Science Questions

How long does it take for a comet to form?

Tue, 23rd Feb 2016

Listen Now    Download as mp3 from the show Could The Internet Die?


Jeffrey Cobb asked:

I'm just wondering how long it takes for a comet to form?


Kat quizzed Stuart with this spacey question...Comet Holmes

Stuart - So a comet is this mixture of frozen gases and frozen ice and dust compacted together into an object, and itís different to a meteor so itís different to just the rock that we see.   Because comets, particularly, have this phenomena that as they come into our solar system, as they get near to the sun, they get bathed in sunlight, that some of these gases will start to melt and vaporise and thatís what give comets itís atmosphere and sometimes itís tail that travels across the universe.  And how long do they take to form - you kinda need to ask where do they come from? So it goes all the way back to the start to the start of our solar system. So 4.6 billion years ago, where the solar system basically consisted of a large cloud of dust and particles in a large field and, over time, these dust particles start to aggregate, start to clump together and form combinations of material that got larger and larger.  Now some of those went on to be very big and become planets but some of them remained quite small and developed into comets. And itís very difficult to say exactly how long they take to form because itís a very long time ago.  So things that are a very long time back we have quite large uncertainty, we have quite large error bars on our calculations, but some of the estimates put it around 10,000 to 100,000 years for a comet to form in the form itís in.  And surround our solar system is something called the oort cloud, which is a giant cloud of comets just sitting there waiting there and, occasionally, one of them gets bashed into and starts its journey into our solar system and either does an orbit around the sun, or goes crashing into a planet, or crashing in and out again.

Kat - I guess thatís like the 67P - Iím going to try and say it.  Come on Chris

Chris - 67P/ChuryumovĖGerasimenko.

Kat - Gerasimenko.  That was a very impressive comet in our solar system that we actually managed to land something on.

Stuart - Incredibly impressive.  And just to show how recent and how our understanding of comets is still developing, in the last few weeks the Rosetta mission has actually announced some new results, saying that their spacecraft Rosella, which is orbiting this comet, has been doing some measurements to understand the composition of the comet.  And actually, we thought whatís a comet like inside, has it got caverns, has it got holes but actually, theyíre very uniform.  This dust and frozen mix is very uniform throughout the entire comet.

Kat - I do love the idea - theyíre like the stuff at the back of the freezer of the universe, arenít they really?  All this stuff is there and has always been there.

Stuart - And thatís why itís so exciting, so it can tell us something about the very origins of our solar system.


Subscribe Free

Related Content


Make a comment

All compact material bodies form out of clouds of dust and gas. There is no set timeframe for a compact body to form. It depends on a lot of variables. The density and composition of the cloud. The amount of Spacetime turbulence plays a big role and can be boosted by a number of ways that will go into speeding the process up.
Generally a molecular cloud will be a turbulent environment to start with. If a violent event like a Supernova goes off in relatively close proximity, then a number of processes happen to the molecular cloud that inject energy in various forms.
First a huge rush of neutrinos blasts it's way through the cloud. Although weakly interacting, there will still be a large number of collisions. These can have effects like getting microscopic dust grains spinning at phenomenal speeds. These dust grains will set up through the agency of frame dragging, small vortexes throughout the cloud that will result in the accumulation of more gas and dust in the centre of each vortex.
Next will arrive ionising radiation from the SN injecting more energy and so amplifying the chaos conditions of the cloud.
This will be followed by the main player in all this.
A shockwave front emanating from the SN is spherically propagating through Spacetime. The physical mass of the star ejected spherically outwards at supersonic speeds into the Interstellar Medium.
I believe it is this fast ejector of material that slams into the Interstellar Medium setting up a Spherical Shock Wave. This freely-expanding ejector hits an inner termination shock, where its kinetic energy is thermalised, producing a very high temperature X-ray emitting plasma. Pressures inside the bubble build which helps balance the build up of interstellar gas and dust in front of the shock and maintain the expansion speed, while at the same time the high energy X-Rays ionise the gasses of the Interstellar medium ahead of the shock front.
This is a very violent event and to top it all off, the magnetic fields associated with the shockfront also act as particle accelerators giving the molecular cloud further high energy impacts.
All of this turns what was already described as a chaotic system into a maelstrom of spacetime vortices of all sizes. Some of those will blend with others, some will orbit others, all of them to different degrees will be focal points for the accumulation of higher concentrations of dust and gas spinning with the Spacetime vortex they find themselves in. The largest of these will turn into stars. Others will turn into planets. The majority will not get that big. They will just be accumulations of matter of various shapes and sizes.
The shockwave will move on triggering this process along the way as well as sending hi energy cosmic rays to travel throughout the Universe.
But now behind it, the spacetime vortexes will keep accumulating matter according to their size. The whole process comes to a stop when the largest vortex in any vicinity starts nuclear fusion. A star is born.
When that star fires up, it immediately ionises the remaining gas in it's neighbourhood and magnetically funnel's it to two opposing polar jets.
This achieves several things and it happens quickly.
By clearing all the unused gas and other ions out of the vicinity, it stops any further build up of massive bodies (planets, moons,asteroids, comets, etc).
Because it drives +ions to one polar jet and -ions to the other, it produces propulsion that drives it out of the original cloud and on it's journey around the Galaxy. Taking with it a large chunk of it's vicinity and everything it contained.
By getting rid of all that ionised gas it now leaves the remaining solid bodies in totally unbalanced orbits. The next period for this young solar system is to find balance. Most will crash into something bigger. Some will survive.

So back to the original question;

It can be a very short time as in hundreds of years, or it can take as long as it takes to build a star.

Welcome to the flowing Space Universe. arthur.manousakis, Tue, 19th Jan 2016

See the whole discussion | Make a comment

Not working please enable javascript
Powered by UKfast
Genetics Society