* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download `It`s Raining, It`s Pouring`
Survey
Document related concepts
History of Solar System formation and evolution hypotheses wikipedia , lookup
Dialogue Concerning the Two Chief World Systems wikipedia , lookup
Definition of planet wikipedia , lookup
IAU definition of planet wikipedia , lookup
Rare Earth hypothesis wikipedia , lookup
Hypothetical types of biochemistry wikipedia , lookup
Circumstellar habitable zone wikipedia , lookup
Comparative planetary science wikipedia , lookup
Late Heavy Bombardment wikipedia , lookup
Exoplanetology wikipedia , lookup
Interplanetary contamination wikipedia , lookup
Planetary habitability wikipedia , lookup
Timeline of astronomy wikipedia , lookup
Transcript
‘It’s Raining, It’s Pouring’... elsewhere in the Universe? Hydrology. Originating from the Greek words ‘hydor’ meaning water and ‘logos’ meaning study, the term ‘hydrology’ came to its current meaning around 1750 and is defined as ‘the study of water and its movement and distribution across our planet and others’¹. The idea of managing this movement first occurred five or six thousand years ago, where rivers such as the Indus, Euphrates, Nile and Hwang Ho had dams, levees, subsurface water conduits and other hydraulic constructions built on them by the world’s first hydraulic engineers, signifying the origins of hydrology. These civilisations were also the first to measure rain fall and flow rate. The first records that provide evidence for a global hydrologic cycle date back to Ancient Greece, where eminent philosophers including Hippocrates, Plato and Aristotle, seem to have had knowledge of the basic outline of the system. However, some of their basic understanding of the hydrologic or water cycle was incorrect, and, in 1500, scientist, artist, and great thinker Leonardo da Vinci used observations of rivers to deduce that the water in the rivers was a result of precipitation. This confirmed the Greek’s theoretical mechanisms to be incorrect and they were either overturned or modified in turn. Then, working in the 17th century, Pierre Perault and Edme Marriotte are widely accredited with having developed the current scientific approach to investigating the hydrologic cycle. They supplied further evidence of da Vinci’s theory, providing investigative results in the form of data and calculations and their work was then built upon by the English scientist Edmund Halley, who estimated the quantity of water engaged in the water cycle in the surrounding area to the Mediterranean Sea. During the 18th century, other areas of science were applied, including hydraulics, mathematics and fluid mechanics, by eminent scientists including Euler, Chezy and many more Europeans and by 1800, John Dalton, a renowned English physicist and chemist, had finally come to globalise the current understanding of the hydrologic cycle. Hydrology is a topic at the forefront of discussion in the Environmental Physics community at the moment, after significant breakthroughs were recently made at the University of Arizona, with regard to the hotly debated topic of whether or not there is life on Mars. The presence of water on Mars would provide some of the strongest evidence yet that life is sustainable there. Recently NASA’s Mars Reconnaissance Orbiter recorded images of ‘dark tendrils a few metres wide’², thought to be channels of water, most probably salt water, running down craters, underneath the planet’s surface. The first supposed sightings of water on Mars was in the 19th century, when astronomers claimed to have seen canals on the surface of the red planet, but were, in fact, mistaken by an optical illusion. The trails were found in the Southern Hemisphere of the planet, and were more pronounced in the warmer times of the year, fading in the winter, which is in keeping with water that runs during the summer but freezes in the winter. There are in excess of a thousand trails and, although they do not provide definite proof of the existence of salt water on Mars, the lowered freezing temperature of water containing salt means that water with the same salt content as the oceans of earth would melt during the summer Natasha Mulley, The Leys School, Cambridge -1- months, even in the harsh, cold climate of Mars. Frozen carbon dioxide and pure water have also both been ruled out, as the sun-facing regions of the planet would be at a too high temperature for the carbon dioxide, and too low a temperature for the pure water. However, there is a possibility that they are the result of dust or sand avalanches. Images of these ‘seasonal streaks’ were recorded by the most powerful camera yet to orbit the planet³, the HiRISE, a shortening of High Resolution Imaging Science Experiment, which was built under the leadership of the Lunar and Planetary Laboratory at the University of Arizona. Its mass is 65 kg and has an aperture reflecting telescope of 0.5m, the largest of any mission yet to explore deep space. Its findings were endorsed by another craft, the Phoenix Lander, which found the soil of Mars to be plentiful in salts. Seasonal Dark Streaks on Mars (source: apod) The scientific search for water on planets other than our own has been long and, so far, reasonably fruitless. However, at the University of Ohio in the late 2000’s, Scott Gaudi, the assistant professor of astronomy at the University, and his team decided to expand the search somewhat and discovered very cold planets, on the edges of distant solar systems, known as ‘Super-Earths’, which have the potential to support extraterrestrial life of some sort⁴. Although they are named very similarly, there are very few similarities between the super-Earths and the Earth that we know. There are stark contrasts between the two, with the super-Earth having a considerably denser atmosphere and icy surface, although both surfaces are of a solid consistency. It is also suggested by experts in the field that up to one third of solar systems could contain super-Earths. Modelling has been carried out by Gaudi, and other scientists Eric Gaidos and Sara Seager, to see if it is possible for life-supporting oceans to have formed on these planets and whether we, on Earth, would be able to