Saturday, 16 February 2008

Apakah Kita Sendiri?

Arip Nurahman
Department of Physics
Faculty of Sciences and Mathematics, Indonesia University of Education


Follower Open Course Ware at Massachusetts Institute of Technology
Cambridge, USA
Department of Physics
Aeronautics and Astronautics Engineering

Sepi, sendiri mengarungi lautan sang kala diatas butir biru kehampaan, terbentang dihorizon langit malam, tidak diragukan kesendirian mengajak kita berderai air mata, melantunkan sajak penderitaan karena terpasung masa yang silam. ada yang datang dan pergi dari palung kalbu, ada yang berdegup ketika kenangan datang, masihkah ada...harapan..ataukah aku memang sendiri disini...Agaknya kesepian masih senantiasa memayungiku. Kesepian ini kini merasuk hingga ke tulang-tulangku...
Adakah disana menungguku....atau Kau melupakanku...

Extraterrestrial life

A 1967 Soviet Union 16 kopeks postage stamp, with a satellite from an imagined extraterrestrial civilization.

A 1967 Soviet Union 16 kopeks postage stamp, with a satellite from an imagined extraterrestrial civilization.
Extraterrestrial life is life originating outside of the Earth. It is the subject of astrobiology, and its existence remains hypothetical. There is no credible evidence of extraterrestrial life that has been widely accepted by the scientific community. There are several hypotheses regarding the origin of extraterrestrial life if it exists. One proposes that it may have emerged, independently, in different places in the universe. An alternative hypothesis is panspermia, which holds that life emerging in one location then spreads between habitable planets. These two hypotheses are not mutually exclusive. The study and theorization of extraterrestrial life is known as astrobiology, exobiology or xenobiology. Speculative forms of extraterrestrial life range from sapient or sentient beings to life at the scale of bacteria.
Suggested locations that might have once developed or continue to host life include the planets Venus[1] and Mars, moons of Jupiter and Saturn (e.g. Europa,[2] Enceladus and Titan). Gliese 581 c and d, recently discovered to be near Earth-mass extrasolar planets apparently located in their star's habitable zone, and having the potential to have liquid water.[3]


Scientific search for extraterrestrial life

The scientific search for extraterrestrial life is being carried out in two different ways, directly and indirectly.

Direct search

The planned NASA Kepler mission for the search of extrasolar planets.

The planned NASA Kepler mission for the search of extrasolar planets.
Scientists are directly searching for evidence of unicellular life within the solar system, carrying out studies on the surface of Mars and examining meteors that have fallen to Earth. A mission is also proposed to Europa, one of Jupiter's moons with a possible liquid water layer under its surface, which might contain life.
There is some limited evidence that microbial life might possibly exist or have existed on Mars.[16] An experiment on the Viking Mars lander reported gas emissions from heated Martian soil that some argue are consistent with the presence of microbes. However, the lack of corroborating evidence from other experiments on the Viking indicates that a non-biological reaction is a more likely hypothesis. Recently, Circadian rhythms have been allegedly discovered in Viking data. The interpretation is controversial, see Viking biological experiments. Independently in 1996 structures resembling nanobacteria were reportedly discovered in a meteorite, ALH84001, thought to be formed of rock ejected from Mars. This report is also controversial and scientific debate continues.
In February 2005, NASA scientists reported that they had found strong evidence of present life on Mars.[17] The two scientists, Carol Stoker and Larry Lemke of NASA's Ames Research Center, based their claims on methane signatures found in Mars' atmosphere that resemble the methane production of some forms of primitive life on Earth, as well as their own study of primitive life near the Rio Tinto river in Spain. NASA officials soon denied the scientists' claims, and Stoker herself backed off from her initial assertions.[18]
Though such findings are still very much in debate, support among scientists for the belief in the existence of life on Mars seems to be growing. In an informal survey conducted at the conference in which the European Space Agency presented its findings, 75 percent of the scientists in attendance reported to believe that life once existed on Mars; 25 percent reported a belief that life currently exists there.[19]
The Gaia hypothesis stipulates that any planet with a robust population of life will have an atmosphere that is not in chemical equilibrium, which is relatively easy to determine from a distance by spectroscopy. However, significant advances in the ability to find and resolve light from smaller rocky worlds near to their star are necessary before this can be used to analyze extrasolar planets

Indirect search

Terrestrial Planet Finder - A planned Infrared interferometer for finding Earth-like extrasolar planets (as of 2007 , it has not received the funding from NASA it needs — that funding is going towards the Kepler mission).

