🪐 行星：太阳系的八位成员🪐 Planets: Eight Members of the Solar System

上一片看了火炉。这片🌌星空向导点名：围炉坐着八位家人。记住口诀，水金地火木土天海，一个不能少。 Last leaf we met the fireplace. Now the 🌌 star guide calls the roll: eight family members around the fire. Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune — all present.

第 1 步：八位按远近排队Step 1: Eight in line by distance

先看全家福——谁离火炉近，谁坐得远。First, the family portrait — who sits near the fire, who sits far.

八大行星全家福：内侧四颗小而硬，外侧四颗大而轻 — 离太阳从近到远：**水金地火木土天海**。内侧四颗小而硬（**类地行星**，有地面可站）。外侧四颗大而轻（**气态巨行星**，大都是氢和氦，没有地面）。越远越冷，走一圈也越久。 Nearest to farthest: **Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune**. The inner four are small and solid (**rocky planets** with ground to stand on). The outer four are big and puffy (**gas giants**, mostly hydrogen and helium, no surface). Farther means colder — and a longer year.

可以前不是九位吗？被开除的那位去哪了。But wasn't there a ninth member? Where did the expelled one go?

第 2 步：冥王星为什么离队Step 2: Why Pluto left the team

2006年冥王星降级为矮行星 — 2006 年，国际天联定了三条行星门槛：绕太阳转、够圆、清空轨道。冥王星前两条过了，第三条没过（它挤在柯伊伯带里）。所以它降级成**矮行星**，和小伙伴谷神星、阋神星作伴。 In 2006 astronomers set three planet rules: orbit the Sun, be round, clear your orbit. Pluto passed the first two but failed the third (it crowds with the Kuiper belt). So it became a **dwarf planet**, keeping company with Ceres and Eris.

队伍整齐了，再看三位明星拿了什么纪录。Team settled — now meet the three record holders.

第 3 步：最大、最热、有环Step 3: Biggest, hottest, ringed

土星环特写：冰块和岩石做的环 — **最大：木星**，能装下 1300 个地球。**最热：金星**，厚二氧化碳捂出 460℃。 **有环：土星**，光环是无数冰块和岩石。记住这三张脸，就记住了半个太阳系。 **Biggest: Jupiter** — 1,300 Earths fit inside. **Hottest: Venus** — thick CO2 bakes it to 460°C. **Ringed: Saturn** — its rings are countless chunks of ice and rock. Know these three faces and you know half the solar system.

🎮 行星排排站（30 秒）🎮 Line up the planets (30 seconds)

道理讲完了。先按远近排好八颗行星，再连过 3 个特征挑战。Theory done — line up all eight by distance first, then clear 3 feature challenges.

一句话记住它：水金地火小而硬，木土天海大而轻；冥王星没清空轨道成了矮行星。 Remember it in one line: small rocky four inside, big puffy four outside — and Pluto, which never cleared its orbit, is a dwarf planet.

排序：水金地火木土天海；内侧类地行星，外侧气态巨行星Order: Mercury to Neptune; rocky planets inside, gas giants outside 冥王星 2006 年降级：没清空轨道，成了矮行星Pluto demoted in 2006: it never cleared its orbit — a dwarf planet 最大木星，最热金星，有环土星（环是冰块和岩石）Biggest Jupiter, hottest Venus, ringed Saturn (rings of ice and rock)

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内容参考 OpenStax 等公开教材，多来源核对 · AI 生成、人工审核 · 发现错误欢迎指正，帮这片叶子长得更好。 Based on OpenStax and other open textbooks, cross-checked across sources · AI-generated, human-reviewed · Spotted a mistake? Tell us — help this leaf grow.