Living in the Local Bubble

3D view of the local bubble (white) and pieces of adjacent parts of the interstellar medium (purple and blue)

Did you know that we live inside a bubble? Believe it or not, the solar system, along with many other stars, sits inside what astronomers call the Local Bubble. It's a region of space that is less dense than the surrounding area of space, and contain very hot gas ( greater than 1,000,000 degrees!) that emit soft x-rays. Inside the bubble, space has about 0.01 hydrogen atoms per cubic inch (compare this to the ~10^20 atoms per cubic inch here on earth!). The bubble is shaped like an egg or a cylinder that is about 10x as tall as it is wide (30x200 parsecs), and sits upright with the plane of our galaxy crossing through the bottom third of the bubble. The solar system itself sits inside a thin sheet of cloud called the Local Fluff (no joke!), that is slightly more dense than the surrounding bubble. So where did this bubble come from? Astronomers are not a hundred percent sure, but the leading theory says that a supernova must have went off somewhere near the sun and essentially "blew" the bubble and heated up the gas inside. This probably happened around 10 million years ago, way after the sun and planets had already formed! So in a sense we survived a supernova explosion! Now the big question is this: are we living inside a supernova remnant that is still actively heating and removing material from the area? Or has the remnant material disappeared and left behind an "empty" bubble. Astronomers are actively trying to answer this question. But for now we are living happily in a sheet of fluff inside our own little galactic bubble!

Our Solar System

After some recent teaching experiences and discussions, I've come to realize that many adults have forgotten the basics about our solar system. So today ADYK presents a Solar System "refresher" to help you recall those astronomy facts you learned back in elementary school.

 

Above is a collection of real telescope images of the planets in our solar system (NOT to scale!). This is what the planets look like when you use very high power telescopes or planet orbiting satellites to observe them.

Our solar system contains 8 planets (Pluto doesn't count anymore),  one star (the Sun) and two large asteroid belts. Mercury, Venus, Earth and Mars and the four closest planets to the sun and are often called the terrestrial or rocky planets. They are basically giant chunks of rock in a roughly spherical shape. Mercury is made mostly of metals and is heavily cratered like the moon. Venus has a thick carbon dioxide atmosphere, and is essentially the poster child for what would happen if global warming got out of hand on earth. Earth is our home and is made of 70% salt water and has a rich Nitrogen atmosphere. Mars is the red planet where all the aliens live, supposedly. (*wink wink*). Beyond Mars sits the first asteroid belt, filled with oddly shaped rocks the size of people to the size of cities. Jupiter, Saturn, Uranus and Neptune sit beyond the asteroid belt and are often called the gaseous or Jovian planets. Jupiter is the largest planet, about 10x the size of Earth, and has that big red spot. Saturn is the one with the prominent ring structure, though all Jovian planets have a slight ring structure around them. Uranus and Neptune are the blue planets, and are about 4x the size of Earth. Uranus is turned on it's side, meaning that its spin axis is tilted 90 degrees from being straight "up and down". Past the Jovian planets is the Kuiper belt, a giant ring of asteroids which defines the edge of the solar system. Pluto, it's moons, and over 70,000 similar objects orbit in this ring. Most everything there is small, cold, and icy.

There you go, elementary school astronomy class in one paragraph!