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A chilling message Gravity maps of moon reveal deeply fractured crust Prof Yash
Pal THIS UNIVERSE
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A chilling message THE polar ice sheets are melting three times faster than they were 20 years ago, according to satellite measurements. More than 4,200 gigatonnes were lost from the polar ice sheets from 1992 to 2011, an average of 223Gt a year and rising. Researchers described the losses as being at “the high end” of forecasts by the Intergovernmental Panel on Climate Change (IPCC) in 2007.
The findings are based on previous satellite readings but have been combined and correlated to provide what scientists believe is “the most accurate assessment” yet of polar ice loss. Accurate calculations of how much ice is lost from Greenland and Antarctica are notoriously difficult. In 2007, the IPCC wasn’t even sure if there was a net loss or gain. Professor Andrew Shephard, of the University of Leeds, said it was “two or three times” more accurate than previous assessments. He said the implications were serious: “The ice sheets used to be a minor player in sea-level rise. Now they seem to be a substantial player.” It provides “baseline” data which will make future forecasts of ice loss and sea-level rises much more accurate. Net losses of ice contribute to sea-level rises and the study found that the rate has increased significantly in only 20 years. During the 1990s, ice sheet loss accounted for 10 per cent of sea-level rises but in the past five years it has risen to more than 30 per cent. Melting ice caps, the new calculations show, caused 11mm of the overall rise since 1992 but the rate of loss is increasing rapidly. In the 1990s, 0.27mm of annual sea-level rise was blamed on polar melting, whereas in the past five years it has risen to 0.95mm annually. Melting of ice in Greenland has had the biggest impact, contributing 7.4mm to sea-level rises since 1992. Antarctica has contributed 3.7mm but there are clear regional differences. While West Antarctica has lost an average 65Gt annually and the Antarctic Peninsular 20Gt, there has been a 14Gt gain in East Antarctica. Annual sea-level rises are still small but are forecast to increase significantly and the study suggests the most pessimistic forecasts will be proved right. It comes after a report published recently showed overall sea levels rose 3.2mm a year between 1993 and 2011, 60 per cent above the 2mm estimate in projections by the IPCC. The findings, published in the journal Science, were made by an international team of scientists jointly led by Prof Shepherd and Dr Eric Ivins at the National Aeronautics and Space Administration’s (NASA) Jet Propulsion Laboratory. Professor Michiel van den Broeke, of Utrecht University in the Netherlands, warned: “Sea-level rises are at the very upper end of what the IPCC has predicted.” The causes and mechanisms behind the increased rate of ice loss are not fully understood but it is widely attributed to global warming. Professor Richard Alley, a climate scientist at Penn State University in the US, who was not involved in the study, said: “This project is a spectacular achievement. The data will support testing of predictive models, and lead to a better understanding of how sea-level change may depend on the human decisions that influence global temperatures.” Enough ice is contained in the ice sheets to cause sea-level rises, if it all melted, of an estimated 63m — 7m from Greenland and 56m from Antarctica. — The Independent |
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Gravity maps of moon reveal deeply fractured crust ASTEROIDS and comets colliding with the moon not only pitted its surface but also severely fractured its crust, researchers with the USA’s National Aeronautics and Space Administration (NASA) said, in a finding that could help crack a Martian puzzle. On Mars, similar fracturing would have given water on the surface a way to penetrate deep in the ground, where it may remain today, they said. “Mars might have had an ancient ocean and we’re all wondering where it went. Well, that ocean could well be underground,” planetary scientist Maria Zuber, with the Massachusetts Institute of Technology, said at the American Geophysical Union conference in San Francisco. The discovery that the moon’s crust is deeply fractured came from a pair of small probes that comprise NASA’s Gravity Recovery and Interior Laboratory, or GRAIL, mission. The identical spacecraft have been following each other around the moon for nearly a year. Scientists have been monitoring the distance between the two, which changes slightly as they fly over denser regions of the moon. The gravitational pull of the additional lunar mass causes first the leading probe and then the other one to speed up, altering the gap between them. The data, assembled into the first detailed gravity maps of the moon, reveal that asteroids and comets cratered the surface and fractured the crust, possibly all the way down to the mantle. “If you look at the surface of the moon and how heavily cratered it is, all terrestrial planets look that way, including Earth,” said Zuber, the lead GRAIL scientist. Evidence of the phenomenon on Earth was wiped out by tectonic plate movements, erosion and other natural events. “If we want to study those early periods, we need to go someplace else to do it and the moon is the closest and the most accessible example,” Zuber said. For Mars, the finding that a planet’s crust can be so deeply fractured has implications in the search for extraterrestrial life. The fractures provide a pathway for water to move from inside the planet to the surface, and vice versa. Scientists believe Mars was once much warmer and wetter than the cold, dry desert it is today. “If there ever were microbes on the surface that had to head away to a better environment, they could have gone very deep within the crust of Mars,” Zuber said. The research is published in this week’s journal Science. — Reuters
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THIS UNIVERSE Why do all planets have a spherical shape? The recognised planets of the solar system are large bodies with a significant mass. All particles of a massive body experience a significant net attraction towards its centre. Such a body is, therefore, forced to acquire a spherical shape. If the mass of the body is low, as for example that of a large number that inhabit the asteroidal belt between the Earth and the Mars, these bodies do not have to be spherical. The argument given above also explains why the Earth cannot support mountains much higher than the Himalayas. Is it true that if the door of a refrigerator is kept open, the room temperature will increase? Please explain. A refrigerator in a room tries to cool the inside of the refrigerator. This necessarily requires that it must transfer some heat from inside to outside of the refrigerator. If refrigerator’s door is open and the refrigerator is working hard to cool its inside, the net result is that some of the heat for running the refrigerator is distributed in the room. As a consequence, the room temperature must necessarily increase — this will definitely happen if the cooling fins of the refrigerator are not connected to outside of the room. Readers can e-mail questions to Prof Yash Pal at palyash.pal@gmail.com
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Explorers to retrace Shackleton’s epic Antarctic journey Science journal urged to retract GM study
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