astronomy

Mesoplanet

Mesoplanet is a astronomy topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Mesoplanet rather than just read about it. In short: Mesoplanets are planetary-mass objects with sizes smaller than Mercury but larger than Ceres. The term was coined by Isaac Asimov.

Key takeaways

Mesoplanet belongs to astronomy; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Mesoplanet to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Mesoplanet from memory before moving on to harder problems.

Reference excerpt

Mesoplanets are planetary-mass objects with sizes smaller than Mercury but larger than Ceres. The term was coined by Isaac Asimov. Assuming size is defined in relation to equatorial radius, mesoplanets should be approximately 500 km to 2,500 km in radius.

History The term was coined in Asimov's essay "What's in a Name?", which first appeared in the Los Angeles Times in the late 1980s and was reprinted in his 1990 book Frontiers; the term was later revisited in his essay, "The Incredible Shrinking Planet" which appeared first in The Magazine of Fantasy and Science Fiction and then in the anthology The Relativity of Wrong (1988).

Asimov noted that the Solar System has many planetary bodies (as opposed to the Sun and natural satellites) and stated that lines dividing "major planets" from minor planets were necessarily arbitrary. Asimov then pointed out that there was a large gap in size between Mercury, the smallest planetary body that was considered to be undoubtedly a major planet, and Ceres, the largest planetary body that was considered to be undoubtedly a minor planet. Only one planetary body known at the time, Pluto, fell within the gap. Rather than arbitrarily decide whether Pluto belonged with the major planets or the minor planets, Asimov suggested that any planetary body that fell within the size gap between Mercury and Ceres be called a mesoplanet, because mesos means "middle" in Greek.... my own suggestion is that everything from Mercury up be called a major planet; everything from Ceres down be called a minor planet; and everything between Mercury and Ceres be called a "mesoplanet" (from a Greek word for "intermediate"). At the moment, Pluto is the only mesoplanet known. — I. Asimov (1988)

Today, the known objects that would be included by this definition are Pluto, Eris, Haumea, Makemake, Gonggong, Quaoar, probably Sedna, and perhaps Orcus. These eight, together with Ceres, are the objects astronomers generally agree are dwarf planets (though with some doubt regarding Orcus).

Worked examples

Example 1 — a first encounter with Mesoplanet

Start with the simplest possible case. Write down what Mesoplanet claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In astronomy, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Mesoplanet before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Mesoplanet ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Mesoplanet

In research: Mesoplanet appears in astronomy research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Mesoplanet in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Mesoplanet is common in secondary-school and first-year university syllabi. It links to neighbouring topics Definition of planet, Dwarf planets, Isaac Asimov, so understanding it makes those chapters shorter.
In everyday life: Look for Mesoplanet outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

Ask Teacher Smith questions about this articleOpens your AI tutor with a question about “Mesoplanet” →

Affiliate

Preply — study more efficiently by working with a personal tutor. 50% off.

How to study Mesoplanet in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Mesoplanet means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Mesoplanet out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Mesoplanet in simple terms?

Mesoplanets are planetary-mass objects with sizes smaller than Mercury but larger than Ceres. The term was coined by Isaac Asimov.

Why does Mesoplanet matter?

Because it connects several astronomy ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Mesoplanet?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Mesoplanet.