B2 - Lesson 09

Part 1 : Video Lesson & Transcript

Part : Listening & Reading comprehension

Part 3 : Use of English

Part 4 : Grammar lesson

Part 5 : Writing an essay & corrections

Part 6 : Speaking, interaction, & explanations.


Please make sure you unfold each content for each part of the lesson.  Merci de déplier chaque contenu pour chaque partie de cette leçon.



See instructions beneath the video.


Where Did the Moon Come from?


Where Did the Moon Come from?

The Earth and Moon are like identical twins, made up of the exact same materials -- which is really strange, since no other celestial bodies we know of share this kind of chemical relationship. What's responsible for this special connection? Looking for an answer, planetary scientist and MacArthur "Genius" Sarah T. Stewart discovered a new kind of astronomical object -- a synestia -- and a new way to solve the mystery of the Moon's origin.




1) Listen to the video without reading the text / transcript

2) Then Listen to the video again reading the transcript as you listen.

3) Then listen to the video again without reading the transcript.



Nobody likes to make a mistake. And I made a whopping one. And figuring out what I did wrong led to a discovery that completely changes the way we think about the Earth and Moon. 


I'm a planetary scientist, and my favorite thing to do is smash planets together. 



In my lab, I can shoot at rocks using cannons like this one. 




In my experiments, I can generate the extreme conditions during planet formation. And with computer models, I can collide whole planets together to make them grow, or I can destroy them. 



I want to understand how to make the Earth and the Moon and why the Earth is so different from other planets. 


The leading idea for the origin of the Earth and Moon is called the "giant impact theory." The theory states that a Mars-sized body struck the young Earth, and the Moon formed from the debris disk around the planet. The theory can explain so many things about the Moon, but it has a huge flaw: it predicts that the Moon is mostly made from the Mars-sized planet, that the Earth and the Moon are made from different materials. But that's not what we see. The Earth and the Moon are actually like identical twins. The genetic code of planets is written in the isotopes of the elements. The Earth and Moon have identical isotopes. That means that the Earth and Moon are made from the same materials. 


It's really strange that the Earth and the Moon are twins. All of the planets are made from different materials, so they all have different isotopes, they all have their own genetic code. No other planetary bodies have the same genetic relationship. Only the Earth and Moon are twins. 


When I started working on the origin of the Moon, there were scientists that wanted to reject the whole idea of the giant impact. They didn't see any way for this theory to explain the special relationship between the Earth and the Moon. We were all trying to think of new ideas. The problem was, there weren't any better ideas. All of the other ideas had even bigger flaws. So we were trying to rescue the giant impact theory. 


A young scientist in my group suggested that we try changing the spin of the giant impact. Maybe making the Earth spin faster could mix more material and explain the Moon. The Mars-sized impactor had been chosen because it could make the Moon and make the length of Earth's day. People really liked that part of the model. But what if something else determined the length of Earth's day? Then there would be many more possible giant impacts that could make the Moon. I was curious about what could happen, so I tried simulating faster-spinning giant impacts, and I found that it is possible to make a disk out of the same mixture of materials as the planet. We were pretty excited. Maybe this was the way to explain the Moon. 


The problem is, we also found that that's just not very likely. Most of the time, the disk is different from the planet, and it looked like making our Moon this way would be an astronomical coincidence, and it was just hard for everyone to accept the idea that the Moon's special connection to Earth was an accident. The giant impact theory was still in trouble, and we were still trying to figure out how to make the Moon. 


Then came the day when I realized my mistake. My student and I were looking at the data from these fast-spinning giant impacts. On that day, we weren't actually thinking about the Moon, we were looking at the planet. The planet gets super-hot and partially vaporized from the energy of the impact. But the data didn't look like a planet. It looked really strange. The planet was weirdly connected to the disk. I got that super-excited feeling when something really wrong might be something really interesting. 


In all of my calculations, I had assumed there was a planet with a separate disk around it. Calculating what was in the disk as how we tested whether an impact could make the Moon. But it didn't look that simple anymore. We were making the mistake of thinking that a planet was always going to look like a planet. On that day, I knew that a giant impact was making something completely new. 


I've had eureka moments. This was not one of them. 



I really didn't know what was going on. I had this strange, new object in front of me and the challenge to try and figure it out. What do you do when faced with the unknown? How do you even start? 


