It has been months of doubts and confirmations and questions that lead to still more questions. In October of last year, Swiss astronomers discovered what they believed to be a planet larger than our Jupiter, orbiting a star known as 51 Pegasus. Planetary discoveries outside of the solar system have become something of a nightmare to the astronomical community. Some astronomer would announce that they had found one, or thought they had. Other astronomers would look at the data, and immediately speculate on what else it might be. If one considers that these people are all dealing with something that cannot even be seen, then one may have more sympathy for their cause. Then, while debates were continuing about this planet, R. Paul Butler, of San Francisco University, and Geoffrey W Marcy of University of California, Berkeley, announced the discovery of two more planets around other stars.
If you recall, in an earlier article we talked about just how these planets were discovered by a technique nicknamed wobble watching. By examining the light emitted by a star, astronomers can tell if it is moving toward or away from us and at what speed. If the light is shifted toward the blue end of the color spectrum, it is moving toward us. If the light is shifted toward the red end of the color spectrum, it is moving away from us. We experience a similar auditory type of "shifting" when we listen to an approaching train whistle. As the train approaches us, the whistle sounds slightly higher in pitch, as the train passes us, we can hear the whistle "shift lower" in pitch.
Similarly, what the astronomers were looking at with the stars was a shifting back and forth of the stars light. This had to mean that something was making the star wobble slightly rather than move in a straight line. The same effect can be experienced if you swing a string with a weight on the end over your head and attempt to walk in a straight line, you will wobble a bit. Wobble watching has resulted in the discovery of 3 planets around 3 different stars (there was an initial report of 2 planets around 51 Pegasus, but the second was never confirmed.) All three stars are sun-like stars. To find planets that have a chance of supporting life, astronomers have limited their search to stars that are like our sun. The planets themselves, however, are quite different from one another.
The planet that orbits 51 Pegasus is nearly an impossible habitat for life of any kind. It is roughly the size of Jupiter (around 12 times the size of earth) and is in an orbit closer to 51 Pegasus than Mercury is to our Sun. So close is this planet’s orbit to 51 Pegasus that it takes only 4.2 days to orbit the star. By comparison, Mercury takes 88 days to orbit our sun. This would put temperatures on the 51 Pegasus planet around 1000 deg C on the sunlit side. It is hard to imagine any life there.
The next planet to be discovered orbits a star called 70 Virginis, in the constellation Virgo. This is estimated to be a massive planet, over 8 times the size of Jupiter. The planets orbit is roughly half the distance of the earth to the sun. Temperatures are about 83 deg C, warm, but not sizzling. What would limit life on this type of planet would be the enormous pressures of gravity.
The third new planet discovery, was around the star 47 Ursa Mojoris, the constellation in which the Big Dipper resides. Of all three planets discovered, this one is the best candidate for a life sustaining planet. This planet orbits its star at roughly twice the distance of Earth’s orbit. The planet would be a cold world, about -90 deg C, but it is not too cold for some form of life to survive there. The size of this planet is about 3.5 times that of Jupiter. Intelligent life, however, would probably need a more friendly climate.
The search for an Earth-like planet is not unlike Goldilocks search for the right porridge, not too hot, not too cold......but one thing is for sure, our universe is becoming more and more interesting!
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