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This week's prize is Jim Bell’s excellent book, "The Interstellar Age: Inside the Forty-Year Voyager Mission," signed by the author.

This week's question:

As of April 11, 2015, about how many near-Earth comets are there known to be?

To submit your answer:

Complete the contest entry form at http://planetary.org/radiocontest or write to us at [email protected] no later than Tuesday, April 28th at 8am Pacific Time. Be sure to include your name and mailing address.

Last week's question:

What is the orbital period of Neptune’s moon Triton?

Answer:

The answer will be revealed next week.

Question from the week before:

What are trans-Neptunian objects in a 2:1 orbital relationship with Neptune called? (2 orbits of Neptune, 1 orbit of the body)

Answer:

Trans-Neptunian objects in a 2:1 relationship with Neptune are called Twotinos.