Terrestrial Planet Finder - A planned Infrared interferometer for finding Earth-like extrasolar planets (as of 2007 , it has not received the funding from NASA it needs — that funding is going towards the Kepler mission).
It is theorised that any technological society in space will be transmitting information. Projects such as SETI are conducting an astronomical search for radio activity that would confirm the presence of intelligent life. A related suggestion is that aliens might broadcast pulsed and continuous laser signals in the optical as well as infrared spectrum;[20] laser signals have the advantage of not "smearing" in the interstellar medium and may prove more conducive to communication between the stars. And while other communication techniques including laser transmission and interstellar spaceflight have been discussed seriously and may not be infeasible, the measure of effectiveness is the amount of information communicated per unit cost, resulting with the radio as method of choice.

Extrasolar planets

Astronomers also search for extrasolar planets that they believe would be conducive to life, such as Gliese 581 c and OGLE-2005-BLG-390Lb, which have been found to have Earth-like qualities.[21][22] Current radiodetection methods have been inadequate for such a search, as the resolution afforded by recent technology is inadequate for detailed study of extrasolar planetary objects. Future telescopes should be able to image planets around nearby stars, which may reveal the presence of life (either directly or through spectrography which would reveal key information such as the presence of free oxygen in a planet's atmosphere):
Artist's Impression of Gliese 581 c, the first extrasolar planet discovered within its star's habitable zone.

Artist's Impression of Gliese 581 c, the first extrasolar planet discovered within its star's habitable zone.
  • Darwin is an ESA mission designed to find Earth-like planets, and analyze their atmosphere.
  • The COROT mission, initiated by the French Space Agency, was launched in 2006 and is currently looking for extrasolar planets -- it is the first of its kind
  • The Terrestrial Planet Finder was supposed to be launched by NASA, but as of 2007, budget cuts have caused it to be delayed indefinitely
  • The Kepler Mission, largely replacing the Terrestrial Planet Finder, to be launched in November 2008
It has been argued that Alpha Centauri, the closest star system to Earth, may contain planets which could be capable of sustaining life.[23]
On April 24, 2007, scientists at the European Southern Observatory in La Silla, Chile said they had found the first Earth-like planet. The planet, known as Gliese 581 c, orbits within the habitable zone of its star Gliese 581, a red dwarf star which is a scant 20.5 light years (194 trillion km) from Earth. It was initially thought that this planet could contain liquid water. However, recent computer simulations of the climate on Gliese 581c by Werner von Bloh and his team at Germany's Institute for Climate Impact Research suggest carbon dioxide and methane in the atmosphere would create a runaway greenhouse effect. This would warm the planet well above the boiling point of water (100 degrees Celsius/212 degrees Fahrenheit), thus dimming the hopes of finding life. As a result of greenhouse models, scientists are now turning their attention to Gliese 581 d, which lies just outside of the star's traditional habitable zone.[24]
On May 29, 2007, the Associated Press released a report stating that scientists identified twenty-eight new extra-solar planetary bodies. One of these newly discovered planets is said to have many similarities with Neptune.[25]
To date, 313 extrasolar planets have been discovered (with 29 multi-planet systems), with new discoveries occuring monthly.[26]

Drake equation

Main article: Drake equation
In 1961, University of California, Santa Cruz astronomer and astrophysicist Dr. Frank Drake devised the Drake equation. This controversial equation multiplied estimates of the following terms together:
  • The rate of formation of suitable stars.
  • The fraction of those stars which contain planets.
  • The number of Earth-like worlds per planetary system.
  • The fraction of planets where intelligent life develops.
  • The fraction of possible communicative planets.
  • The “lifetime” of possible communicative civilizations.
Drake used the equation to scientifically state that there are an estimated 10,000 planets containing intelligent life with the possible capability of communicating with Earth in the Milky Way galaxy.[27]
Based on observations from the Hubble Space Telescope, there are at least 125 billion galaxies in the universe. It is estimated that at least ten percent of all sun-like stars have a system of planets[28], thus if a thousandth of a percent of all stars are sun-like, and there are roughly (estimates may vary) 500 billion stars on average in each galaxy[citation needed], then there are 6.25*1018 stars with planets orbiting them in the universe. If only a billionth of these stars have planets that support life, there are 6.25 billion life-supporting solar systems in the universe.


Pertanyaan ini telah dicoba untuk dirumuskan secara matematis oleh Prof. Frank Drake di tahun 1960-an. Prof. Frank Drake menyusun rumus ini pada pertemuan mengenai SETI (Search of Extra Terrestrial Intelligence /Pencarian Kehidupan yang cerdas di luar Bumi) di Green Bank, Virginia Barat.


