Alien Life May Be More Likely to Flourish in Globular Star Clusters

Wednesday, 06 January 2016 - 1:22PM
Astrobiology
Alien Life
Wednesday, 06 January 2016 - 1:22PM
Alien Life May Be More Likely to Flourish in Globular Star Clusters
Could alien life be hiding right in plain sight? Scientists have thought for years that the dazzling globular clusters in the Milky Way were unfavorable environments for host planets, let alone planets that hosted extraterrestrial life. But according to one astronomer's new findings, it's possible that globular clusters not only have planets, but that these planets are particularly friendly towards the formation of life.

Globular clusters are spherical collections of stars found in the halo of a galaxy. There are approximately 150 known clusters in the Milky Way, with an estimated 10-20 yet to be discovered. They are extremely dense, containing many more stars than open clusters, and are also significantly older. Scientists have long thought that these particular star clusters were unlikely to be conducive to planetary system formation, both because the density of the cluster would disturb the planets' orbits and because there is very low metallicity, which means that the elements required for planet formation may not be present.

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"Globular clusters are very old, and they formed at a time when heavy element content in the universe was smaller than it is today," Rosanne Di Stefano of the Smithsonian Astrophysical Observatory told Gizmodo. "Planets are rich in these heavier elements, and it wasn't clear if you'd expect to find planets in these low metallicity environments."
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But according to a new study from Di Stefano and Alak Ray of the Tata Institute in Mumbai, both concerns have been greatly exaggerated. Rocky, earthlike exoplanets have been found around stars with only one-tenth the metallicity of our Sun, which demonstrates that the formation of smaller planets isn't dependent on metallicity.

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"We now know that Jupiter-like gas giants are metal dependent," she said. "But today, as a result of Kepler, we also know that small planets orbiting in the habitable zone of low-mass stars aren't."
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So while larger planets probably wouldn't form, there is nothing precluding the smaller, rockier planets that are more likely to host life. And since the red dwarfs that compose globular clusters are dimmer than our Sun, habitable planets would necessarily be closer to their stars, which would make the density of the cluster a non-issue.

Di Stefano argues that if these planets did form, they may be ideal locations for advanced alien civilizations. The clusters are ancient, so if any planets formed near the beginning of the stars' lifetimes, life would have billions of years to evolve. Plus, as a result of the density of the clusters, the planets would be much closer together, making it much easier for planets to seed each other with life and for advanced species to become interplanetary.

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"Traveling at a hundredth the speed of light, it'd take us over 400 years to get to the nearest star," Di Stefano said. "If that star were 100 times closer, it'd take four years. We'd be in a totally different situation in terms of interstellar communication and travel, if we lived in a globular cluster."
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This is all hypothetical and somewhat speculative, especially since we've only found one exoplanet within a globular cluster. But, Di Stefano argues, as a result of the common wisdom about these clusters, astronomers haven't been looking for them.

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"Globular clusters may be an opportunity," she said. "Whether anyone is there to take advantage of the opportunity, is not yet clear."
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