ALAM SEMESTA YANG HILANG

Para ahli astronomi telah mengetahui bahwa objek di alam semesta ini jauh lebih banyak daripada yang bisa kita lihat secara langsung. Itu mirip gunung es. Bagian gunung es yang kita lihat mengapung di atas permukaan air hanya sepersepuluh dari keseluruhan bongkahan gunung es. Sembilan persepuluh sisanya tersembunyi di bawah air, tak tampak.

Di alam semesta kita, gas, bintang-bintang, dan galaksi-galaksi yang bisa kita lihat hanyalah sekitar 4 persen dari keseluruhan objek yang ada. Kita bisa mengetahui ada yang tidak bisa kita lihat karena "sesuatu" yang tak tampak itu mengerahkan gaya gravitasi. Gravitasi itu menarik objek yang bisa kita lihat. Namun, gravitasi-lah satu-satunya petunjuk yang kita punyai. Objek tak tampak itu tidak memancarkan radiasi yang bisa kita deteksi sehingga para ahli astronomi menyebutnya sebagai zat gelap (dark matter).

Tersusun dari apakah zat gelap itu? Kita tidak tahu. Zat gelap bukan sekedar bintang gelap atau planet gelap atau bahkan lubang hitam. Bisa jadi zat gelap itu zarah-zarah sangat kecil yang berjumlah banyak sekali. Kita tahu, apapun wujudnya, 23% alam semesta berupa zat gelap,

ENERGI GELAP

Jadi, jika sekitar 27% alam semesta berupa zat biasa dan zat gelap, 73% sisanya berupa apa? Sesuatu yang lebih misterius lagi, bernama energi gelap. Hingga akhir 1990-an kita bahkan tidak mengenal energi gelap. Kemudian ahli astronomi menemukan bahwa alam semesta tidak hanya mengembang, tapi pengembangannya mengalami percepatan. Penemuan ini mengejutkan mereka.

Kita masih belum mengetahui sumber energi yang menyebabkan percepatan ini. Apakah sejenis medan energi ataukah sifat ruang itu sendiri? Ataukah kita sama sekali keliru dalam hal beberapa fakta dasar terkait fisika dan gravitasi? Apakah energi gelap akan menyebabkan para pakar fisika menulis ulang hukum fisika supaya bisa memahami alam semesta? Satu hal yang betul-betul kita ketahui adalah alam semesta lebih aneh dari yang pernah kita bayangkan.

Zat misterius bernama zat gelap menyelubungi semua galaksi di alam semesta, menjaganya supaya tetap bersatu dan mencegahnya tercerai berai . Kekuatan lai bernama energi gelap melakukan hal yang berlawan berusaha memisahkan segala sesuatu di alam semesta. Gabungan zat gelap dan energi gelap menyusun 96% alam semesta kita. Keduanya tak tampak bagi kita.

SEGALA SESUATU YANG KITA LIHAT ADALAH SEJARAH

Teleskop adalah mesin waktu, tapi mesin waktu yang membawa kalian ke masa lalu saja. Itu karena objek-objek di langit bukan sebagaimana keaadaan sekarang melainkan keadaannya dahulu.

Untuk memahaminya, coba ingat kalau teleskop itu mengumpulkan cahaya dari langit. Cahaya membutuhkan waktu sampai ke kita, bahkan meskipun bergerak dengan kecepatan 186.000 mil (300.000 km) per jam yang disebut kecepatan cahaya. Cahaya dari Matahari mencapai bumi dalam waktu delapan menit, jadi kita melihat matahari dalam kondisi delapan menit yang lalu.Cahaya dari pluto membutuhkan waktu empat jam untuk sampai ke kita karena harus menempuh jarak 3 milyar mil (5 milyar km)/

JARAK JAUH

Begitulah kalian bergerak keluar tata surya, jarak menjadi bukan main besarnya. Dalam setahun Bumi, cahaya menempuh jarak enam trilyun mil. Bintang terdekat dengan Matahari, Alpha Centauri, berjarak 24 trilyun mil (41 trilyun km). Pusat Bimasakti berjarak 125 ribu trilyun mil.

