NASAs Kepler mission may have made planet-hunting seem easy, but the hard truth is that most of the time looking for planets around other sun-like stars is painstakingly slow. And most of the extrasolar planetary search grunt work is still done on the ground using tried and true methods first put into place some two decades ago.

Enter Ivan Ramirez, an astronomer at the University of Texas at Austin, and colleagues, using the Magellan Clay Telescope in Chile, have taken high-resolution stellar spectra from 88 solar twins that lie within 326 light years of Earth. The hope is that they can prove their hypothesis that these spectra contain signatures of depleted metals caused by the presence of rocky planets. In fact, Ramirez says

In a forthcoming paper in Astronomy & Astrophysics, lead author Ramirez and colleagues note that their idea is that they would actually see less metals in a star that has planets. Ramirez notes that our own Sun has a slightly lower metallicity which Ramirez ascribes to a depletion of certain elements that like to stick together to form rocks.

This artistic image depicts the view from a hypothetical planet orbiting Alpha Centauri A, Alpha Centauri B is clearly seen in the background, as the dimmer star. (Credit: Wikipedia)

Thats how this work started, said Ramirez. We saw this effect first in the Sun and we are extending it to these solar twin stars. Our idea is that these missing rocky elements are in the planets.

Today, says Ramirez, its only possible to measure chemical composition with that kind of precision for stellar solar twins that are roughly the same age, mass and chemical makeup of our sun.

So, instead of calculating how many atoms of titanium are in the target star, said Ramirez, we only care about how much more or less there is compared to the Sun. We look for a depletion of rocky elements relative to non-rocky elements.

Which elements would be missing?

Elements that cover a range of the condensation sequence, said Ramirez, who explains thats the temperature at which such elements change their phase from gas to rock. For example, Ramirez says our own Sun is depleted in specific elements that indicate that we have a planetary system; such as barium, aluminum, iron, magnesium, titanium, chromium, silicon, and yttrium.

The team is still in the process of proving the hypothesis, but has found that five or six stars in the current survey have chemical depletions which could signal planetary systems.

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