SCIENCE

The clearest image ever taken of planets forming around an infant star has been snapped by the ALMA telescope array in high desert of Chile. (BBC)

Use our resources to understand planet formation.

Teachers, scroll all the way down for a short list of key resources in our “Teachers’ Toolkit.”

Discussion Questions

• The short BBC article describes a “vast disc of dust and gas” around the far-away planet HL Tau. Read through our very short, basic encyclopedic entry on “planet.” What is this “vast disc of dust and gas” called?
  • A nebula! Specifically, this type of nebula is called a protoplanetary nebula—proto means “earliest form.” This disc of space dust is the earliest form of what will become planets in a solar system.

• According to the BBC, HL Tau’s nebula can’t be observed using visible light. Using ALMA, scientists “snapped the impressive new image using much longer wavelengths.” Look at our illustration of the electromagnetic spectrum. What type of radiation do you think ALMA astronomers used to get the new image?
  • Radio, microwaves, and infrared waves—those are radio telescopes in the pretty picture above.

• Compare the high-resolution ALMA image at the top of this post to the Hubble image of the same region above. Why do you think the two images look so different?
  • The Hubble view has a much, much wider angle—you see the whole region of space, not just the star. In other words, it’s not as focused as the ALMA image.
  • The Hubble image uses visible light, which is obscured by that big, bright dust cloud. The ALMA image, using radio waves, cuts through the cloud to see the protoplanetary nebula itself.

• Compare the beautiful ALMA image at the top of this post with the equally beautiful view of the planet Saturn above. What is the most striking similarity between the two outer-space images?
  • Both the star and the planet have ring systems. Both systems have light and dark rings.

• Do you think the rings around HL Tau and the rings around Saturn formed in a similar way?
  • Yep, they formed in pretty much the same way. In fact, four billion years later, the rings around Saturn are still condensing and forming new moons! Those moons, in turn, are clearing paths in the rocky dust cloud around the planet—forming Saturn’s the mostly empty “dark rings.”

• According the BBC, ALMA’s image matches scientists’ predictions of what such a disc would look like. So, what is so surprising about HL Tau’s protoplanetary nebula?
  • It formed so fast! “When we first saw this image we were astounded at the spectacular level of detail. HL Tau is no more than a million years old, yet already its disc appears to be full of forming planets. This one image alone will revolutionize theories of planet formation,” explained one ALMA scientist.

• Extra Credit: How many planets do you think are forming around HL Tau?
  • Your guess is as good as an astronomer’s! Take a look at the dark areas of the HL Tau nebula, where you think a massive object is clearing a path. One of our favorite astronomers, Phil Plait, guesses three. We’re not astronomers, we say four.

TEACHERS TOOLKIT

BBC: Planet formation captured in photo

Bad Astronomy: A Dusty Disk Heralds the Birth of a New Solar System

Nat Geo encyclopedic entry: planet

Nat Geo illustration: Electromagnetic Spectrum