Selasa, 17 November 2009

asteroid



Liputan6.com, Jakarta: Badan Intelijen Negara (BIN) mensinyalir adanya agenda tersembunyi dalam misi kemanusiaan pihak asing di wilayah bencana Tsunami, Nanggroe Aceh Darussalam. Demikian diungkapkan Kepala BIN Syamsir Siregar dalam rapat kerja dengan Komisi I DPR di Gedung MPR/DPR, Senayan, Jakarta Pusat, Kamis (20/1). Hadir pula Panglima TNI Jenderal Endriartono Sutarto, Menteri Pertahanan Juwono Sudarsono.

Syamsir mengatakan, pihak asing pasti akan memanfaatkan setiap aktivitas untuk tujuan tertentu, seperti mencari tahu kondisi geografis Indonesia. Amerika Serikat, misalnya. Menurut Syamsir, pihak AS sudah lama meminta supaya Selat Malaka dikontrol oleh mereka. Dan kini ada kesempatan. Syamsir yakin sekarang AS telah memiliki foto-foto Selat Malaka dan wilayah NAD, sebelum dan sesudah diterjang gelombang Tsunami. "Saya sudah ada data mereka," tambah Syamsir.

Dengan alasan itulah, BIN sependapat dengan pembatasan waktu tiga bulan bagi militer asing di Aceh oleh pemerintah [baca: Kehadiran Militer Asing Dibatasi Hingga Maret 2005]. Dengan jangka waktu itu, Syamsir yakin Indonesia sudah mampu mengambil alih penanganan Aceh pasca-Tsunami.

Berdasarkan data yang dihimpun www.liputan6.com, BIN telah menempatkan 15 stafnya di NAD. Data BIN menunjukkan militer asing mencapai 19 ribu personel, sedangkan ribuan lainnya termasuk dalam daftar relawan. Sementara data lain menyebutkan, pascabencana gempa dan Tsunami, ada sekitar tiga ribu personel pasukan dari 11 negara yang beroperasi di daratan Aceh. Adapun belasan ribu personel militer asing berada di kapal-kapal perang.(DEN/Frans Ambudi dan Julianus Kriswanto)


On the first day of January 1801, Giuseppe Piazzi discovered an object which he first thought was a new comet. But after its orbit was better determined it was clear that it was not a comet but more like a small planet. Piazzi named it Ceres, after the Sicilian goddess of grain. Three other small bodies were discovered in the next few years (Pallas, Vesta, and Juno). By the end of the 19th century there were several hundred.

Several hundred thousand asteroids have been discovered and given provisional designations so far. Thousands more are discovered each year. There are undoubtedly hundreds of thousands more that are too small to be seen from the Earth. There are 26 known asteroids larger than 200 km in diameter. Our census of the largest ones is now fairly complete: we probably know 99% of the asteroids larger than 100 km in diameter. Of those in the 10 to 100 km range we have cataloged about half. But we know very few of the smaller ones; there are probably considerably more than a million asteroids in the 1 km range.

The total mass of all the asteroids is less than that of the Moon.

11 comets and asteroids have been explored by spacecraft so far, as follows: ICE flyby of Comet Giacobini-Zinner. Multiple flyby missions to Comet Halley. Giotto (retarget) to Comet Grigg-Skellerup. Galileo flybys of asteroids Gaspra and Ida (and Ida satellite Dactyl). NEAR-Shoemaker flyby of asteroid Mathilde on the way to orbit and land on Eros. DS-1 flybys of asteroid Braille and Comet Borrelly. Stardust flyby of asteroid Annefrank and recent sample collection from Comet Wild 2. For future we can expect: Hayabusa (MUSES-C) to asteroid Itokawa, Rosetta to Comet Churyumov-Gerasmenko, Deep Impact to Comet Tempel 1, and Dawn to orbit asteroids Vesta and Ceres.

