Question 8.1

Why are extreme life-forms on Earth, such as those shown in the photograph that opens this chapter, of interest to astrobiologists?

Question 8.2

What is meant by “life as we know it”? Why do astrobiologists suspect that extraterrestrial life is likely to be of this form?

Question 8.3

How have astronomers discovered organic molecules in interstellar space? Does this discovery mean that life of some sort exists in the space between the stars?

Question 8.4

Mercury and Venus are both considered unlikely places to find life. Suggest why this should be.

Question 8.5

Many science-fiction stories and movies—including The War of the Worlds, Invaders from Mars, Mars Attacks!, and Martians, Go Home—involve invasions of Earth by intelligent beings from Mars. Why Mars rather than any of the other planets?

Question 8.6

Describe how the Viking Landers looked for evidence of life on Mars.

Question 8.7

Explain which variable in the Drake equation is the most difficult to estimate and suggest why this would be.

Question 8.8

Suppose someone brought you a rock that he claimed was a Martian meteorite. What scientific tests would you recommend be done to test this claim?

Question 8.9

Why are most searches for extraterrestrial intelligence made using radio telescopes? Why are most of these carried out at frequencies between 10³ MHz and 10⁴ MHz?

Question 8.10

Explain why planet-hunting infrared telescopes need to be placed in space.

Question 8.1

Suppose someone told you that the Viking Landers failed to detect life on Mars simply because the tests were designed to detect terrestrial life-forms, not Martian life-forms. How would you respond?

Question 8.2

Science-fiction television shows and movies often depict aliens as looking very much like humans. Discuss the likelihood that intelligent creatures from another world would have (a) a biochemistry similar to our own, (b) two legs and two arms, and (c) about the same dimensions as a human.

Question 8.3

The late, great science-fiction editor John W. Campbell exhorted his authors to write stories about organisms that think as well as humans but not like humans. Discuss the possibility that an intelligent being from another world might be so alien in its thought processes that we could not communicate with it.

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Question 8.4

If a planet always kept the same face toward its star, just as the Moon always keeps the same face toward Earth, most of the planet’s surface would be uninhabitable. Discuss why.

Question 8.5

How do you think our society would respond to the discovery of intelligent messages coming from a civilization on a planet orbiting another star? Explain your reasoning.

Question 8.6

What do you think will set the limit on the lifetime of our technological civilization? Explain your reasoning.

Question 8.7

The first of all Earth spacecraft to venture into interstellar space were Pioneer 10 and Pioneer 11, which were launched in 1972 and 1973, respectively. Their missions took them past Jupiter and Saturn and eventually beyond the solar system. Both spacecraft carry a metal plaque with artwork (reproduced below) that shows where the spacecraft is from and what sort of creatures designed it. If an alien civilization were someday to find one of these spacecraft, which of the features on the plaque do you think would be easily understandable to them? Explain.

Question 8.1

Any living creatures in the subsurface ocean of Europa would have to survive without sunlight. Instead, they might obtain energy from Europa’s inner heat. Search the Internet for information about “black smokers,” which are associated with high-temperature vents at the bottom of Earth’s oceans. What kind of life is found around black smokers? How do these life-forms differ from the more familiar organisms found in the upper levels of the ocean?

Question 8.2

Like other popular media, the Internet is full of claims of the existence of “extraterrestrial intelligence,” namely, UFO sightings and alien abductions. (a) Choose a Web site of this kind and analyze its content using the idea of Occam’s razor, the principle that if there is more than one viable explanation for a phenomenon, one should choose the simplest explanation that fits all the observed facts. (b) Read what a skeptical Web site has to say about UFO sightings. A good example is the Web site of the Committee for the Scientific Investigation of Claims of the Paranormal, or CSICOP. After considering what you have read on both sides of the UFO debate, discuss your opinions about whether aliens really have landed on Earth.

Question 8.3

Imagine that astronomers have discovered intelligent life in a nearby star system. Your group is submitting a proposal for who on Earth should speak for the planet and what 50-word message should be conveyed. Prepare a maximum one-page proposal that states (a) who should speak for Earth and why; (b) what this person should say in 50 words; and (c) why this message is the most important compared to other things that could be said.

Question 8.1

Use Starry Night™ to examine the planet Mars. Select Favourites > Explorations > Mars. Zoom in or out on Mars and use the location scroller to examine the planet’s surface. Based on what you observe, where on the Martian surface would you choose to land a spacecraft to search for the presence of life? Explain the reasons for your choice.

Question 8.2

Use the Starry Night™ program to examine Jupiter’s moon Europa. Select Favourites > Explorations > Europa to view this enigmatic moon of our largest planet. Use the location scroller and Zoom controls to examine the surface of this moon. Are there any surface features that suggest that this moon might harbor life? Is there any other evidence, perhaps not visible in this simulation, which suggests the possibility that life exists there?

Question 8.3

Use Starry Night™ to investigate the likelihood of the existence of life in the universe beyond that found on Earth. Select Favourites > Explorations > Atlas and then open the Options pane. Expand the Stars layer and the Stars heading and click the checkbox to turn on the Mark stars with extrasolar planets option. Then use the hand tool or cursor keys to look around the sky. Each marked star in this view has at least one planet orbiting around it. Click and hold the Increase current elevation button in the toolbar until the viewpoint is about 1000 light-years from Earth. Note that the stars with extrasolar planets are contained in a small knot of stars in the region of our Sun, our solar neighborhood. This is because present techniques place a limit upon the distance to which we can find extrasolar planets in space. There is no logical reason why the same proportion of stars in the rest of the Milky Way, or indeed the rest of the universe, should not have companion planets. Increase current elevation again to about 90,000 light-years from Earth to see a view of the Milky Way Galaxy. Use the location scroller to view the Milky Way face-on and compare the clump of stars representing the solar neighborhood to the size of the Milky Way Galaxy. Click the Increase current elevation button again until the Viewing Location panel indicates a distance to Earth of about 0.300 Mly (300,000 light-years). In this view, each point of light represents a separate galaxy containing hundreds of billions of stars. Now, gradually Increase current elevation to about 1500 Mly (1.5 billion light-years from Earth) to see the entire database of 28,000 galaxies included in the Starry Night™ data bank. The borders of this cube of galaxies reaching out to about 500 million light-years from Earth represent less than 5% of the size of the observable universe and galaxies beyond the limits of this view. To view images of some of these very distant galaxies, open the view named Hubble Deep Field from the Explorations folder in the Favourites pane. This view from the center of Earth is centered upon a seemingly empty patch of sky. Zoom in to see this image of more than 1500 very distant galaxies that were found by the Hubble Space Telescope in a small region of our sky. Then open the view named Hubble Ultra Deep Field and Zoom in on an image of over 10,000 galaxies that extends to the limits of our observable universe. (a) Do these views influence your thoughts on the likelihood that life, including intelligent life, might exist elsewhere in the universe other than Earth? Explain your reasoning using the Drake equation as a guide. (b) Why is it unlikely that we will be able to communicate with life-forms that might exist on planets in these very distant regions of space?

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