Astrobiology: What Are the Characteristics of Life?

The Pale Blue Dot
Figure 3 is the so-called "Pale Blue Dot" photo that was taken by Voyager 1 as it was going out of the solar system.

Figure 3

As you may know, Voyager 1 is now essentially out of the solar system and has probably passed through the heliopause. This was taken in 1990 at the recommendation of Carl Sagan. The camera was turned around and looked backwards so that it could see our Earth. It took a sort of family picture of the solar system and there is this Pale Blue Dot, the Earth.

This notion of a Pale Blue Dot is often used when people are looking for life on other planets. For example, a few years ago, we had a Pale Blue Dot Conference at NASA and the issue was: How could you distinguish a habitable or inhabited place? How could you find another Pale Blue Dot? 

Astrobiology
The definition of astrobiology that is often used is "the study of the origin, evolution, distribution and future of life on Earth and in the universe." This is quite a large task. In this approach, the scientific process is used. 

There are other areas of interest in biology and space. One is a broad program that's referred to as "life beyond this planet of origin." That means, what happens when life from Earth goes in to space? The pertinent issue is what happens to astronauts when they go into low-earth orbit, as they now are and have been. Humans are now extraterrestrials in the sense that we've inhabited space stations for many years now. The Russian space station was mostly inhabited for fifteen years or more. The International Space Station has been inhabited for four or five years now. And the hope is that that will continue, but as you may know, that's in question. In these contexts, we can ask the question: If you take any kind of life out into space, what happens to it in that hostile environment? 

The general questions that are asked in astrobiology are: How did life begin?  Are we alone in the universe? If there is life elsewhere, did it come from elsewhere to here, or did we colonize other places through meteorites and other objects that travel from one place to another? And what's the future of humans on Earth and as we travel out into space?  Then that naturally raises the question, what is life and how would you know if you found it?  And what is death?  It's actually not that easy to tell if something has died or not.