243 Ida and 951 Gaspra were photographed by the Galileo spacecraft on its way to Jupiter. The NEAR mission flew by 253 Mathilde (left) on 1997 June 27 returning many images. eros NEAR (now renamed "NEAR-Shoemaker") entered orbit around 433 Eros (right) in January 1999 and returned a wealth of images and data. At the end of its mission it actually landed on Eros.

The largest asteroid by far is 1 Ceres. It is 933 km in diameter and contains about 25% of the mass of all the asteroids combined. The next largest are 2 Pallas, 4 Vesta and 10 Hygiea which are between 400 and 525 km in diameter. All other known asteroids are less than 340 km across.

There is some debate as to the classification of asteroids, comets and moons. There are many planetary satellites that are probably better thought of as captured asteroids. Mars's tiny moons Deimos and Phobos, Jupiter's outer eight moons, Saturn's outermost moon, Phoebe, and perhaps some of the newly discovered moons of Saturn, Uranus and Neptune are all more similar to asteroids than to the larger moons. (The composite image at the top of this page shows Ida, Gaspra, Deimos and Phobos approximately to scale.)

Asteroids are classified into a number of types according to their spectra (and hence their chemical composition) and albedo:

  • C-type, includes more than 75% of known asteroids: extremely dark (albedo 0.03); similar to carbonaceous chondrite meteorites; approximately the same chemical composition as the Sun minus hydrogen, helium and other volatiles;
  • S-type, 17%: relatively bright (albedo .10-.22); metallic nickel-iron mixed with iron- and magnesium-silicates;
  • M-type, most of the rest: bright (albedo .10-.18); pure nickel-iron.
  • There are also a dozen or so other rare types.
Because of biases involved in the observations (e.g. the dark C-types are harder to see), the percentages above may not be representative of the true distribution of asteroids. (There are actually several classification schemes in use today.)

There is little data about the densities of asteroids. But by sensing the Doppler effect on radio waves returning to Earth from NEAR owing to the (very slight) gravitational tug between asteroid and spacecraft, Mathilde's mass could be estimated. Surprisingly, its density turns out to be not much greater than that of water, suggesting that it is not a solid object but rather a compacted pile of debris.

Asteroids are also categorized by their position in the solar system:

  • Main Belt: located between Mars and Jupiter roughly 2 - 4 AU from the Sun; further divided into subgroups: Hungarias, Floras, Phocaea, Koronis, Eos, Themis, Cybeles and Hildas (which are named after the main asteroid in the group).
  • Near-Earth Asteroids (NEAs): ones that closely approach the Earth
    • Atens: semimajor axes less than 1.0 AU and aphelion distances greater than 0.983 AU;
    • Apollos: semimajor axes greater than 1.0 AU and perihelion distances less than 1.017 AU
    • Amors: perihelion distances between 1.017 and 1.3 AU;
  • Trojans: located near Jupiter's Lagrange points (60 degrees ahead and behind Jupiter in its orbit). Several hundred such asteroids are now known; it is estimated that there may be a thousand or more altogether. Curiously, there are many more in the leading Lagrange point (L4) than in the trailing one (L5). (There may also be a few small asteroids in the Lagrange points of Venus and Earth (see Earth's Second Moon) that are also sometimes known as Trojans; 5261 Eureka is a "Mars Trojan".)
Between the main concentrations of asteroids in the Main Belt are relatively empty regions known as the Kirkwood gaps. These are regions where an object's orbital period would be a simple fraction of that of Jupiter. An object in such an orbit is very likely to be accelerated by Jupiter into a different orbit.

There also a few "asteroids" (designated as "Centaurs") in the outer solar system: 2060 Chiron (aka 95 P/Chiron) orbits between Saturn and Uranus; the orbit of 5335 Damocles ranges from near Mars to beyond Uranus; 5145 Pholus orbits from Saturn to past Neptune. There are probably many more, but such planet-crossing orbits are unstable and they are likely to be perturbed in the future. The composition of these objects is probably more like that of comets or the Kuiper Belt objects than that of ordinary asteroids. In particular, Chiron is now classified as a comet.

