Tata Surya

Tata Surya[a] adalah kumpulan benda langit yang terdiri atas sebuah bintang yang disebut Matahari dan semua objek yang terikat oleh gaya gravitasinya. Objek-objek tersebut termasuk delapan buah planet yang sudah diketahui dengan orbit berbentuk elips, lima planet kerdil/katai, 173 satelit alami yang telah diidentifikasi[b], dan jutaan benda langit (meteor, asteroid, komet) lainnya.

Tata Surya terbagi menjadi Matahari, empat planet bagian dalam, sabuk asteroid, empat planet bagian luar, dan di bagian terluar adalah Sabuk Kuiper dan piringan tersebar. Awan Oort diperkirakan terletak di daerah terjauh yang berjarak sekitar seribu kali di luar bagian yang terluar.

Berdasarkan jaraknya dari matahari, kedelapan planet Tata Surya ialah Merkurius (57,9 juta km), Venus (108 juta km), Bumi (150 juta km), Mars (228 juta km), Yupiter (779 juta km), Saturnus (1.430 juta km), Uranus (2.880 juta km), dan Neptunus (4.500 juta km). Sejak pertengahan 2008, ada lima obyek angkasa yang diklasifikasikan sebagai planet kerdil. Orbit planet-planet kerdil, kecuali Ceres, berada lebih jauh dari Neptunus. Kelima planet kerdil tersebut ialah Ceres (415 juta km. di sabuk asteroid; dulunya diklasifikasikan sebagai planet kelima), Pluto (5.906 juta km.; dulunya diklasifikasikan sebagai planet kesembilan), Haumea (6.450 juta km), Makemake (6.850 juta km), dan Eris (10.100 juta km).

Enam dari kedelapan planet dan tiga dari kelima planet kerdil itu dikelilingi oleh satelit alami, yang biasa disebut dengan "bulan" sesuai dengan Bulan atau satelit alami Bumi. Masing-masing planet bagian luar dikelilingi oleh cincin planet yang terdiri dari debu dan partikel lain.

http://id.wikipedia.org/wiki/Tata_surya

The Planets and Dwarf Planets

A planet is a large space object which revolves around a star. It also reflects that star's light. Eight planets have been discovered in our solar system. Mercury, Venus, Earth, and Mars are the planets closest to the Sun. They are called the inner planets. The inner planets are made up mostly of rock. The outer planets are Jupiter, Saturn, Uranus, and Neptune. Jupiter, Saturn, Uranus, and Neptune are large balls of gases with rings around them. All eight planets travel around the Sun in a different orbit. In its orbit, there are not many other objects like the planet.

Dwarf planets are objects that are similar to planets except that they orbit the Sun in areas where there are many similar objects.

The Inner Planets The Outer Planets Dwarf Planets
Mercury Jupiter Pluto
Venus Saturn Ceres
Earth Uranus Eris
Mars Neptune Haumea

http://starchild.gsfc.nasa.gov/docs/StarChild/solar_system_level1/planets.html

Why do the planets orbit the sun?

The basic reason why the planets revolve around, or orbit the sun (rotate actually is used to describe their spin, for example, the Earth completes one rotation about its axis every 24 hours, but it completes one revolution around the Sun every 365 days), is that the gravity of the Sun keeps them in their orbits. Just as the Moon orbits the Earth because of the pull of Earth's gravity, the Earth orbits the Sun because of the pull of the Sun's gravity.

Why, then, does it travel in an elliptical orbit around the Sun, rather than just getting pulled in all the way? This happens because the Earth has a velocity in the direction perpendicular to the force of the Sun's pull. If the Sun weren't there, the Earth would travel in a straight line. But the gravity of the Sun alters its course, causing it to travel around the Sun, in a shape very near to a circle. This is a little hard to visualize, so let me give you an example of how to visualize an object in orbit around the Earth, and it's analogous to what happens with the Earth and the Sun.

Imagine Superman is standing on Mt. Everest holding a football. He throws it as hard as he can, which is incredibly hard because he's Superman. Just like if you threw a football, eventually it will fall back down and hit the ground. But because he threw it so hard, it goes past the horizon before it can fall. And because the Earth is curved, it just keeps on going, constantly "falling," but not hitting the ground because the ground curves away before it can. Eventually the football will come around and smack Superman in the back of the head, which of course won't hurt him at all because he's Superman. That is how orbits work, but objects like spaceships and moons are much farther from the Earth than the football that Superman threw. This same situation can be applied to the Earth orbiting the Sun - except now Superman is standing on the Sun (which he can do because he's Superman) and he throws the Earth.

