Questions for ‘The pebbled path to planets’

Artist and astronomer Robert Hurt at Caltech created this illustration of a possible newfound planet near the star CoKu Tau 4. It’s forming in a clearing in the star's dusty, planet-forming disc. The possible planet could be at least as big as Jupiter, and may look like the giant planets in our solar system when they were young.

R. Hurt (SSC-Caltech)/JPL-Caltech/NASA

To accompany “The pebbled path to planets


Before Reading:

1.  What is a planet? How many can you name?

2.  Draw a diagram of the solar system, including the paths of Earth and the other planets.

During Reading:

1.  Describe two strange planets found outside our solar system.

2.  What is pebble accretion?

3.  How did Emanuel Swedenborg in the 18th century describe planet formation?

4.  In terms of astronomy, what is dust? What are planetesimals and protoplanets?

5.  According to a popular theory from the 20th century, how are planets formed from a disk of gas and dust?

6.  What are two reasons why colliding planetesimals could not have formed Jupiter and Saturn?

7.  What is drag and what would the drag from gas in a disk likely do to pebbles in space?

8.  Why does the timing have to be just right for a planet to form by pebble accretion?

9.  Why does Alessandro Morbidelli doubt that rocky planets like Earth formed by planet accretion?

After Reading:

1.  A lot of the starting material that would eventually go into making planets will ultimately be jettisoned from a star system or lead to the formation of other types of objects. Based on what you read, what types of celestial bodies (besides planets) can come from this starting mix of gases, dust and more? If they’re not in our solar system now, where did they likely go?

2.  Scientists have identified a number of what they call rogue planets — planets without a sun. From what you have read in the story, do you think such galactic wanderers were jettisoned during the planet-forming process or after? Use what you read in the story to explain your reasoning.