How many Planets are there in Space

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For over a hundred years, our radio signals have begun spreading into space at the speed of light. For fifty years, we have included television pictures.

In our immediate stellar neighbourhood, just five parsecs (16.308 lightyears) out, there are at least 65 known stars in 50 stellar systems. Stretch it out to a hundred lightyears, and the total jumps to at least the 7,031 stars listed in the Lepine Shara Proper Motion Catalog, with more previously unknown stars being discovered everyday. Over five hundred of these are G-type stars, like our own Sol.

The Milky Way galaxy is 100,000 lightyears in diameter and a thousand lightyears thick, containing between 100 billion and 400 billion stars. The edge of the observable universe is believed to be 46.5 billion lightyears away. Even when limiting only to the stars along the main sequence or even only to the G-type yellow dwarf stars, the number of possible planets in the universe is almost beyond human comprehension.

Even hampered as we are by distance, dozens of planets have already been identified. The Spitzer Space Telescope has even managed to catch the collision of two tiny planets a hundred lightyears away.

Our current level of technology, appropriately applied, could send a spacecraft to Alpha Centauri, the closest star system, and arrive within fifty years.

It is entirely possible that a nearby civilisation has already received and translated our signals. If they themselves use a wired form of information, if a planetary or stellar quirk happens to channel their own signals away from us, if for other reasons they have not widely broadcast into the aether in the bands we use, even if they stopped doing so just fifty years ago, they could well have decided about us ... and we might never know that they are out there.

It is also possible that they have already judged us by what they have seen. What they would have to work with could range all the way from that first radio transmission to the ships at sea from Ocean Bluff-Brant Rock, Massachusetts on Christmas Eve, 1906, through any number of coded military messages covering two world wars, the Cold War, and over a hundred smaller conflicts, through a small but dedicated amateur radio network, to our daily television cable diet and now our Internet diet as well.

From all this, what kinds of conclusions might they reach?

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