4 Vesta has been studied recently with HST (left). It is a particularly interesting asteroid in that it seems to have been differentiated into layers like the terrestrial planets. This implies some internal heat source in addition to the heat released by long-lived radio-isotopes which alone would be insufficient to melt such a small object. There is also a gigantic impact basin so deep that it exposes the mantle beneath Vesta's outer crust.

Though they are never visible with the unaided eye, many asteroids are visible with binoculars or a small telescope.

Asteroid table

A few asteroids and comets are listed below for comparison. (distance is the mean distance to the Sun in thousands of kilometers; masses in kilograms).
No.  Name      Distance  Radius     Mass  Discoverer   Date
---- --------- -------- ------ ------- ---------- -----
2062 Aten 144514 0.5 ? Helin 1976
3554 Amun 145710 ? ? Shoemaker 1986
1566 Icarus 161269 0.7 ? Baade 1949
433 Eros 172800 33x13x13 Witt 1898
1862 Apollo 220061 0.7 ? Reinmuth 1932
2212 Hephaistos 323884 4.4 ? Chernykh 1978
951 Gaspra 330000 8 ? Neujmin 1916
4 Vesta 353400 265 3.0e20 Olbers 1807
3 Juno 399400 123 ? Harding 1804
15 Eunomia 395500 136 8.3e18 De Gasparis 1851
1 Ceres 413900 466 8.7e20 Piazzi 1801
2 Pallas 414500 261 3.18e20 Olbers 1802
243 Ida 428000 35 ? ? 1880?
52 Europa 463300 156 ? Goldschmidt 1858
10 Hygiea 470300 215 9.3e19 De Gasparis 1849
511 Davida 475400 168 ? Dugan 1903
911 Agamemnon 778100 88 ? Reinmuth 1919
2060 Chiron 2051900 85 ? Kowal 1977


NASA CLAIMS BUDGET CUTBACKS DAMNING EARTH TO FIERY HELL

August 23 2009

Washington, D.C. – The first fifteen years of human space exploration involved some of the most remarkable engineering and engaged some of the greatest of human dreams. From Sputnik to the Moon landings the exploration of space gripped the buzz aldrin moon
world’s fascination and elicited the hopes and dreams of the entire species. Since then our exploration of the heavens have been limited, at least in respect to people’s fascination. The Space Shuttle, the Hubble telescope, and the ISS have all contributed to our scientific understanding of the universe but have done little to engage the public, which has further inhibited the progress beyond the Earth.

That decline in public interest has also caused a decline in public monies being used in the advance of space exploration. NASA, the chief proponent of space travel, has for years suffered with ever declining budgets which has further inhibited their ability to inspire the kind of awe once associated with the space program. Those budgetary restrictions have also caused other issues for asteroid collision
NASA, specifically their efforts to track potentially deadly asteroids and comets coming into Earth’s realm, bodies which could destroy all life on Earth. With only one-third of the bodies currently being tracked, NASA has become frustrated with the budgetary problems and has indicated that they may give up entirely, dooming humanity to extinction.

“It shows we have a problem we're not addressing. The program is a little bit of a lame duck. There is not a big enough group pushing for the money,” said space advocate Louis Friedman. “It’s a continual source of frustration for many people within the organization and many of them are just sick of wasting their breath fighting for the necessary dollars. There has been a growing movement within NASA to just ditch the whole project and let the politicians burn with the rest of us when a comet finally comes hurtling into Earth. Of course that puts us all in a tough spot.”asteroid collision

NASA will continue to track two rocks in particular, at least for the time being. One in particular is believed to have a 1 in 3000 chance of slamming into the planet in 2048, an event that would likely obliterate all life on the planet and render it a lifeless rock.

