Time! In the search for life in the universe, time and the sheer scale of the cosmos are enemies of our all too brief human-life span. A few basic facts provide a startling and eye-opening perspective on both our mortality and the obstacles confronting our search for life beyond the Solar System.
A prime target for our early efforts to find a twin Earth is our nearest star system, Alpha Centauri, 4.4 million light years away, which means that light (or an extraterrestrial message) takes 4.4 years to reach us.
It's been the destination of interstellar travelers in science fiction writing for so long now that one would almost be forgiven for thinking we'd already colonized it. But Alpha Centauri, the three-star system closest to our own Sun, is now the center of some very exciting science.
Javiera Guedes who headed up a NASA-funded project to analyze the possibility of detecting an Earthlike planet in orbit around Alpha Centauri B, has shown that terrestrial planets are likely to have formed around Alpha Centauri B, and that these planets should be orbiting in the "habitable zone."
“It’s so close to us, and the position of the other stars is such that it should be very possible to find a small planet,” she explained. She also found that, based on astronomers’ current understanding of how solar systems form, the existence of a planet the size of our own is very likely, and that there’s also a chance that it would lie in the habitable zone.
Now, the planet-hunting team is using a telescope in Chile to keep an eye on the star for the next three years, in order to collect enough data to determine whether or not the next Earthlike planet lies next door.
“If they exist, we can observe them,” said Guedes also showed that such planets would be observable if a telescope was dedicated to their search.
Guedes used a series of planet formation computer simulations to determine that terrestrial planets have probably formed around the star. The team ran repeated computer simulations which ran on a time frame of 200 million years each time. They varied the beginning conditions each time, and thus created a different result each time. However, each time a system of multiple planets evolved with at least one planet – approximately the size of Earth – forming. In many of these simulations, this planet was often found to be orbiting within the habitable zone of the star.
Its brightness and its position in the sky are both positive factors that make the Alpha Centauri search plausible; the latter giving the team a long period of observability each year from the Southern Hemisphere.
But the profound implication of the iron-clad law of astronomical time is that we see Alpha Centauri only as it was 4.4 years ago.In other words any message from inhabitants of Alpa Cenauri saying “Our planet is dying!” and our reply would consume a total of almost nine years.
The effect becomes even more starkly dramatic at greater distances. If we look at the awesome beauty of the Orion Nebula, we see it as the inhabitants of the Roman Empire saw it 1500 light years ago. A radio message we sent to a planet in the region would take some 3000 years for us to get their reply.
An even more extreme example would a message sent to us from the extreme outer edge of the Milky Way, which is 100,000 light years in diameter. Earth is located about 28,000 light years from the galactic center. A message reaching us now would have been sent 70,000 years ago.
To put astronomical time in an even more awesome perspective, scientists have located a giant 13-billion year old galaxy at the edge of the observable universe. The galaxy, which is 12.8 billion light-years from Earth, is as large as the Milky Way galaxy and harbors a supermassive black hole that contains at least a billion times as much matter as does our Sun. A message received from a planet that existed in this ancient would have to have been sent some eight billion years before the Earth was formed when the universe was only one-sixteenth of its present age. And, would that planet, indeed, that galaxy, still exist?
Casey Kazan
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