Angka-angka jarak menjadi sangat besar sehingga para ahli astronomi menciptakan istilah untuk menjelaskan jarak di jagat raya: tahun cahaya. Satu tahun cahaya adalah jarak yang ditempuh cahaya dalam waktu satu tahun Bumi, jadi satu tahun cahaya sama dengan enam trilyun mil (10 trilyun km). Karena cahaya dari Alpha Centauri membutuhkan waktu empat tahun hingga sampai ke kita, kita mengatakan Alpha Centauri berada pada jarak 4 tahun cahaya.

WAKTU LIHAT - KEMBALI

Waktu lihat-kembali (look-back time) adalah seberapa jauh kita kembali ke masa lalu ketika melihat objek di langit. Waktu lihat-kembali Alpha Centauri adalah 4 tahun. Bintang merah Aldebaran di rasi Taurus sekitar 65 tahun cahaya jauhnya, jadi bintang ini punya waktu lihat-kembali 65 tahun. Ketika menatap Aldebaran, kita melihat bintang itu sebagaimana keadaannya 65 tahun lalu. Itu seperti melihat foto kakek-nenek kalian ketika mereka masih anak-anak. Waktu tempuh cahaya menjadi semakin lama ketika kalian menatap keluar Galaksi Bimasakti. Sebagai contoh , galaksi terdekat dengan kita adalah galaksi spiral Andromeda, yang jauhnya 2,5 juta tahun cahaya. Cahaya yang kita lihat dari galaksi Andromeda meninggalkan galaksi tersebut ketika nenek moyang pertama manusia muncul di bumi lebih daripada 3 juta tahun lalu.

Teleskop bagaikan mesin waktu karena kita bisa melihat objek-objek sebagaimana keadaannya pada masa lalu. Cahaya dari Matahari membutuhkan waktu 8 menit 20 detik untuk sampai di Bumi, jadi kita melihat Matahari sebagaimana keadaannya 8,3 menit yang lalu.

SIKLUS HIDUP BINTANG

Para penyair boleh mengatakan bintang hidup selamanya, tapi para ilmuwan tahu itu tidak benar. Semua bintang pada akhirnya akan mati kalau bahan bakar nya habis.

Kalian mungkin mengira kalau bintang yang lebih besar akan hidup lebih lama karena punya lebih banyak bahan bakar. Tapi, makin cepat bintang membakar bahan bakarnya, dan makin pendek masa hidupnya. Bintang paling masif akan hidup beberapa juta tahun saja, sedangkan yang paling tidak masif bisa hidup selama trilyunan tahun.

Semua bintang menghabiskan sebagian besar hidupnya  untuk menggabungkan hidrogen dan mengubahnya menjadi helium di intinya. Fusi nuklir ini menciptakan energi yang kita lihat sebagai cahaya bintang. Akhirnya inti bintang pun kehabisan hidrogen. Seperti itulah akhir hidup bintang bermassa rendah seperti Matahari kita.

Ketika bintang bermassa lebih tinggi kehabisan hidrogen, bintang tersebut bisa mulai membakar helium di inti dan menghasilkan karbon dan oksigen. Bintang yang paling masif bisa membakar unsur yang lebih berat dan lebih berat lagi hingga intinya penuh dengan besi yang sangat rapat dan panas. Itulah akhir perjalanan hidup bintang tersebut, karena tidak ada energi yang dihasilkan dari reaksi fusi besi.

Semua bintang berasal dari nebula (ilustrasi kiri atas), tapi masing-masing menempuh jalan hidup yang berlainan. Bintang-bintang yang lebih kecil (baris atas) berakhir sebagai katai putih yang mungil. Namun, bintang yang lebih masif (baris bawah) meledak sebagai supernova, meninggalkan lubang hitam atau bintang neutron

International Space Station Enables Interplanetary Space Exploration

Technology demonstrations aboard the International Space Station help drive space exploration.

