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January 2022

Current Events: Moon Formation around Exoplanets

By Stacy Palen

ALMA continues to delight us with its unsurpassed and exquisite resolution and sensitivity. In this case, we have the first clear detection of a moon-forming disc around a planet orbiting a very, very young star.

Below are some questions to ask your students based on this article.

1). What is extraordinary about this observation?

Answer: For the first time, astronomers clearly identified a disc around a planet and estimated its size.

2). What sort of planet is PDS 70b at the center of this disc?

Answer: A gas giant, like Jupiter.

3). How large (in AU) is the moon-forming disc, and how much mass does it have?

Answer: The disc is about 1 AU in diameter, and it has the mass of about 3 of Earth’s moons.

4). Why is such a disc not detected around PDS 70b?

Answer: That planet did not have enough dust around it, because its dust was “stolen” by PDS 70c.

5). Does this observation support or refute the basic theory of star and planet formation that you learned about in the text?

Answer: This observation supports that theory and is basically exactly what we would predict we should find!