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Chapter 8: Problem 25

What does it mean for a planet to transit a star? What can we learn from such events?

Short Answer

Expert verified
A planet transits a star when it passes across the star's face from the observer's viewpoint. This event causes a slight dip in the star's observed brightness. The length of the transit provides the estimated size of the planet. Repeated transits reveal the planet's orbit and distance from its star, and any changes in the star's light spectrum can show the composition of the planet's atmosphere. Thus, planetary transits provide key details about the size, orbit, and atmospheric composition of the planet, as well as overall planetary system dynamics.

Step by step solution

01

Understanding Planetary Transit

A planet transits a star when it passes across the face of that star, as seen from the observer's viewpoint. Essentially, it involves the movement of the planet coming between the observer and the star.\nThis can be compared to a solar eclipse on Earth, where the Moon (in this case, the 'transiting' body) comes between the Earth (the observer) and the Sun (the 'star'). However, given the vast cosmic distances, the 'eclipse' that a planet causes on its star is incredibly minute, often leading to just a small dip in the observed brightness of the star.
02

Transit Duration

The length of the transit or how long the star's light dims lets astronomers estimate the planet's size. The larger the planet, the longer it will take to cross the star's face.
03

Light Curve Analysis

The degree by which the star's light dims during the transit indicates the size of the planet in relation to the star. The greater the dip in light, the larger the planet. This light curve analysis allows astronomers to determine the radius of the exoplanet.
04

Repeated Transits

Observing regular transits by the same planet gives astronomers an accurate estimate of the planet's orbit and distance from its star. The time interval between transits gives the length of the planet's year, that is, how long it takes to orbit its star.
05

Atmosphere Analysis

If a planet has an atmosphere, the star's light will interact with the atmospheric gases, leaving measurable fingerprints in the star's spectra. This observation can tell astronomers what the planet's atmosphere is composed of.

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Most popular questions from this chapter

What is the radial velocity method used to detect planets orbiting other stars? Why is it difficult to use this method to detect planets like Earth?

Propose an explanation why the Jovian planets are orbited by terrestrial-like satellites.

(a) If the Earth had retained hydrogen and helium in the same proportion to the heavier elements that exist elsewhere in the universe, what would its mass be? Give your answer as a multiple of the Earth's actual mass. Explain your reasoning. (b) How does your answer to (a) compare with the mass of Jupiter, which is 318 Earth masses? (c) Based on your answer to (b), would you expect Jupiter's rocky core to be larger, smaller, or the same size as the Earth? Explain your reasoning.

Is there evidence that planets have fallen into their parent stars? Explain.

Why did the terrestrial planets form close to the Sun while the Jovian planets formed far from the Sun?
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