Let's zoom in a bit this week, and focus on areas of our universe closer to home:

Exoplanets

Prior to 1992, the only known, confirmed planets that we knew about were in our solar system. Starting in that year, our detection methods became sophisticated enough that we could begin to find “super-Jupiter”-sized planets around other stars. Before this point in time, we didn’t know if ours was the only solar system to contain planets. After this time, using Earth-based telescopes (of various types), we started to compile a list of hundreds of large exoplanets--planets around other stars outside of our solar system.

In 2009, NASA launched the Kepler spacecraft, designed to find planets the size of Earth or larger around other stars. Kepler kept its instruments focused on 145,000 nearby stars to detect sudden changes in brightness levels or other gravitational wobbles that could indicate a planet passing between it and the star or near the star. Kepler has found over 2,300 confirmed exoplanets, with 3,601 potential, unconfirmed exoplanets. With all spacecraft and telescopes combined, as of August 1, 2017, we now know of of 3,639 confirmed planets in other solar systems.

Those are a lot of potential places to explore! Here is a high-level breakdown image of all these exoplanets categorized by size (relative to Earth, Neptune, and Jupiter), how many days the planet takes to orbit its star, and how the planet was detected:

Earth Type Planets?

But the real question on everyone’s mind seems to be--are any of these planets like the Earth? Or, do they have the potential to harbor life in some form? Or, are they suitable candidates for us to colonize them at some point in the future?

We can actually now begin to start to try to answer those types of questions. (I’m leaving the question of *should* we colonize planets out there for another time.)

First of all, what is needed for life?

Water! All life that we know of is dependent upon liquid water. In order to be liquid, water has to exist at a certain temperature, and therefore we can determine whether a planet circles a star within its “habitable zone”--essentially a distance from the star where the temperatures on the planet might allow liquid water to exist.

Second is planet size and composition!

Life as we know it needs 2 things--a rocky foundation (i.e., gas giant planets need not apply!) and not too much, nor too little gravity. Something around half the mass of Earth, to maybe about 3 times the mass of Earth (although that’s very heavy!).

Conservatively, we know of 13 potentially habitable exoplanets, and optimistically, you can add another 30 potential planets onto that. These are planets that are the right size, are rocky, and are in an orbit where liquid water is possible.

NASA has a nice chart focusing on only Kepler-discovered habitable-zone planets. Note the Earth, Venus, and Mars in there for comparison of size, and the bright green is the conservative habitable zone, with the darker green a more optimistic range for liquid water.

Most of the planets there are larger than the Earth. A lot of that is because our capabilities with Kepler are just on the edge of being able to detect Earth-sized planets, although sometimes we do get lucky and are able to detect down to Mars-sized planets (there are a handful!).

Final Analysis

Just to be clear, we don’t know whether any of these planets do support life, or even can. They could have no water at all, or their atmospheres may be incompatible with life. Or maybe they don’t have atmospheres! We are only looking at possibilities at this point.

Using the Kepler data, astronomers have calculated that our Milky Way galaxy has at least 40 billion planets, 11 billion of which are probably rocky planets. This is likely a very low estimate, because we can barely detect Earth-sized planets and smaller, and there are a lot of reasons some of the stars Kepler is looking at might have planets even though they don’t seem to (e.g., the angle of Kepler’s view might not be optimal, etc.).

But we do now know that there are a lot of planets out there! Which increases the chance for life out there! Which gives us a lot more reason to try to explore out there!

Sources:

Pictures above courtesy of NASA.

https://en.wikipedia.org/wiki/Exoplanet

https://en.wikipedia.org/wiki/List_of_exoplanets_(full)

https://en.wikipedia.org/wiki/List_of_potentially_habitable_exoplanets

https://en.wikipedia.org/wiki/Kepler_%28spacecraft%29

Previous Science Escape story:

https://caucus99percent.com/content/science-escape-2-our-interstellar-sp...