What will happen to Comet Holmes?

[flying red fox]

Iam thinking it collided with an Asteriod and smashed to pieces, i hope its not the case, will it return?

I was watching it for a while early this morning while not getting much sleep, was a nice clear night and the temp was -3, brrr! Luckily it was within view of my bedroom window.

[brucemstrs]

As far as I aware nothing unusual has happened to comet Holmes. apart from the sudden eruptions of gases which have increased by many times the comets magnitude.

Even this has happened before, though I don't believe anyone knows exactly why it should happen in this erretic way.

It's orbital period is about 7 years, and almost circular around the sun, so it is not so eccentric in it's movements like most comets are, and it has no points at which it's closeness to the sun is greatly changed.

It does inhabit that area where asteroids also exist, but it has done so successfully for an awful long time.

[carlos_dfc]

3 possibilities as to what happened...

As has already been mentioned - asteroid strike - well it IS currently smack-bang in the middle of the asteroid belt.
Not all that likely though, because as Bruce says - it's been successfully passing through the asteroid belt for literally eons - and asteroids aren't nearly as close to each other as Sc-Fi movies etc would have you believe.

Asteroid near-miss - more likely than a 'strike'.
Many comets are not one solid lump, but are a conglomeration of smaller pieces, held together by gravity, with the gaps filled in with loose dust/gravel/ice.
A near-miss could cause some pieces to move relative to each other, dislodging the loose 'packing' - which has subsequently 'outgassed' to form the huge coma that we are seeing now.
(That coma is actually larger in extent than Jupiter )

Third, and most likely cause is a collapsing 'sink-hole'
As I said, many comets made up of smaller pieces, but sometimes the gaps aren't completely filled - these gaps are 'sink-holes'
If one collapsed, you'd get pretty-much the same effect as a near-miss by another object.

Holmes has done this before - in 1892 - in fact, it was the 1892 outburst which made it prominent enough to be discovered by Holmes in the first place.

And as for what will happen to it - well, the coma is already beginning to be blown away from the comet by the solar wind, creating a (currently very dim) tail. The main body of the comet itself, will continue to orbit, the same way it alwasy has.
Even if it breaks up - the pieces will all still pretty-much follow the same orbit that the original comet had.

Comet Schwassmann-Wachmann (SW3) broke up last year - all the pieces continued merrily on their way - following each other, all on a fairly similar course.

[brucemstrs]

Well explained Carlos - Thanks for that.

[petermcgain]

That coma is actually larger in extent than Jupiter

Good to get more info on the comet, thanks for that, but I'm slightly puzzled as to the comet's size as it must be MANY times bigger than Jupiter as it appears so large. I understand the comet is somewhere between Mars and Jupiter in its distance from Earth and would therefore appear quite small. What am I missing here?!

[wildlifesnapper]

Hi

according to one of the papers holmes is now larger than the sun making it the largest thing in the solar system.

Just to compare;

here is a photo taken on 3rd of november.



and here is one taken with the same telescope and at the same magnification last night.



neil

[The Black Rabbit]

What SUPERB photographs Neil!
Cheers for sharing them!
Doug

[brucemstrs]

Refer back to the explanation given by Carlos above.

The Comet is indeed a small object, made up mainly of ice. When comets approach the Sun they start to give off material as gas as they become affected more and more by radiated energy from the Sun. The closer they approach, the more they become affected, the brighter becomes their Corona and Tail.

Imagine it as a kind of evaporation which becomes visibly brighter as a Corona around the comet. The solar wind, energy radiating from the Sun, sweeps this gas away from the parent,forming a trail across space , this is the Comet's tail, which will always be formed in the direction diametrically away from the Sun. ( The direction of the Solar Wind ).

The reason for some puzzlement with Comet Holmes, is in its more stable orbit out near Jupiter. It does not approach the Sun in any drastic way, making these eruptions of gassy Corona a little more difficult to explain.

[sometimes]

What are the chances that the trajectory of the comet will change with the presumed (on my part) expulsion of material? I guess a comet is relatively light so any force would tend to have an effect. The effect may be a fraction of a degree in one direction, but over the course of it's orbit it might have significance? A fraction of a degree might bring it closer to earth next time round?

