Scientists have long known of “Super Earths,” large-scale planets that orbit giant stars outside our galaxy. But now astronomers using the Keck Telescope in Hawaii have discovered a new planet called HD156668b. This planet is just the size of four Earths, making it the second time a smaller planet has been found.  

To date, more than 400 planets outside our solar system have already been discovered. But the majority of these planets are giants closer to the size of Jupiter than to Earth.

Then planet HD156668b exists in a star system about 80 light-years from Earth in the constellation Hercules. It orbits its star once every four days. Andrew Howard is an astronomer out of the University of California at Berkeley. As he tells Space.com, "This is quite a remarkable discovery." Further, "It shows that we can push down and find smaller and smaller planets."

Astronomers discover these planets by detecting “wobbles” that move across the parent star. Called their “tried-and-true planet detection method,” scientists measure the effects of a planet's gravity on its parent star. A planet’s gravity tugs slightly on the star as it passes by, causing the starlight to shift to a redder wavelength in the light spectrum. That means that when the planet passes in front of the star, light appears to be bluer.

It is a well-known goal amongst astronomers to find planets similar in scale and size to our own Earth.