science

Mare Crisium

Mare Crisium is a science 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 Mare Crisium rather than just read about it. In short: Mare Crisium (Latin, 'Sea of Crises') is a lunar mare located in the Moon's Crisium basin, just northeast of Mare Tranquillitatis. Mare Crisium is a basin of Nectarian age.

Key takeaways

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

Reference excerpt

Mare Crisium (Latin, 'Sea of Crises') is a lunar mare located in the Moon's Crisium basin, just northeast of Mare Tranquillitatis. Mare Crisium is a basin of Nectarian age. It was formed by the flooding of basaltic lava that filled an ancient asteroid impact.

Characteristics Mare Crisium is 556 km (345 mi) in diameter, and 176,000 square kilometres (68,000 sq mi) in area. It has a very flat floor, with a ring of wrinkle ridges (dorsa) toward its outer boundaries. These are Dorsa Tetyaev, Dorsum Oppel, Dorsum Termier, and Dorsa Harker. The cape-like feature protruding into the southeast of the mare is Promontorium Agarum. On the western rim of the mare is the palimpsest Yerkes, and Lick to the southeast is similar. The crater Picard is located just to the east of Yerkes, and northwest of Picard are the craters Peirce and Swift. The ray system of the crater Proclus overlie the northwestern mare. Mare Anguis can be seen northeast of Mare Crisium. A mass concentration (mascon), or gravitational high, was identified in the center of Mare Crisium from Doppler tracking of the five Lunar Orbiter spacecraft in 1968. The mascon was confirmed and mapped at higher resolution with later orbiters such as Lunar Prospector and GRAIL.

Names Like most of the other maria on the Moon, Mare Crisium was named by Giovanni Riccioli, whose 1651 nomenclature system has become standardized. By the 17th century, Mare Crisium had acquired the name 'Caspian Sea', being labelled as such by Thomas Harriot, Pierre Gassendi and Michael van Langren. Ewen A. Whitaker speculates that it received this name because it occupies roughly the same position on the Moon's face as does the Caspian Sea on Earth, with respect to maps of Europe, North Africa and the Middle East. The English astronomer William Gilbert's map of c.1600 calls it 'Brittania' after Britain.

Observation and exploration Mare Crisium is just visible from Earth with the naked eye as a small dark spot on the edge of the Moon's face. It is the site of the 21 July 1969 crash-landing of the Soviet Luna 15 probe, occurring the same day that two Apollo 11 astronauts walked on the Moon. A soil sample from Mare Crisium was successfully brought to Earth on 22 August 1976 by the Soviet lunar mission Luna 24. Firefly Aerospace's lunar lander carried NASA-sponsored experiments and commercial payloads as a part of Commercial Lunar Payload Services program to Mare Crisium. Landing was completed successfully on 2 March 2025 northwest of Mons Latreille at 18.56°N 61.81°E / 18.56; 61.81. The mission ended on 16 March 2025 after completing all of its objectives, including a test of an electrodynamic dust shield to prevent lunar regolith building up on spacecraft surfaces.

In popular culture and literature Mare Crisium is used as the location for Arthur C. Clarke's 1948 seminal short-story "The Sentinel". In the story, a mysterious structure is found in one of the mountains surrounding the Mare. Clarke describes Mare Crisium as follows:

It is the great walled plain, one of the finest on the Moon, known as the Mare Crisium - the Sea of Crises. Three hundred miles in diameter, and almost completely surrounded by a ring of magnificent mountains, it had never been explored until we entered in the late summer of 1996. In Warhammer 40k, it is the location of the Somnus Citadel, a base for the Sisters of Silence. Mare Crisium is seen and mentioned throughout the 2022 film Moonfall. It is where the alien A.I. swarm and the astronauts go into the Moon to reach the megastructure beneath the surface.

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Illustrations

Worked examples

Example 1 — a first encounter with Mare Crisium

Start with the simplest possible case. Write down what Mare Crisium claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, 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 Mare Crisium 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 Mare Crisium 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 Mare Crisium

In research: Mare Crisium appears in science 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 Mare Crisium 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: Mare Crisium is common in secondary-school and first-year university syllabi. It links to neighbouring topics LQ13 quadrangle, Maria on the Moon, so understanding it makes those chapters shorter.
In everyday life: Look for Mare Crisium 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.

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How to study Mare Crisium in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Mare Crisium 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 Mare Crisium out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Mare Crisium in simple terms?

Mare Crisium (Latin, 'Sea of Crises') is a lunar mare located in the Moon's Crisium basin, just northeast of Mare Tranquillitatis. Mare Crisium is a basin of Nectarian age.

Why does Mare Crisium matter?

Because it connects several science 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 Mare Crisium?

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 Mare Crisium.