Ask us About Space: Vol. 1

How big is the Universe?

Our best estimate is that the Universe is 93 billion light years in diameter.

Currently this is a question with no definite answer. The current limit on how much Universe there is comes from the age of the Universe. At 13.7 billion years old, any light seen from Earth has only had 13.7 billion years to travel here from its source. Using the known speed of light it is possible to calculate a limit of how far into the Universe is visible from Earth, but this is not the true size.

The Universe is expanding, meaning that even though any light has only had 13.7 billion years to travel here, because the space it is moving through is expanding, it has covered a much greater distance.

The current best estimate for the size of the observable universe is around 93 billion light years in diameter. This puts the Earth around 46 billion light years from the observable edge.

If the Universe started with a big bang, will it end with one?

Maybe, we aren’t really sure.

There are many theories as to how our universe will end. The 3 main ones are sort of related and all depend on the density of the universe. The first is called the Big Rip. We know that the universe is currently expanding, and it seems to be accelerating. It is thought that if it keeps expanding, we could get to a point where it starts to break down. It is unsure what would happen as the universe tore itself apart.

Another idea is that we will get something called the Big Crunch. As the universe expands, we may one day see this expansion start to slow. If it slows enough the universe may stop expanding and start to collapse in on itself. We could then have the universe as everything crashes back together and heats up to recreate the conditions found moments after the Big Bang.

The final element of this trio is the Big Bounce. This is a postulated scenario that has another Big Bang following the Crunch, restarting our Universe. These three represent a small selection of the possible ends to our Universe. As it currently stands, we don’t have enough information to work out what will be the ultimate fate of the Universe.

Will the rings around Saturn eventually make a moon?

It is thought to be unlikely that Saturn’s ring system will ever form one large moon.

Saturn’s rings are an extensive ring system, with more than ten different sections of rings but the ring system is extremely thin, only an average of ten meters thick, and made up of mostly very small ice particles so even a moon made from all the ring particles would only be a few hundred kilometres across.

There are many moonlets within the ring system which are proposed to have formed from material in the rings, but these are usually from several hundred metres to a few kilometres in diameter, much smaller than the objects we usually call rings.

Some of the rings are known to be actively replenished by mechanisms such as the moon Enceladus shooting ice from cryovolcanoes into the ring system. This type of process would make it difficult for particles in that ring to coalesce together to form another moon, or even a moonlet.

There is evidence for other moons of the Solar System to have formed this way, for example our own Moon is thought to have formed from the left-over debris after a planet sized body crashed into Earth early in its history.

How much junk is there in space?

The simple answer: too much.

It is extremely difficult to calculate or observe how much there actually is, but the latest numbers have found more than 20,000 objects larger than 10cm being tracked, and an estimated 700,000 objects larger than 1cm, not to mention a possible 170 million objects larger than 1mm.

Due to the incredibly high speeds of these objects, up to 56,000km per hour, even tiny debris can seriously damage operational spacecraft. The amount of debris left over in orbit around the Earth is becoming a significant concern for many organisations and governments.

With this in mind, there have been many proposed missions to help clean up debris from around the Earth. One of the more popular ideas is a space harpoon; a ‘chasing’ satellite could harpoon larger debris before dragging it down to burn up in the Earth’s atmosphere. Whether this design or any other triumphs, this category of space missions will certainly see great advances over the next five to ten years.

How different is Moon rock and Earth rock?

They are very different, because they formed in different environments.

While most of the minerals in Moon rocks are found on Earth, they were formed in very different environments. Moon rock shows evidence of formation in an extremely dry setting, with low gravitational influence and very little surrounding oxygen.

This is completely opposed to the Earth environment at the time of formation, between three and four billion years ago. Lunar rocks also contain trapped gases from the solar wind passing them at the time of formation. The solar wind is a continuous stream of charged, highly energetic particles originating at the Sun and moving out in all directions. The gases found in lunar samples match the isotope ratios expected for gas from this source, and significantly different to isotope ratios found on Earth.

Overall there are many differences between Moon rock and Earth rock; some were expected but others were great discoveries made by investigating the samples brought back by the Apollo missions.

Are there any caves on the moon and could we put a moon base there?

There is no conclusive evidence for any caves on the Moon at this time but there are some theories.

Some photos from both the Japanese SELENE and American Lunar Reconnaissance Orbiter mission have indicated that caverns may exist on the Moon. It is impossible to determine from the photos whether these caverns stretch down into caves under the surface.

If caves did exist on the Moon there is certainly an argument that they could make a suitable location for a Moon base. The temperatures on the Moon vary between about 100 degrees C in daytime sunlight and down to -150 degrees C during the Moon’s night (the Moon’s day equals roughly 29.5 Earth days). The temperatures inside a cave, once you get a few metres under the Moon’s surface, should stay roughly constant at about -40 degrees C – much easier to deal with!

What is the longest period comet we know about?

Comet West takes about 250,000 years to go around the Sun.

Comets can have short periods of up to 200 years (such a Halley’s Comet with a period of 76 years) or long periods between 200 to potentially millions of years.

Ideally, to know the period of a comet you would need to observe it twice and measure the time between observations to ascertain its period.  However, while comets have been observed for thousands of years it is very difficult to state with certainty whether a long period comet observed today could be one, we have seen before.

Consequently, scientists have to map the trajectory of a comet and extend it to estimate its period.  This process is by no means accurate as interactions with other solar system bodies and loss of mass due to evaporation of volatile materials can all alter the orbital properties of comets.

Can I contribute to science as an amateur?

Yes, there are many projects looking for assistance from amateurs.

For as long as people have been experimenting amateurs have been contributing to science. Some of our humanities biggest discoveries were made by non-professionals.

A great example of that is Reverend Robert Evans who is one of the most prolific supernova hunters, using only a 10-inch reflecting telescope and his spare time. Getting involved in science is now incredibly easy thanks to the internet. One of the most famous citizen science projects is SETI, which is searching for alien life. On top of that the fantastic zooniverse project covers all sorts of science for finding galaxies to counting animals on the Serengeti.