Friday, October 29, 2010

Moons in the Solar System (2 of 2)

Our Moon was thought to be the only one in the solar system until Galileo discovered four celestial objects orbiting Jupiter through his telescope back in 1610. Today, we know there are many more moons in the Solar System.  Here are some that are special:

Saturn's Rings
Saturn's thirty plus rings are technically made of billions of moons.  They can be as small as a pebble and as big as a city.  The rings of Saturn were believed to have formed when comets pushed Saturn's early moons too close for comfort.  Those moons were ripped and shredded into pieces by Saturn's gravity, eventually forming rings of rocks and ice debris around the planet.

Enceladus (Saturn)
Enceladus is Saturn's sixth largest moon and is only 300 miles across.  It is one of the brightest objects in the Solar System, reflecting almost all light from the sun thanks to its ice covered surface. Saturn's gravity acts on  Enceladus' core to create active volcanic eruptions. Surprisingly the plumes are short on lava, but consist mainly of salt, ice vapours and simple organic compounds.  This makes the planet a very intriguing place for those studying astrobiology.

Titan (Saturn)
Titan is Saturn's largest moon, and the second largest in the Solar System. It has a dense atmosphere composed of nitrogen and methane.  Here in Titan, where temperatures are cold, methane exists in liquid form. When it rains liquid methane, you can expect rain drops to be twice as large as those on Earth. The overall terrain here is like that of Earth, but instead of water, you have lakes and rivers of CH 4. The abundance of methane makes Titan another interesting place to study for life.

Europa (Jupiter)
Europa is the smallest of the Galilean satellites.  It is believed to be covered by a layer of ice as its surface temperature is -200°C. Underneath the thick ice however, there is a warm ocean underneath heated by the moon's core due to Jupiter's gravity influence. Life? Maybe.

Io (Jupiter)
Io is the innermost of Jupiter's Galilean moons.  It has no visible geologic feature from space because of its ferocious geologic activities. The moon has over 400 active volcanoes and they constantly change the face of the moon. Io's active core is due to tidal frictional forces between Jupiter and the other three Galilean moons.

Triton (Neptune)
Triton is Neptune's largest moon. It is the only moon that spins opposite to the spin of its planet. As such, Triton is said to be a captured planet years ago from the outer reaches of the Solar System. The moon is in danger of being teared apart by Neptune's gravity at some point in the future.


Monday, October 11, 2010

Moons in the Solar System (1 of 2)

Moons are interesting celestial bodies.  Until recent years, they are often overlooked in favour of other astronomical objects like stars and planets.  So what really is a moon?  By definition, a moon is a natural satellite that orbits a planet.  

It is important to note that gravity plays a role in shaping a planet's moons. Too much gravity and the moon is destroyed. Too little of it and the moon floats away until is no longer a moon. In this and the next articles, we will focus on the moons in our Solar System. Let's start with the one we know best!

Earth's Moon and the Giant Impact Hypothesis

Several theories have been postulated on the formation of our moon. The Apollo mission was sent to the moon in 1969 during which rock samples were secured. These moon rocks were found to be almost identical to those of Earth's crust.  The catch however, is that the rocks were super heated. How could this be? 

The story goes that Earth was actually hit by a Mars-sized planet named Theia about 4.5 billion years ago. This was back in Earth's formative days and the orbits of the planets in the solar system were still unstable. At one point, Earth's gravity distorted Theia's orbit and it eventually collided with Earth at just under 4m/s. The impact destroyed Theia and Earth barely survived. The debris of the impact were ejected into space and gravity eventually pulled it all into the moon. 

The angle of the impact had significant implications. A head-on collision would have destroyed both planets.  A glancing blow would have only sliced off a piece of our planet.  Laboratory experiments showed that it was a 45-degree angle impact which took out a big chunk of Earth and led to cirumstances we see today.

In its current orbit, the moon is 260 000 miles from Earth.  When it first formed  however, it was only 1 500 miles from Earth.  It was the moon's gravity that slowed down Earth's rotation cycle from 6 hrs to 24 hrs. Thanks to the moon, we now have 4x more time to use in a day!