14 August, 2009

;

Pengertian dan Pengelompokan Peta

Kapan peta mulai ada dan digunakan manusia? Peta mulai ada dan digunakan manusia, sejak manusia melakukan penjelajahan dan penelitian. Walaupun masih dalam bentuk yang sangat sederhana yaitu dalam bentuk sketsa mengenai lokasi suatu tempat. Pada awal abad ke 2 (87 M – 150 M), Claudius Ptolomaeus mengemukakan mengenai pentingnya peta. Kumpulan dari peta-peta karya Claudius Ptolomaeus dibukukan dan diberi nama “Atlas Ptolomaeus”.

Istilah peta diambil dari bahasa Inggris yaitu map. Kata itu berasal dari bahasa Yunani mappa yang berarti taplak atau kain penutup meja. Menurut ICA (International Cartographic Association), peta adalah suatu gambaran atau representasi unsur-unsur kenampakan abstrak yang dipilih dari permukaan bumi, yang ada kaitannya dengan permukaan bumi atau benda-benda angkasa. Dengan demikian, peta adalah gambar, akan tetapi tidak semua gambar adalah peta.

Penggunaan skala pada peta merupakan perbandingan antara bidang gambar dengan permukaan bumi sebenarnya. Permukaan bumi tidak mungkin digambar sesuai ukuran aslinya, sehingga harus diperkecil dengan perbandingan tertentu. Karena peta sebagai gambaran permukaan bumi pada sebuah bidang datar, sedangkan bumi merupakan benda berbentuk bola maka untuk membuat

peta, baik sebagian maupun seluruh permukaan bumi harus menggunakan teknik proyeksi tertentu. Ilmu yang mempelajari tentang pengetahuan dan teknik pembuatan peta disebut kartografi, sedangkan orang yang ahli membuat peta disebut kartografer.

Pada awalnya, pembuatan peta hanya untuk menggambarkan permukaan bumi yang bersifat umum. Setelah itu, peta berkembang sehingga menggambarkan hal-hal khusus yang disesuaikan dengan kebutuhan pembuat dan pengguna peta. Dengan demikian, peta yang biasa kamu temukan sangat benyak jenisnya. Banyaknya jenis peta tersebut disebabkan oleh beberapa faktor, misalnya tujuan pembuatan peta, jenis simbol dan skala yang digunakan, atau kecenderungan penonjolan bentuk fenomena yang akan digambarkan. Dari sekian banyak jenis peta, pada dasarnya dapat dibagi ke dalam dua kelompok besar yaitu berdasarkan isi peta dan skala peta.

Menurut isi peta, dibedakan atas peta umum dan peta khusus.
1. Peta umum, adalah peta yang menggambarkan seluruh penampakan yang ada di permukaan bumi, baik bersifat alamiah (misalnya sungai, danau, gunung, laut, hutan, dan lain-lain) maupun budaya atau buatan manusia (misalnya: batas wilayah, jalan raya, kota, pelabuhan udara, perkebunan, dan lain-lain). Contoh peta umum antara lain: peta dunia, peta korografi, peta rupa bumi dan peta topografi.
2. Peta khusus disebut pula peta tematik, adalah peta yang menggambarkan atau menyajikan informasi penampakan tertentu (spesifik) di permukaan bumi. Pada peta ini, penggunaan simbol merupakan ciri yang ditonjolkan sesuai tema yang dinyatakan pada judul peta. Beberapa contoh peta tematik antara lain: peta iklim, peta geologi, peta penggunaan lahan, peta persebaran penduduk, dan lain-lain.

Menurut skala yang dibuat, peta dapat dikelompokkan sebagai berikut:
1. Peta kadaster, yaitu peta yang memiliki skala antara 1 : 100 sampai dengan 1 : 5.000. Contoh: Peta hak milik tanah.
2. Peta skala besar, yaitu peta yang memiliki skala antara 1 : 5.000 sampai dengan 1: 250.000. Contoh: Peta topografi
3. Peta skala sedang, yaitu peta yang memiliki skala antara 1 : 250.000 sampai dengan 1 : 500.000. Contoh: Peta kabupaten per provinsi.
4. Peta skala kecil, yaitu peta yang memiliki skala antara 1 : 500.000 sampai dengan 1 : 1.000.000. Contoh: Peta Provinsi di Indonesia.
5. Peta geografi, yaitu peta yang memiliki skala lebih kecil dari 1 : 1.000.000. Contoh: Peta Indonesia dan peta dunia.

