# Question: a In May 2008 the United States successfully landed a

(a) In May 2008, the United States successfully landed a spacecraft named Phoenix near the northern polar regions of Mars. Immediately upon landing, the craft sent a message indicating that all had gone well. Using the astronomical data in the appendix of this book, determine the shortest amount of time it took this signal to reach the Earth.
(b) If the Phoenix transmitter sent out spherical electromagnetic waves with a power of 100 W, how many watts per square meter would arrive at the Earth, assuming that Mars was in its closest location to Earth?
(c) A radio signal was sent to a deep space probe traveling in the plane of the solar system. Earth received a response 3.5 days later. Assuming the probe computers took 4.5 hours to process the signal instructions and to send out the return message, was the probe within the solar system? (Assume a solar system radius of about 40 times the Earth– Sun distance.)

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