astronomy

HD 10180

HD 10180 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 HD 10180 rather than just read about it. In short: HD 10180 is a Sun-like star in the southern constellation Hydrus that is notable for its large planetary system. Since its discovery, at least six exoplanets have been observed orbiting it, and some studies have proposed up to nine potential planets, which would make it potentially the largest of all known planetary systems, including the Solar System.

Key takeaways

HD 10180 belongs to astronomy; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect HD 10180 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of HD 10180 from memory before moving on to harder problems.

Reference excerpt

HD 10180 is a Sun-like star in the southern constellation Hydrus that is notable for its large planetary system. Since its discovery, at least six exoplanets have been observed orbiting it, and some studies have proposed up to nine potential planets, which would make it potentially the largest of all known planetary systems, including the Solar System.

Characteristics Based upon parallax measurements, it is located at a distance of 127 light-years (39 parsecs) from Earth. The apparent visual magnitude of this star is 7.33, which is too faint to be viewed with the naked eye although it can be readily observed with a small telescope. At a declination of −60°, this star cannot be seen at latitudes north of the tropics. HD 10180 is a G-type main-sequence star, and thus generates energy at its core through the thermonuclear fusion of hydrogen. The mass of this star is estimated as 6% greater than the Sun's mass, it has a radius of 120% that of the Sun, and is radiating 149% of the Sun's luminosity. The effective temperature of the star's chromosphere is 5,911 K, giving it a yellow-hued glow like the Sun. HD 10180 has a 20% higher abundance of elements other than hydrogen/helium compared to the Sun. With an estimated age of 7.3 billion years, it is a stable star with no significant magnetic activity. The estimated period of rotation is about 24 days. A survey in 2015 ruled out the existence of any stellar companions at projected distances from 13 to 324 astronomical units.

Planetary system On August 24, 2010, a research team led by Christophe Lovis of the University of Geneva announced that the star has at least five planets, and possibly as many as seven. The planets were detected using the HARPS spectrograph, in conjunction with the ESO's 3.6 m telescope at La Silla Observatory in Chile, using Doppler spectroscopy.

On April 5, 2012, astronomer Mikko Tuomi of the University of Hertfordshire submitted a paper to Astronomy and Astrophysics approved for publishing on April 6, 2012 that proposed a nine-planet model for the system. Re-analysing the data using Bayesian probability analysis, previously known planets' parameters were revised and further evidence was found for the innermost planet (b) as well as evidence of two additional planets (i and j). Subsequent studies since 2014 have found that a six-planet model is the best fit to the data. The system is not known to be a transiting planetary system, and as such planets are unlikely to be detected or verified by the transit method.

In 2017, an orbital simulation showed that the formation of dynamically stable families of comets in the HD 10180 system is unlikely. The identified reason for the instability of cometary orbits was the location of the most massive planet HD 10180 h in the outermost orbit.

Orbital arrangement

The system contains six planets with minimum masses from 12 to 46 times Earth's (ranging in mass from roughly Uranus to sub-Saturn) at orbital radii of 0.06, 0.13, 0.27, 0.49, 1.43 and 3.38 AU. In the Solar System this set of orbits would fit within the main asteroid belt. There are no planets known to be in mean-motion resonances, although the system has a number of near resonances including 3c:2i:1d and 3e:2j:1f. The approximate ratios of periods of adjacent orbits are (proceeding outward): 1:5, 1:3, 1:3, 2:5, 1:5, 3:11. Since the inclination of the planets' orbits is unknown, only minimum planetary masses can presently be obtained. Dynamical simulations suggest that the system cannot be stable if the true masses of the planets exceed the minimum masses by a factor of greater than three (corresponding to an inclination of less than 20°, where 90° is edge-on). A 2020 study set upper limits on the masses of the confirmed planets based on non-detections in Gaia astrometry: planet c is <8.626 MJ, planet d is <10.37 MJ, planet e is <20.44 MJ, planet f is <14.03 MJ, planet g is <10.62 MJ, and planet h is <22.63 MJ. While some of these upper limits are in the mass range of brown dwarfs, it is likely that the true masses are significantly smaller.

Planets

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with HD 10180

Start with the simplest possible case. Write down what HD 10180 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 HD 10180 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 HD 10180 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 HD 10180

In research: HD 10180 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 HD 10180 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: HD 10180 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Durchmusterung objects, G-type main-sequence stars, Henry Draper Catalogue objects, so understanding it makes those chapters shorter.
In everyday life: Look for HD 10180 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 HD 10180 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what HD 10180 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 HD 10180 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is HD 10180 in simple terms?

Why does HD 10180 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 HD 10180?

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 HD 10180.