02 August, 2009

;

Teori Fisika

Fisika (Bahasa Yunani: φυσικός (physikos), "alamiah", dan φύσις (physis), "Alam") adalah sains atau ilmu tentang alam dalam makna yang terluas. Fisika mempelajari gejala alam yang tidak hidup atau materi dalam lingkup ruang dan waktu. Para fisikawan atau ahli fisika mempelajari perilaku dan sifat materi dalam bidang yang sangat beragam, mulai dari partikel submikroskopis yang membentuk segala materi (fisika partikel) hingga perilaku materi alam semesta sebagai satu kesatuan kosmos.

Beberapa sifat yang dipelajari dalam fisika merupakan sifat yang ada dalam semua sistem materi yang ada, seperti hukum kekekalan energi. Sifat semacam ini sering disebut sebagai hukum fisika. Fisika sering disebut sebagai "ilmu paling mendasar", karena setiap ilmu alam lainnya (biologi, kimia, geologi, dan lain-lain) mempelajari jenis sistem materi tertentu yang mematuhi hukum fisika. Misalnya, kimia adalah ilmu tentang molekul dan zat kimia yang dibentuknya. Sifat suatu zat kimia ditentukan oleh sifat molekul yang membentuknya, yang dapat dijelaskan oleh ilmu fisika seperti mekanika kuantum, termodinamika, dan elektromagnetika.

Fisika juga berkaitan erat dengan matematika. Teori fisika banyak dinyatakan dalam notasi matematis, dan matematika yang digunakan biasanya lebih rumit daripada matematika yang digunakan dalam bidang sains lainnya. Perbedaan antara fisika dan matematika adalah: fisika berkaitan dengan pemerian dunia material, sedangkan matematika berkaitan dengan pola-pola abstrak yang tak selalu berhubungan dengan dunia material. Namun, perbedaan ini tidak selalu tampak jelas. Ada wilayah luas penelitan yang beririsan antara fisika dan matematika, yakni fisika matematis, yang mengembangkan struktur matematis bagi teori-teori fisika.

Sekilas tentang riset Fisika

Fisika teoretis dan eksperimental

Budaya penelitian fisika berbeda dengan ilmu lainnya karena adanya pemisahan teori dan eksperimen. Sejak abad kedua puluh, kebanyakan fisikawan perseorangan mengkhususkan diri meneliti dalam fisika teoretis atau fisika eksperimental saja, dan pada abad kedua puluh, sedikit saja yang berhasil dalam kedua bidang tersebut. Sebaliknya, hampir semua teoris dalam biologi dan kimia juga merupakan eksperimentalis yang sukses.

Gampangnya, teoris berusaha mengembangkan teori yang dapat menjelaskan hasil eksperimen yang telah dicoba dan dapat memperkirakan hasil eksperimen yang akan datang. Sementara itu, eksperimentalis menyusun dan melaksanakan eksperimen untuk menguji perkiraan teoretis. Meskipun teori dan eksperimen dikembangkan secara terpisah, mereka saling bergantung. Kemajuan dalam fisika biasanya muncul ketika eksperimentalis membuat penemuan yang tak dapat dijelaska teori yang ada, sehingga mengharuskan dirumuskannya teori-teori baru. Tanpa eksperimen, penelitian teoretis sering berjalan ke arah yang salah; salah satu contohnya adalah teori-M, teori populer dalam fisika energi-tinggi, karena eksperimen untuk mengujinya belum pernah disusun.

Teori FISIKA Utama

Meskipun fisika membahas beraneka ragam sistem, ada beberapa teori yang digunakan secara keseluruhan dalam fisika, bukan di satu bidang saja. Setiap teori ini diyakini benar adanya, dalam wilayah kesahihan tertentu. Contohnya, teori mekanika klasik dapat menjelaskan pergerakan benda dengan tepat, asalkan benda ini lebih besar daripada atom dan bergerak dengan kecepatan jauh lebih lambat daripada kecepatan cahaya. Teori-teori ini masih terus diteliti; contohnya, aspek mengagumkan dari mekanika klasik yang dikenal sebagai teori chaos ditemukan pada abad kedua puluh, tiga abad setelah dirumuskan oleh Isaac Newton. Namun, hanya sedikit fisikawan yang menganggap teori-teori dasar ini menyimpang. Oleh karena itu, teori-teori tersebut digunakan sebagai dasar penelitian menuju topik yang lebih khusus, dan semua pelaku fisika, apa pun spesialisasinya, diharapkan memahami teori-teori tersebut.

