Sunday, October 7, 2012

Stellar Fingerprinting


As most of you are aware, since the 90's, astronomers have been scouring the galaxy, looking for alien planets that circle distant stars. Some of which, may harbor intelligent species that may or may not be anything like the life we're accustomed to here on Earth. Their efforts haven't been in vain as there are thousands of exoplanets that have been observed and confirmed. Most though are hot-Jupiter exoplanets that are composed primarily of gas, but orbit their parent stars at only a fraction of the distance that separates Mercury from our sun. Due to the difficulty of spotting the smaller, terrestrial planets that could harbor earth-like life -- not many of those discovered have been seriously considered as viable options for extraterrestrial beings to exist on. However, astronomers have developed a new system that could radically alter our terrestrial planet hunting methods.

This new method of discovery, nicknamed 'stellar fingerprinting,' is a technique that was first developed for looking for telltell signs of Earth-like planets that may exist in the Alpha Centauri A system, which is one of the brightest stars in the night sky and it just so happens to be one of the primary contenders for observation in the search for Earth-like exoplanets. In the past through our observations, one thing has became clear. Stars that are host to terrestrial planets appear to be slightly anemic (containing less iron than as per usual) compared to stars that are found to be wandering the galaxy alone.

Our best planet formation hypothesis says that a small fraction of heavy elements are locked up in the terrestrial planets, comets, asteroids, meteoroids and planetesimals in alien solar systems. Most of the rocky objects are born from the dust disk that encircles a star when it's still wrapped in its proto-star cocoon before the star transitions to main-sequence star, capable of fusing hydrogen into helium in its core. In this scenario, the star will lack certain elements for enrichment since most of them will never manage to be captured by the star's gravitational influence, before being engulfed by the star. Even a planet that's only a few times more massive than the Earth will in theory, use up a noticeable amount of the elements present in the planetary system.

When an astronomer from the University of Texas, Ivan Ramirez studied the composition of 11 targeted stars using spectroscopy to separate the starlight from various stars into a prism to see which elements are present in the stars, which corresponds to different wavelengths of light. What he found in his 'spectroscopic survey' was that 15 percent of solar type stars bears circumstantial evidence that the stars harbor terrestrial planets simply by observing the chemical composition of the star's spectral fingerprints. His number came in a bit lower than that of NASA's Kepler Space Observatory, which has detected over 2,300 alien planets to date -- with the numbers of confirmed exoplanets growing exponentially by day.

Ramirez used 16 Cygni, a triple star system that's located approximately 70 light-years from Earth as a test subject of some sorts. One of the stars in the system is host to a confirmed exoplanet, while its companion appears to be planet-less. In this system, the star with the planet was found to have a slight deficiency of heavier elements compared to its companion that doesn't have any.

As I mentioned earlier, by far, the most exciting candidate to use this technique lies only 4.3 light-years from Earth in the constellation of Centaurus, Alpha Centauri A -- the largest star in a triple star system, which are our closest stellar neighbors. Out of 85% of the stars that were studied in Ramirez's spectroscopic survey, Alpha Centauria A is the most similar to our sun in temperature and and iron abundance. To him, this strongly suggests that this is strong circumstantial evidence that one or more terrestrial planet is circling the star. Indeed, it may be MORE surprising if we *didn't* find an orbiting rocky planet since it's far enough away from the other stars in the multiple star system -- Alpha Centauri B, for a planet to remain in stable orbit around its primary parent star.

So far, no evidence by Kepler or Hubble has been presented to suggest any planets exist in Alpha Centauri A's system, but searches remain underway as I type this article. I think I speak for the entire scientific community when I say it would be a truly exhilarating moment to discover a terrestrial Earth-like planet located so closely to home. Not only is the distance pretty small in cosmological distances, but Alpha Centauri is approximately the same age as the sun. Therefore, it wouldn't be a ridiculous assumption to believe that its solar system could have evolved in a similar way and time-span to our own. If a terrestrial planet was discovered to have an atmosphere laced biotracers like methane, oxygen, carbon dioxide and ozone -- it may be that any life present on the planet may have had the time to evolve into multicellular forms of life.. perhaps even life that is semi intelligent? Regardless of whether life has began to thrive on this hypothetical exoplanet or not, there is a lot that could be learned from its discovery.. even moreso, it may aid us in understanding where planets of similar composition with similar stars went wrong in not allowing creatures such as you and I to exist.

- Jaime

Source Material:
"Stellar Fingerprinting Hints Nearest Star Hosts Planets:"
http://news.discovery.com/space/earth-like-planet-might-whirl-around-alpha-centauri-a-121003.html

"Our Galaxy May Have 50 Billion Exoplanets–and It’s Still Making More:"
http://blogs.discovermagazine.com/80beats/2011/02/25/our-galaxy-may-have-50-billion-exoplanets-and-its-still-making-more/

Further Reading:

"How do scientists know what stars are made of?"
http://wiki.answers.com/Q/How_do_scientists_know_what_chemicals_are_in_stars
"Kepler space telescope finds 1,091 new exoplanet candidates
http://www.wired.co.uk/news/archive/2012-02/29/kepler-data-dump

Image Credit: L. Cal├žada/ESO

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