Podcast
Questions and Answers
What is an extrasolar planet?
What is an extrasolar planet?
A planet that orbits a star that is not our own Sun.
The first confirmed detections of extrasolar planets occurred in __________.
The first confirmed detections of extrasolar planets occurred in __________.
the 1990's
What do the astrometric, Doppler, and transit methods share in common?
What do the astrometric, Doppler, and transit methods share in common?
They all search for planets by measuring properties of a star rather than of the planets themselves.
The astrometric method looks for planets with careful measurements of a star's __________.
The astrometric method looks for planets with careful measurements of a star's __________.
In essence, the Kepler mission searched for extrasolar planets by __________.
In essence, the Kepler mission searched for extrasolar planets by __________.
Can we determine orbital distances for extrasolar planets using the astrometric, Doppler, or transit methods?
Can we determine orbital distances for extrasolar planets using the astrometric, Doppler, or transit methods?
Why do we say that the Doppler method gives a planet's 'minimum mass'?
Why do we say that the Doppler method gives a planet's 'minimum mass'?
Which of the following statements is not true about the planets so far discovered around other stars?
Which of the following statements is not true about the planets so far discovered around other stars?
What do we mean by a 'hot Jupiter'?
What do we mean by a 'hot Jupiter'?
Overall, what do current data suggest about planetary types in other planetary systems?
Overall, what do current data suggest about planetary types in other planetary systems?
Based on current data, about what fraction of stars have one or more planets?
Based on current data, about what fraction of stars have one or more planets?
Which new idea has been added into our theory of solar system formation as a result of the discoveries of extrasolar planets?
Which new idea has been added into our theory of solar system formation as a result of the discoveries of extrasolar planets?
Which of the following might explain the lack of 'water worlds'—small planets made mostly of water or other hydrogen compounds—in our own solar system?
Which of the following might explain the lack of 'water worlds'—small planets made mostly of water or other hydrogen compounds—in our own solar system?
How is the GAIA mission relevant to the search for extrasolar planets?
How is the GAIA mission relevant to the search for extrasolar planets?
From the viewpoint of an alien astronomer, how does Jupiter affect observations of our Sun?
From the viewpoint of an alien astronomer, how does Jupiter affect observations of our Sun?
Suppose you are using the Doppler method to look for planets around another star. What must you do?
Suppose you are using the Doppler method to look for planets around another star. What must you do?
In general, which type of planet would you expect to cause the largest Doppler shift in the spectrum of its star?
In general, which type of planet would you expect to cause the largest Doppler shift in the spectrum of its star?
Suppose a planet is discovered by the Doppler method and is then discovered to have transits. In that case, we can determine all the following about the planet except __________.
Suppose a planet is discovered by the Doppler method and is then discovered to have transits. In that case, we can determine all the following about the planet except __________.
The transit method allows us in principle to find planets around __________.
The transit method allows us in principle to find planets around __________.
You observe a star very similar to our own Sun in size and mass. This star moves very slightly back and forth in the sky once every 4 months, and you attribute this motion to the effect of an orbiting planet. What can you conclude about the orbiting planet?
You observe a star very similar to our own Sun in size and mass. This star moves very slightly back and forth in the sky once every 4 months, and you attribute this motion to the effect of an orbiting planet. What can you conclude about the orbiting planet?
Which of the following will allow you to learn something about a transiting planet's atmospheric composition?
Which of the following will allow you to learn something about a transiting planet's atmospheric composition?
Very few of the known extrasolar planets have sizes as small as Earth. The most likely reason for this fact is that __________.
Very few of the known extrasolar planets have sizes as small as Earth. The most likely reason for this fact is that __________.
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Study Notes
Extrasolar Planets
- Extrasolar planets orbit stars beyond our Sun.
- First confirmed detections occurred in the 1990s, with a significant discovery around 51 Pegasi in 1995.
Planet Detection Methods
- Astrometric, Doppler, and transit methods measure stellar properties rather than the planets themselves.
- The astrometric method analyzes a star's position in the sky for the presence of orbiting planets.
- Kepler mission identified extrasolar planets by monitoring stars for dimming caused by passing planets.
- All three methods provide orbital period information, allowing calculation of a planet's distance using Kepler's third law.
Mass and Size of Extrasolar Planets
- The Doppler method provides a planet's "minimum mass," as the detected Doppler shift is influenced by the orbital tilt.
- Hot Jupiters are large planets located very close to their stars.
- Current data indicates a broader range of planetary types compared to those in our solar system.
Frequency and Formation of Planets
- Approximately 70% of stars are estimated to have one or more planets, confirming the commonality of planetary systems.
- Discoveries have led to the idea that Jovian planets can migrate from their original orbits during formation.
Characteristics of Extrasolar Planets
- The absence of "water worlds" in our solar system may be due to the solar wind’s late clearing of gas.
- GAIA mission will potentially discover thousands of planets using the astrometric method.
Observational Effects
- Jupiter causes our Sun to move in a small ellipse with a 12-year orbital period, impacting perceptions from alien astronomers.
- The Doppler method requires comparing numerous spectra over extended periods to identify planets.
Observing Transiting Planets
- A massive, close planet to its star will produce the largest Doppler shift in its star's spectrum.
- Detecting a planet via the Doppler method and later discovering transits does not provide information about the planet's rotation period.
- The transit method is applicable to a limited fraction of stars that host planets.
Orbital Conclusions
- A star moving slightly every four months suggests an orbiting planet is closer than Earth is to the Sun.
- Analyzing spectra before and during a planet’s transit can reveal its atmospheric composition.
Size of Known Extrasolar Planets
- Few discovered extrasolar planets match Earth's size, likely due to the difficulty of detecting smaller planets.
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