astronomy

K2-137b

K2-137b 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 K2-137b rather than just read about it. In short: K2-137b (also designated EPIC 228813918 b) is a hot, iron-rich, rocky exoplanet around the red dwarf K2-137 in the constellation Virgo about 99 parsecs (320 light-years) from Earth. It orbits the star very rapidly, with an orbital period of 0.1797 days (4.31 h), at a distance of just 0.0058 AU (870,000 km).

Key takeaways

K2-137b belongs to astronomy; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect K2-137b to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of K2-137b from memory before moving on to harder problems.

Reference excerpt

K2-137b (also designated EPIC 228813918 b) is a hot, iron-rich, rocky exoplanet around the red dwarf K2-137 in the constellation Virgo about 99 parsecs (320 light-years) from Earth. It orbits the star very rapidly, with an orbital period of 0.1797 days (4.31 h), at a distance of just 0.0058 AU (870,000 km). It has received the Guinness World Record for the shortest orbital period for a confirmed planet, though the planetary candidate KOI-1843.03 has a period four minutes shorter.

Physical properties K2-137b is a sub-Earth in terms of radius. The discovery paper gives an estimate of 0.89±0.09 R🜨, similar to Venus (0.949 R🜨), whereas Adams et al. (2021) provides a smaller value of 0.64±0.10 R🜨, slightly larger than Mars (0.532 R🜨). If the latter is true, this would be one of the smallest exoplanets discovered so far. Despite the small size, it is somewhere between 1.01 and 2.80 times as massive as Earth, comparable to some super-Earths. Because it has yet to be disrupted by tidal forces from the host star, it can be inferred that iron makes up at least 42±5 % of its mass. Still, the planet is tidally stretched to an aspect ratio of between 1.21 and 1.66. Its equilibrium temperature is approximately 1,471 K (1,198 °C; 2,188 °F), hot enough to melt silicate minerals. While K2-137b itself displays no signs of evaporation, such iron-rich USP planets may be higher-mass counterparts to disintegrating planets e.g., Kepler-1520b.

Host star The planet orbits a red dwarf star, K2-137, with the spectral type M3V. Smith et al. (2018) gives it a mass of 0.463±0.052 M☉, a radius of 0.442±0.044 R☉, and an effective temperature of 3492±70 K, while Adams et al. (2021) presents a substantially smaller mass of 0.29±0.06 M☉ but a slightly hotter temperature of 3697±109 K.

Formation Several hypotheses exist as to how K2-137b became such an iron-rich, short-period planet. It could have been stripped of its outer silicate layers through high-velocity giant impacts, much like how Mercury came to have a high iron content according to several theories. Such collisions are projected to be common among USP planets due to high orbital speeds, reaching 270 km/s for K2-137b compared to the 29.8 km/s of Earth. On the other hand, it may have formed out of iron-rich material. Matter near the inner edge of the protoplanetary disk could be enriched in iron due to iron condensing at higher temperatures than enstatite and photophoresis separating iron grains from silicate grains by the difference in thermal conductivity. Finally, it is possible that the planet is situated at the Roche limit and has been slowly losing the silicate crust and mantle to Roche lobe overflow as its orbit slowly decays.

Worked examples

Example 1 — a first encounter with K2-137b

Start with the simplest possible case. Write down what K2-137b 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 K2-137b 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 K2-137b 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 K2-137b

In research: K2-137b 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 K2-137b 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: K2-137b is common in secondary-school and first-year university syllabi. It links to neighbouring topics Exoplanets discovered by K2, Exoplanets discovered in 2017, Sub-Earth exoplanets, so understanding it makes those chapters shorter.
In everyday life: Look for K2-137b 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 K2-137b in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what K2-137b 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 K2-137b out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is K2-137b in simple terms?

Why does K2-137b 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 K2-137b?

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 K2-137b.