Mari kita sedikit bermain hitung-hitungan, menggunakan persamaan yang dirumuskan oleh Prof. Drake, sbb:

N = R* × fp × fe × fl × fi × fc × ft

N = jumlah peradaban di dalam galaksi kita, yang memungkinkan kita bisa melakukan kontak.;

R* = rasio pembentukan bintang di dalam galaksi kita

fp = fraksi dari bintang-bintang yang mempunyai planet

fe = rata-rata jumlah planet yang berpotensi punya penunjang hidup per-bintang (yang mempunyai planet)

fl = fraksi dari yang di atas dimana ada kehidupannya berkembang

fi = fraksi dari yang di atas dimana kehidupannya mengembangkan kecerdasan

fc = fraksi dari peradabaan yang mengembangkan teknologi, yang bisa mengirimkan sinyal tentang keberadaannya, ke luar angkasa

ft = rentang waktu peradaban tersebut untuk mengirimkan sinyal ke luar angkasa

Tentu saja angka-angka yang berada pada sisi kanan tidaklah selalu disepakati oleh banyak pihak. Tetapi, tidaklah salah untuk mencobakan satu atau dua angka tertentu sebagai pendekatan awal, sehingga bisa menggambarkan kemungkinannya. Bahkan kita bisa mencoba asumsi kita sendiri.

Pada tahun 1961, Prof. Drake mempergunakan pendekatan angka-angka sebagai berikut:

R* = 10/tahun (10 bintang terbentuk dalam setahun)

fp = 0.5 (setengah dari setiap bintang terbentuk punya planet)

fe = 2 (2 planet per bintang memungkinkan adanya kehidupan)

fl = 1 (100% dari setiap planet mengembangkan kehidupan)

fi = 0.01 (1% dari setiap kehidupan mengembangkan kecerdasan)

fc = 0.01 (1% yang bisa berkomunikasi)

ft = 10000 tahun (hanya bisa terjadi komunikasi setelah 10000 tahun, setelah sinyal dikirimkan)

Maka N = 10 × 0.5 × 2 × 1 × 0.01 × 0.01 × 10,000 = 10. Baiklah, ada 10 kemungkinan peradaban lain di luar sana yang mungkin berkomunikasi dengan kita. Tapi apakah benar demikian adanya?

Nilai R* bisa diterima karena memang banyak ditemukan di alam dari pengamatan-pengamatan; demikian juga dengan nilai fp tidak terlalu diperdebatkan. Tetapi angka-angka yang lain masih harus di uji lagi, dan disesuaikan dengan pengamatan-pengamatan terkini.

Penemuan terkini tentang planet-planet gas di dekat orbit bintang menyebabkan nilai fe semakin tidak pasti, karena memberikan keragu-raguan apakah planet yang mempunyai penunjang-hidup, dapat bertahan di dalam sistem bintang? Sebagai tambahan, kebanyakan bintang di dalam galaksi merupakan raksasa merah, dengan radiasi UV yang sangat kecil, menambah kecil kemungkinan adanya planet yang bisa ditinggali. Alih-alih terjadi semburan energi bintang pada UV oleh bintang, semburan terjadi pada sinar-X, yang malah menyebabkan adanya erosi pada atmosfer planet. Jadi apakah mungkin suatu planet dengan penunjang kehidupan bertahan dalam kondisi seperti itu?

Selain itu, adanya kemungkinan jika planet-planet gas tersebut mempunyai bulan yang mempunyai kemungkinan adanya kehidupan
(seperti contoh kasus satelit Jupiter Europa) menambah ketidak-pastian-nya menjadi semakin besar.

Angka-angka untuk fl, fi dan fc, sampai sekarang masih menjadi perdebatan.

Perdebatannya melibatkan Geologi, Biologi dan semua ilmu yang berkaitan dengan bagaimana asal muasal planet Bumi serta kehidupannya. Penemuan adanya kehidupan di Mars menambah keruwetan dalam menentukan angka-angka tersebut, jika kehidupan di Mars berasal dari proses pembentukan yang berbeda dengan di Bumi, maka angka fl harus lebih lagi. Itu pun, jika ada kecerdasan lain, apakah mereka akan berpartisipasi dalam mencari kehidupan di luar planet-nya? Apakah mereka peduli mereka sendirian atau tidak di alam semesta? Mempunyai kecerdasan, berarti mempunyai kebebasan untuk memilih, sekalipun memiliki teknologinya, tetapi jika tidak berminat mencari tahu, maka kita di Bumi tidak akan pernah tahu. Atau, jangan-jangan, malah mereka sudah datang kesini, sudah mencoba berkomunikasi dengan kita?

