astronomy

Kepler-9c

Kepler-9c 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 Kepler-9c rather than just read about it. In short: Kepler-9c is one of the first seven extrasolar planets, exoplanets, discovered by NASA's Kepler Mission, and one of at least two planets orbiting the star Kepler-9. Kepler-9c and Kepler-9b were the first exoplanets confirmed to be transiting their star.

Key takeaways

Kepler-9c belongs to astronomy; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Kepler-9c to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Kepler-9c from memory before moving on to harder problems.

Reference excerpt

Kepler-9c is one of the first seven extrasolar planets, exoplanets, discovered by NASA's Kepler Mission, and one of at least two planets orbiting the star Kepler-9. Kepler-9c and Kepler-9b were the first exoplanets confirmed to be transiting their star. The planet's discovery was announced by the Kepler Mission team on August 26, 2010 after its initial discovery by Kepler. At the time, it was one of 700 planetary candidates noted by Kepler. Observations of the planet have suggested that it is a hydrogen–helium gas giant that is slightly smaller than Saturn, and that it orbits nearby its star at .225 AU. Kepler-9c and b are notable in that the planets share a pattern of orbital resonance, in which the orbit of each planet stabilizes the orbit of the other. During the time it was observed by the spacecraft, the planet's orbit, which lasts on average approximately 38 days, shortened by 39 minutes every orbital period because of this effect. Its orbit, over time, oscillates slightly above and below a 2:1 ratio with planet b.

Nomenclature and history As with most exoplanets, the name "Kepler-9c" denotes that it is the second planet discovered in the orbit of the star Kepler-9. Kepler-9 itself was named after the Kepler Mission, a NASA project oriented towards discovering planets that are transiting their home stars. The planet was one of 700 planetary candidates considered by Kepler in its first 43 days of operation. It was highlighted as a part of one of five star systems that seemed to hold multiple transiting planets. Kepler-9c and Kepler-9b were confirmed as the first planets discovered to transit the same star. Initial estimates concerning Kepler-9c's mass were refined by follow-up observations made by the Keck 1 Telescope at the W.M. Keck Observatory at Mauna Kea, Hawaii. Keck was able to confirm that Kepler-9c and Kepler-9b were planets that were slightly smaller than planet Saturn.

Characteristics Kepler-9c is a gas giant that is smaller and slightly less massive than planet Saturn. It is approximately 0.171 MJ, or 17% the mass of planet Jupiter. It also has a radius of 0.823 RJ, which makes it slightly smaller (1.5%) than Saturn. The planet is, on average, situated 0.225 AU from the star. It is probable that the planet is composed of hydrogen and helium. The planet orbits on the same plane as Kepler-9b, a second and larger gas giant located in the Kepler-9 system. While observing the planet, the Kepler team noticed that Kepler-9b and c orbited in a 1:2 ratio, where Kepler-9b orbits its star every 19 days and Kepler-9c orbits every 38 days. The gravitational pull that each planet has on the other, known as orbital resonance, keeps the planets in a stable orbit. This phenomenon is the first of its kind seen outside the Solar System. Every time Kepler-9c completed an orbit during the observation period, its orbital period decreased by about 39 minutes. At some point, however, this trend will reverse and its orbit will increase. The lengths of its orbit will oscillate slightly above and below the 2:1 ratio.

See also Kepler-4b Kepler-5b Kepler-6b Kepler-7b Kepler-8b

References

External links Media related to Kepler-9 c at Wikimedia Commons

Illustrations

Worked examples

Example 1 — a first encounter with Kepler-9c

Start with the simplest possible case. Write down what Kepler-9c 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 Kepler-9c 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 Kepler-9c 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 Kepler-9c

In research: Kepler-9c 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 Kepler-9c 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: Kepler-9c is common in secondary-school and first-year university syllabi. It links to neighbouring topics Exoplanets discovered by the Kepler space telescope, Exoplanets discovered in 2010, Exoplanets with Kepler designations, so understanding it makes those chapters shorter.
In everyday life: Look for Kepler-9c 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 Kepler-9c in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Kepler-9c 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 Kepler-9c out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Kepler-9c in simple terms?

Why does Kepler-9c 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 Kepler-9c?

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 Kepler-9c.