Bidang utama dalam fisika

Riset dalam fisika dibagi beberapa bidang yang mempelajari aspek yang berbeda dari dunia materi. Fisika benda kondensi, diperkirakan sebagai bidang fisika terbesar, mempelajari properti benda besar, seperti benda padat dan cairan yang kita temui setiap hari, yang berasal dari properti dan interaksi mutual dari atom. Bidang Fisika atomik, molekul, dan optik berhadapan dengan individual atom dan molekul, dan cara mereka menyerap dan mengeluarkan cahaya. Bidang Fisika partikel, juga dikenal sebagai "Fisika energi-tinggi", mempelajari properti partikel super kecil yang jauh lebih kecil dari atom, termasuk partikel dasar yang membentuk benda lainnya. Terakhir, bidang Astrofisika menerapkan hukum fisika untuk menjelaskan fenomena astronomi, berkisar dari matahari dan objek lainnya dalam tata surya ke jagad raya secara keseluruhan.

Bidang yang berhubungan

Ada banyak area riset yang mencampur fisika dengan bidang lainnya. Contohnya, bidang biofisika yang mengkhususkan ke peranan prinsip fisika dalam sistem biologi, dan bidang kimia kuantum yang mempelajari bagaimana teori kuantum mekanik memberi peningkatan terhadap sifat kimia dari atom dan molekul. Beberapa didata di bawah:

Akustik - Astronomi - Biofisika - Fisika penghitungan - Elektronik - Teknik - Geofisika - Ilmu material - Fisika matematika - Fisika medis - Kimia Fisika - Dinamika kendaraan - Fisika Pendidikan

;

Sistem Jaringan Listrik Nirkabel

fisikaDalam sebuah konferensi hi-tech di TED Global Conference, Oxford beberapa waktu lalu, diperkenalkan sebuah sistem jaringan listrik yang tidak menggunakan kabel (wireless). Sistem ini mempergunakan teknik fisika yang cukup sederhana yang mampu menyuplai tenaga ke beberapa perangkat elektronik. Pada konferensi tersebut, pemateri menunjukkan telepon seluler dan televisi yang ditenagai oleh listrik secara wireless. Dia mengatakan bahwa sistem tersebut bisa menggantikan ribuan mil kabel dan baterai yang mahal. "Hampir 40 juta baterai diproduksi tiap tahun", katanya. Milyaran dolar juga telah dihabiskan untuk membangun infrastruktur jaringan kabel untuk menyalurkan energi listrik, lanjutnya. Ilmuwan tersebut mencontohkan dengan memakai ponsel Google G1 dan iphone Apple yang ditenagai dengan sistem tersebut. Selain ponsel, dia juga menampilkan televisi yang memakai sistem kelistrikan wireless ini. "Bayangkan, anda bisa menaruh televisi ini menggantung di dinding rumah anda tanpa perlu mencari stop kontak," ujarnya.

Bagaimanakah sebenarnya ja
ringan listrik wireless tersebut?


fisikaSistem jaringan listrik wireless berdasarkan pada teori yang awalnya dikemukakan oleh ahli fisika Marin Soljacic dari MIT (Massachusetts Institute of Technology). Konsep utama yang dipakai adalah konsep resonansi, dimana transfer energi berlangsung lebih efisien. Ketika dua benda mempunyai frekuensi resonan yang sama, akan terjadi transfer energi dengan kuat tanpa mempengaruhi benda-benda lain di sekitarnya. Sebagaimana halnya resonansi bisa memecahkan gelas saat seorang penyanyi melengking pada frekuensi yang tepat sama dengan frekuensi getar gelas. Sistem jaringan listrik wireless menggunakan 2 kumparan (salah satu pada jaringan listrik utama, dan yang lain pada perangkat elektronik). Frekuensi yang dipakai merupakan frekuensi rendah. Masing-masing kumparan dibuat sedemikian hingga mempunyai frekuensi resonan yang sama. Ketika kumparan utama dihubungkan dengan power suply, medan elektromagnetik yang dihasilkan akan berresonansi dengan kumparan kedua, sehingga terjadi aliran energi listrik. Listrik pada kumparan kedua merupakan GGL (gaya gerak listrik) induksi.

