaped planets. As interesting as those may sound, they don’t hold up with the laws of physics. And that’s actually one of the defining features of what makes a planet is its shape. Planets have to be nearly spherical. But that doesn’t quite answer the question, does it? Why are planets all spherical?

The short answer is gravity. Gravity acting essentially from the center of the planet pulls inwards on the surface equally in all directions, causing a sphere to form. 

So I suppose that this means that in Minecraft the rules of gravity must be completely different.

Question Number Five
Doubra would like to know: Is Neptune a water planet?

Essentially yes. Neptune does have a very small rocky core at the center of the planet. But the majority of Neptune is actually made up of liquid water, ammonia and methane. This part of the planet is called the mantle. On top of the mantle it does also have a layer of gas, which I suppose makes Neptune the seaworld of our solar system.

And now for our final question…

Question Number Six
Logan would like to know: How do you measure the distance between planets?

I’ll talk about both the old fashioned way and the current way to get these measurements. 

Let’s start with the old-fashioned way. Early astronomers used a method called parallax, which is the apparent movement of an object based on a change in the location of the observer. You can actually try parallax right now. Close one eye, take your finger, point at an object, and then switch which eye you have closed, and you may notice, or you should notice, that you’re no longer pointing at the object that you originally were. But your finger didn’t move, so it’s merely that you changed the perspective that you were looking at that object from.

The exercise that you just practiced was actually used by early astronomers. They would find a planet in the night sky, and they would use the parallax effect to measure the distance from Earth to that planet. And that method actually was pretty decently accurate. But the big problem was that you could only use it to measure something that was visible to the naked eye, and that’s not everything that you want to be measuring the distance to.

Thankfully we now have a more accurate and more widely usable method. Nowadays, the way we measure the distance to a planet is by sending a radio wave to the planet, bouncing it off the surface, and then recording the amount of time that it takes for that radio wave to return. And because we know how fast radio waves travel, we’re then able to use that information to determine how far away the planet is. 

In order to do this we use our handy dandy speed equation, which tells us that speed = distance / time. So if you rearrange that you get that distance = speed x time. And you can plug in the things you know here. You know the speed that radio waves travel at, and you also know the time that it took for the radio wave to reach the planet and return. So once you plug those two numbers in… ba-da bing, ba-da boom – you’ve got your distance!

Today we talked about all about planets! We learned how planets form, why they’re the shape they are, how old they are, and even how to measure the distance to planets.

Thanks for watching! To send in a question you can Tweet me with the hashtag #AskAbby, or by submitting it at The Mars Generation website which is linked below.

And until next time, keep safe, keep healthy, and keep learning!

So long fellow travelers of spaceship Earth.

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