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| SCIENCE & TECHNOLOGY |
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Extra-solar planets Environment Alert
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Extra-solar planets Till 1995 the only definitely known planets in the universe were those nine or so around our sun. We had known for a long time that our sun was only one of the billions upon billions of stars in the universe and it was impossible that it should be the only one to have a family. But the fact remained that it had not been possible to identify another one to have that distinction, in spite of all the progress made in the field of astronomy. It was argued that we should give up the impossible attempt, at least for the time being, of trying to do something akin to seeing a lighted candle in the beam of a lighthouse from a thousand kilometers distance! Instead we should concentrate on detecting what the presence of a planet or planets would do to the motion of the star itself. The high school student I mentioned above would tell you after some thinking that when a planet is moving in an orbit the star itself couldn’t be sitting still; it also moves, in a smaller orbit, but with the same period as the planet. This being so, we should see how we could best detect this motion. An analysis of this motion would then tell us about the existence of a planet as also particulars like its mass and distance from the star. The method that has been employed is to measure the radial velocity of the star; in other words to find out whether the star has a swinging motion towards and away from us, and if so what is its amplitude and period. If it does it is a good candidate for study over months, even years. It should be possible then to deduce what kind of orbital motion would lead to the radial swing measured. The amplitude of the swing would depend on the mass of the planet that is causing the perturbation. Other parameters of the orbit can also be derived. The measurement of the radial motion is done using Doppler effect. This is the effect that leads to change in the wavelengths of spectral lines of the star. The lines would be red shifted when the star is moving away from us and blue shifted when it is moving toward us. It is through painstaking and detailed studies like this that over two hundred solar systems have been detected during last 12 years. We are truly living at an important turning point in the history of astronomy. Yes, the solar systems have been detected but many interesting and bewitching findings have also resulted. For example most of the early detections led to planets that were as heavy or heavier than the giant gas planets like Jupiter and Saturn, many of with short orbital periods of a few days! Such planets would not be of much interest as candidate homes for some form of life. But it was soon realised that we were seeing an observational bias. Giant planets, close to a star would lead to more easily detectable perturbations of the star motion. Smaller planets like our earth would not produce big enough a signal. In this sense one can say that the search has just begun and one needs to find ways of achieving higher sensitivity, even thinking of other techniques that do not suffer from biases of the kind mentioned above. Activity in this field has increased. Scientific, technological, and computational challenges are significant. Years of patient measurements are often required. And behind all these there is the supreme urge to find planets that, like the one on which we live, might be capable of evolving and supporting life. There cannot be a stronger driving force. Some of the efforts have been to look for transits of possible planets across the face of candidate stars. Such a transit would reduce the light coming from the star a wee bit. Fluctuations of measurement would show a periodic pattern if caused by transit of a planet. Another technique being used is called micro-lensing. This makes use of the fact that light from a point source can be “lensed” by the gravitational field of a massive object in its path. If the candidate star (C) comes in front of a more distant star (D), then micro-lensing of (D) by (C) would show a periodic variation of its image if (C) is being perturbed by a planet (or planets) around it. This is much like the movement of the image of the sun by a hand-held magnifying glass if the latter is not kept steady. A few planets have been discovered by these two techniques. Biases inherent in using these techniques might be less and/or different than for the predominant method so far used, namely measuring the radial velocity (Doppler effect). Let me in the end refer briefly to an ambitious international effort that will need superlative techniques and accuracies. Work on this project called Darwin has begun with the lead being taken by the European Space Agency. It will involve a flotilla of satellite telescopes located on the other side of the moon, working as a single instrument to concentrate on finding signals of the kind one expects from an inhabited or habitable planet. The strong light from the star itself would be blocked or “nulled” using clever interference with a delayed beam. |
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Environment Alert The map of Greenland will have to be redrawn. A new island has appeared off its coast, suddenly separated from the mainland by the melting of Greenland’s enormous ice sheet, a development that is being seen as the most alarming sign of global warming. Several miles long, the island was once thought to be the tip of a peninsula halfway up Greenland’s remote east coast but a glacier joining it to the mainland has melted away completely, leaving it surrounded by
sea. The US Geological Survey has confirmed its existence with satellite photos, that shows it as an integral part of the Greenland coast in 1985, but linked by only a small ice bridge in 2002, and completely separate by the summer of 2005. It is now a striking island of high peaks and rugged rocky slopes plunging steeply to a sea dotted with icebergs. As the satellite pictures and the main photo make clear, Warming Island has been created by a quite undeniable, rapid and enormous physical transformation and is likely to be seen around the world as a potent symbol of the coming effects of climate change. But is only one more example of the disintegration of the Greenland Ice Sheet, that scientists have begun to realise, only very recently, is proceeding far more rapidly than anyone thought. The second-largest ice sheet in the world (after Antarctica), if its entire 2.5 million cubic kilometres of ice were to melt, it would lead to a global sea level rise of 7.2 metres, or more than 23 feet. That would inundate most of the world’s coastal cities, including London, swamp vast areas of heavily-populated low-lying land in countries such as Bangladesh, and remove several island countries such as the Maldives from the fact of the earth. However, even a rise one tenth as great would have devastating consequences. Sea level rise is already accelerating. Sea levels are going up around the world by about 3.7 mm per year, the average for the period 1993-2003. That is itself sharply up from an average of 1.8mm per year over the longer period 1961-2003. Greenland ice now accounts for about 0.5 millimetre of the total. (Much of the rest of the rise is coming from the expansion of the world sea water as it warms.) Until two or three years ago, it was thought that the breakup of the ice sheet might take 1,000 years or more but a series of studies and alarming observations since 2004 have shown the disintegration is accelerating and, as a consequence, sea level rise may be much quicker than anticipated. — By arrangement with The Independent, London |
Our telescopes remained powerless against odds that a planet like our earth around a star like our sun would be a thousand million times fainter than the star. The star would blind our telescopes, no matter how powerful, and we would not be able to see any planets around it. The clever method through which this problem was finally addressed was something that could have occurred to a high school student. The argument can be summarised as below:
Shaped like a three-fingered hand some 400 miles north of the Arctic Circle, it has been discovered by a veteran American explorer and Greenland expert, Dennis Schmitt, who has named it Warming Island (Or Uunartoq Qeqertoq in Inuit, the Eskimo language, that he speaks
fluently).