Indicate to students the map represents the planets known in our solar system in Note to Educators: Ceres, Pallas, Juno and Vesta were identified as planets upon their discovery , , and , respectively. While astronomer William Herschel, famous for his discovery of Uranus, advocated to reclassify these celestial objects into a new class of rocky objects - asteroids - as early as , they seem to have maintained their status as planets until at least the mids sources vary on this point.
Provide students time in the Alone Zone independent thinking time to make and record observations. Students will likely have a range of knowledge of the solar system. Encourage students more familiar with the solar to notice what's included on the map and not "what's missing" from it.
Refrain from answering individual questions; instead direct students to record their questions in their science notebooks. Next, ask students to turn to a partner and share observations. As you move around the room, listen for students to describe some or all of the following observation:. Ask students to share their observations with the class, first calling on one of the student pairs who shared their noticing of 12 or maybe 11 planets.
Create a class record of observations. Students may have many questions about the map; either create a class list or ask students to make sure to record them in their science notebook. Tell students you have another solar system map you need to share with them - Rand McNally's Modern Space Map published circa Again, project the map or share the link with students.
This time, ask students to work in pairs to make and record observations. Remind them not to worry about what's not on the map, but to notice what's included. Encourage them to continue to record questions as well.
Assign pairs to form groups of four students. Ask them to first share their noticings with each other. As you move around the room, help keep students focused on sharing observations of the Modern Space Map and not yet comparing the two maps. You might ask students to use the talking stick protocol described in the Why are plane designs so different? Daily Do. Next, ask the groups to work collaboratively to identify and record differences between the two maps.
Listen specifically for groups to talk about the the absence of Vulcan from the Modern Space Map , the appearance of the planets Neptune and Pluto , Ceres identified as an asteroid Pallas, Vesta and Juno are not labeled , and the notation "1, to 50, known" with regards to the number of asteroids.
Record these differences and any others the groups have identified. Which three questions about the phenomenon of the changes in the solar system maps between and are the most puzzling to them? Ask students to share these questions with their group and note the two most common questions and the one question the group votes is the most intriguing or unique.
Bring the groups together to share these three group-selected questions with the class. Students will likely ask. Then point out Ceres, Pallas, Vesta and Juno and say, "These planets were already discovered in Why do you think they are not included on the Modern Space Map?
Were they undiscovered? Point out these differences and ask, "We have a lot of ideas about why these celestial objects aren't included as planets on the Modern Space Map. We see Ceres classified as an asteroid and presumably Pallas, Vesta and Juno. Should we investigate what changed between and that caused astronomers to demote Ceres and the other objects from planets to asteroids?
Tell students you have data to share for the planets identified on each map. This will enable them to make a copy of the Excel file which contains Table 1. Sharing the Excel version of the data tables allows students to easily sort data which may help reveal patterns. PDF versions of the data tables can be found in the Why isn't Pluto a planet anymore?
Say to students, "These are the data astronomers had available to them - in addition to the data contained on the maps - to reach consensus on reclassifying Ceres, Pallas, Vesta, and Juno from planets to a new class of rocky celestial objects called asteroids. You may need to share with middle school students that eccentricity is a measure of how close a planet's orbit is to a perfect circle.
The closer the eccentricity is to 0. Students might ask you the difference between the two classifications; make sure to let them know formal definitions for neither planets nor asteroids existed during this time period. Put the question back to students, "How might you decide how to categorize the celestial objects represented as planets on the map?
Ask students to work in the Alone Zone to identify patterns in each of the two data sets and between the two data sets. Encourage students to sort the data in a variety of ways to see if any patterns emerge. As you move around the room, you might ask students some or all of the following questions:. Next, move students into small groups of three or four students. Ask students to share patterns they noticed with their group.
Upon his discovery, Tombaugh rushed to the observatory director. Tombaugh was referring to a ninth planet that had been predicted to orbit the sun beyond Neptune. In , an object about a tenth as wide as Pluto was seen orbiting out beyond it.
More than 2, icy bodies have since been found hiding in this frigid outskirt of the solar system known as the Kuiper KY-pur Belt.
And there may be many more still. Finding that Pluto had so many neighbors raised questions. What did these strange new worlds have in common with more familiar ones? What set them apart? In , he spotted the first Kuiper Belt body that appeared larger than Pluto.
This icy body was left over from the formation of the solar system. If Pluto was the ninth planet, Brown argued, then surely Xena should be the 10th.
Tensions over how to categorize Pluto and Xena came to a head in Pluto and Xena were deemed dwarf planets. Xena was renamed Eris, the Greek goddess of discord. A fitting title, given its role in upsetting our concept of the solar system. On Twitter, Brown goes by plutokiller, since his research helped knock Pluto off its planetary pedestal.
Right away, textbooks were revised and posters reprinted. But many planetary scientists — especially those who study Pluto — never bothered to change.
In part, that might be sass or spite. One appeared as a report in Icarus. The other one is due out soon. For these, the researchers examined hundreds of scientific papers, textbooks and letters. Some of the documents dated back centuries. And why was often not straightforward. Consider Ceres. This object sits in the asteroid belt between Mars and Jupiter.
Like Pluto, Ceres was considered a planet after its discovery. By the end of the s, scientists knew Ceres had hundreds of neighbors. Since Ceres no longer appeared special, the story goes, it lost its planetary title. The largest asteroids still looked like planets. Most small ones, however, turned out to be weird, lumps. This provided evidence that they were fundamentally different than the bigger, rounder planets.
And what about moons? The change was driven by nonscientific publications, such as astrological almanacs. The short answer is no, Pluto is no longer a planet. It is now classified as a type of object called a dwarf planet. The key discovery took place in , when an object called Eris, which is actually more massive than Pluto, was discovered.
This caused a large debate over what should be called a planet. So in the International Astronomical Union IAU had a meeting and one of the biggest items on their agenda was to establish a rigorous definition of what was a planet. They came up with three criteria to be a planet:. Pluto passes the first two requirements, but fails the third.
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