In Lesson 7 & 8, we will explore Exoplanets.

An exoplanet is a planet outside our own solar system.

As of 12 Nov 2015, astronomers have discovered and confirmed 1,905 exoplanets outside our solar system!

Of which, 476 planetary systems have multiple planets much like our own!
(Source: NASA Exoplanet Archive)

Image Credit: ESA, NASA, and L. Calcada (ESO for STScI)

One planetary system KOI-351 was discovered to contain seven planets!

Configuration of the planets is similar to our Solar System with gas giants at the outer ring and smaller rocky planets closer to the star.

Above diagram compare KOI-351 system with our Solar System.

Image Credit: DLR / CC-BY 3.0

Astronomers estimate there are at least 100 to 400 billions planets in our Milky Way galaxy, based on the average of one planet per star.

Some studies further estimate 1 in every 5 stars there is an Earth-sized planet which lies in the habitable zone. So there could be around 20 to 80 billions exoplanets having the potential of harvesting life!

Image Credit: ESO/M. Kornmesser / CC BY 3.0

When a planet passes in front of its parent star, it will block out a very small portion of the star’s light. The star will appear just a little dimmer (usually 1% or less) during the transit period.

Using sensitive equipments, we are able to measure the brightness of the star and the decrease in brightness when a planet transits its star.

This is called the Transit Method.

Transit method is currently the most active technique of exoplanets searching due to many advantages.

Image Credit: Courtesy NASA/JPL-Caltech