For more than a year, astronomers have eagerly watched as an icy visitor from the outer limits of the solar system has hurtled toward the sun. This cosmic “ghost” has now entered our neighborhood among the inner planets, and it’s expected to provide an impressive light show that could last into January.
If it holds together, and if you know when and where to look, you may be able to catch a glimpse of comet ISON – a 3-mile-wide chunk of ice and dust that has journeyed billions of miles over billions of years.
The Mini Page spoke with an astronomer and comet specialist at the McDonald Observatory in Austin, Texas, to learn more about these ancient and mysterious objects.
A comet recipe
All of the comets we know of – nearly 5,000 of them – are as old as the solar system itself, at about 4.5 billion years old. This makes them primordial, or “from the beginning.”
The same processes that later created the planets also created comets, asteroids and many moons. While asteroids are composed mainly of solid rock and metals, comets are more like balls of dust and dirt, loosely packed together. They also contain a large amount of ice and frozen gases. These key ingredients make them special.
It was long believed that comets formed in the coldest reaches of the solar system. However, in the past 10 years, NASA probes have discovered that certain comets include particles that are created only in extreme heat, which means they must have formed near the sun before moving to the outer solar system. This brought up many more questions for astronomers to answer: How did comets end up so far out? What moved them? Why do they return?
Where comets live
Most comets likely come from two regions of the solar system located beyond Neptune. The closer area is called the Kuiper Belt. This group of objects includes Pluto, which was once considered a planet but is now classified as a dwarf planet.
The other region is known as the Oort Cloud. This dark, unknown area of space is believed to be a massive cloud of icy objects that surrounds the entire solar system. However, the existence of the Oort Cloud has not been confirmed, as no one has ever observed it.