Банк рефератов содержит более 364 тысяч рефератов, курсовых и дипломных работ, шпаргалок и докладов по различным дисциплинам: истории, психологии, экономике, менеджменту, философии, праву, экологии. А также изложения, сочинения по литературе, отчеты по практике, топики по английскому.
Полнотекстовый поиск
Всего работ:
364150
Теги названий
Разделы
Авиация и космонавтика (304)
Административное право (123)
Арбитражный процесс (23)
Архитектура (113)
Астрология (4)
Астрономия (4814)
Банковское дело (5227)
Безопасность жизнедеятельности (2616)
Биографии (3423)
Биология (4214)
Биология и химия (1518)
Биржевое дело (68)
Ботаника и сельское хоз-во (2836)
Бухгалтерский учет и аудит (8269)
Валютные отношения (50)
Ветеринария (50)
Военная кафедра (762)
ГДЗ (2)
География (5275)
Геодезия (30)
Геология (1222)
Геополитика (43)
Государство и право (20403)
Гражданское право и процесс (465)
Делопроизводство (19)
Деньги и кредит (108)
ЕГЭ (173)
Естествознание (96)
Журналистика (899)
ЗНО (54)
Зоология (34)
Издательское дело и полиграфия (476)
Инвестиции (106)
Иностранный язык (62792)
Информатика (3562)
Информатика, программирование (6444)
Исторические личности (2165)
История (21320)
История техники (766)
Кибернетика (64)
Коммуникации и связь (3145)
Компьютерные науки (60)
Косметология (17)
Краеведение и этнография (588)
Краткое содержание произведений (1000)
Криминалистика (106)
Криминология (48)
Криптология (3)
Кулинария (1167)
Культура и искусство (8485)
Культурология (537)
Литература : зарубежная (2044)
Литература и русский язык (11657)
Логика (532)
Логистика (21)
Маркетинг (7985)
Математика (3721)
Медицина, здоровье (10549)
Медицинские науки (88)
Международное публичное право (58)
Международное частное право (36)
Международные отношения (2257)
Менеджмент (12491)
Металлургия (91)
Москвоведение (797)
Музыка (1338)
Муниципальное право (24)
Налоги, налогообложение (214)
Наука и техника (1141)
Начертательная геометрия (3)
Оккультизм и уфология (8)
Остальные рефераты (21697)
Педагогика (7850)
Политология (3801)
Право (682)
Право, юриспруденция (2881)
Предпринимательство (475)
Прикладные науки (1)
Промышленность, производство (7100)
Психология (8694)
психология, педагогика (4121)
Радиоэлектроника (443)
Реклама (952)
Религия и мифология (2967)
Риторика (23)
Сексология (748)
Социология (4876)
Статистика (95)
Страхование (107)
Строительные науки (7)
Строительство (2004)
Схемотехника (15)
Таможенная система (663)
Теория государства и права (240)
Теория организации (39)
Теплотехника (25)
Технология (624)
Товароведение (16)
Транспорт (2652)
Трудовое право (136)
Туризм (90)
Уголовное право и процесс (406)
Управление (95)
Управленческие науки (24)
Физика (3463)
Физкультура и спорт (4482)
Философия (7216)
Финансовые науки (4592)
Финансы (5386)
Фотография (3)
Химия (2244)
Хозяйственное право (23)
Цифровые устройства (29)
Экологическое право (35)
Экология (4517)
Экономика (20645)
Экономико-математическое моделирование (666)
Экономическая география (119)
Экономическая теория (2573)
Этика (889)
Юриспруденция (288)
Языковедение (148)
Языкознание, филология (1140)

Топик: The Snows of Mars

Название: The Snows of Mars
Раздел: Топики по английскому языку
Тип: топик Добавлен 17:52:07 01 августа 2005 Похожие работы
Просмотров: 27 Комментариев: 2 Оценило: 0 человек Средний балл: 0 Оценка: неизвестно     Скачать

NASA scans the polar wastelands.( около 5000 знаков. )

Mars holds a special place in the human imagination as the planet most like the Earth. It has an atmosphere, seasons, and distinctive polar ice caps. The ice caps, first observed by Giovanni Cassini in 1666, immediately raised tantalizing questions. Are they made of water ice like the giant glaciers that smother Antarctica? Are they the frozen remains of long-vanished oceans? If they melted, could Mars become a habitable place? NASA's Mars Global Surveyor, currently in orbit about the Red Planet, is finally providing some solid answers.

The Surveyor has already revealed unexpected details about the size and structure of Mars's northern cap. By the end of February, the spacecraft will begin mapping, for the first time, the topography and composition of the even more poorly understood southern polar ice cap. The new information (along with upcoming data from the Mars Polar Lander, which will arrive in December) will strip away many of the lingering mysteries of the Martian poles.