“I think there’s a bit of bluffing going on to be completely honest. NASA often uses threats like this to try and extract more dollars out of the government, to mixed effect, and are likely doing the same thing here. The one advantage they do have here is the nature of the hell islam
event. Getting people behind studies on growth rates of raspberries in space is a tough task, but getting them to buy into a global apocalypse? Much easier,” said Scrape TV Science analyst Dr. Howard Poe. “Luckily for NASA Hollywood has been preparing the people for such an event. Movies like ‘Armageddon’ and ‘Deep Impact’ have gotten the people concerned about such an event so they are now able to capitalize on that fear. Ultimately that could mean more dollars for NASA and potentially the salvation of all life as we know it.”

Many scientists have been warning for years that an impact, much like the one that likely doomed the dinosaurs, could end human life on Earth and possibly send the planet into nuclear winter which would eventually destroy all life permanently.cardinals in hell

“Preserving life on Earth should of course be of significant interest to all people even if it means a slight increase in tax dollars. Of course the principal complaint will be why Americans should be footing the bill for the rest of the planet but sometimes that’s the price you pay for being the wealthiest country,” continued Poe. “What we can’t get caught up in is a kind of fear-mongering from NASA. Yes we know the danger is real and potentially devastating but there are only so many dollars to go around and not all of them can be allocated to one division. Any future dollars should also directed towards stopping a collision and not just spotting one, otherwise it’s really just a waste of money.”

Many critics of the NASA initiative have pointed to the relative lack of comet strikes against the planet, noting that Earth has survived for at least 65 million years previous to the space agencies efforts.


BREAKING NEWS

by Skip DeKades

asteroidJanuary 9, 2029 — Scientists at NASA Corp. revealed this morning that they have detected an asteroid heading straight for Earth, threatening to annihilate civilization. The news could have dire economic consequences, including declining consumer spending, lower advertising revenue for the Super Bowl, and a distraction from President-elect Angelina Jolie’s Jan. 20 inauguration.

NASA officials said the asteroid, detected by deep-space probes and estimated to be two miles wide, is expected to strike Earth within the year and could have the effect of 40 million Kirstie Alleys simultaneously hitting the ground and passing wind upon impact.

“Unless we can somehow change the course of the asteroid, it will wipe out civilization as we know it,” said NASA chief science officer Armand Getton during a somber press conference. “And that could have devastating effects on the economy.”

In addition to devastating a massive swath of the area surrounding the point of impact, the asteroid strike would result in the Sun being blocked for months or years by the dust dispersed, Getton said. Much of life on Earth would perish, as it did 65 million years ago when an asteroid hit Earth and wiped out the dinosaurs.

“It’s a real bummer for the dinosaurs, since it’s only been a few years since we learned how to clone them,” he said. “Now they have to go through this end-of-the-world thing all over again.”

President George Prescott Bush, who leaves office Jan. 20, said he won’t take any responsive action to the news since space is the responsibility of NASA, which became a private enterprise in 2015. NASA officials, however, have warned that they could go bankrupt trying to stop the asteroid from hitting the planet, and may have to ask for a multi-billion-dollar federal aid package.

Lotta Prepp, head of Jolie’s transition team, said the president-elect will make a statement on the crisis over the weekend. Prepp added that Jolie is angry that NASA chose to announce the pending disaster just days before her inauguration.

“It’s just gonna bum people out at a time when we want them to be celebrating,” Prepp said. “Couldn’t this bad news have waited until after Jan. 20?”








Asteroid to Crash Into Mars. Earth Saved

Mars AsteroidMars is in danger of being struck by an asteroid at the end of next month, astronomers have calculated.

The impact, however, would be tiny in comparison to that of the asteroid that struck Chicxulub in Mexico 65 million years ago, which caused a worldwide cataclysm that is thought to have wiped out the dinosaurs. The new asteroid is 100 times smaller than the 10km diameter rock that caused that event. Nothing that the 2006 hurricane season did to the US.

