astronomy

WASP-15b

WASP-15b 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-15b rather than just read about it. In short: WASP-15b, formally named Asye, is an extrasolar planet discovered in 2008 by the SuperWASP collaboration, which seeks to discover exoplanets that transit their host stars. The planet orbits its host star at a distance of 0.05 AU every four days.

Key takeaways

WASP-15b 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-15b to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of WASP-15b from memory before moving on to harder problems.

Reference excerpt

WASP-15b, formally named Asye, is an extrasolar planet discovered in 2008 by the SuperWASP collaboration, which seeks to discover exoplanets that transit their host stars. The planet orbits its host star at a distance of 0.05 AU every four days. The mass of this planet is about one half that of Jupiter, but its radius is nearly 50% larger than Jupiter's, making the density of this planet only one quarter that of water; it is thought that some other form of heating must explain its extremely low density. WASP-15b's discovery was published on April 29, 2009.

Discovery WASP-15 was first observed by the WASP-South branch of the SuperWASP project, which operates from the South African Astronomical Observatory, between May 4, 2006, and July 17, 2006. It was later observed by WASP-South from January 31, 2007, to July 17, 2007, and from January 31, 2008, to May 29, 2008. Further analysis taken from 24,943 collected data points revealed eleven full or partial transits. Follow-up observations were conducted by a European and American science team at the 1.2 m Leonhard Euler Telescope at La Silla Observatory in Chile, which further raised the possibility of the existence of a planet in WASP-15's orbit; use of the CORALIE spectrograph on the Euler Telescope between March 6, 2008, and July 17, 2008, revealed that the variations in radial velocity measurements were not because of an eclipsing binary star system. CORALIE and the High Resolution Echelle Spectrometer (HIRES) revealed the spectrum of WASP-15, which was used to derive the star's characteristics. The science team studying WASP-15 found that, after running best-fit models, WASP-15's radial velocity and transit shifts were most likely due to the existence of a planet. WASP-15's planet, WASP-15b, had one of the lowest densities known amongst extrasolar planets when it was discovered. Its discovery paper was published by the American Astronomical Society on April 29, 2009, in the Astronomical Journal.

Host star

WASP-15 is an F-type star located in the Centaurus constellation. It is located approximately 290 parsecs (900 light years) from Earth and has an apparent magnitude of 10.9, making it invisible to the unaided eye. The star is 1.18 times more massive than the Sun, and has a radius that is 1.477 times larger than that of the Sun, making it more diffuse. WASP-15 has an effective temperature of 6300 K, and is thus hotter than the Sun, although at 3.9 billion years, it is also younger. WASP-15 has a metallicity of [Fe/H] of -0.17, which means that it has 68% of the iron found in the Sun.

Characteristics WASP-15b has a mass of 0.542 times Jupiter's mass and a radius that is 1.428 times Jupiter's radius. Due in part to its proximity to its host star, a distance of 0.0499 AU (7,500,000 km), WASP-15b is greatly inflated, with a density of 0.247 g/cm3. Another factor, such as an internal heat source, is suspected to add to this extremely high radius and extremely low density. WASP-15b orbits its host star every 3.7520656 days. It also has an orbital inclination of 85.5º, making it almost edge-on as seen from the Earth's perspective. The study in 2012, utilizing a Rossiter–McLaughlin effect, have determined the planetary orbit is strongly misaligned with the equatorial plane of the star, misalignment equal to -139.6+4.3−5.2°. This spin-orbit angle makes the orbit of WASP-15b retrograde.

Naming In 2019 the IAU announced as part of NameExoWorlds that WASP-15 and its planet WASP-15b would be given official names chosen by school children from The Ivory Coast.

Illustrations

Worked examples

Example 1 — a first encounter with WASP-15b

Start with the simplest possible case. Write down what WASP-15b 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-15b 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-15b 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-15b

In research: WASP-15b 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-15b 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-15b is common in secondary-school and first-year university syllabi. It links to neighbouring topics Centaurus, Exoplanets discovered by WASP, Exoplanets discovered in 2009, so understanding it makes those chapters shorter.
In everyday life: Look for WASP-15b 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-15b in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what WASP-15b 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-15b out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is WASP-15b in simple terms?

Why does WASP-15b 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-15b?

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-15b.