astronomy

Mu Arae c

Mu Arae c 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 Mu Arae c rather than just read about it. In short: Mu Arae c, also known as HD 160691 c, formally named Dulcinea (pronounced or ), is an extrasolar planet orbiting the star Mu Arae of the constellation Ara. It was the first 'hot Neptune' to be discovered.

Key takeaways

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

Reference excerpt

Mu Arae c, also known as HD 160691 c, formally named Dulcinea (pronounced or ), is an extrasolar planet orbiting the star Mu Arae of the constellation Ara. It was the first 'hot Neptune' to be discovered. None of the four planets orbiting Mu Arae are directly visible from Earth using currently available tools. All four were found using the radial velocity method of extrasolar planet detection.

Discovery The planet's discovery was announced on August 25, 2004. At the time, its minimum mass was reported at just 14 times that of Earth, although later work established a value of 10.5 Earth masses. It orbits very close to Mu Arae, completing one revolution every 9.6 days. The discovery was made with the aid of the High Accuracy Radial Velocity Planet Searcher (HARPS) spectrograph, at the European Southern Observatory's La Silla Observatory in Chile. The data that revealed the presence of this planet was gathered on 8 nights of observations in June 2004.

Name In July 2014 the International Astronomical Union (IAU) launched NameExoWorlds, a process for giving proper names to certain exoplanets and their host stars. The process involved public nomination and voting for the new names. In December 2015, the IAU announced the winning name was Dulcinea for this planet. The winning name was submitted by the Planetario de Pamplona, Spain. Dulcinea was the love interest of the lead character of the novel Don Quixote.

Characteristics Assuming its true mass is comparable to those of Neptune and Gliese 436 b, the authors of the discovery paper speculated that Mu Arae c could be a terrestrial planet, though they expect a gaseous envelope to compose 5-10% of its mass. A rocky planet this size could possibly have formed, since Mu Arae has a higher metallicity than the Sun. Also, it is thought to have formed well inside the system's "snow line" at 3.2 AU. However, various models of the system's formation have since converged that the planet attracted large amounts of volatiles before its star had cleared out the ice, and that it now has a core of only six Earth masses. Its core is likely enveloped in so much hot ice and gas that the planet would behave more like Neptune. Indeed, it is now understood that planets this massive are rarely rocky. Mu Arae c is too far from its star to be subject to coronal mass ejections. There is disagreement as to whether it is and has always been a hot Neptune in mass (Lammer), or if it could have developed from a gas giant, losing most of its mass on the way (Baraffe). If an eroded gas giant, the star would have boiled the planet from a larger protoplanet, of 20 Earth masses up to half Jupiter's mass. If the latter, its current radius could be as high as 0.6 Jupiter. The planet must be hot because of its proximity to its star. The discoverers chose for it an albedo of 0.35, lighter than albedos chosen to calculate the temperatures of hot Jupiters such as Tau Boötis b. This was perhaps due to the discoverers' assumption that the planet would be a silicate super-terrestrial with neither clouds nor a deep Rayleigh scattering atmosphere. If so the surface temperature would be about 900 K.

Worked examples

Example 1 — a first encounter with Mu Arae c

Start with the simplest possible case. Write down what Mu Arae c 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 Mu Arae c 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 Mu Arae c 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 Mu Arae c

In research: Mu Arae c 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 Mu Arae c 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: Mu Arae c is common in secondary-school and first-year university syllabi. It links to neighbouring topics Ara (constellation), Exoplanets detected by radial velocity, Exoplanets discovered in 2004, so understanding it makes those chapters shorter.
In everyday life: Look for Mu Arae c 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 Mu Arae c in 20 minutes

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

Frequently asked questions

What is Mu Arae c in simple terms?

Why does Mu Arae c 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 Mu Arae c?

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 Mu Arae c.