Friday, May 28, 2010

Beyond the Planets

Welcome back to What's Up?

Over the last two months we have explored the eight planets and even ventured through the asteroid belt. Moving beyond the planets, we come across dwarf-planet Pluto.

Pluto and its three moons; Charon,
Nix, and Hydra.
Pluto used to seem like a very peculiar object because it is tiny and so far from the sun, beyond chilly Neptune's orbit. When discovered in 1930 by Clyde Tombaugh it was supposed be Planet X.

Planet X had been made up to explain Uranus' strange orbit. Pluto just happened to be near where the hypothetical planet was supposed to be. It turns out the math was wrong and there wasn't a need for Planet X!

Pluto itself is remarkably small, even smaller than our moon, and is more like a giant comet in composition. This world hardly spans the width of the United States!

Pluto has three moons, one of which is almost half the diameter of the dwarf-planet! It is so big compared to Pluto, that the two orbit around each other, almost as if they were dancing. 

It even turns out that this "unique" object is actually one of hundreds or possibly thousands! Dwarf-planet Eris, another icy world, is even bigger than Pluto and there are many of these objects left to be discovered.

This region from Neptune's orbit and outwards is now known as the Kuiper belt. The Kuiper belt is similar to the asteroid belt, but almost all of the objects are icy worlds.

In 2015 we will get our first up-close look at Pluto and hopefully other icy worlds as NASA's New Horizon's space probe will zoom past Pluto and fly through the Kuiper belt.

Getting to Pluto and other Kuiper belt objects is nothing short of remarkable. Pluto lies fifty times further from the Sun than the Earth! This distance is greater than 7 billion kilometers (4.5 billion miles).

This may seem like a ridiculous distance but there are even more distant objects that orbit the Sun. Welcome to the Oort cloud. The Oort cloud is a spherical cloud of city-sized icy comets that orbit the Sun at a distance of up to one thousand times farther away than the Kuiper belt.

This distance so immense that it takes light a full year to travel from the Sun to the outermost comets. Astronomers call this distance the "light-year," which is roughly 10 trillion kilometers (6 trillion miles).

There are potentially billions of comets at this distance and the scary part is if another star comes close enough, the gravitational nudge from the star can knock some of the comets out of their orbits and send them flying towards the inner solar system. Thankfully, the nearest star is four light years away and has little effect on the Oort cloud.

Although most of the comets don't come very close to the Sun, some do. Many, like Halley's Comet, are quite spectacular with very beautiful tails of gas and dust streaming off of them as they are heated up and partly vaporized by the Sun.

These beautiful and graceful objects also have a dark side. The effects from a large rogue comet slamming into the Earth would be the same as an asteroid hitting us.

Let's just hope that funding for Earth-based observatories hunting for these dangerous objects isn't cut. A little advance warning could allow us to intercept the comet and push it off-course so it wouldn't hit us.

The last really big impact was 65 million years ago. Comets and asteroids don't hit very often so there isn't too much to worry about.

There won't be any close-ups with a comet next month, so let's see what else is up in next month's sky.

The new moon will be on May 14 and will become full by May 27.

Brilliant Venus will be visible low in the western sky shortly after sunset throughout the month. It will be the brightest star-like object in the sky.

At the same time, Mars will be a dull orange-red colour, spending the month in the south-western area of the sky in the constellation Leo, the lion.

Saturn will be a dim yellow this month in the constellation Virgo the virgin (southern sky after sunset) just off to the left of Leo.

The monthly meeting of the Athena Community Astronomy Club will be on the last Sunday of the month, May 30. The meeting goes from 7pm to 9pm at the Wilmot Community Centre. Guests are always welcome.

Until next month, just look up!

Hey Kids...
Did you know that orbits of the planets and moons don't stay the same? Our moon is drifting away from the Earth by a little over an inch per year. There are even two of Saturn's moons that like to change things up. Every four years the inner moon catches up to the outer moon and they swap orbits! These moons, Janus and Epithemius, are very similar to a large asteroid or comet. Who knows what else is out there? The sky is the limit.