astronomy

TOI-2180 b

TOI-2180 b 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 TOI-2180 b rather than just read about it. In short: TOI-2180 b is a giant exoplanet orbiting the G-type star TOI-2180, also known as HD 238894. It was discovered with the help of the Transiting Exoplanet Survey Satellite and is currently the exoplanet with the longest orbital period TESS was able to uncover (as of September 2022).

Key takeaways

TOI-2180 b belongs to astronomy; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect TOI-2180 b to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of TOI-2180 b from memory before moving on to harder problems.

Reference excerpt

TOI-2180 b is a giant exoplanet orbiting the G-type star TOI-2180, also known as HD 238894. It was discovered with the help of the Transiting Exoplanet Survey Satellite and is currently the exoplanet with the longest orbital period TESS was able to uncover (as of September 2022). TOI-2180 b orbits its host star every 260.16 days.

Discovery TOI-2180 b was first identified as an exoplanet candidate due to a single transit with TESS at 12./13. December 2019 by a group of citizen scientists called the Visual Survey Group, which includes Thomas Lee Jacobs, a former U.S. naval officer. The group was using the light curve processing tool lcTools. In May 2020 the Planet Hunters: TESS collaboration announced this object as a Community TESS Object of Interest (CTOI) and it was soon promoted into a regular TOI. The TESS-Keck Survey collaboration performed radial velocity follow-up observations for nearly 2 years with the Automated Planet Finder and Keck I. The follow-up observations uncovered that the single transit was caused by a long-period planet.

Orbital properties TOI-2180 b has a long orbital period of 260.16 days, which also leads to a long transit duration of 24 hours. The distance to the host star is 82.8% the sun-earth distance. The planet does not orbit inside the habitable zone, despite this close resemblance in semi-major axis. TOI-2180 b has a high eccentricity of the orbit at 0.37. The second transit was not detected from the ground and the third transit was not observed. The fourth transit was observed at 31. January/01. February 2022, refining the orbital period. The next transit will occur on 2022 October 18 at 21:28 UTC.

Physical properties The planet has the same size as Jupiter, but is 2.8 times heavier than Jupiter. TOI-2180 b stand out because of its cold estimated temperature of about 348 Kelvin (74.9 °C, 166.7 °F). This is closer to Jupiters 165 K than most discovered giant exoplanets. TOI-2180 b belongs to a small sample of temperate Jupiters with a temperature <400 K that transit, such as Kepler-167 e, WD 1856+534 b, Kepler-1704 b, KOI-3680 b, Kepler-1514 b and Kepler-539 b. TOI-2180 b has by far the brightest host star with a visual magnitude of 9.16, which is about 3 magnitudes brighter than the next brightest system in this sample. The planet is likely enriched in metals compared to its host star. The discovery team inferred that TOI-2180 b is enriched in metals by a factor of about 5 compared to its host star. This means it has about 100 M🜨 of heavy elements in its envelope and interior.

Future observations The exoplanet is a poor target for transmission spectroscopy because of its high surface gravity and the large radius of the host star. The large radius of the star causes a relative shallow transit depth of about 0.5%. The system is still an excellent target to find rings and exomoons around TOI-2180 b. It is also a good target to study the migration of exoplanets. It could be one of the best targets for exomoon searches.

Host star The host star is a 9.16 magnitude bright and slightly evolved star with a spectral type of G5. It has a mass of 1.1 M☉ and a radius of 1.6 R☉. The radius is increased due to the evolved nature of the star. The star is 116 parsec (379 light-years) distant from earth and has an age of about 8.1 billion years.

Habitable Zone Currently the habitable zone around TOI-2180 is between 1.5 and 2.2 astronomical units. Because TOI-2180 is slightly evolved, it had a habitable zone closer to the star in the past. At an age of about 3 billion years the habitable zone was located between 1.1 and 1.6 astronomical units.

Outer planet candidate The radial velocity monitoring also showed acceleration of TOI-2180 b due to an outer planet or low-mass star in the system. A later analysis of RV data has shown that an outer companion has an orbital period of 1558+68−19 days, an eccentricity of about 0.31 and a minimum mass of 3.94+0.27−0.22 MJ, making it likely a giant planet. The acceleration (TTV) and the outer companion detected in the RV could be the same object.

Notes

References

Illustrations

Worked examples

Example 1 — a first encounter with TOI-2180 b

Start with the simplest possible case. Write down what TOI-2180 b 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 TOI-2180 b 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 TOI-2180 b 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 TOI-2180 b

In research: TOI-2180 b 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 TOI-2180 b 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: TOI-2180 b is common in secondary-school and first-year university syllabi. It links to neighbouring topics Exoplanets detected by radial velocity, Exoplanets discovered by Planet Hunters, Exoplanets discovered by TESS, so understanding it makes those chapters shorter.
In everyday life: Look for TOI-2180 b 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 TOI-2180 b in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what TOI-2180 b 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 TOI-2180 b out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is TOI-2180 b in simple terms?

Why does TOI-2180 b 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 TOI-2180 b?

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 TOI-2180 b.