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Western Slope Skies - Discovering Planets Outside Our Solar System

An artist’s impression of K2-33b, a young exoplanet only 5-10 million years old.
NASA/JPL-Caltech/R. Hurt
An artist’s impression of K2-33b, a young exoplanet only 5-10 million years old.

In school we learn about our solar system. Our Sun, Mercury, Venus, Mars, Jupiter, Saturn, Uranus, Neptune, and our home planet, Earth. The Milky Way galaxy is so large, and still just a small fraction of the universe. There are so many galaxies that contain stars like our own, but what about other planets? Are there more planets out there that are like ours? The answer to these questions is yes, and they are called exoplanets.

A star begins its life as a cloud of gas and dust. These are called molecular clouds, and they can range between 1,000 to 10 million times the mass of the sun. At some point the particles in this gas cloud begin to come together. Molecular clouds are cold, so as temperatures drop the particles in the gas start to clump together. This creates what NASA likes to call high density pockets in the gas cloud. Gravity then causes some of the clumps to collapse, creating friction that causes materials in the collapsed clump to heat up, birthing a baby star, or protostar to be specific. The remaining material keeps orbiting the young star.

This remaining material is thought to be small specs of dust with widths the size of human hair. Scientists believe that through gravity and other forces, these dust particles begin to collide with one another. If these collisions aren’t too aggressive, the dust will form small rocks and eventually large bolder sized clumps. Much like when you roll a snowball down a hill, little by little the snow grows into a large bundle. Except the result in this case in not a snow man, but what they call planetesimals. The planets in our solar system are thought to be formed in this way, therefore bringing up the idea that other stars likewise have orbiting planets.

In 1995, astronomers confirmed the first exoplanet orbiting a main sequence star named 51 Pegasi. Of course, the first thought for us non-astronomers is, how in the world did they find this? For that there is not just one answer but many. I will describe three ways to discover if a star has orbiting planets.

There is the transit method, which is when astronomers wait for objects to cross in front of a star. They then measure how much light is blocked by the object. If they find that the same amount of dimming is happening periodically, they can then conclude that it is a planet.

Another method used to find these planets is the Doppler method or Radial Velocity. This method is more indirect, where they measure the Doppler shifts (or wobble) of a star’s light. This lets them know there is a planet orbiting, due to the periodic change in frequency or wavelength of of light received from the star. This is similar to how a siren gets higher pitched as it gets closer and then lower pitched as it moves farther away.

The final method commonly used is called Direct Imaging. For Direct Imaging, astronomers take pictures of the light reflection from a star’s atmosphere using infrared wavelengths. This method is said to be the most difficult method because the star is often 1 million times brighter than the orbiting planet, and because planets are small and not very bright, causing them to get lost in the reflection of the star.

I think that we can all agree that looking up in the sky and seeing how vast the universe is can be pretty amazing. Now we know that there are a tremendous number of other planets out there. . As of May 1st, 2024, astronomers have confirmed 5,662 exoplanets and 4,169 planetary systems, and this is barely scratching the surface of the universe we live in.

You’ve been listening to Western Slope Skies, produced by the Black Canyon Astronomical Society and KVNF Community Radio. This feature was written and recorded by Trecia Smith, an astronomy student of Dr. Catherine Whiting at Colorado Mesa University.