European astronomers have made a surprising discovery. They have found one of the smallest planets known outside of our solar system. Oddly this small planet is rocky and is orbiting a regular star similar to our Sun. The discovery was made with a European Southern Observatory telescope at La Silla, Chile, using a HARPS spectrograph on ESO’s 3.6-m telescope.

The team detected the planet — which is far smaller than its parent star — by observing subtle shifts in the spectrum of light from the star as the planet orbited it and gravitationally tugged it backward and forward, subtly altering the stellar velocity. During 8 nights in June of 2004 they closely monitored the spectrographic shifts of the star in an attempt to detect the small acoustic waves that pulsate which cause the surface of a star to periodically pulsate. After examining the records they noticed that on top of the expected signature of the acoustic waves there was also an unmistakable nine and a half day cycle in the star’s spectrum. Follow-up observations confirmed the researcher’s initial uncertainties, there was indeed a planet orbiting close by Mu Arae and completing each revolution in nine and a half days.

This discovery is significant, because no planet so small has ever been found orbiting a normal star. This finding exposes a solar system more similar to our own than anything else we’ve discovered, and this new planet is being called a “super-Earth”.

The star, mu Arae, is very similar to our Sun and is 50 light years away, in the southern constellation of the Altar. Almost all other extrasolar planets are hundreds if not thousands of light years away. The star is visible from the Southern Hemisphere. Mu Arae harbors two other planets as well. The first is as big as Jupiter and has a 650-day annual orbit. The other planet is even further out. The new rocky planet has an orbit of only 9.5 days.

This discovery is unique because most of the more than 120 planets found beyond our solar system are gaseous worlds larger than Jupiter, mostly in tight orbits that would not permit a rocky planet to survive. A handful of planets smaller than Saturn have been found, but none anywhere near as small as this rocky mystery.

At 14 times the mass of Earth, the newfound planet — circling a star similar in size and brightness to our Sun — is about as heavy as Uranus, a world of gas and ice and the smallest giant planet in our solar system. Theorists say 14 Earth-masses is roughly the upper limit for a planet to possibly remain rocky. Because this planet is so close to its host star, it likely had a much different formation history than Uranus.

In the solar system, the four innermost planets are rocky. The prominent theory on how planets are formed start with them having a rocky core. The core develops over time, and then gravity collects a huge envelope of gas. This theory would indicate that the newfound planet never reached this critical point in its formation; otherwise the planet would have been much more massive.

The discovery of this new rocky planet has given scientists hope that there is the possibility for life on other planets. They have been long looking for faraway planets that, like Earth, are relatively small, rocky bodies where plants and creatures might evolve. This new terrestrial type planet has an iron core like Earth.

Over the last ten years, more than 100 new planets orbiting distant stars have been observed by astronomers. Up until now, they’ve been far too massive to be regarded as Earth-like objects. They’ve been “gas giants” similar to the enormous planets Jupiter and Saturn in our own solar system. Jupiter and Saturn have atmospheres thousands of miles thick and are far too cold to support Earth-like life, experts say.

 

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