Image Credit: 

NASA

The first 3-D printer ever tested in orbit, now operating aboard the International Space Station, may help to manufacture parts quickly and cheaply in space.

Image Credit: 

NASA

If necessity is the mother of invention, then survival in space breeds many “children.” These children are the research and technologies demonstrated aboard the International Space Station. For 16 years, the station has provided researchers a platform in microgravity where they perform experiments and test technologies to allow humans to travel farther into the solar system than ever before. From life support systems to growing plants in space, the space station continues to drive human exploration for missions beyond low-Earth orbit.

NASA’s Orion spacecraft, which is set to blast off on its first flight test in December, will demonstrate many technologies first tested aboard the space station. Orion, built to transport humans into deep space, embarks on a two-orbit, four-hour "Trial By Fire" on Dec. 5 to test many of its critical systems.

"Without what we’ve learned from having a continuous human presence in space for more than a decade, we wouldn’t be able to think about sending people into deep space onboard Orion,” said Mark Geyer, Orion Program manager. “We’re testing out technologies and concepts on the space station right now that are necessary for the kind of long-duration trips Orion enables.”

Technology demonstrations aboard the station beget new systems and concepts for on Earth and for space exploration. For example, the amine swingbed, which uses organic compounds with modified ammonia atoms, controls carbon dioxide and humidity in Orion. This type of recovery system also can operate on Earth to help remove carbon dioxide and humidity in tight spaces, like in mine tunnels or submarines.

With successful demonstrations of 3-D printing on the space station, the potential now exists to manufacture parts quickly and cheaply in space. Instead of waiting for a cargo delivery, astronauts could replace filters or faulty equipment simply by printing new parts. Researchers are gaining insight into improving 3-D printing technology on Earth by testing it in microgravity. This knowledge could help advance industry printing methods.

Environmental control and life support systems (ECLSS) aboard the station support humans in space. ECLSS includes wastewater recycling to provide clean water for bathing and drinking. It also includes oxygen generation systems to provide air for crews to breathe. These and other components of ECLSS help cut transportation costs for resupply and provide astronauts a habitable environment. This technology demonstration helps engineers design and develop improved closed-loop life support systems for long duration spacecraft.

"Testing various life support sub-systems is an ideal use of the space station," said George Nelson, manager of NASA’s International Space Station Technology Demonstration. "Reliability of these systems on long duration missions is paramount. We can verify design reliability in the microgravity environment by using them on the station without any mission or crew risk, since the existing space station systems are always available."

Human behavioral health and performance also is taken into account for deep space missions where crew members reside in confined spaces for long periods of time. One study evaluates the effects of delayed communications for interplanetary crews that have to handle medical and other emergencies. This type of research also may help refine procedures for Earth-based teams that operate in extreme or remote environments with limited contact with a home base and its experts. Additionally, NASA recently announced funding for three proposals to help answer questions about neurological conditions related to behavioral health and performance on deep space exploration missions.

Finally, plant growth facilities on the station like Veggie may one day produce safe, fresh and nutritious crops for astronauts while giving the crew opportunities for relaxation and recreation. Using these facilities, researchers can glean knowledge about plant growth and development in microgravity. This information may improve growth, biomass production and farming practices on Earth.

Necessities for survival in space breed innovations aboard the space station. Like a mother to her child, these inventions areimproving life on Earth and, one day, may support humans on the planets beyond. 

Jay Perry, Environmental Control and Life Support Systems engineer, discusses how systems aboard the International Space Station provide and recycle air and water to eliminate the need for resupply on cargo spacecraft.

Laura Niles
International Space Station Program Science Office and Public Affairs Office
NASA’s Johnson Space Center

( http://www.nasa.gov/mission_pages/station/research/news/orion_tests_technology/index.html#.VIV6WDGG9uA )

Exploring Comets and Asteroids is an International Endeavor

NASA and space agencies across the globe are opening up new possibilities for space exploration with missions to comets, asteroids, and other celestial bodies.

