Monday, December 05, 2011

Discovering Life on Distant Planets

This post concerns an item of personal interest.

It is really looking like, by the end of this decade - indeed, within the next couple of years - we will be able to point to a spot in the sky and say, "Over there, there is an earth-like planet with life on it."

It will likely only have single-celled life, but it will be life, and we will know that it exists.

Today, at a science conference held by the team that operates the Kepler space telescope, researchers announced that the Kepler telescope has now discovered 2,326 planet candidates.

(See NASA: NASA's Kepler Mission Confirms Its First Planet in Habitable Zone of Sun-like Star)

The way science works, a scientist can't just shout out that he knows something. She has to say why she thinks she knows something, and then wait for somebody else to confirm the findings.

With the Kepler telescope, a "planet candidate" is evidence that a sun has dimmed three times at regular intervals - hypothetically because an orbiting planet has orbited between that sun and the earth (blocking a part of its light). There has to be at least three dimmings because that is the minimum required to determine that the equally strong dimmings are evenly spaced.

But even then, some other telescope has to take a look at the star and determine if it, too, sees evidence of a planet.

So, the Kepler observatory has, in effect, turned over 2,326 suspected planets to other researchers to confirm (or not).

At this conference, it was also announced that researchers have confirmed that one of Kepler's planet candidates is an actual planet - a little larger than earth (about twice its size) - orbiting in the "goldilocks’ zone". That's the distance at which a planet is not too hot or not too cold but just warm enough to create a warm, wet, life-making planet.

The next part of the discovery comes from the fact, if the planet has an atmosphere, then some of the sunlight will travel through that atmosphere on its way to earth. As light goes through the atmosphere, its gasses will absorb certain frequencies of light depending on the gasses present. We will be able to tell, for example, whether the planet has an atmosphere rich in nitrogen and oxygen, or some other chemical compounds.

This will not determine with absolute certainty whether the planet has life, but there are some atmospheric mixtures where the presence of life will be the best explanation of how that planet maintains the atmosphere that it has.

On earth, for example, our atmosphere filled with oxygen was created by several billion years of plant life freeing oxygen from carbon dioxide and trapping the carbon in oil, coal, natural gas, and sedimentary rocks.

By the way, these tricks that will allow us to find another planet around a distant star and determine if it has life - beings living on other planets can apply to Earth. If that alien life lives in a narrow part of the sky that will see the earth pass in front of our sun, and if they are close enough given the size and complexity of their scientific instruments, they will see our sun dim once every 365.2 days. They will get a reading of our atmosphere showing a lot of nitrogen and oxygen and a little bit of everything else.

They wouldn't get much of an indication of human intelligence - at least not yet. If they were 1000 light years away, then they are seeing today what our atmosphere looked like 1000 years ago.

However, in about 900 years, they will start to notice changes in the data that comes from Earth. Carbon dioxide levels will increase. There will be a sudden increase in night-time luminescence - meaning that the dark side of the earth is not as dark as it once was. This will be due to the array of city lights shining on the dark side of the Earth.

There is no telling what they will think of these changes, however. Perhaps it will be attributed to volcanic activity, or a large forest fire. I am certain that these will not be the first abrupt changes they have seen on Earth.

However, with continued observation, focusing instruments on the Earth that we already know how to build but which we have not yet built – they can get some very precise images of Earth. They would even be able to see cloud patterns, the shapes of the continents, and the pattern of lights that identify our cities at night. They would know that we are here.

Or, they would know that we were here 1000 years ago. They will have to wait to discover what happens next.

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