astronomy

HIP 65Ab

HIP 65Ab 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 HIP 65Ab rather than just read about it. In short: HIP 65Ab (TOI-129 b) is a hot Jupiter discovered in 2020 orbiting the K-type main-sequence star HIP 65A, located approximately 202 light-years (62 parsecs) distant in the southern constellation of Phoenix. It completes one orbit around its host star every 23.5 hours (0.98 days), making it an ultra-short period planet.

Key takeaways

HIP 65Ab belongs to astronomy; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect HIP 65Ab to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of HIP 65Ab from memory before moving on to harder problems.

Reference excerpt

HIP 65Ab (TOI-129 b) is a hot Jupiter discovered in 2020 orbiting the K-type main-sequence star HIP 65A, located approximately 202 light-years (62 parsecs) distant in the southern constellation of Phoenix. It completes one orbit around its host star every 23.5 hours (0.98 days), making it an ultra-short period planet. Its radius is likely smaller than 1.5 RJ—another estimate of 2.03+0.61−0.49 RJ is likely an overestimate. Due to the planet's vicinity to the star, tidal interactions are slowly causing its orbit to decay. As such, the planet is expected to spiral into HIP 65A and be destroyed by its Roche limit within somewhere between 80 million years and a few billion years.

Physical properties HIP 65Ab is a massive super-Jupiter with a mass of about 3 MJ. Its unusually large radius of roughly 2 RJ is likely overestimated, caused by the grazing nature of its transit, that is to say the planet only partially transits the disc of the host star. This is also why the radius has such a large margin of error. It orbits extremely close to its star at a distance of 0.01782 AU (2,666,000 km), or about twice the radius of the Sun. As a result, the planet receives 661 times the flux Earth does, placing its equilibrium temperature at 1,411 K (1,138 °C; 2,080 °F), just above the melting point of copper. Based on the planet's mass and temperature, HIP 65Ab is unlikely to be larger than 1.5 RJ. A 2024 study agrees with this, stating that the planet's true radius is close to the presented lower limit. The characteristics of the massive planet and its 23.5-hour orbit make it a prime target for accurate atmospheric observations. Its atmosphere was analysed spectroscopically for the first time in 2024, revealing absorption lines of water and carbon monoxide. Both molecules, however, are less abundant than they would be if the planet had a Sun-like composition. The results are consistent with the planet having a sub-solar metallicity but an overabundance of carbon and oxygen. This implies the planet may have formed beyond the snow line and migrated inward after the protoplanetary disk dissipated, or alternatively that some of the oxygen has precipitated out of the atmosphere.

Host star HIP 65A is a K-type main-sequence star with the spectral type K4V, which corresponds to its effective temperature of 4590±49 K (4,320 °C; 7,800 °F). This, combined with a radius of 0.7242 R☉, means that it radiates around 21% of the luminosity of the Sun from its photosphere. The star has a mass of 0.74 M☉, a rotation period of 13.2 days, and an age of 4.1+4.3−2.8 billion years. Despite its planet's low metallicity, the star itself is richer in heavy elements than the Sun with a metallicity of 0.18±0.08 dex. It is a planetary transit variable, dimming by about 8% each time the planet passes in front of the star. This large transit depth, along with the star's high X-ray luminosity of 3.97+0.81−0.72 erg/cm−2 s−1 make HIP 65A one of the best candidates for transit observations using X-ray telescopes. The star is part of a wide binary system with HIP 65B, an M-type red dwarf star which has a mass of 0.3 M☉ and an effective temperature of 3,861 K (3,588 °C; 6,490 °F). The two stars are separated by 3.95 arcseconds in the sky as seen from Earth, which corresponds to a distance of 269 AU.

References

Worked examples

Example 1 — a first encounter with HIP 65Ab

Start with the simplest possible case. Write down what HIP 65Ab 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 HIP 65Ab 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 HIP 65Ab 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 HIP 65Ab

In research: HIP 65Ab 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 HIP 65Ab 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: HIP 65Ab is common in secondary-school and first-year university syllabi. It links to neighbouring topics Exoplanets discovered in 2020, Giant planets, Hot Jupiters, so understanding it makes those chapters shorter.
In everyday life: Look for HIP 65Ab 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.

Affiliate

Preply — study more efficiently by working with a personal tutor. 50% off.

How to study HIP 65Ab in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what HIP 65Ab 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 HIP 65Ab out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is HIP 65Ab in simple terms?

Why does HIP 65Ab 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 HIP 65Ab?

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 HIP 65Ab.