We questioned everything: What is a planet? When is a planet no longer a planet anymore? We played with new ideas. We had to get rid of our old way of thinking, and by playing, I could throw away all of the data, all of the rules of the real world, and free my mind to explore. And by making a mental space where I could try out outrageous ideas and then bring them back into the real world to test them, I could learn. And by playing, we learned so much. I combined my lab experiments with computer models and discovered that after most giant impacts, the Earth is so hot, there's no surface. There's just a deep layer of gas that gets denser and denser with depth. The Earth would have been like Jupiter. There's nothing to stand on. And that was just part of the problem. I wanted to understand the whole problem. I couldn't let go of the challenge to figure out what was really going on in giant impacts. It took almost two years of throwing away old ideas and building new ones that we understood the data and knew what it meant for the Moon. 


I discovered a new type of astronomical object. It's not a planet. It's made from planets. A planet is a body whose self-gravity is strong enough to give it its rounded shape. It spins around all together. Make it hotter and spin it faster, the equator gets bigger and bigger until it reaches a tipping point. Push past the tipping point, and the material at the equator spreads into a disk. It's now broken all the rules of being a planet. It can't spin around together anymore, its shape keeps changing as it gets bigger and bigger; the planet has become something new. 


We gave our discovery its name: synestia. We named it after the goddess Hestia, the Greek goddess of the hearth and home, because we think the Earth became one. The prefix means "all together," to emphasize the connection between all of the material. A synestia is what a planet becomes when heat and spin push it over the limit of a spheroidal shape. 


Would you like to see a synestia? 


In this visualization of one of my simulations, the young Earth is already spinning quickly from a previous giant impact. Its shape is deformed, but our planet would be recognizable by the water on its surface. The energy from the impact vaporizes the surface, the water, the atmosphere, and mixes all of the gases together in just a few hours. We discovered that many giant impacts make synestias, but these burning, bright objects don't live very long. They cool down, shrink and turn back into planets. While rocky planets like Earth were growing, they probably turned into synestias one or more times. 


A synestia gives us a new way to solve the problem of the origin of the Moon. We propose that the Moon formed inside a huge, vaporous synestia. The Moon grew from magma rain that condensed out of the rock vapor. The Moon's special connection to Earth is because the Moon formed inside the Earth when Earth was a synestia. The Moon could have orbited inside the synestia for years, hidden from view. The Moon is revealed by the synestia cooling and shrinking inside of its orbit. The synestia turns into planet Earth only after cooling for hundreds of years longer. In our new theory, the giant impact makes a synestia, and the synestia divides into two new bodies, creating our isotopically identical Earth and Moon. Synestias have been created throughout the universe. And we only just realized that by finding them in our imagination: What else am I missing in the world around me? What is hidden from my view by my own assumptions?

The next time you look at the Moon, remember: the things you think you know may be the opportunity to discover something truly amazing. 


  1. Listen to the video and answer all questions below  without reading the transcript /text of the video.
  2. Then read the transcript of the video and check your answers, before looking at the corrections.




According to the video, are the following statements true or false? Explain Why.

  1. The Earth and the moon are made from different materials.
  2. Planetary “twins” are a common phenomenon.
  3. Dr. Stewart decided to abandon the “Giant Impact theory”.
  4. After giant impacts, a planet’s surface generally remains solid.
  5. A planet is an astronomical body whose own gravity holds it together.
  6. “Synestia” was named after the Roman Goddess of agriculture, Hestia.
  7. The prefix “Syn” means togetherness.
  8. Many giant object collisions create Synestias.
  9. Typically, Synestias last for a long time.
  10. During Earth’s formation, the earth became a synestia at least twice.
  11. The moon formed within a gaseous synestia.






  1. False. The earth and the moon have the same isotopes, which means that they are made from the same materials.
  2. False. Planetary twins are extremely rare. The moon and the earth are the only known example.
  3. False. Dr. Stewart tried to save the giant impact theory.
  4. False. After most giant impacts, the surface of a planet is vaporized.
  5. True.
  6. False. Synestia is named after the Greek goddess of hearth and home, Hestia.
  7. True.
  8. True.
  9. False. They typically cool down and turn back into planets quite quickly.
  10. False. During earth’s formation, it probably turned into an synestia once or twice, but not more.
  11. True.





English in Use: By + verb+ing


In the video, we can find the following sentence: “And by playing, we learned so much.”


We can use the structure “by + verb + ing” to explain how someone did something. For example, take a look at the following sentence.


“The astrophysicist worked very hard and won the Nobel Prize.”


