01/16/2003
New Sightings
What manmade structure can be seen from the moon? The Great Wall of China, of course. Over the years, I’ve seen or heard this claim stated perhaps a dozen times. But is it true? In the January 2003 issue of National Geographic there’s an article, “Chasing the Wall” by Peter Hessler, who drove over 7,000 miles observing the present state of the Wall and its environs. According to Hessler, you cannot see the Great Wall from the moon. That was a claim dreamed up by Western writers back in the early 1900s. It seems that Westerners, notably Europeans visiting China starting in the 1600s, were much more impressed with the Wall than were the Chinese themselves. Apparently, it’s only within the past century that China has recognized the value of the Wall as a unifying theme, not to mention a significant tourist attraction.
The unsubstantiated claim about the Wall being visible from the moon resembles one of those canonical stories we discussed last week. If you didn’t read last week’s column, these are stories that have attained the stamp of authority but are not actually true. In a skeptical frame of mind, I wondered what else is not visible. How about moons of Neptune? In the January 14 Star Ledger, There is a brief item about the Harvard-Smithsonian Center for Astrophysics discovering three new moons of that far out planet Neptune. Their invisibility to date is not surprising, given the fact that they are only 18 to 24 miles in diameter. We earthlings have been short changed with only one moon. Neptune now has eleven.
While discovery of such small objects is impressive, I was shocked to read another news item about something rather monumental that had been invisible until recently. An international group of astronomers has discovered a sort of warped doughnut or hula-hoop of hundreds of millions of stars that surrounds our Milky Way galaxy. What surprises me is that astronomers have been peering out into the universe as far as 10 billion light years away, yet they’ve just found those hundreds of millions of stars circling right here in our own neighborhood. For perspective, we on Earth are sailing along with our sun, orbiting about 28,000 light years out from the center of the Milky Way galaxy. Our surrounding doughnut of stars just discovered is about 60,000 light years from the center. Actually, I shouldn’t be surprised. It’s not easy to observe certain features of a galaxy from within the galaxy because of all the billions of stars, gases and other stuff getting in the way.
Where did all these stars come from? If you Google “Milky Way collision”, you’ll come up with all kinds of sites relating to a collision of our own Milky Way galaxy with the Andromeda galaxy. We’ve mentioned before that sometime in the far distant future these two galaxies will collide. But not to worry, by the time that happens the chances are quite good that we humans will have long been extinct. Your Googling will also bring up sites such as those of the Washington Post, BBC and space.com citing the discovery of the doughnut of stars.
The doughnut of stars orbiting outside us is thought to have arisen from a collision with another galaxy in our distant past. The gravitational attraction of our galaxy for the stars is believed to have pulled these hundreds of millions of stars from the other galaxy into orbit around us. However, there is also a possibility that the stars arose out of leftover gases from when the Milky Way was formed. As with any new discovery, it will take time to sort things out. Stay tuned.
The last couple of weeks have been loaded with astronomical news. There was also the report of the discovery of a new planet about 5,000 light years away. According to the reports, this planet is the most distant planet outside our solar system detected to date. While I’m surprised that hundreds of millions of stars were missed, I’m amazed that we can “see” this latest planet so far away.
You may recall that we’ve discussed in a previous column how planets outside our solar system are detected. One method is the “wobble” method, in which the light from the parent star wobbles as the planet’s gravity pulls the star a bit one way and then the other as the planet orbits the star. The “transit” method is the one used to detect the most distant planet. In the transit approach, you look at the dimming of the star’s light as the planet comes between the star and our earth. An article by Robert Britt on the space.com Web site likens the finding of this planet to watching a mosquito fly in front of a searchlight 200 miles away! (I have the uneasy feeling that I’ve used a similar quote in a past column. Let’s hope it’s not one of those canonical myths.)
Not only have astronomers detected this distant planet but they also have reason to believe that it could be raining iron there! As we discussed before, the transit method has the advantage that we can look at the spectrum of the light passing through the atmosphere of the planet and deduce the composition of the atmosphere, or at least some of its elements. The planet is estimated to be about 2 to 3 times bigger than Jupiter and orbiting closer to its star than Mercury is to our sun. As a result, the temperature is so hot that metals are molten or vaporized. From the spectra it is concluded that tiny molten droplets of iron “rain” are probably falling from its atmosphere. Obviously, this planet is not likely to harbor life as we know it!
The number of planets found outside our solar system now numbers 100 or more and with the transit method in full swing it is expected that more and more planets will be discovered. Of course, the ultimate goal is to find a planet like our own that might support life. Where do we look? I imagine that, with current telescopes, we don’t have a chance of detecting such a planet outside our own galaxy. The distances are just too great. So far, we can’t truly “see” any planet outside our solar system until much more powerful telescopes come on line.
I guess when it comes to looking for “life”, I personally would be concerned with “interesting” life, creatures that swim or walk or fly - something more than just single cells or bacteria. For such life to prosper, at the very least you must have water, specifically lots of liquid water. For any given star, if you’re smart enough, you can figure out a zone in which a planet would have to orbit to have a temperature at which its oceans would not evaporate into space or freeze up entirely. This is a bare minimum condition for life and obviously there are a few other necessities such as oxygen, at least for our own species to evolve.
There must be billions of stars in our Milky Way that could have planets. How do we narrow our search? It doesn’t take a rocket scientist to decide that, since we’re here on Earth, we should look around in our neighborhood of the galaxy. Not only are we more likely to spot that mosquito passing in front of the searchlight but also we know that this neighborhood has been kind enough to provide the necessary conditions for life to exist and flourish.
I’ve just found my unread October 2001 issue of Scientific American under my pile of books and journals. Appropriately, there’s an article titled “Refuges for Life in a Hostile Universe” by Guillermo Gonzalez, Donald Brownlee and Peter D. Ward, three members of the astrobiology program at the University of Washington. They actually consider not only the most likely regions of our Milky Way galaxy for complex life to exist but even speculate on what other types of galaxies would be more likely to support life. If you’re a regular reader, you know that another column on this subject is almost assured.
Allen F. Bortrum
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