HAT-P-7b

Key takeaways

HAT-P-7b belongs to astronomy; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect HAT-P-7b to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of HAT-P-7b from memory before moving on to harder problems.

Reference excerpt

HAT-P-7b (or Kepler-2b) is an extrasolar planet discovered in 2008. It orbits very close to its host star and is larger than Jupiter. Due to the extreme heat that it receives from its star, the dayside temperature is predicted to be 2,630–2,880 K (2,360–2,610 °C; 4,270–4,720 °F), while nightside temperatures are 2,211–2,238 K (1,938–1,965 °C; 3,520–3,569 °F). HAT-P-7b is also one of the darkest planets ever observed, with an albedo of less than 0.03—meaning it absorbs more than 97% of the visible light that strikes it.

Discovery The HATNet Project telescopes HAT-7, located at the Smithsonian Astrophysical Observatory's Fred Lawrence Whipple Observatory in Arizona, and HAT-8, installed on the rooftop of Smithsonian Astrophysical Observatory's Submillimeter Array building atop Mauna Kea, Hawaii, observed 33,000 stars in HATNet field G154, on nearly every night from late May to early August 2004. The light curves resulting from the 5,140 exposures obtained were searched for transit signals and a very significant periodic drop in brightness was detected in the star GSC 03547–01402 (HAT-P-7), with a depth of approximately 7.0 millimagnitude, a period of 2.2047 days, and a duration of 4.1 hours. Fortunately HAT-P-7 was located in the overlapping area between fields G154 and G155 allowing the transit to be independently confirmed by the HAT-6 (Arizona) and HAT-9 (Hawaii) telescopes which observed the neighboring field G155. Field G155 was observed from late July 2004 to late September 2005 gathering an additional 11,480 exposures for a total of 16,620 data points.

History The GSC 03547-01402 system was within the initial field of view of the Kepler Mission spacecraft, which confirmed the transit and orbital properties of the planet with significantly improved confidence and observed occultation and light curve characteristics consistent with a strongly absorbing atmosphere with limited advection to the night side. In testing itself on HAT-P-7b, Kepler proved it was sensitive enough to detect Earth-like exoplanets. On July 4, 2011, HAT-P-7b was the subject of the Hubble Space Telescope's one millionth scientific observation.

Characteristics

In August 2009, it was announced that HAT-P-7b may have a retrograde orbit, based upon measurements of the Rossiter–McLaughlin effect. This announcement came only a day after the announcement of the first planet discovered with such an orbit, WASP-17b. A study in 2012, utilizing the Rossiter–McLaughlin effect, determined the planetary orbit inclination with respect to the rotational axis of the star, equal to 155±37°. It is believed HAT-P-7b origined in a much wider orbit around its host star (around 3 AU) but was doomed to its current close and retograde orbit due to gravitational interactions with HAT-P-7 C, a red dwarf which orbits HAT-P-7 A at an orbital separation of 32 astronomical units in a highly eccentric orbit. HAT-P-7 A also has a wider companion, HAT-P-7 B, at a separation of 700 AU. This outer star may have started a Kozai mechanism by exciting the eccentricity of the inner companion, which on its turn excited the eccentricity of the primordial planet, until tidal forces circularized the planet's orbit and HAT-P-7b migrated to its current position. In January 2010, it was announced that ellipsoidal light variations were detected for HAT-P-7b, the first detection of such kind. This method analyses the brightness variation caused by the rotation of a star as its shape is tidally distorted by the planet.

Weather In December 2016, a letter published in Nature Astronomy by Dr. David Armstrong and his colleagues described evidence of strong wind jets of variable speed on HAT-P-7b. High variation in wind speed would explain similar variations in light reflected from HAT-P-7b's atmosphere. In particular, the brightest point on the planet shifts its phase or position on a timescale of only tens to hundreds of days, suggesting high variation in global wind speeds and cloud coverage. Condensation models of HAT-P-7b predict precipitation of Al2O3 (corundum) on the night side of the planet's atmosphere. The clouds themselves are likely made up of corundum, the mineral which forms rubies and sapphires.

Illustrations

Worked examples

Example 1 — a first encounter with HAT-P-7b

Start with the simplest possible case. Write down what HAT-P-7b 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 HAT-P-7b 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 HAT-P-7b 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 HAT-P-7b

In research: HAT-P-7b 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 HAT-P-7b 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: HAT-P-7b is common in secondary-school and first-year university syllabi. It links to neighbouring topics Cygnus (constellation), Exoplanets discovered by HATNet, Exoplanets discovered in 2008, so understanding it makes those chapters shorter.
In everyday life: Look for HAT-P-7b 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.

How to study HAT-P-7b in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what HAT-P-7b 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 HAT-P-7b out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is HAT-P-7b in simple terms?

HAT-P-7b (or Kepler-2b) is an extrasolar planet discovered in 2008. It orbits very close to its host star and is larger than Jupiter.

Why does HAT-P-7b 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 HAT-P-7b?

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 HAT-P-7b.