Perangkat elektronik yang memakai sistem ini akan langsung ter-charge manakala berada dalam area jangkauan medan magnetik kumparan pertama.


Aspek keamanan


Menurut ilmuwan yang mengenalkan sistem tersebut, sistem ini cukup aman karena transfer energi dilakukan melalui gelombang elektromagnetik. "Manusia dan objek-objek disekitar kita adalah benda-benda non-magnetik.", ujarnya.



fisikaPada kesempatan lain, sistem penghantaran listrik wireless ini juga diterapkan pada sistem lampu penerangan. Perusahaan Intel di San Francisco berhasil membuat rangkaian wireless lampu bohlam 60 watt yang bisa menyala pada jarak 3 kaki (36 cm) dari kumparan utama. Rangkaian ini cukup efisien, hanya kehilangan 1/4 energi mula-mula. Pada jarak yang lebih jauh (kira-kira 7 kaki atau 84 cm) tingkat efisiensinya berkisar 40-45 %.Pihak intel menamakan sistem ini dengan WREL (Wireless Resonant Energy Link) sedangkan pihak MIT menamakan witricity (singkatan wireless dan electricity)

>>www.fisikaasik.com

01 August, 2009

;

Mars (planet)

I


INTRODUCTION



mars

Mars

Unpiloted spacecraft have allowed scientists to determine thatMars’s atmosphere is mostly made up of carbon dioxide (CO2), with small amountsof nitrogen, oxygen, and water vapour. Owing to the thinness of the atmosphere,daily temperatures often vary by as much as 100° C (180° F). Surfacetemperatures are too cold and surface pressures too low for water to exist in aliquid state on Mars, so the planet resembles a cold, high-altitude desert.This view is centred on the Valles Marineris, a great chasm some 4,000 km(2,500 mi) long.


NASA

Mars (planet), planet named after the Romangod of war, the fourth from the Sun and the third in order of increasing mass.Mars has two small, heavily cratered satellites, or moons, Phobos and Deimos,which some astronomers consider to be asteroid-like objects captured by theplanet very early in its history. Phobos is about 21 km (13 mi) across; Deimos,only about 12 km (7y mi).

MarsFacts and Figures


Equatorial radius

3,396 km (2,111 mi)


Equatorial inclination

25.2°


Mass

6.42×1023 kg


Average density

3.9 g/cm3


Rotational period

1.03 days


Orbital period

1.881 years


Average distance from the Sun

228 million km (142 million mi)


Perihelion

206.7 million km (128.5 million mi)


Aphelion

249.3 million km (155 million mi)


Orbital eccentricity

0.0935


Orbital inclination

1.85°


Moons

2


Source

Data are from the US Naval Observatory's annual Astronomical Almanac and various other publications.

II


APPEARANCE FROM EARTH

When viewed without a telescope, Mars is a reddishobject whose brightness depends on its distance from the Earth. At its closest(56 million km/35 million mi), Mars is, after Venus, the brightest object inthe night sky. Mars is best observed when it is both at opposition (directlyopposite the Sun in the sky) and near perihelion (its closest approach to theSun). Such favourable circumstances repeat every 15 or 17 years.

Through a telescope Mars is seen to have brightorange regions and darker, less red areas, the outlines and tones of whichchange with Martian seasons. (Because of the 25° tilt of its axis and theeccentricity of its orbit, Mars has short, relatively warm southern summers andlong, relatively cold southern winters.) The reddish colour of the planetresults from its heavily oxidized, or rusted, surface. The dark areas arethought to consist of rocks similar to terrestrial basalts, the surfaces ofwhich have been weathered and oxidized. The brighter areas seem to consist ofsimilar but even more weathered and oxidized material and apparently containmore fine, dust-sized particles than do the dark regions. The mineralscapolite, relatively rare on Earth, seems widespread; it may serve as a storefor carbon dioxide (CO2) from the atmosphere.

