astronomy

Pi Mensae

Pi Mensae 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 Pi Mensae rather than just read about it. In short: Pi Mensae (π Men), also known as HD 39091, is a G-dwarf star in the constellation of Mensa. This star has a high proper motion.

Key takeaways

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

Reference excerpt

Pi Mensae (π Men), also known as HD 39091, is a G-dwarf star in the constellation of Mensa. This star has a high proper motion. The apparent magnitude is 5.67, which can be visible to the naked eye in exceptionally dark, clear skies. It is nearly 60 light-years away. The star is slightly larger than the Sun in terms of mass, size, luminosity, temperature and metallicity, and is about 730 million years younger. It hosts three known planets.

Planetary system On October 15, 2001, an extrasolar planet was found orbiting the star. Pi Mensae b is one of the most massive planets ever discovered, and has a very eccentric orbit that takes approximately 2,151 days (5.89 years) to complete. Because of its eccentricity, and being a massive brown dwarf that passes through the habitable zone, it would have disrupted the orbits of any Earth-like planets, and possibly thrown them into the star, or out into the interstellar medium. Incorporating more accurate Hipparcos data yields a mass range for the companion to be anywhere from 10.27 to 29.9 times that of Jupiter, confirming its substellar nature with the upper limit of mass putting it in the brown dwarf range. In 2020, the true mass of Pi Mensae b was measured to be 14.1 MJ via astrometry. Since this is greater than 13 Jupiter masses, the object could be considered a brown dwarf, although more recent astrometric results suggest a slightly lower mass. Pi Mensae was ranked 100th on the list of top 100 target stars for the planned (but now-canceled) Terrestrial Planet Finder mission to search for Earth-like planets. On September 16, 2018, a preprint was posted to arXiv detailing the discovery of a super-Earth on a 6.27-day orbit around the star, the first exoplanet detection by the Transiting Exoplanet Survey Satellite (TESS) submitted for publication. This was confirmed two days later, where the attention was called that the system is amenable for future planet atmospheric studies. In 2020, an analysis with Gaia DR2 and Hipparcos astrometry showed that planets b and c are located on orbits mutually inclined by 49°−131° (1 sigma), which causes planet c to not transit most of the time, and acquire large misalignments with its host star's spin axis. Planet c likely formed on a wide orbit, and then migrated inward under the gravitational influence of the planet or brown dwarf b. It is likely to retain a portion of primordial, highly volatile atmosphere. In 2022, the discovery by the radial velocity method of a third planet, Pi Mensae d, on a 125-day orbit was announced. Another 2022 study did not confirm this planet, but a 2023 study did detect it.

See also Gliese 777 HD 70642 Lists of exoplanets

References

External links The Extrasolar Planet Encyclopedia: HD 39091 Solstation: Pi Mensae SIMBAD: Pi Mensae ARICNS: Pi Mensae

Illustrations

Worked examples

Example 1 — a first encounter with Pi Mensae

Start with the simplest possible case. Write down what Pi Mensae 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 Pi Mensae 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 Pi Mensae 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 Pi Mensae

In research: Pi Mensae 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 Pi Mensae 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: Pi Mensae is common in secondary-school and first-year university syllabi. It links to neighbouring topics Bayer objects, Bright Star Catalogue objects, Durchmusterung objects, so understanding it makes those chapters shorter.
In everyday life: Look for Pi Mensae 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 Pi Mensae in 20 minutes

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

Frequently asked questions

What is Pi Mensae in simple terms?

Pi Mensae (π Men), also known as HD 39091, is a G-dwarf star in the constellation of Mensa. This star has a high proper motion.

Why does Pi Mensae 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 Pi Mensae?

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 Pi Mensae.