Brave New Worlds and Goldilocks

In this photograph, taken by an astronaut on board the International Space Station, Venus is seen moving in front of, or transiting, the sun. Although the planet is small in comparison to the sun, it blocks part of the light reaching the earth. Using very sensitive instruments, scientists can now measure the very slight dimming that occurs when an exoplanet blocks part of the light from a distant star it orbits. (Photo: NASA)
In this photograph, taken by an astronaut on board the International Space Station, Venus is seen moving in front of, or transiting, the sun. Although the planet is small in comparison to the sun, it blocks part of the light reaching the earth. Using very sensitive instruments, scientists can now measure the very slight dimming that occurs when an exoplanet blocks part of the light from a distant star it orbits. (Photo: NASA)
Do we know if there are planets orbiting other stars? Until about 20 years ago, the answer would have been “NO!” Most astronomers believed that there were probably planets going around other stars, but that it was not possible to find them. Planets are just so small compared to stars and the stars are so far away.

Then, in the 1990s, some really smart scientists thought up some crazy ideas to detect planets orbiting distant stars.

The simplest one became known as the Transit Method. When Mercury or Venus travel across the disc of the Sun (known as transiting the Sun), the amount of sunlight hitting the Earth goes down.

Think about a light bulb burning and a fly buzzing around it. While you look at the bulb as the fly buzzes by, the amount of light you see from the bulb is slightly less than when the fly is gone. It’s a very small amount, but the bulb does in fact become dimmer.

Now what if we could measure the brightness of a distant star incredibly accurately, and see if it dims? And what the star dims and brightens on a regular basis (like once a year)?

If that’s the case, it might be caused by a planet orbiting the star.

Let me pause and be the science grammar policeman. Technically, as poor Pluto learned, there are only 8 planets; a planet is now defined as a celestial body that, among other things, orbits our Sun. So if we’re talking about worlds orbiting some other star, they cannot be called planets. Astronomers call them exoplanets. “Exo” means “outside,” so exoplanet means a planet orbiting a star outside our solar system.

Using the Transit Method and other ingenious methods, astronomers started finding exoplanets, lots of them. It takes a long time to be sure. It takes multiple observations by multiple teams using multiple methods before an exoplanet is confirmed.

Now, hundreds of exoplanets have been confirmed. Thousands more listed as probable but haven’t been confirmed yet. The number keeps growing.

The artist's concept depicts NASA's Kepler mission's smallest habitable zone planet. Seen in the foreground is Kepler-62f, a super-Earth-size planet in the habitable zone of a star smaller and cooler than the sun, located about 1,200 light-years from Earth in the constellation Lyra. Kepler-62f orbits it's host star every 267 days and is roughly 40 percent larger than Earth in size. The size of Kepler-62f is known, but its mass and composition are not. However, based on previous exoplanet discoveries of similar size that are rocky, scientists are able to determine its mass by association. Much like our solar system, Kepler-62 is home to two habitable zone worlds. The small shining object seen to the right of Kepler-62f is Kepler-62e. Orbiting on the inner edge of the habitable zone, Kepler-62e is roughly 60 percent larger than Earth. (Image credit: NASA Ames/JPL-Caltech/Tim Pyle)
The artist’s concept depicts NASA’s Kepler mission’s smallest habitable zone planet. Seen in the foreground is Kepler-62f, a super-Earth-size planet in the habitable zone of a star smaller and cooler than the sun, located about 1,200 light-years from Earth in the constellation Lyra. Kepler-62f orbits it’s host star every 267 days and is roughly 40 percent larger than Earth in size. The size of Kepler-62f is known, but its mass and composition are not. However, based on previous exoplanet discoveries of similar size that are rocky, scientists are able to determine its mass by association. Much like our solar system, Kepler-62 is home to two habitable zone worlds. The small shining object seen to the right of Kepler-62f is Kepler-62e. Orbiting on the inner edge of the habitable zone, Kepler-62e is roughly 60 percent larger than Earth. (Image credit: NASA Ames/JPL-Caltech/Tim Pyle)
In 2009, NASA launched the Kepler Space telescope to find stars with exoplanets. It tracked the brightness of over 100,000 stars for over 4 years. It has discovered at least 900 confirmed exoplanets, and has provided scientists with so much data that will take years to completely review.

The Kepler scientist have found lots of weird planets. Huge planets bigger than Jupiter yet closer to their star than Mercury, orbiting every few days! They found planets twice the size of Earth, dubbed “Super Earths” really far away from their stars. They found planets orbiting two stars!

Scientists have even been able to determine all sorts of characteristics about these exoplanets including:

  • How big they are.
  • How long is their year.
  • How far away from their star is their orbit.
  • What chemicals are in their atmosphere

Naturally, astronomers want to locate planets that have the right conditions for life. They are looking for exoplanets that have orbits that means they are not too hot and not too cold, planets that are “just right” for life. They call this the Goldilocks zone. They have many candidates, so who knows what they’ll learn in the future?

The Gemini Planet Imager’s first light image of Beta Pictoris b (Processing by Christian Marois, NRC Canada)
The Gemini Planet Imager’s first light image of Beta Pictoris b (Processing by Christian Marois, NRC Canada)
In just a few years exoplanets have gone from science fiction to science fact. Earlier this year, scientists in Chile used special techniques and even took a photograph of an exoplanet! See below the image of Beta Pictoris b, a planet orbiting the star Beta Pictoris. In the picture below, the light of the star itself is blocked out by a disk so the planet can be seen. It’s great to see science in action.

Keep up with the latest exoplanet discoveries yourself at http://kepler.nasa.gov/Mission/discoveries/