[paulchandler6]

A very informative thread. Something I am interested in but know little about. Thanx

Paul

[brucemstrs]

Hi Sometimes. You are correct that the emissions from Comet Holmes would push it into a new orbit ( Newtons first Law, ' To every action there is an equal and opposite reaction'.)

But consider. The Corona formed around Holmes is spherical. It is therefore reasonable to assume there are emissions from all around the Comet, and any acting in opposing directions will cancel each other out. Only the excess energy will remain to affect the orbit, and the forces produced by sublimation (the conversion of ice into gas) are very small indeed in the first place. Certainly nothing like like enough to overcome the forces holding in it's present orbit

The force required to push Comet Holmes into an orbital collision with Earth is far in excess of that available.

Even if it were possible, you still have the minor problem of hitting a moving bullseye at 400,000,000 miles away whilst you are moving in a different direction at the same time.

Is it possible ?? Well, I suppose it might be if you have a very vivid imagination, but you have far more chance of winning the lottery.

[Muggsy]

fascinating, would it be possible to see this comet from the southern hemisphere ?
forgive me if that is a really stupid question please I know even less than Paul.

[brucemstrs]

Unfortunately, apart from the slight tilt of the Earth to the orbital plane, which allows minor seasonal overlaps of astral views, the Northern and Southern hemispere have their own separate views of the heavens.

Comet 17P Holmes is a northern hemisphere object, mostly out of view very far south of the equator. It appears in our Northern sky at around 50 degrees above the horizon.

A little additional afterthought for 'Sometimes' who was wondering if the emissions could change the Comet's orbit. I'm sure we have all seen the steamy evaporation of the water drops on our car when the sun shines on them. Well, it's a little bit like wondering if those forces of evaporation could push our car up the road. We know there are forces involved but not in any way significantly.

[sometimes]

I must admit I don't have an appreciation of how big comets are. And I guess the only force likely to affect is when particles leave the object, so if the whole mass is still travelling as one then I presume there will be no trajectory change, but if some mass is leaving then a slight trajectory change might occur.

The exhaust of a car would have impact I'm sure if the car were in space, without air resistance, and overwhelming gravity. I know that the tiniest forces can have a cumulative effect. We are talking about years of travel in the case of a comet. In this case, it sounds like it takes a bit of a nudge every time it comes close the sun - perhaps something similar as it passes (if does) the bigger planets.

I presume some boffin somewhere will have calculated the size of the activity and worked out relative forces.

[brucemstrs]

Hi Sometimes, You are right of course, those forces do have an effect, and it is accumulative, but they are so small when compared to any objects sizeable enough to be seen from such a distance.

Do you remember Comet Shoemaker/Levy? That did get tugged out of it's orbit, but it took a planet the size of Jupiter and even then it took many orbital passes before the cumulative effect caused the break-up of the comet, and then it's fatal plunge right into Jupiter itself. It completed it's final orbit around the Sun in bits.

Go to :- Comet Shoemaker-Levy 9 FAQ

It records the end of that Comet which broke into over 70 pieces, the largest of which was still over 2 kilometers wide, and impacted Jupiter with a fireball that would have incinerated most of the Earth.

Not something easily pushed about, even in pieces.

Now of course, it has become another one of those ancient wanderers now gone. In the early days of the Solar System, there were masses of bits and pieces flying everywhere, aggregating together to form the Planets themsleves. When the Planets became established they were still very much in the firing line of all the remaining uncaptured bits. These were responsible for the masses of impact craters on Planets and Moons throughout our system. These impacts becoming less and less frequent as the objects diminished in number.

Those remaining are less and less likely to fall foul of anything since their orbits have avoided problems for billions of years.

[carlos_dfc]

Originally Posted by Muggsy

fascinating, would it be possible to see this comet from the southern hemisphere ?
forgive me if that is a really stupid question please I know even less than Paul.

It's current position is right next to the bright star Mirfak, in Perseus - at a declination of about 50° North.

This means that it is only possible to see it if yor lattitude is further North than 40° South.
In practical terms though, you really need to be no more than 35° south - from there it will get a maximum of 5° above the Northern horizon - at 25°s it will get 15° above the Northern horizon - etc........