The next question, then, is how did Earth get that velocity, since in real life there's no Superman throwing it. For that, you need to go way back to when the Solar System formed.

http://www.blogger.com/post-create.g?blogID=1569584289110040120

Kepler craft reports apparent planetary bonanza

Surveying thousands of stars for telltale twinkles that signal the passage of an orbiting planet, NASA’s Kepler spacecraft has discovered a whopping 706 candidate planets beyond the solar system. If confirmed, that motherlode would boost the number of known extrasolar planets, now estimated at 460, to well over a thousand.

The trove, announced June 15, includes evidence of five stars that have full-fledged planetary systems. These exoplanet systems, if verified, would be the first known in which each planet creates a minieclipse as it transits, or passes in front, of its parent star. The amount of dimming and the duration of a transit offer information about planets, including their size, that cannot be gleaned by less direct methods of detection.

A team including Kepler lead scientist William Borucki of NASA’s Ames Research Center in Moffett Field, Calif., has posted the findings online (at lanl.arxiv.org/abs/1006.2799 and at lanl.arxiv.org/abs/1006.2763) at arXiv.org. The discoveries were made by analyzing Kepler’s first few months of data, recorded in the spring of 2009 when the telescope examined 156,000 stars.

“This is a massively historic discovery,” says study coauthor Sara Seager, a theorist at MIT. “This is showing how the Kepler mission will revolutionize exoplanets and change the way we do exoplanet science.”

The newly reported findings don’t include details about the most interesting 400 of the 706 candidate planets, which orbit the brightest stars Kepler has surveyed. These cases may offer the most promise for finding planets with masses close to Earth‘s own. Information on these 400 planets won’t be made public until next February.

Although the five planetary systems still have to be verified, “they show that Kepler will find dozens — and likely over a hundred — stars having multiple planets that all transit in front of their host star,” says veteran planet hunter and study coauthor Geoffrey Marcy of the University of California, Berkeley. “Apparently, stars commonly house multiple planets.”

One candidate system consists of three orbs, while the other four contain two. The orbiting objects range in size from twice Earth’s diameter to slightly larger than that of Jupiter. They reside relatively close to their stars, at distances ranging from roughly one-quarter to one-half Mercury’s average separation from the sun. They are not yet confirmed planets, however, because their masses have yet to be determined.

Astronomers are already attempting to measure those masses, using ground-based telescopes to discern the tiny wobble induced in the motion of a parent star due to the tug of orbiting bodies.

“We're using the Keck telescope [atop Hawaii’s Mauna Kea] 20 nights per year just to follow up the Kepler planets,” Marcy says.

Because these stars are dim and the expected wobble signal weak, researchers may have to weigh the bodies using another method — variations in the timing and duration of transits due to the gravitational interplay among the planets in each system, says study coauthor Jason Steffen of the Fermi National Accelerator Laboratory in Batavia, Ill.

Even though the masses of the candidate planets remain unknown, the team says it has already ruled out that the bodies are companion stars that might be mimicking the minieclipses generated by transiting planets. It would be particularly unlikely that a companion star could create the pattern of eclipses seen in the candidate multiple planet systems, notes Steffen. The main confounding source that the team hasn’t entirely excluded would be a planet orbiting a neighboring star.

Once the masses of the candidates are measured and combined with their diameters from the transit observations, researchers can determine the average densities of the bodies.

“From those densities, we can distinguish rocky planets from gas giants and water worlds,” says Marcy. “Kepler is opening a future for planet hunting in which the orbits, masses, densities and architectures of full planetary systems will be captured as a quantitative family portrait.”

The findings may also bode well for finding systems similar to the Earth’s solar system and for hunting habitable planets, comments Alan Boss of the Carnegie Institution for Science in Washington, D.C., who is not a coauthor of the article analyzing the candidate planetary systems.

“The fact that multiple transiting planets are seen means that they must all orbit more or less in the same plane, like our solar system,” he says. In contrast, some recently identified planets don’t all lie in the same plane (SN Online: 5/14/10) and have probably been thrown around by gravitational interactions with other planets in the system. More sedate systems might be more likely to support life.

http://www.sciencenews.org/view/generic/id/60302/title/Kepler_craft_reports_apparent_planetary_bonanza