Conspicuous bright caps, composed of frozen water and CO2,mark the planet’s polar regions. Their seasonal cycle has been followed formore than two centuries. Each Martian autumn, bright clouds form over theappropriate pole. Below this so-called polar hood, a thin cap of carbon dioxidefrost is deposited during the autumn and winter. By late winter, the cap mayextend down to latitudes of 45°. By the spring, and the end of the long polarnight, the polar hood dissipates, revealing the winter frost cap; the cap’sboundary then gradually recedes poleward as sunlight evaporates the accumulatedfrost. By midsummer the steady recession of the annual cap stops, and a brightdeposit of frost and ice survives until the following autumn. These remnantpolar caps consist mostly of frozen water. They are about 300 km (185 mi) wideat the south pole and 1,000 km (620 mi) wide in the north. Although their truethickness is not known, they must contain ice and frozen gases to a thicknessof possibly 2 km (1 mi).

In addition to the polar hoods—thought toconsist largely of frozen CO2—other clouds are common on the planet.High-altitude hazes and localized water-ice clouds are observed. The latterresult from the cooling associated with air masses rising over elevated obstacles.Extensive yellow clouds, consisting of dust lifted by Martian winds, areespecially prominent during southern summers.

III


OBSERVATION BY SPACECRAFT

mars

Mars Polar Lander

Mars Polar Lander was scheduled to reach the planet Mars in late1999, however it apparently crashed on landing and disappeared without trace.The lander was designed to descend to the surface with a parachute and with itsown braking rockets. Once there, its mission was to study the weather andclimate near Mars's south pole.

© Microsoft Corporation. All Rights Reserved.

The first spacecraft views of the planet wereobtained in 1965 when Mariner 4 flew past Mars and revealed the presence ofcraters on its surface, and further information was gained in 1969 from thefly-by missions of Mariners 6 and 7. Then, in 1971, Mariner 9 went intoorbit around Mars. It studied the planet for almost a year, giving scientiststheir first comprehensive global view of Mars and the first detailed images ofits satellites, Phobos and Deimos. In 1976 two Viking landers touched downsuccessfully on Mars and carried out the first direct investigations of theatmosphere and surface. The Viking mission also included two orbiters thatstudied the planet for almost two full Martian years (from 1976 to 1980). In1988 the Soviet Union sent two probes to land on Phobos; both missions failed,although one relayed back some data and photographs before radio contact waslost.

In the mid-1990s a new exploratory effortbegan, with pairs of spacecraft being sent to the planet every two years (tocoincide with each Mars opposition). The US Mars Observer probe, launched in1994, failed during 1995 just as it was entering Mars orbit, but on July 4,1997, Mars Pathfinder, comprising a 895 kg (1,973 lb) lander and a 10 kg (22lb) rover (called Sojourner), successfully put down in Ares Vallis, a sitecarefully selected at the mouth of a major outflow channel system in ChrysePlanitia. Multi-spectral cameras identified several different rock types andvariable degrees of weathering. An alpha-proton spectrometer aboard Sojournerobtained chemical analyses of selected boulders, as a result of which andesiticlavas were recorded for the first time. Sedimentary rocks containing pebbleswere also found. Some drifted material was finer than talcum powder, andseveral boulders had become coated by this strongly oxidized, windblown dustthat appears to be derived from the breakdown of basaltic bedrock. No organicor meteoritic matter was detected.

mars

Mars Odyssey Spacecraft

NASA's Mars Odyssey spacecraft carried instruments designed todetermine the minerals that make up the surface of the planet. The spacecraftalso had instruments to analyse the amount of radiation present in the planet'sorbit. This data was required in order to help scientists establish how muchradiation protection a human mission to Mars might require.

JPL/NASA

The American Mars exploration programme sufferedsetbacks at the end of 1999 with the loss of two NASA spacecraft—the MarsClimate Orbiter and the Mars Polar Lander. However, the Mars Global Surveyor(MGS), launched in 1996, went into orbit and began a detailed topographicalmapping of the planet on April 1, 1999, using a laser altimeter that enablesmeasurements to be made to an accuracy of 2 m (6 ft). A map released by NASA in1999 revealed that the northern hemisphere is about 5 km (3 mi) lower inaltitude than the south, indicating that the northern regions may have held anyoceans that existed on Mars in the past. Further support was given to the oceantheory by the profile of the Martian crust produced by the MGS, which revealed200-km (125-mi) wide subterranean channels that would once have been surfacefeatures. The three-dimensional mapping also showed that the distance betweenthe highest and lowest points on Mars is one-and-a-half times as great as thatbetween Mount Everest and the deepest ocean trench on Earth, and that thethickness of the crust is about 80 km (50 mi) beneath the southern highlandsand Tharsis ridge, compared to about 35 km (22 mi) beneath the northernlowlands and Arabia Terra. In April 2001 another probe, Mars Odyssey, waslaunched; it reached the planet’s orbit in October 2001. In May 2002 scientistsannounced that the probe had detected large quantities of water-ice crystalsless than 1 m (3 ft) below the surface over much of the planet.

mars


The Spirit Rover Lands on Mars

The panoramic camera on board the Spirit rover reveals the first360-degree view of the Martian surface. Part of the landing craft is visible inthis image taken in January 2004 after the Spirit spacecraft landed in GusevCrater, a region thought to be an ancient lake bed, located near the Martianequator.

