astronomy

WASP-18b

WASP-18b 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 WASP-18b rather than just read about it. In short: WASP-18b is an exoplanet that is notable for having an orbital period of less than one day. It has a mass equal to 10 Jupiter masses, just below the boundary line between planets and brown dwarfs (about 13 Jupiter masses).

Key takeaways

WASP-18b belongs to astronomy; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect WASP-18b to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of WASP-18b from memory before moving on to harder problems.

Reference excerpt

WASP-18b is an exoplanet that is notable for having an orbital period of less than one day. It has a mass equal to 10 Jupiter masses, just below the boundary line between planets and brown dwarfs (about 13 Jupiter masses). Due to tidal deceleration, it is expected to spiral toward and eventually merge with its host star, WASP-18, in less than a million years. The planet is approximately 3.1 million km (1.9 million mi; 0.021 AU) from its star, which is about 400 light-years (120 parsecs) from Earth. A team led by Coel Hellier, a professor of astrophysics at Keele University in England, discovered the exoplanet in 2009. Scientists at Keele and at the University of Maryland are working to understand whether the discovery of this planet so shortly before its expected demise (with less than 0.1% of its lifetime remaining) was fortuitous, or whether tidal dissipation by WASP-18 is actually much less efficient than astrophysicists typically assume. Observations made over the next decade should yield a measurement of the rate at which WASP-18b's orbit is decaying. The closest example of a similar situation in the Solar System is Mars' moon Phobos. Phobos orbits Mars at a distance of only about 9,000 km (5,600 mi), 40 times closer than the Moon is to the Earth and is expected to be destroyed in about eleven million years. A study in 2012, utilizing the Rossiter–McLaughlin effect, determined that the planetary orbit is well aligned with the equatorial plane of the star, with a misalignment equal to 13±7°.

Temperature The planet's dayside temperature, as measured in 2020, is 3,029 ± 50 K (2,755.8 ± 50.0 °C; 4,992.5 ± 90.0 °F). A 2023 study found an average dayside temperature of 2,781+25−13 K (2,508 °C; 4,546 °F). It has been theorized that highly irradiated ultra-hot Jupiters like WASP-18b have large variations in atmospheric temperature and chemistry as a function of longitude, latitude and altitude. WASP-18b was observed with the Near Infrared Imager and Slitless Spectrograph instruments on JWST creating a resolved atmosphere in multiple dimensions. Mapping confirmed theoretical models revealing a weaker longitudinal temperature gradient. It also indicated the importance of hydrogen dissociation and/or nightside clouds role in shaping thermal emission on the global scale.

Atmosphere A 2017 study detected carbon monoxide in the planet's atmosphere, without signs of water vapor. However, in 2023, the James Webb Space Telescope detected water vapor in the planet's atmosphere. There are two thermally distinct identified regions on the planets atmosphere. The first is the “hotspot” surrounding the substellar point. near the dayside limbs. The hotspot region shows a strongly inverted thermal structure due to the presence of optical absorbers and a water abundance marginally lower than average. The second region is a “ring” near the dayside limb. This region shows colder temperatures and poorly constrained chemical abundances.

Illustrations

Worked examples

Example 1 — a first encounter with WASP-18b

Start with the simplest possible case. Write down what WASP-18b 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 WASP-18b 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 WASP-18b 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 WASP-18b

In research: WASP-18b 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 WASP-18b 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: WASP-18b is common in secondary-school and first-year university syllabi. It links to neighbouring topics Exoplanets discovered by WASP, Exoplanets discovered in 2009, Giant planets, so understanding it makes those chapters shorter.
In everyday life: Look for WASP-18b 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 WASP-18b in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what WASP-18b 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 WASP-18b out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is WASP-18b in simple terms?

Why does WASP-18b 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 WASP-18b?

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 WASP-18b.