The scientists, at the Jet Propulsion Laboratory in La Canada Flintridge, put the chances that it will hit the Red Planet on Jan. 30 at about 1 in 75.

A 1-in-75 shot is “wildly unusual,” said Steve Chesley, an astronomer with the Near-Earth Object office, which routinely tracks about 5,000 objects in Earth’s neighborhood.

The likely impact would be on the threshold of visibility from the largest of Earth’s observatories, but its effects would readily be seen by probes orbiting the Red Planet such as the European Space Agency’s Mars Express. It will not be visible with domestic telescopes or the naked eye.

According to one of the researchers, typically the odds they look at for solar system strikes are a million to one. Anytime they have something that’s 100 to 1 or less, they sit up straight and tall in their chairs and take notice. And whereas normally they hope against the asteroid striking the surface (when Earth is in the cross-hairs), this time they’re totally behind the idea of it impacting upon the surface of Mars especially so with so many NASA assets ready to take front-row pictures.

Mars Surface

Currently the Mars Reconnaissance Orbiter is mapping Mars, and the Spirit and Opportunity rovers are on the surface preparing for a cold winter (see previous TGDaily.com coverage on Spirit and Opportunity). This would be the first time that humans have significant assets in place to observe a potentially devastating crash. In 1908 in Siberia, Russia, a similar sized asteroid broke up in the atmosphere and rained debris over an 830 square mile area, knocking down over 80 million trees. It was the largest impact with the Earth in recent history. Now wasn’t the Space Shuttle mission STS-114 supposed to study asteroid collisions?

With the thin Martian atmosphere, the asteroid will likely make it all the way to the surface, creating an impact crater 1/2 mile wide when it strikes. NASA will likely be able to get some high-gloss 8-1/2″ x 11″ photos of the asteroid as it passes through the atmosphere and impacts upon the surface.

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Tonight the largest asteroid (2007 TU24) in over 20 years will pass close to Earth

January 29, 2008 by Daniel
Filed under News

asteroid to pass close to Earth
Two nights ago I watched a program on the history channel all about asteroids and comets, today we are hearing news of the largest asteroid to pass close to the Earth in 20 years…and that will happen tonight.

Astronomers are hoping for clear skies tonight so they can get a chance to catch images of 2007 TU24 Read more




Liputan6.com, Jakarta: Badan Intelijen Negara (BIN) mensinyalir adanya agenda tersembunyi dalam misi kemanusiaan pihak asing di wilayah bencana Tsunami, Nanggroe Aceh Darussalam. Demikian diungkapkan Kepala BIN Syamsir Siregar dalam rapat kerja dengan Komisi I DPR di Gedung MPR/DPR, Senayan, Jakarta Pusat, Kamis (20/1). Hadir pula Panglima TNI Jenderal Endriartono Sutarto, Menteri Pertahanan Juwono Sudarsono.

Syamsir mengatakan, pihak asing pasti akan memanfaatkan setiap aktivitas untuk tujuan tertentu, seperti mencari tahu kondisi geografis Indonesia. Amerika Serikat, misalnya. Menurut Syamsir, pihak AS sudah lama meminta supaya Selat Malaka dikontrol oleh mereka. Dan kini ada kesempatan. Syamsir yakin sekarang AS telah memiliki foto-foto Selat Malaka dan wilayah NAD, sebelum dan sesudah diterjang gelombang Tsunami. "Saya sudah ada data mereka," tambah Syamsir.

Dengan alasan itulah, BIN sependapat dengan pembatasan waktu tiga bulan bagi militer asing di Aceh oleh pemerintah [baca: Kehadiran Militer Asing Dibatasi Hingga Maret 2005]. Dengan jangka waktu itu, Syamsir yakin Indonesia sudah mampu mengambil alih penanganan Aceh pasca-Tsunami.