On Mars, the presence of water--essential for life, past or present--is always an issue of great interest. "Some people have proposed that there were oceans early in Martian history; others have said there were not. "But for all of those theories, one needs to understand the water cycle: how much water there was, where it went to, and where it's at now." If scientists find substantial reserves of frozen water, it would bolster the view that Mars was once a balmy, moist world where life could have started.

Until about two months ago, planetary astronomers believed that the southern cap contained nothing but frozen carbon dioxide, also known as dry ice. New research suggests otherwise: a thick sheet of carbon dioxide ice would be too soft to stay stable. "The thought now is that carbon dioxide ice is so weak that it would flow away, like a glacier, even at very low temperatures," Zuber explains. "So to maintain the topography of the south polar cap, there has to be water ice in there stiffening it up."

Zuber and her colleagues also analyzed Mars's much larger northern polar cap. The ice cap is cut by deep troughs and chasms; some of these depressions extend down over a mile to the base of the planet's crust. Many researchers off guard. "There are no troughs of that kind in any of the ice caps on Earth," said Global. "We don't know how this formed

Zuber's results confirmed that the northern cap is composed entirely of water ice, in some areas interspersed with layers of wind-blown dust and sediment. That piece of good news came as no surprise, because summer temperatures at the cap (which has an elevation several miles lower than the southern cap) are high enough to vaporize frozen carbon dioxide. But the Global Surveyor also produced the first accurate measurement of the size of the northern cap--and that was a surprise.

Seven hundred and fifty miles across, and up to two miles thick, the northern cap has a volume just half that of the Greenland ice sheet. It may sound large, but doesn't contain nearly enough water to account for the flood channels and other erosion features that appear all over the place on Mars. "It's not even close to what is generally believed to have once been on the surface," says Zuber. Scientists like Michael Carr at the U.S. Geological Survey who believe oceans once covered much of Mars face a serious challenge from the Global Surveyor studies. The northern cap contains no more than one tenth the amount of water needed to fill an ancient ocean. On the other hand, the fissures and ring of residual ice around the perimeter of the cap suggest it has lost a great deal of water over the millennia.

The Global Surveyor has also provided some clues about the way water circulated about on Mars in the distant past. The northern ice cap sits nestled within a deep depression that covers essentially the entire northern hemisphere of Mars and drops in elevation as it nears the pole. The cap "looks something like a hockey puck in that depression," David Smith of NASA's Goddard Space Flight Center reported at the AGU press conference. Researchers are not sure how the giant lowland formed (perhaps through a large impact), but they do know that it has been there since very early in Martian history, and so has clearly played an important role in the planet's water cycle.

"Before we made these measurements of the northern hemisphere, it used to be thought that the only way you could get water to the north pole of Mars was through the atmosphere," Zuber says. But because the northern cap lies at a lower elevation than the rest of the planet, "water than you put down almost anywhere in the northern hemisphere is going to flow toward the pole. It is quite probable, then, that you once had standing bodies of water at high northern latitudes. They might not have persisted for very long, because we don't know how warm it was and things may have frozen over quickly. But you clearly could get the water up close to the pole."

Clearly, Mars was not always the frozen wasteland it is today. What happened? Some of the ancient water could have been lost to the atmosphere and then, over countless millennia, ejected into space through complicated interactions with the Martian magnetic field. Some might still be locked in aquifers and other formations beneath the surface. And some may exist in the southern polar cap--but not much. The southern cap is significantly smaller than the northern one. Even if the Mars Global Surveyor finds water ice in the south, it won't come close to eliminating the water shortage, according to Zuber.

"We haven't either improved or diminished the possibility of life on Mars," she says. "Essentially, what we have done is exacerbate the problem of there being too little water on Mars today compared to where there was earlier. Now those people who have proposed oceans have a bigger task in explaining where the water went."

--Kathy Svitil

Posted 2/19/99

Оценить/Добавить комментарий
Имя
Оценка
Комментарии:
Где скачать еще рефератов? Здесь: letsdoit777.blogspot.com
Евгений22:39:50 18 марта 2016
Кто еще хочет зарабатывать от 9000 рублей в день "Чистых Денег"? Узнайте как: business1777.blogspot.com ! Cпециально для студентов!
11:29:36 24 ноября 2015

Работы, похожие на Топик: The Snows of Mars

Назад
Меню
Главная
Рефераты
Благодарности
Опрос
Станете ли вы заказывать работу за деньги, если не найдете ее в Интернете?

Да, в любом случае.
Да, но только в случае крайней необходимости.
Возможно, в зависимости от цены.
Нет, напишу его сам.
Нет, забью.



Результаты(150408)
Комментарии (1831)
Copyright © 2005-2016 BestReferat.ru bestreferat@mail.ru       реклама на сайте

Рейтинг@Mail.ru