News by Levels · Level 3 · For teachers
Teacher guide & answers
Rubin Team Reports Dwarf Planet Candidate 2026 ED138
How to use these two pages
Give learners the student worksheet. It contains the story and questions, without the answers. Keep this guide for yourself. Use it to lead the activity and explain the answers afterwards.
Student worksheetA simple 15–20-minute lesson
- Before reading · 2 minutes
Show the title. Ask: “What do you think this story is about?”
- Read and answer · 8–10 minutes
Give out the student worksheet. Learners read for the main idea, then reread to answer the 2 questions. They can compare answers with a partner.
- Discuss and write · 5–8 minutes
Check the answers below together. Ask learners to point to the clue in the story, then finish with the open question.
Adjust the support: Let learners use word help or Level 1 if needed. For a challenge, compare the wording in another level. This activity is not a proficiency test.
Answers to the 2 questions
The question numbers match the student worksheet. Each answer includes a reason and the clue learners can find in the story.
What happened on October 13?
Correct answer: A — Matthew Holman identified the object in data
Why: Holman identified it on October 13; the announcement followed on October 27.
Clue in the story: A distant object detected in Vera C. Rubin Observatory data could join the solar system's dwarf planets, although its classification is not yet established. The discovery of 2026 ED138 was announced on October 27; researcher Matthew Holman had identified it in data on October 13.
How could infrared measurements help the researchers?
Correct answer: B — They could narrow its estimated size and clarify its classification
Why: The article says infrared measurements could reduce size uncertainty and help establish its dwarf-planet status.
Clue in the story: The body is currently about 46 times as far from the Sun as Earth is. Its estimated diameter ranges from 600 to 1,500 kilometres because its surface reflectivity is uncertain. Infrared measurements could narrow the size estimate and help establish whether it qualifies as a dwarf planet.
The open question: accept different answers
Ask learners: Contrast the October 13 identification with the October 27 announcement and explain one remaining uncertainty.
One possible answer: Holman identified the object in data on October 13; the discovery was announced on October 27. Its surface reflectivity is uncertain, so the diameter estimate is still a wide range.
This is an example, not the only correct answer. Look for a relevant idea, a reason and the learner’s own words. Learners can answer aloud or write one or two sentences.