Berdasarkan data yang dihimpun www.liputan6.com, BIN telah menempatkan 15 stafnya di NAD. Data BIN menunjukkan militer asing mencapai 19 ribu personel, sedangkan ribuan lainnya termasuk dalam daftar relawan. Sementara data lain menyebutkan, pascabencana gempa dan Tsunami, ada sekitar tiga ribu personel pasukan dari 11 negara yang beroperasi di daratan Aceh. Adapun belasan ribu personel militer asing berada di kapal-kapal perang.(DEN/Frans Ambudi dan Julianus Kriswanto)

Selasa, 10 November 2009

asteroid

KometTaufiq (Klub Astronomi Bondowoso)
PADA tahun 2004 ada dua komet yang bisa diamati dengan mata telanjang. Hari ini, 7 Mei, salah satu komet itu mencapai kecerlangan maksimum.
Komet atau bintang berekor adalah anggota Tata Surya yang mempunyai orbit hiperbola. Ekornya kian panjang bila mendekati Matahari. Begitu panjangnya hingga bisa mencapai 150 juta kilometer, atau sejauh jarak Bumi-Matahari atau biasa dinamakan 1 Satuan Astronomi (SA). Dengan begitu komet bisa dibilang anggota Tata Surya terbesar.
Di tahun 2004 ada dua komet yang bakal bisa diamati dengan mata telanjang, yaitu Komet C/2001 Q4 (NEAT) dan C/2002 T7 (LINEAR). Dengan bantuan teleskop kecil dan binokular, kedua komet tersebut sudah bisa diamati sejak Februari lalu. Mulai bulan Maret, baru bisa diamati dengan mata telanjang setelah kecerlangannya lebih kecil dari 6 magnitudo semu.
Magnitudo adalah skala kecerlangan obyek langit yang terlihat oleh pengamat, semakin kecil magnitudo maka akan semakin terang. Perbedaan sebesar 5 magnitudo setara dengan perbedaan kecerlangan 100 kali. Obyek terlemah yang bisa diamati oleh mata telanjang di langit memiliki magnitudo 6,5. Sebagai perbandingan magnitudo semu matahari sebesar - 26,8 dan bintang langit malam terterang, yaitu Sirius sebesar - 1, 46. Rata-rata bintang yang terang bermagnitudo dari 1 hingga 2.
Komet NEAT ditemukan pada 28 Agustus 2001 melalui program Near Earth Asteroid Tracking (NEAT), saat itu magnitudonya 20 setara dengan 400 ribu kali lebih lemah dari bintang teredup yang bisa diamati dengan mata telanjang. Namun, pada bulan April akan memiliki magnitudo sebesar 1-2 dan mencapai kecerlangan maksimum pada 7 Mei 2004, saat sejarak 48 juta kilometer dari Bumi. NEAT bergerak dalam arah rasi Canis Mayor, melewati Cancer, dan tiba di arah Ursa Mayor pada akhir Mei. Bisa diamati setelah matahari terbenam dari arah Barat-Utara bola langit. Lalu, sekitar tanggal 12-16 Mei ada pemandangan yang menakjubkan dikarenakan keberadaan empat planet terterang, yaitu Venus, Mars, Saturnus, dan Yupiter di sekitar komet.
Adapun Komet LINEAR ditemukan melalui program Lincoln Laboratory Near Earth Asteroid Research (LINEAR) pada 29 Oktober 2002 dan akan mencapai kecerlangan maksimum 19 Mei 2004 pada jarak 40 juta kilometer dari Bumi. Komet ini bergerak dari arah rasi Pisces melewati Cetus, Eridanus, dan Lepus menuju Canis Mayor. Pada pertengahan April hingga awal Mei, komet ini bisa dilihat pagi hari di arah timur. Setelah itu, komet akan terlihat di arah Barat, setelah matahari terbenam.
Kedua komet tersebut bisa dinikmati pemandangannya selama bulan Mei dengan mata telanjang bila kondisi langit cerah. Memasuki bulan Juni, kedua komet tersebut menjauhi Bumi dan Matahari.