Nilai ft, hanya berlaku untuk daerah di sekitar Matahari, sementara berapa jauh alam semesta ini? Luas sekali. Jika saja ada suatu peradaban yang mengirimkan pesan ke Bumi setelah 10ribu tahun dan baru kita terima sekarang,

Sampai saat ini, angka-angka yang diterapkan dalam perumusan tersebut masih dianggap spekulatif, tetapi, spekulatif atau bukan; rumus yang dibuat oleh Prof. Drake memberikan harapan, bahwa, secara statistik, masih ada kemungkinan kehidupan lain di luar Bumi, dan ini menjadi pijakan untuk kita terus menerus melakukan pengamatan, studi astronomi dan mencari tahu tentang banyak hal yang sampai saat ini belum kita ketahui tentang alam semesta kita.


"Akan tiba masanya ketika sang kala mempertemukan kita dan kita telah benar2 siap memulai awal dan mengarungi akhir dibawah payung kebesaran sang Maha cerdas semoga tetap lestari kenangan ini serta harapan yang dikandungnya"

-(for u all)-.

See also

Events and objects
Searches for extraterrestrial life


  1. ^ "Venus clouds 'might harbour life'". BBC News (2004-05-25). Retrieved on 2007-12-05.
  2. ^ a b c"
  3. ^ "The Habitability of Super-Earths in Gliese 581". Retrieved on 2007-12-01.
  4. ^ "Ammonia based life".
  5. ^ Plants on Other Planets
  6. ^ "Variety of extraterrestrial life".
  7. ^ "Star Struck, a letter to a Rabbi".
  8. ^ Kaplan, Rabbi Aryeh. "Extraterrestrial life".
  9. ^ Revelation, Rationality, Knowledge & Truth, by Mirza Tahir Ahmad. Chapter; The Quran and Extraterrestrial Life
  10. ^ Wiker, Benjamin D.. "Christianity and the Search for Extraterrestrial Life".
  11. ^ "Rheita.htm".
  12. ^ An intelligent design : Controlled hominization in cosmic apartheid
  13. ^ Crichton, Michael (January 17, 2003). "Aliens Cause Global Warming".
  14. ^ SETI: Search For Extra-Terrestial Intelligence
  15. ^ Rare Earth: Why Complex Life is Uncommon in the Universe: Books: Peter Ward,Donald Brownlee
  16. ^ Spherix: Makers of Naturlose (tagatose), a natural, low-calorie sugar made from whey that may be useful as a treatment for Type 2 diabetes
  17. ^ Berger, Brian (2005). "Exclusive: NASA Researchers Claim Evidence of Present Life on Mars".
  18. ^ "NASA denies Mars life reports", (2005).
  19. ^ Spotts, Peter N. (2005-02-28). "Sea boosts hope of finding signs of life on Mars", The Christian Science Monitor. Retrieved on 2006-12-18.
  20. ^ "The Search for Extraterrestrial Intelligence (SETI) in the Optical Spectrum". The Columbus Optical SETI Observatory.
  21. ^ "" .
  22. ^ - Major Discovery: New Planet Could Harbor Water and Life
  23. ^ 1997AJ 113.1445W Page 1445
  24. ^ Hopes dim for life on distant planet -
  25. ^ BBC NEWS | Science/Nature | Planet hunters spy distant haul
  26. ^ Extrasolar Planets Encyclopedia
  27. ^ Boyd, Padi. "The Drake Equation". Imagine the Universe. NASA. Retrieved on 2008-02-05. "Frank Drake's own current estimate puts the number of communicating civilizations in the galaxy at 10,000"
  28. ^ Marcy, G.; Butler, R.; Fischer, D.; (2005). "Observed Properties of Exoplanets: Masses, Orbits and Metallicities". Progress of Theoretical Physics Supplement 158: 24 – 42. doi:10.1143/PTPS.158.24.
  29. ^ Possibility of Life on Europa
  30. ^ BBC NEWS | Science/Nature | Water 'flowed recently' on Mars
  31. ^ - Scientists Reconsider Habitability of Saturn's Moon
  32. ^ - Lakes Found on Saturn's Moon Titan
  33. ^ "Lakes on Titan, Full-Res: PIA08630" (2006-07-24).
  34. ^ Venusian Cloud Colonies :: Astrobiology Magazine - earth science - evolution distribution Origin of life universe - life beyond :: Astrobiology is study of earth science evolution distribution Origin of life in universe terrestrial

Further reading

External links

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