identify them from here. They have Natasha Mulley, The Leys School, Cambridge -2- discovered that it may be possible, provided that there is a dense enough atmosphere or if these super-Earths are either very young, very large, or a combination of the two. New techniques are also being discovered for identifying potentially life-supporting planets and exoplanets, planets that orbit a star outside of our solar system. One of the latest, and the one favoured by Gaudi and his team, is gravitational microlensing. It originates from the work of the likes of Newton, von Soldner, Einstein and Orest Chwolson, but the current theoretical framework is accredited to Yu Klimov, Sidney Liebes and Sjur Refsdal. It allows stars a great distance away to be magnified, using the gravitational field of a nearby collinear star. Much of the research using gravitational microlensing is being focused in what is known as the ‘habitable zone’ of other solar systems, places that are the ideal distance away from a star to create the correct temperature for liquid water. However, there is a far greater proportion of water outside of this ‘habitable zone’, although it is mostly found on frozen moons, in the core of gas planets, and on super-Earths, as ice, rather than flowing or liquid water. Gaudi and his team, therefore, took the approach to look for super-Earths, which would already have water already in place upon formation, rather than planets that, like Earth, are warmer, but which obtained their water at a point after formation. The team then looked at the possibility that these super-Earths manage to retain a core warm enough from its formation to keep water in a liquid state underneath the ice. They concluded that it was possible for a planet approximately ten times the size of our Earth to form a liquid ocean under the ice in this way. Gaudi also discovered that, using microlensing, it would be possible to detect these faraway planets, and what was, in fact, the optimum distance for a microlense. Despite the often fruitless nature of searches for water on other planets, and the possibilities arising from this, including the opportunity for life, the last few years have seen many great breakthroughs in the field. In 2007, water vapour was found in the spectrum of the planet HD189733b, by NASA’s Spitzer Space Telescope, the first time water had been detected on any exoplanet⁵. Then, in 2008, astronomers used the Hubble Telescope to reveal the first signs of an organic molecule on an exoplanet, by again analysing planet HD189733b⁶. Further discoveries are being made almost daily on the Kepler Mission, a mission for habitable planets launched in 2009, which is able to observe thousands of stars at any one time, and is looking for planets similar to our own, including the presence of water. The results will reveal just how many planets there are in our galaxy similar to earth.⁷ The Kepler Mission has already discovered 2,362 planet candidates, as of 5 December 2011⁸, but it is unclear yet whether they are truly habitable. Its principal investigator, Bill Borucki, has said ‘Certainly in three years, we will give you the first good answers. And after that they will be even better’⁹. It is a very exciting time for space exploration into the hydrology of other planets, and therefore the possibility of life elsewhere than Earth. It is a tantalizing idea, one that has tormented mankind since almost the beginning of time, and produced the world-famous, mythical alien, who has gone on to be the star of countless novels, films, and even advertising campaigns. Natasha Mulley, The Leys School, Cambridge -3- Space exploration such as this has also provided fuel for some of the best loved fictional characters, such as those in the hit 1960’s TV series ‘Star Trek’. It is an area of science saturated with mystery and intrigue, still very much a dark corner, each discovery awaited with huge anticipation and abundant media attention. It is an exciting time for humankind, teetering on the brink of discoveries that could prove categorically whether or not we are alone in this Universe, a discovery that could change the world, and whatever lies beyond, forever. Natasha Mulley Sources: ¹ The Encyclopaedia of Earth: http://www.eoearth.org/article/History_of_hydrology - Article on History of th Hydrology, Lead Author Jason A. Hubbart Ph.D., published February 11 2008. Jason A. Hubbart is an assistant professor of forest hydrology at University of Missouri, Columbia. First paragraph informed from here. Citation: Jason A. Hubbart (Lead Author);Jim Kundell (Topic Editor) "History of hydrology". In: Encyclopaedia of Earth. Eds. Cutler J. Cleveland (Washington, D.C.: Environmental Information Coalition, National Council for Science and the Environment). [First published in the Encyclopaedia of Earth February 11, 2008; Last revised Date February 11, 2008; Retrieved August 23, 2011 <http://www.eoearth.org/article/History_of_hydrology> ² From an article written by David Batty for The Guardian, from page 16 of the main section of the Friday 5 th August 2011 issue, and also online at guardian.co.uk at 22:07 on Thursday 4 August 2011 (http://www.guardian.co.uk/science/2011/aug/04/strongest-evidence-yet-water-mars) th ³ From an online article in the magazine ‘Science’, published by Richard A. Kerr on August 4 2011 at 2:06 PM (http://news.sciencemag.org/sciencenow/2011/08/is-mars-weeping-salty-tears.html) ⁴ Ohio State University (2008, December 16). Ocean-bearing Planets: Looking for Extraterrestrial Life in All the Right Places. ScienceDaily. Retrieved September 2, 2011, from (http://www.sciencedaily.com/releases/2008/12/081215091011.htm) ⁵,⁶,⁷ NASA PlanetQuest Historical Timeline, Jet Propulsion Laboratory, California Institute of Technology (http://www.nasa.gov/externalflash/PQTimeline/) ⁸ The Kepler Mission Official Website, Ames Research Centre (http://kepler.nasa.gov/Mission/discoveries/) ⁹ Bill Borucki Podcast interview with Scientific American, July 18 2011 (http://www.scientificamerican.com/podcast/episode.cfm?id=kepler-searches-for-habitable-plane-11-07-18) Picture: NASA Astronomy Picture of the Day, August 8 2011 (http://apod.nasa.gov/apod/ap110808.html) Natasha Mulley, The Leys School, Cambridge -4-