We can change this sentence to explain how the astrophysicist won the Nobel prize with “by +verb+ing”:


“By working very hard, the astrophysicist won the Nobel Prize.”


“The astrophysicist won the Nobel Prize by working very hard.”


As we can see, we can use “by + verb +ing” in either clause.


Change the following sentences using “by + verb +ing” to explain how someone did something:


  1. The man used his intelligence to fix the table.
  2. I watched French television series and learnt French.
  3. He worked in a bank and made lots of money.
  4. He experimented with stem cells and found the cure for cancer.
  5. She used a torch to find her way home.
  6. I took the motorway and got here 15 minutes early.




English in Use:

  1. By using his intelligence, the man fixed the table/ The mn fixed the table by using his intelligence.
  2. By watching French television series, I learnt French/ I learnt French by watching French television series.
  3. By working in a bank, he made lots of money/ He made lots of money by working in a bank.
  4. By experimenting with stem cells, he found the cure for cancer/ He found the cure for cancer by experimenting with stem cells.
  5. By using a torch she found her way home/ She found her way home by using a torch.
  6. By taking the motorway, I got here 15 minutes early. I got here 15 minutes early by taking the motorway.




Traduire les phrases suivantes en anglais, issues du texte, puis retrouver ces phrases dans les deux premiers paragraphes du texte en anglais:

1. Et la decouverte de ce que j'avais fait faux a apporté une decouverte qui change completement la façon dont nous pensont par rapport à la terre et le lune.

2. La théorie dit qu'un objet de la taille de Mars a heurté la jeune terre, et a formé la Lune avec le disque de debris autour de la planete.




Essential Grammar in use p 200-201

Unit 96    at 8 o'clock   on monday   in april



Write on/in/at ?

  1. ............... 6 june.
  2. ............... the evening.
  3. .............. half past two.
  4. .............. Wednesday
  5. ...............1987
  6. ............... September.
  7. ...............24 September
  8. .............. Thursday
  9. .............. 11.45
  10. .............. Christmas day
  11. .............. Christmas
  12. .............. the morning.
  13. .............. Friday morning
  14. ............. Saturday night
  15. ............. night
  16. ............. the end of the week
  17. ............. the weekend
  18. ............. winter


  1. on
  2. in
  3. at
  4. on
  5. in
  6. in
  7. on
  8. on
  9. at
  10. on
  11. at
  12. in
  13. on
  14. on
  15. at
  16. at
  17. at
  18. in




whopping: adj. Informal. Very big.

smash: verb. To break into small pieces.

cannon: noun. A large powerful gun.

collide: verb. To hit something forcefully.

origin: noun. The beginning of something.

debris: noun. Small, broken pieces of something which has been destroyed.

flaw: noun. A mistake or imperfection.

isotopes: noun. Scientific. An atom which has the same structure but a different atomic weight to other atoms of the same element.

reject: verb. Refuse to accept or believe.

rescue: verb. To save.

coincidence: noun When two or more similar things happen at the same time through chance.

vaporize: verb. To turn something into gas.

to figure out something: phrasal verb. To work out the solution to a problem.

throw away: phrasal verb. To abandon or get rid of something.

tipping point: noun. A moment when massive changes and effects cannot be stopped.

hearth: noun. The area around a fireplace or fire.

cool down: phrasal verb. To become colder or to lose temperature.

to orbit: verb. To follow a curved path around something, usually a planet or star.

to shrink: verb. To become smaller.

turn into: phrasal verb. To transform. To change into something else.



Peseshet is a doctor and a teacher. The video describes a typical day of her life.

Now it is you turn. Write a text :

- Present yourself.

- Describe your profession.

- Tell what you did to get this job.

- Describe a typical day of your life : what usually happens when you are at work?




You can book a one to one class with a teacher who will correct your writing exercise.  One to one classes can be online, with a video call, anytime of the day. 

This gives you full flexibility for your timetable.

Please send us an email at afterschool at afterschoollyon.com.




You can book a one to one class with a teacher for the speaking.  One to one classes can be online, with a video call, anytime of the day. 

This gives you full flexibility for your timetable.

Please send us an email at afterschool at afterschoollyon.com.

Our online classes range from A1 to C2 levels, including specific class contents and online video classes.  They are designed to improve communication of spoken and written English with learner-centred lessons which help build students’ confidence, accuracy and fluency.

Our online learning classes offer an extensive level of flexibility for individual students, with comprehensive syllabus and content.