© Microsoft Corporation. All Rights Reserved.

Three probes were launched to Mars in 2003—theEuropean Space Agency’s Mars Express and NASA’s two Mars Exploration Rovers.Mars Express went into orbit around Mars in December that year for a two-yearsurvey of the planet. As Mars Express approached the planet it released aBritish-built lander called Beagle 2, which was targeted to land on IsidisPlanitia, a lowland plain, but no communications were received from it. MarsExpress carried a stereoscopic camera, a spectrometer to map the mineralcomposition of the surface, other instruments to measure the composition of theatmosphere and plot its circulation, and a radar to penetrate the upper 2-3 km(1-2 mi) of Martian crust in search of subsurface ice and water. Inan early finding, the spectrometer confirmed that the south polar cap wascomposed of water ice and frozen CO2, thereby achieving one of itsgoals, that of identifying water in some form on Mars.

mars

Martian Rocks

This photograph, taken by the Mars Pathfinder lander in 1997,shows the surface of Mars littered with rocks. The lander had successfully putdown in Ares Vallis, which is at the mouth of a major outflow channel system inChryse Planitia.

NASA

In January 2004 two American landers, calledSpirit and Opportunity, touched down on opposite sides of the planet—Spirit ina crater called Gusev that is once thought to have held a lake, and Opportunityin an area called Meridiani Planum, where deposits of grey haematite, a mineralthat forms in the presence of water, have been detected. Both rovers weredesigned to spend at least three months exploring the surface, analysing rockand soil samples, but continued to function long beyond this limit. In August2005, NASA’s Mars Reconnaissance Orbiter was launched as a follow-up to theEuropean Space Agency’s Mars Express, and in August 2007 NASA’s Phoenix waslaunched with the aim of landing on the planet in May 2008 to explore itsclimate and geology and to continue the search for life. Next to leave for Marswill be NASA’s Mars Science Laboratory, due to be launched in 2009. Futuremissions will continue the exploration of the surface, leading eventually to areturn of Mars samples to Earth.

IV


ATMOSPHERE

The Martian atmosphere consists largely of carbondioxide (95 per cent), with smaller quantities of nitrogen (2.7 per cent),argon (1.6 per cent), and oxygen (0.2 per cent), and trace amounts of watervapour, carbon monoxide, and noble gases. The atmospheric pressure at thesurface of Mars fluctuates by about 30 per cent owing to the seasonal freezingand evaporation of CO2 at the poles; the average is about 0.6 percent of that on Earth and equal to the pressure at a height of 35 km (22 mi) inthe Earth’s atmosphere. Surface temperatures vary greatly with time of day,season, and latitude. Maximum summer temperatures may reach 17° C (63° F), butaverage daily temperatures at the surface do not exceed -33° C (-27° F). Owingto the thinness of the atmosphere, daily temperature variations of 100° C (180°F) are common. Poleward of about 50° latitude, temperatures remain cold enough(less than -123° C/-189° F) throughout the winter for some of the atmosphere’sCO2 to freeze out into the white deposits that make up much of thepolar caps.

The amount of water vapour present in theMartian atmosphere is extremely small and variable. The concentration isgreatest near the edges of the receding polar caps in spring. Mars is like avery cold, high-altitude desert. Surface temperatures and pressures are too lowfor water to exist in the liquid state in most places on the planet, althoughit exists in frozen form at the poles and just below the surface.

At certain seasons, some areas on Mars are subjectto winds strong enough to move sand on the surface and to suspend dust in theatmosphere. In the southern hemisphere between late spring and early summer,when Mars is near perihelion and the heating of southern near-equatoriallatitudes is most intense, dust storms begin to form and may reach globalproportions, obscuring the planet’s surface for weeks or even months. The dustentrained in these clouds is very fine and takes a long time to settle.