Asal-usul
Ternyata ada kepercayaan yang mengaitkan kedatangan komet dengan munculnya bencana, seperti wabah, peperangan, dan paceklik. Dalam rekaman Babad Tanah Jawi dikisahkan pertarungan keris pusaka Kyai Sangkelat dan Kyai Condongcatur milik kerajaan Majapahit. Ternyata, Kyai Condongcatur kalah dan ujung kerisnya patah. Kemudian oleh Prabu Brawijaya, Raja Majapahit waktu itu, keris itu diperbaiki dengan cara ditempa. Sesaat akan dipalu, Kyai Condongcatur melesat ke langit, berubah menjadi komet dan mulai melakukan balas dendam dengan menurunkan bencana.
Beberapa contoh yang mengaitkan komet dengan bencana adalah peristiwa kedatangan Komet Ikeya-Seki pada tahun 1965 dengan G30S PKI. Lalu, kejatuhan kerajaan Normandia pada tahun 1066 oleh kerajaan Inggris.
Kehadiran ilmu pengetahuan modern menjadikan manusia bisa memandang kedatangan komet secara rasional. Yang menjadi pertanyaan kemudian adalah dari mana asalnya komet itu?
Adalah seorang astronom Belanda, Jan Oort mengemukakan teori bahwa Tata Surya dikelilingi awan dengan jari-jari antara 50.000 SA-100.000 SA. Awan ini tersusun dari materi berukuran kecil yang menjadi tempat pembentukan dan kemunculan komet. Untuk menghormati Jan Oort, awan itu lalu dinamai Awan Oort, dengan perkiraan populasi komet sekitar seratus triliun dan bermassa total 10-100 kali massa Bumi. Akibat gangguan bintang-bintang sekitar Matahari terhadapnya, sebagian materi awan jatuh ke bidang Tata Surya, selanjutnya tertarik oleh gravitasi Matahari dan bergerak ke pusat Tata Surya.
Fred L Whipple, astronom dari Universitas Harvard, mengusulkan pertama kali di tahun 1950 mengenai struktur komet yang berupa gumpalan es kotor (Dirty Snowballs) berdiameter 1-10 kilometer karena tersusun dari beragam senyawa seperti karbondioksida, sianida, amonia, metana, air, serta berbagai macam logam yang bercampur dengan debu dan batuan.
Ketika komet bergerak mendekati Matahari pada jarak kurang dari 3 SA, muncullah selubung gas dan debu yang berukuran 100.000 hingga 1 juta kilometer, yang dinamai Coma. Dalam bahasa latin Coma berarti 'rambut'. Dari kata inilah sebutan komet berasal. Gas dalam Coma beragam seperti CO, CO, HCN, CH, CN, air dan formaldehid. Coma ini diselubungi oleh awan hidrogen berukuran jutaan kilometer yang muncul dari disosiasi radikal hidroksil (OH) akibat radiasi Matahari pada materi yang ada di Coma.
Saat jarak komet kian dekat ke Matahari muncullah ekor komet akibat partikel-partikel yang dipancarkan Matahari (embusan angin Matahari) menguapkan materi yang menyelubungi inti komet. Ada dua jenis ekor Matahari, yaitu ekor ion yang arahnya selalu menjauhi Matahari (segaris arah Matahari-komet), dan ekor debu yang berarah melengkung ke Matahari, akibat tarikan gravitasi Matahari. Meskipun ekor itu sedemikian panjang, kerapatannya amat kecil, bahkan lebih kecil dari kerapatan ruang hampa yang mampu dibuat di Bumi.
Semakin dekat ke Matahari, maka ekor komet kian panjang. Materi yang hilang pun kian banyak. Sebaliknya, ketika menjauhi Matahari, ekor komet memendek. Komet pun kembali ke bentuk semula, namun dengan massa yang telah berkurang, ketika berada jauh dari Matahari menuju ke tempat asalnya.
