Hubble Eye of infinity

The Hubble telescope, with a new camera installed in March 2002, reveals the cosmos more clearly than ever before, sending back exquisite views of a complex universe.
Hubble was built to be tuned up in orbit. But it wasn't designed for the major overhaul NASA astronauts undertook during its fourth servicing mission, 3B, in March 2002. They delved into the telescope's guts during long space walks, like the one shown here illuminated by a sunlit crescent of Earth, and replaced parts that the original designers never thought they'd need to.
Installation of a new power-control unit forced an unprecedented and nerve-wracking shutdown of the entire satellite—a move comparable to a surgeon stopping a patient's heart during surgery, says Anne Kinney, NASA's director of astronomy and physics. Astronaut John Grunsfeld raced to finish the task before the temperature of the switched-off telescope dropped far enough to damage it. Would it power back up? "When you run a computer for 12 years, you don't know what kind of ghosts you have in the system," Kinney says. When all systems reactivated as planned, the astronauts, as well as astronomers and mission controllers on the ground, breathed a collective sigh of relief. The rest of the mission went like clockwork, including installation of a new cooling system for Hubble's near-infrared camera—NICMOS—useful for surveying dusty and cold areas of space, and installation of new solar panels and other science equipment.

It was the most challenging service mission ever attempted in space, and its success elated astronomers. Chief among the wonders was the long-awaited ACS, or Advanced Camera for Surveys. It essentially made Hubble into a new telescope. "ACS has roughly ten times the discovery power of the previous camera," says Mario Livio, astronomer at the Space Telescope Science Institute in Baltimore. Translation: Hubble can now see twice as much with five times more light sensitivity.

Tragically, this mission would be the last successful voyage for space shuttle Columbia;. The disaster in February 2003 grounded Discovery, Atlantis, and Endeavour, the three remaining shuttles, and will delay plans to bring Hubble a spectrograph and a new wide-field camera with ultraviolet and infrared capability.

Asteroid Belt

An asteroid is a bit of rock. It can be thought of as what was "left over" after the Sun and all the planets were formed. Most of the asteroids in our solar system can be found orbiting the Sun between the orbits of Mars and Jupiter. This area is sometimes called the "asteroid belt". Think about it this way: the asteroid belt is a big highway in a circle around the Sun. Think about the asteroids as cars on the highway. Sometimes, the asteroid cars run into one another. When this happens, the asteroids may break up into smaller asteroids. Scientists think that most asteroids are the result of collisions between larger rocky space bodies.

Asteroids can be a few feet to several hundred miles wide. The belt probably contains at least 40,000 asteroids that are more than 0.5 miles across.

If an asteroid is captured by the gravitational pull of a planet, the asteroid can be pulled out of the belt and go into orbit as a moon around the planet that pulled on it.

Solar System Live

Welcome to Solar System Live, the interactive Orrery of the Web. You can view the entire Solar System, or just the inner planets (through the orbit of Mars). Controls allow you to set time and date, viewpoint, observing location, orbital elements to track an asteroid or comet, and a variety of other parameters. Click on the title of any control to display a help page explaining it, or go directly to the help table of contents. You can compose a request with custom settings and save the results in your browser's hotlist or bookmark table, allowing direct access to Solar System Live with all the controls preset to your own preferences.

Condensation of Protosun and Protoplanets

As the nebula collapses further, instabilities in the collapsing, rotating cloud cause local regions to begin to contract gravitationally. These local regions of condensation will become the Sun and the planets, as well as their moons and other debris in the Solar System.


While they are still condensing, the incipient Sun and planets are called the protosun and protoplanets, respectively.

Collapsing Clouds of Gas and Dust

A great cloud of gas and dust (called a nebula) begins to collapse because the gravitational forces that would like to collapse it overcome the forces associated with gas pressure that would like to expand it (the initial collapse might be triggered by a variety of perturbations---a supernova blast wave, density waves in spiral galaxies, etc.).
It is unlikely that such a nebula would be created with no angular momentum, so it is probably initially spinning slowly. Because of conservation of angular momentum, the cloud spins faster as it contracts.

Nobula information

The Spinning Nebula Flattens
Because of the competing forces associated with gravity, gas pressure, and rotation, the contracting nebula begins to flatten into a spinning pancake shape with a bulge at the center, as illustrated in the following figure.

Evidence for the Nebular Hypothesis

Because of the original angular momentum and subsequent evolution of the collapsing nebula, this hypothesis provides a natural explanation for some basic facts about the Solar System: the orbits of the planets lie nearly in a plane with the sun at the center (let's neglect the slight eccentricity of the planetary orbits to simplify the discussion), the planets all revolve in the same direction, and the planets mostly rotate in the same direction with rotation axes nearly perpindicular to the orbital plane.

The nebular hypothesis explains many of the basic features of the Solar System, but we still do not understand fully how all the details are accounted for by this hypothesis. As we discuss in the next section, we now have some direct observational evidence in support of the nebular hypothesis.

The Solar System

What is the solar system? It is our Sun and everything that travels around it. Our solar system is elliptical in shape. That means it is shaped like an egg. The Sun is in the center of the solar system. Our solar system is always in motion. Eight known planets and their moons, along with comets, asteroids, and other space objects orbit the Sun. The Sun is the biggest object in our solar system. It contains more than 99% of the solar system's mass. Astronomers think the solar system is more than 4 billion years old.

Astronomers are now finding new objects far, far from the Sun which they call dwarf planets. Pluto, which was once called a planet, is now called a dwarf planet.

The Solar System

The Solar System consists of the Sun those celestial bound to it by gravity. These objects are the eight planets and their 166 known moons; three dwarf planets (Ceres, Pluto, and Eris) and their four known moons; and billions of small bodies, including asteroids, Kuiper belt objects, comets, meteoroids, and interplanetary dust.

In broad terms, the charted regions of the Solar System consist of the Sun, four terrestrial inner planets, an asteroid belt composed of small rocky bodies, four gas giant outer planets, and a second belt, the Kuiper belt, composed of icy objects. Beyond the Kuiper belt is the scattered disc, the heliopause, and ultimately the hypothetical Oort cloud.

In order of their distances from the Sun, the terrestrial planets are:

• Mercury
  
• Venus
  
• Earth
  
• Mars
  

The outer gas giants (or Jovians) are:

• Jupiter
  
• Saturn
  
• Uranus
  
• Neptune
  

The three dwarf planets are

• The asteroid belt.
• Pluto, the largest known object in the Kuiper belt.
• Eris, the largest known object in the scattered disc.

Six of the eight planets and two of the dwarf planets are in turn orbited by natural satellites, usually termed "moons" after Earth's Moon, and each of the outer planets is encircled by planetery rings of dust and other particles. All the planets except Earth are named after deities from Greco-Roman mythology.