V


SURFACE AND INTERIOR

mars

Olympus Mons

Olympus Mons, in the Tharsis region of Mars, is the highestknown mountain in the solar system, rising some 25 km (15y mi) above thesurrounding plain and measuring about 600 km (370 mi) across at the base. It isa shield volcano, now extinct, which built up over millions of years insuccessive eruptions.

NASA/Corbis

In terms of geodesy, the shape of Mars isnon-spherical: there is a major bulge over the volcanic region of Tharsis, anda smaller one on the opposite side of the planet, over Elysium. Beneath Tharsisisostatic compensation (thickening of the crust below ground as well as above,to support the mass of mountainous regions) is incomplete at shallow depths,indicating that the bulge must in part be supported dynamically. Muchcontroversy surrounds its development. There is a strong likelihood thatTharsis developed over a region of thin lithosphere (the outer rock layer ofthe planet), allowing long-lived constructional volcanism.

Flying Over Mars

The Viking orbiters took more than 50,000 pictures of thesurface of Mars. This animation was created by making a mosaic of Vikingorbiter images and enhancing the natural colour to make features more apparent.The path of the animation is along Valles Marineris, a system of Martiancanyons over 4,000 km (2,400 mi) long and over 7 km (4 mi) deep in some places.

NASA

The Martian surface can be divided into twoprovinces by a great circle inclined at about 30° to the equator. The southerntwo thirds of the planet consists of ancient cratered terrain dating from theplanet’s earliest history, when Mars and the other planets were subjected tointense meteoroidal bombardment. Considerable erosion and filling of even thelargest craters have occurred since then.

Mars Pathfinder Spacecraft

The Mars Pathfinder spacecraft, launched by the United States in1997, was made up of a lander containing weather equipment and cameras, and asmall rover, which explored the surface of Mars around the lander. The landerfolded up around the equipment and the rover for the journey to Mars, and thenunfolded when it reached the planet's surface.

© Microsoft Corporation. All Rights Reserved.

The northern third of Mars has a much lesscratered, and hence younger, surface, believed to be underlain largely byvolcanic flows. Two major centres of past volcanic activity have beenidentified: the Elysium plateau and the Tharsis ridge. Some of the solarsystem’s largest volcanoes occur in Tharsis. Olympus Mons, a structure showingall the characteristics of a basaltic shield volcano, reaches an elevation ofmore than 21.3 km (13ƒ mi) and measures more than 600 km (370 mi) across its base. Nodefinite evidence exists of current volcanic activity anywhere on the planet.

Faults and other features suggestive of crustalextension are widespread on Mars. The most spectacular feature is theequatorial canyon network, Valles Marineris, which runs eastward from the crestof the Tharsis ridge for some 4,000 km (2,500 mi), ending in a region of collapsedchaotic terrain at 15° south, 40° west. In places the canyon system is 600 km(370 mi) wide and 7 km (4y mi) deep. The rectilinear pattern of its side canyons and detailsof its canyon walls indicate that it developed largely in response to tectonicforces associated with the Tharsis ridge.

mars

Searching for Water on Mars

Scientists believe that these channels in a crater wall on Marswere formed by water. The sharpness of the features and the lack of smallimpact craters covering them imply that the channels formed relatively recentlyin the history of the planet. Liquid water, therefore, could exist below thesurface of Mars.

NASA/Science Photo Library/Photo Researchers, Inc.

On the other hand, no features resulting fromlarge-scale compression have been found. Specifically, folded mountain belts,so common on Earth, are lacking, apparently indicating an absence of platetectonics. However, some scientists have suggested that during the earlyhistory of the planet some lateral crustal movements may have taken place. Thissuggests, in turn, that Mars may have developed a thicker lithosphere and mayhave had a thermal history rather different to that of the Earth. In 1999magnetic observations made by Mars Global Surveyor unexpectedly strengthenedthe case for plate tectonics in Mars's early history. They showed long stripsof rock with alternating magnetic polarities, similar to the pattern found onEarth's sea floors on either side of mid-ocean ridges where new crust is slowlyforming and spreading apart. This seems to indicate that at some point in itspast Mars's interior was hot enough both to produce a global magnetic field(which regularly switched direction, as the Earth's does) and to drive platetectonics.

