Artist’s impression of the view from a hypothetical planet orbiting Alpha Centauri A, Alpha Centauri B is clearly seen in the background, as the dimmer star.
Credit: Wikimedia
SYDNEY: Using the light from the triple-star system Alpha Centauri, astronomers have figured out the chemical composition of any rocky planets that may orbit the stars.
Alpha Centuari is a group of three stars that includes our nearest neighbour, the faint Proxima Centauri, a mere 4.2 light-years (40 trillion km) away, as well as the bright, close binary of Alpha Centauri A and B.
Astronomer Charles Lineweaver from the Australian National University in Canberra presented his study of the Alpha Centauri triple-star system last week at the 9th Australian Space Sciences Conference at the University of Sydney.
Hold of the Sun
The chemical composition of the Earth is similar to the chemical composition of the Sun. They have a similar abundance of non-volatile elements, such as calcium, aluminum, uranium and titanium. However, volatile elements are more abundant in the Sun, as its enormous gravitational pull can hold on to them more easily.
By applying this relationship to other stellar systems, the chemical compositions of extrasolar rocky planets can be estimated from the spectra elemental abundances of their host stars, the researchers argue.
Along with Bart Schoenberger from Radboud University in Nijmegen, the Netherlands, Lineweaver compared the spectra of Alpha Centauri A and B with the most recent estimates of the composition of the Sun and Earth.
"Chemical habitable zone"
This composition can indicate a "chemical habitable zone" - a region where the chemistry is conducive to life, Lineweaver said.
For example, a habitable planet might have enough heat-producing radiogenic isotopes to keep the interior of the planet molten and drive plate tectonics, or enough iron to produce a magnetic field to shield the surface from the stellar winds.
The researchers found that compared to Earth, any planets in the Alpha Centauri system would have more magnesium and fewer radiogenic isotopes, which would be a negative in terms of their habitability.
The exoplanets thought to exist around Alpha Centauri haven't even been detected yet. But researchers from San Francisco State University and the University of California, Berkeley, are using the 1.5-m CTIO (Cerro Tololo Inter-American Observatory) telescope in Chile to search for them.
Recent modelling of the system led by astrophysicist Javiera Guedes, of Berkeley, and accepted for publication in the Astrophysical Journal suggests that exoplanets will be found in the system.
"We are talking about exoplanets that we are most interested in because they are the closest and therefore the ones we will visit first when we make the leap to be able to send probes and colonists beyond the solar system," Lineweaver said.
Astrophysicist Brad Carter from the University of Southern Queensland, who wasn't involved in the research, said it was a "promising technique" although he added that it would be nice to try it in a system known to host exoplanets.
"If you can be reasonably certain that the composition of a planetary system is the same as its star except for the material lost through heat then you have a very powerful technique in terms of learning what the planets are made of, and I can't think of a better way to do this," he said.
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