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Chapter 3: Problem 65

Planet Probabilities. Suppose that one in ten million stars is orbited by an Earth-like planet. If there are 100 billion stars in the Milky Way Galaxy, how many Earth-like planets are there in the galaxy? If there are 100 billion galaxies in the observable universe, how many Earth-like planets are there in the observable universe?

Short Answer

Expert verified
10,000 in the Milky Way and 1 quadrillion in the observable universe.

Step by step solution

01

Understanding the Given Probabilities

We are given that 1 in 10 million stars has an Earth-like planet. This means for every 10,000,000 stars, there is 1 Earth-like planet.
02

Calculate Earth-like Planets in the Milky Way

The Milky Way contains 100 billion (or 100,000,000,000) stars. To find how many Earth-like planets exist in the Milky Way, divide the number of stars by the number of stars needed per planet: \[ \frac{100,000,000,000}{10,000,000} = 10,000 \] Hence, there are 10,000 Earth-like planets in the Milky Way.
03

Calculate Earth-like Planets in the Observable Universe

There are 100 billion galaxies in the observable universe, each with approximately 10,000 Earth-like planets (as calculated for the Milky Way). So, multiply the number of galaxies by the Earth-like planets per galaxy: \[ 100,000,000,000 \times 10,000 = 1,000,000,000,000,000 \] Therefore, there are 1 quadrillion Earth-like planets in the observable universe.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Probability in Space Exploration
The concept of probability in space exploration fascinates scientists and space enthusiasts alike. Probability helps us quantify the likelihood of certain events occurring in space. When studying space, especially planets, probability can help predict how many Earth-like planets exist.

Let's take an example from our exercise. If one in every ten million stars has an Earth-like planet, we use probability to deduce how many such planets exist in a galaxy or even the universe. How? By understanding the total number of stars and applying the given probability ratio, we can make educated estimates about the population of Earth-like planets.
  • This method relies heavily on statistical data and known patterns.
  • Accurate estimates can guide future missions and research.
  • It also helps prioritize exploration targets, especially those with high potential for life.
Milky Way Galaxy
The Milky Way Galaxy is our cosmic neighborhood. A majestic spiral galaxy, it's home to our solar system, including Earth. The Milky Way contains around 100 billion stars. Within this sea of stars, there are stars of various sizes, ages, and stages of life.

When pondering the existence of Earth-like planets, the vast number of stars in the Milky Way provides a significant number of opportunities for such planets to form. As stated in the exercise, if one in 10 million stars harbors an Earth-like planet, with 100 billion stars in the Milky Way, that translates to about 10,000 such planets.
  • The composition and age of stars might affect planet formation.
  • The position of a star within the galaxy can influence the type of planets that might form.
  • The Milky Way serves as a perfect laboratory for studying planet formation and evolution.
Observable Universe
The observable universe is the part of the whole universe that we can see or observe from Earth, thanks to the finite speed of light. The massive scale of the observable universe is mind-boggling, containing an estimated 100 billion galaxies, each with potentially billions of stars.

By considering the number of stars and applying probability, we can estimate the number of Earth-like planets across the observable universe. If each of these 100 billion galaxies mirrors the Milky Way in terms of Earth-like planets, there could be an astounding one quadrillion Earth-like planets in the observable universe.
  • Understanding the observable universe helps contextualize our place in the cosmos.
  • This vastness also illustrates the challenges of space exploration, given the immense distances involved.
  • Yet, it also contributes to the excitement of discovering potential life-supporting planets.
Earth-like Planets
Earth-like planets are celestial bodies outside our solar system that share similar characteristics with Earth. These characteristics might include a rocky surface, the presence of liquid water, and a similar atmospheric composition that could theoretically support life.

In recent years, the discovery of exoplanets (planets beyond our solar system) has made the search for Earth-like planets a prime area of interest in astronomy. With many stars in the Milky Way and other galaxies, the potential number of Earth-like planets is enormous, as illustrated by the exercise calculations.
  • Scientists use data from telescopes and satellites to identify potential Earth-like planets.
  • Finding such planets involves analyzing light from stars and seeking minute changes that signal a planet passing by (transiting).
  • The search for Earth-like planets not only tests human ingenuity but also fuels hopes for finding extraterrestrial life.

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Most popular questions from this chapter

What do we mean by the observable universe? How big is it? Answer both in absolute terms (that is, a size in light-years) and by describing a way of putting its vast size into perspective.

Origin of Your Energy. Suppose you have just thrown a ball, and it is now in mid-flight so that it has energy of motion. Trace back the origin of that energy in as much detail as you can; for example, the ball got its energy from the throwing motion of your arm, but where did your arm get this energy? If possible, trace the energy all the way back to the Big Bang.

The Milky Way Galaxy is (a) another name for our solar system; (b) a small group of stars visible in our night sky; (c) a collection of more than 100 billion stars, of which our Sun is one.

The Changing Limitations of Science. In \(1835,\) French philosopher Auguste Comte stated that science would never allow us to learn the composition of stars. Although spectral lines had been seen in the Sun's spectrum by that time, not until the mid-nineteenth century (primarily through the work of Foucault and Kirchhoff) did scientists recognize that spectral lines give clear information about chemical composition. Why might our present knowledge have seemed unattainable in \(1835 ?\) Discuss how new discoveries can change the apparent limitations of science. Today, other questions seem beyond the reach of science, such as the question of why there was a Big Bang. Do you think such questions will ever be answerable through science? Defend your opinion.

Patterns of Motion. In one or two paragraphs, explain why the existence of orderly patterns of motion in our solar system should suggest that the Sun and the planets all formed at one time from one cloud of gas, rather than as individual objects at different times.
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