Evidence of subsurface water ice prevails, especially inthe form of petal-shaped ejecta blankets around some craters, vast areas ofcollapsed chaotic terrain, and so-called patterned ground at high northernlatitudes. Among the more spectacular geological discoveries have been the hugevolcanoes of Tharsis, the equatorial canyon system, and numerous channels thatsuperficially resemble the valleys of dried-up rivers. Two major types ofchannels are known. Large outflow channels may have been formed by the suddencatastrophic release of vast amounts of liquid water from areas of collapsedchaotic terrain. Most of these channels drain from the higher southernhemisphere to the generally lower northern hemisphere. The cause of thelocalized melting of the ground ice in the source areas remains uncertain, butthese features probably date from the first third of the planet’s4.6-billion-year history. In addition to the large outflow channels, there arenumerous small channel-like features, which appear to pre-date the outflowchannels; erosion by liquid water is likely to be the cause of these, too,though the evidence is less compelling. Because liquid water cannot existpermanently on the surface of Mars today, the channels have been singled out asproof that the planet had higher pressures and warmer temperatures in the past.In the northern plains, there is considerable evidence for former strand linesand other shoreline landforms, which implies that shallow “palaeolakes” oncecovered a large part of this area. High-resolution images of the surface obtainedfrom Mars Global Surveyor have shown up features that suggest the possibilitythat water may have flowed over the Martian surface rather more recently,geologically speaking. Further than this, it was suggested in 2003 thatgeothermal activity driven by volcanic heat below ground may be able to forceunderground ice deposits to melt and briefly flow across the surface leavingtemporary “dark stains”, although evidence is inconclusive.

Yet the surface of Mars today is essentially awindblown desert. Vast expanses of sand dunes encircle the polar regions, andat much lower latitudes other wind-formed erosional features abound, allattesting to the efficacy of both depositional and erosional wind processes inthe current Mars environment.

Little is known about the interior of Mars. Theplanet’s relatively low mean density indicates that it cannot have an extensivemetallic core. Furthermore, any core that may be present is probably not fluid,because Mars does not have a measurable magnetic field. Judging from itsability to support such massive topological features as the Tharsis ridge, thecrust of Mars may be as thick as 200 km (125 mi)—five or six times as thick asthe Earth’s crust. A seismometer on board the Viking 2 lander failed to detectany definite “Marsquakes”.

VI


SEARCH FOR LIFE

The idea that life could, or even does, existon Mars has a long history. In 1877 the Italian astronomer GiovanniSchiaparelli claimed to have seen a planet-wide system of channels (Italian canali).The American astronomer Percival Lowell then popularized these faint lines ascanals and held them out as proof of a vast attempt by intelligent beings toirrigate an arid planet. Subsequent spacecraft observations have shown thatthere are no canals on Mars, and various other alleged proofs of life on theplanet have turned out to be equally illusory. The dark areas once thought tobe oases are not green, as contrast effects had made them seem to terrestrialobservers, and their spectra contain no evidence of organic materials. Theseasonal changes in the appearance of these areas are not due to any vegetativecycle, but to seasonal Martian winds blowing sterile sand and dust. Water isonly known to occur as ice on and below the surface and as trace amounts ofvapour or ice crystals in the Martian atmosphere. The strongest evidenceagainst the presence of life, however, is the thinness of the atmosphere andthe fact that the surface of the planet is exposed not only to lethal doses ofsolar ultraviolet radiation but also to the chemical effects of highlyoxidizing substances (such as hydrogen peroxide) produced by photochemistry.

Perhaps the most fundamental and far-reachingresult obtained by the Viking landers is that the Martian soil contains noorganic material (there is no reason to assume that the two landing sites arenot representative of the planet as a whole). Although small amounts of organicmolecules are continually being supplied to the surface of Mars by carbonaceousmeteoroids, this material is apparently destroyed before it has a chance toaccumulate. The results of the soil analysis for organic molecules carried outby the Viking landers provide no evidence for the existence of life.

A more difficult question is whether life has everexisted on Mars, given the strong evidence of climatic change and theindications of a previously warmer, thicker atmosphere. Suggestions thatstructures found in a meteorite discovered in Antarctica, which may have beenblasted off the Martian surface, were fossil traces of bacteria-like organismshave since been discounted. However, answering the question of life on Marswill probably involve collecting carefully selected subsurface samples andreturning them to Earth for detailed analysis.



 

1001 Ilmu Copyright © 2009 Classicstudio