Fig. 1 shows a simple transit observation. A distant star produces a steady light signal. A planet passes in front of the star once every 3.0 days, causing ...
Question 1 Report
Fig. 1 shows a simple transit observation. A distant star produces a steady light signal. A planet passes in front of the star once every 3.0 days, causing a small fall in the light received by a space telescope. The telescope circuit records the signal as a repeating dip. The planet cannot be seen directly because the star is much brighter.
(a) What causes each dip in the light signal? [1]
(b) Calculate the number of transits expected in 30 days. [2]
(c) Describe why a larger planet produces a deeper dip in the received light. [2]
(d) Explain why this method is useful for finding planets orbiting distant stars. [3]
(e) Give two measurements, other than light level, that astronomers could use to investigate an orbiting planet. [2]
Answer Details
(a) Each dip occurs when the planet passes in front of the star and blocks some of its light [1]. This is called a transit.
(b) The planet transits once every 3.0 days:
\[\frac{30\text{ days}}{3.0\text{ days per transit}}=10\]
So there are 10 transits [2].
(c) A larger planet covers a larger area of the star [1]. It therefore blocks more light and causes a greater reduction in received light intensity [1].
(d) Planets emit very little visible light [1], and are difficult to see beside a much brighter star [1]. However, repeated dips provide evidence that an object is orbiting the star and allow its orbital period to be found [1].
(e) Two acceptable measurements are the star’s radial velocity and the wavelength shift of the star’s light [2]. Transit duration, planet mass and planet radius are also accepted.
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