Following NASA, European Space Agency (ESA), and Indian Space Research Organisation (ISRO) spacecraft observations of the close flyby of Mars by comet Siding Spring in October, and the successful November landing of ESA’s Philae lander on comet 67P/Churyumov–Gerasimenko, the Japan Aerospace Exploration Agency (JAXA) successfully launched its Hayabusa2 mission on Dec. 3 to rendezvous with an asteroid, land a small probe plus three mini rovers on its surface, and then return samples to Earth.

Asteroid Explorer “Hayabusa2” is a successor of “Hayabusa” (MUSES-C), which revealed several new technologies and returned to Earth in June 2010.

Image Credit: 

JAXA and Akihiro Ikeshita

NASA and JAXA are cooperating on the science of the mission and NASA will receive a portion of the Hayabusa2 sample in exchange for providing Deep Space Network communications and navigation support for the mission.

Hayabusa2 builds on lessons learned from JAXA’s initial Hayabusa mission, which collected samples from a small asteroid named Itokawa and returned them to Earth in June 2010. Hayabusa2’s target is a 750 meter- wide asteroid named 1999 JU3, because of the year when it was discovered by the NASA-sponsored Lincoln Near-Earth Asteroid Research project, Lexington, Massachusetts. This is a C-type asteroid which are thought to contain more organic material than other asteroids. Scientists hope to better understand how the solar system evolved by studying samples from these asteroids.

“We think of C-type asteroids as being less altered than others,” says Lucy McFadden, a planetary scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “Bringing that material back and being able to look at it in the lab — I think it’s going to be very exciting.”

On Nov. 17, NASA and JAXA signed a Memorandum of Understanding for cooperation on the Hayabusa2 mission and NASA’s Origins, Spectral Interpretation, Resource Identification, Security – Regolith Explorer (OSIRIS-REx) mission to mutually maximize their missions’ results. OSIRIS-REx is scheduled to launch in 2016. It will be the first U.S. asteroid sample return mission. OSIRIS-REx will rendezvous with the 500-meter-sized asteroid Bennu in 2019 for detailed reconnaissance and a return of samples to Earth in 2023.

Hayabusa2 and OSIRIS-REx will further strengthen the two space agencies’ relationship in asteroid exploration.

The missions will also help NASA choose its target for the first-ever mission to capture and redirect an asteroid. NASA's Asteroid Redirect Mission (ARM) in the 2020s will help NASA test new technologies needed for future human missions for the Journey to Mars.

Comets and asteroids contain material that formed in a disk surrounding our infant sun. The hundreds of thousands of known asteroids are leftovers from material that didn't coalesce into a planet or moon in the inner solar system. The thousands of known comets likely formed in the outer solar system, far from the sun's heat, where water exists as ice.

Larger objects, like dwarf planets Pluto and Ceres, also formed in the outer solar system, where water ice is stable. Pluto and Ceres will soon be explored by NASA missions New Horizons and Dawn, respectively. Asteroids and comets are of unique interest to scientists, though, because they could hold clues to the origins of life on Earth.

These missions have greatly increased scientific knowledge on Earth about our solar system and the history of our planet. Many scientists suspect we could find organic material in asteroids and comets, like amino acids—critical building blocks for life, which could help answer questions about the origins of life on Earth. These questions drive us to continue exploring the intriguing asteroids and comets of our solar system.

Multiple missions that are operating in space or in development by NASA and international partners could bring us much closer to answering that question in our lifetimes and also help identify Near-Earth Objects that might pose a risk of Earth impact, and further help inform developing options for planetary defense. 

Follow the latest missions and discoveries at:

http://www.nasa.gov/asteroid-and-comet-watch/

( http://www.nasa.gov/content/exploring-comets-and-asteroids-is-an-international-endeavor/index.html#.VIV5ODGG9uA )