HW 41 Q's

In searching for signs of intelligence elsewhere in the universe, scientists begin with assumptions based on biological and chemical properties of Earth. They also examine how signals from Earth might appear to an observer in space. Select the statements that correctly describe what an extraterrestrial observer outside our Galaxy might see when viewing Earth.

- a pulsating radio signal that varies in intensity during each cycle - spectral evidence that NITROGEN and oxygen are the most abundant gases - natural emissions MINIMIZED in the 18-cm to 21-cm wavelength range called the "water hole"

The key factor in the Drake equation that determines whether humans will ever make contact with intelligent life in the universe is the average lifetime of technologically advanced societies. Assume that the life expectancy of advanced civilizations is generally low. Which of the following statements explain why it is unlikely that we will ever communicate with other civilizations?

All that apply: -The distance between advanced civilizations in light-years is GREATER than their lifetimes in years -There are too FEW advanced civilizations in the galaxy

The last few factors in the Drake equation cannot be scientifically evaluated using current technologies. Astronomers can only estimate their values from either a pessimistic or an optimistic point of view. Choose the statements from the list below that indicate a high probability (optimistic estimate) that life exists elsewhere in the universe.

All that apply: -Chemical reactions leading to complex molecules are COMMON -Planets with conditions that remain stable over long periods of time are COMMON -Environments suitable for the creation of organic molecules are COMMON

The third factor of the Drake equation is an estimate of the number of habitable planets each planetary system might contain. Two key parameters that need to be considered when determining a planet's ability to sustain life are the planet's distance from its parent star, which determines whether the planet is in the stellar habitable zone, and the parent star's distance from the galactic center, which determines if the star is in the galactic habitable zone. Consider the following sets of conditions, and sort each set according to whether it has a high or low probability of supporting life.

High probability of life: -planet and star in habitable zone. Low probability of life: -planet in habitable zone, star is not. -star in habitable zone, planet is not. -planet and star not in habitable zone.

Currently, astronomers are observing the universe across many different regions of the electromagnetic spectrum, from gamma rays to radio waves. One of the primary issues when considering communication with potential life outside our planet is how an extraterrestrial signal would be distinguished from natural radiation sources. Sort the following source properties by whether they might be considered as originating from intelligence or simply be natural phenomena.

Probably Cosmic: -constant, unchanging signal -random radio fluctuations -single strong visible light burst that fades away over months -identical repetitive pulses Possibly Extraterrestrial: -sequence of pulses varying over time

Consider the planet that causes the stellar motion shown in Plot 2 (be sure you have clicked the "Plot 2" button in the lower window of the animation). What can be said about a different planet orbiting the same star with an orbital period of 500 days?

The planet must be closer to the star.

As an artificial radio source, the spinning Earth would have a period of about a day.

True

As yet, no human probe has left our solar system and approached another star.

True

The Allen Telescope Array is one of the many radio searches for extraterrestrial life.

True

If we communicated with a civilization from another star, how long would a conversation with them take?

Years

Each factor within the Drake equation can be estimated individually. However, some factors are largely grounded in astronomical data, while others are based on speculation of how life evolved on the Earth. Identify which factors in the Drake equation are estimated from astronomical observations and which are based on speculation.

astronomical data: -Fraction of stars having planetary systems. -Rate of star formation, averaged over the lifetime of the galaxy. -Average number of habitable planets within planetary systems. speculation: -Fraction of those habitable planets on which life arises. -Fraction of those intelligent-life planets that develop a technological society. -Average lifetime of a technologically competent civilization. -Fraction of life-bearing planets on which intelligence evolves.

Most SETI searches are done at

radio wavelengths.

Which of the following properties can be inferred from the star's orbital period?

the planet's orbital radius

Is it possible to determine the planet's mass from the star's velocity curve?

yes, by measuring both the stars orbital period and its change in velocity over the orbit