- Search the Internet for pictures of planets in our solar system. Now search for planets outside our solar system.
- What differences do you notice in the pictures that are shown? Why do you think the exoplanet pictures are mostly drawings?
An exoplanet is a planet orbiting another star besides our Sun. An exoplanet is not one of the eight planets in our solar system. “Exo” just means “on the outside.” So an exoplanet is outside of the solar system.
An animal with its skeleton on the outside is said to have an exoskeleton like this scorpion. Another term used to describe planets outside our solar system is “extra-solar planet.”
Since 1991 thousands of planets have been discovered that orbit other stars, and based on what we have found so far, there are probably about 100 billion planets in our galaxy alone. Using our current technology, we have a very limited search area within our galaxy. Consider though that prior to the 1990’s we had no means of detecting planets orbiting other stars.
We assumed that planets around other stars were common, but we could not confirm it.
Earth-based telescopes cannot generally see exoplanets, but very sensitive space telescopes like Spitzer and Kepler can. Without orbital telescopes, we would still not be able to prove without a doubt that other stars have planets too and that our Sun’s system is not an anomaly.
In 2009 NASA launched the Kepler Space Telescope which looks at 145,000 stars continuously for variations in their light emission which would indicate a planet passing in front of the stars.
Kepler first introduced us to “Hot Jupiters” (large gaseous planets orbiting very close to the star) and circumbinary planet systems (planets orbiting two stars that orbit one another).
We have learned that stars with planets rotating around them are common in our galaxy, but this does not mean that other solar systems are replicas of our own. Models of how solar systems should look were based on ours: smaller rocky planets closest to the Sun like Mercury, Venus, Earth and Mars, and larger gaseous planets further out like Jupiter, Saturn, Uranus and Neptune.
As if to remind us in our excitement of discovering many new worlds that we do not know everything, the first planets Kepler found are what we call “Hot Jupiters.” “Hot Jupiters” are large gaseous planets like Jupiter that are very close to their stars, the complete opposite of how we thought an exosolar system would look.
Before 1991 we did not know for sure that there were other planets besides the 8 that orbit our start, the Sun. Since then we have discovered thousands of planets using a technique called Orbital Brightness Modulation. That sounds complicated, but it’s not really.
We have ultra-sensitive light detecting telescopes like the Kepler Space Telescope focused on a star, and if the star dims even a little bit it could mean that a planet is passing in front of it.
For example, if a star is as bright as 10,000 light bulbs and an earth-like planet passes in front of it, it would be like taking away one of the light bulbs. These are very light-sensitive telescopes.
Exoplanet discovery and the subsequent studying of those planets are one of the hottest areas of astronomy today.