Could Ancient Aliens Live on Methuselah Planets?
The announcement of a pair of planets orbiting a 12.5 billion-year old star flies in the face of conventional wisdom that the earliest stars to be born in the Universe shouldn't possess planets at all.
12.5 billion years ago, the primeval universe was just beginning to make heavier elements beyond hydrogen and helium, in the fusion furnace cores of the first stars. It follows that there was very little if any material for fabricating terrestrial worlds or the rocky seed cores of gas giant planets.
This argument has been used to automatically rule out the ancient and majestic globular star clusters that orbit our galaxy as intriguing homes for extraterrestrials.
The star that was announced to have two planets is not in a globular cluster (it lives inside the Milky Way, although it was most likely a part of a globular cluster that was cannibalized by our galaxy), but it is similarly anemic as the globular cluster stars because it is so old.
This discovery dovetails nicely with last year's announcement of carbon found in a distant, ancient radio galaxy. These findings both suggest that there were enough heavy elements in the early universe to make planets around stars, and therefore life.
However, a Hubble Space Telescope search for planets in the globular star cluster 47 Tucanae in 1999 came up empty-handed. Hubble astronomers monitored 34,000 stars over a period of eight days. The prediction was that some fraction of these stars should have "hot Jupiters" that whirl around their star over a period of days (pictured here in an artist's rendition). They would be detected if their orbits were tilted edge-on to Earth so the stars would briefly grow dimmer during each transit of a planet.
A similar survey of the galactic center by Hubble in 2006 came up with 16 hot Jupiter planet candidates. This discovery was proof of concept and helped pave the way for the Kepler space telescope planet-hunting mission.
Why no planets in a globular cluster? For a start, globular clusters are more crowded with stars than our Milky Way — as is evident in the observation of the dwarf galaxy M9 below. "It may be that the environment in a globular was too harsh for planets to form," said Harvey Richer of the University of British Columbia. "Planetary disks are pretty fragile things and could be easily disrupted in such an environment with a high stellar density."
However, in 2007 Hubble found a 2.7 Jupiter mass planet inside the globular cluster M4. The planet is in a very distant orbit around a pulsar and a white dwarf. This could really be a post-apocalypse planet that formed much later in a disk of debris that followed the collapse of the companion star into a white dwarf, or the supernova explosion itself.
Hubble is now being used to look for the infrared glow of protoplanetary disks in 47 Tucanae. The disks would be so faint that the infrared sensitivity of the planned James Webb Space Telescope would be needed to carry out a more robust survey.
If planets did form in the very early in the universe, life would have made use of carbon and other common elements as it did on Earth billions of years ago. Life around a solar-type star, or better yet a red dwarf, would have a huge jump-start on Earth's biological evolution. The earliest life forms would have had the opportunity to evolve for billions of years longer than us.
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This inevitably leads to speculation that there should be super-aliens who are vastly more evolved than us. So… where are they? My guess is that if they existed, they evolved to the point where they abandoned bodies of flesh and blood and transformed themselves into something else — be it a machine or something wildly unimaginable.
However, it's clear that despite (or, because of) their super-intelligence, they have not done anything to draw attention to themselves. The absence of evidence may set an upper limit on just how far advanced a technological civilization may progress — even over billions of years.
Keep in mind that most of the universe would be hidden from beings living inside of a globular star cluster. The sky would be ablaze with so many stars that it would take a long time for alien astronomers to simply stumble across the universe of external galaxies — including our Milky Way.
There will be other searches for planets in globular clusters. But our present understanding makes the question of a Methuselah civilization even more perplexing. If the universe made carbon so early, then ancient minds should be out there, somewhere.
Perhaps they really are "vast, cool, and unsympathetic," as science fiction writer H.G. Wells once put it.
Image credit: NASA