No idea where you are Muggsy - but it is possible to see it from as far South as Australia.
Obviously the further North, the better, but a couple of examples - From Darwin, it will be about 25° above the Northern horizon, at midnight - from Sydney, it will be only 6° above the horizon

[petermcgain]

There's some really interesting info on this thread, but I have a couple more queries, if only to answer people who are asking me questions simply because I keep telling them there's a comet in the sky and they should be looking at it! It hasn't appeared to move very much in relation to Perseus - how fast is it actually travelling and in which direction is it going and for how long will it remain visible? Sorry, that's three questions.

[carlos_dfc]

Originally Posted by petermcgain

There's some really interesting info on this thread, but I have a couple more queries, if only to answer people who are asking me questions simply because I keep telling them there's a comet in the sky and they should be looking at it! It hasn't appeared to move very much in relation to Perseus - how fast is it actually travelling and in which direction is it going and for how long will it remain visible? Sorry, that's three questions.

First-off
How long will it be visible?
Well - as it disperses, it's getting dimmer - still naked-eye, but may not be for much longer. Will probably be a binocular/small telescope object for at least a few weeks after that though.

I made this little chart more than a week ago - it shows Holmes' track against the sky - it is currently MUCH closer to Mirfak than in that chart, VERY close now, and expected to pass 'above' Mirfak on 19th/20th Nov (tonight/tomorrow)
It'll probably no longer be naked-eye by the time it gets much beyond the end of the dotted line on that chart.



As for it's ACTUAL speed - not sure, but a quick work-out.........
Average orbital radius - about 3.6 AU (335 million miles)
*1AU is the average distance of Earh from the Sun - about 93 million miles*
(335 million x 2) multiplied by 'pi' gives the distance it travels in one orbit....
2105 million miles
One orbit takes about 6.9 years - so 2105 / 6.9 = 305 million miles per year
305 mil / 365 = 835,000 miles a day
Or roughly 35,000 mph

***important note***
These figures are by no means accurate - they are only a rough 'ball-park' estimate.
Above figures are all worked out from averages - comets have an elliptical orbit, and travel faster when near 'perihelion' (nearest point to the Sun - and slower at 'aphelion' (furthest point)
Holmes is currently headed out towards aphelion, so should be going slower than that 35,000 mph.

[petermcgain]

Thanks for the response Carlos. Again, it's very helpful and informative.

[Muggsy]

has anyone answered "elementary my dear Watson" yet ?

sorry, I'll get my coat.

[Strontium]

These threads are annoying, as I dont have much cash to spend on a telescope!

I have a general question about this comet though, and I know bits and pieces about astronomy - no expert. If the comet has a more circular orbit so close to the sun, (is it actually part of the asteroid belt called a main belt comet?) does it mean it has something to do with the theory of the planet that might have existed there, or failed to form, and if so is the composition likely not to be exactly the same as other commets from the kuiper belt etc? Just interested if this may be why its not so stable, more rocky ect. Could solar activity make it flare up more?

[carlos_dfc]

Originally Posted by Strontium

If the comet has a more circular orbit so close to the sun, (is it actually part of the asteroid belt called a main belt comet?) does it mean it has something to do with the theory of the planet that might have existed there, or failed to form.....

The material left over from planet formation in the inner solar system is generally rocky - whereas comets formed further out, and are mostly ice. Some ateroids actually have orbits that are pretty similar to comets.
Main belt asteroids are thought to be from - as you say - either a planet that failed to form, or a planetessimal that broke up (probably because it was too near to Jupiter, and was constantly tugged at by Jupiter's gravity)

Difference being, that comets didn't originate in the inner solar system, and because they 'outgas' material on every orbit, they only have a limited lifespan in the inner solar system, before they either fade away, or break up. Much less than the 5 billion years that the SS has been in existence

Comets 'fall' into the inner SS due to gravitational purturbations from other objects out there - they then fall in towards the Sun,
The vast majority are catapulted back out again, after passing the Sun, never to be seen again.
Very occasionally though, one will come in at just the right speed and angle to go into a stable orbit - or may pass close to a planet's gravitational field and have it's trajectory altered so that it can go into a stable orbit.

Remember Comet Shoemaker-Levy 9 ??
It passed close to Jupiter on it's way in, Jupiter's gravity made it simultaneosly break up, and go into an unstable orbit which brought it back to Jupiter - on it's next pass close to the giant planet, it was drawn in and crahed into jupiter's cloud-tops.

The periodoc comets we see now, will have all fallen into the innner SS at some point within the last hundred million years or so.