Namun, tidak semua komet memiliki nasib seperti itu. Ada komet yang ditakdirkan hancur akibat gravitasi Matahari seperti Komet West yang ditemukan pada tahun 1976. Selain gravitasi Matahari, juga ada yang tertarik oleh gravitasi planet raksasa, Yupiter, yaitu Komet Halley. Komet yang terkenal ini dihitung elemen orbitnya oleh astronom Inggris, Edmund Halley, pada tahun 1705 dan ditemukan periode orbitnya yaitu setiap 76 tahun sekali. Komet yang juga mengitari planet raksasa akan memiliki bentuk orbit yang amat eksentrik, kelengkungannya besar.
Dalam catatan sejarah, pengamatan komet sudah dilakukan ratusan tahun lalu. Seiring perkembangan teknologi pengamatan, penemuan komet semakin banyak. Sudah ada ribuan komet yang ditemukan sekarang ini. Sering komet diberi nama sesuai dengan nama penemunya, baik seorang, dua atau lebih, bila ditemukan secara serentak. Contohnya Komet Shoemaker-Levy 9 yang sebagian materinya menabrak Yupiter pada tahun 1994. Komet itu ditemukan oleh pasangan Eugene dan Carolyn Shoemaker serta David H Levy pada 23 Maret 1993.
Tata cara penamaan lainnya adalah menurut tahun ditemukan dan diikuti huruf kecil pada tahun ditemukannya. Misalnya, komet ketujuh yang ditemukan pada tahun 2004 adalah 2004g.
Misi penelitian
Kandungan materi dalam komet menarik perhatian kalangan ilmuwan. Ada pendapat bahwa sumber air dan materi organik di planet-planet berasal dari komet. Dalam perjalanan melanglang ruang, komet mengumpulkan mikroorganisme beku. Kemudian selama menuju Matahari, sebagian materi itu dilepaskan lalu masuk ke Bumi dan berkembang di planet ini. Teori ini disebut Panspermia.
Tidak seperti planet, asteroid, atau obyek di Kuiper Belt, keberadaan komet seperti menyimpan banyak misteri. Hal itu dikarenakan jauh dan luas tempatnya serta jumlahnya yang amat banyak. Selain itu, juga karena tidak adanya jalur khusus orbit komet. Hal lain, materi komet semakin berkurang, setiap melewati Matahari, lalu akan mati. Karena itu, upaya penelitiannya menjadi begitu menantang. Sebagai contoh kedatangan Komet Halley pada 1986 mengundang komunitas internasional untuk melakukan penelitian seperti Uni Soviet dengan pesawat antariksa Vega 1 dan 2, Badan Penerbangan Antariksa Eropa dengan Giotto, Jepang dengan Sakigake, serta Suisei dan NASA dengan International Cometary Explorer (ICE).
Yang teranyar adalah wahana antariksa Rosetta (diluncurkan 2 Maret 2004) untuk menyelidiki Komet 67P/Churyumov-Gerasimenko selama dua tahun. Rosetta akan mendaratkan instrumen ilmiah ke komet, yang saat ini sedang mendekati Matahari, di tahun 2014.
Wahana lainnya adalah Stardust (diluncurkan 7 Februari 1999) yang menyelidiki Komet Wild 2 dan akan membawa pulang ke Bumi contoh materi koma dari komet ini pada 15 Januari 2006. Diduga, materi yang ada dalam komet merupakan materi yang terbentuk di awal kelahiran Tata Surya 4, 6 miliar tahun lampau.
Diharapkan dengan beragam misi itu akan membuka rahasia Tata Surya miliaran tahun lampau. Dengan begitu, akan lebih baik kita menikmati pemandangan komet dengan semangat ilmiah.
Sumber : Kompas (7 Mei 2004)