How is comet Leonard able to reach escape velocity from the solar system?

[geminid]

Per the interview with the comet's discoverer: Leonard. He is saying that the comet is at escape velocity and will escape our solar system. HOw is that possible since the comet has apparently made a previous revolution around the sun? Did it get a gravitational assist or something?

 

[Helio]

Great question! Its orbit is retrograde so its one encounter with Venus should slow it down, not speed it up. Did it come down with higher speed than free-fall? This would imply some sort of major impact, perhaps.

Celestial mechanics can be harder than it looks, however, so I hope someone who understands it better than I will answer.

 

[Helio]

Here is an article that shows stars passing through the Oort Cloud can perturb objects (i.e. comets) into hyperbolic orbits. The initial tug by the passing star will give an object the initial extra velocity to send it sailing out of the solar system.

Perhaps the known passage of Schulz’s Star, 70k years ago, was the trigger for Leonard. Just a guess.

 

[geminid]

OK I think we have to rethink whether this comet ever visited us in the past.

I read some of the article which was very informative. There are a number of possible origins for Leonard's comet:

1 interstellar space, quite possible
2 disrupted from the Oort Cloud by a passing body e.g. a dwarf star such as Scholt's star as you mention, questionable.
3. disrupted from the Kuiper belt by Neptune, maybe although the news report seem to rule this out. Should not be completely dismissed though as the alternatives might not be plausible.

4. a normal comet with normal trajectory that was disrupted by Jupiter or another planet. Apparently 4 has been ruled out from what I read. Because the trajectory of Leonards comet does not take it near Jupiter.

If Leonard was dislodged from the Oort cloud that would have to be a one time event. Its not like Oort cloud objects orbit, like comets, with a close approach to the sun. No, those objects normally just rotate out there in the Oort cloud remaining at one light year distance more or less.

so it seems extremely unlikely that Leonard was dislodged from the oort cloud say 150,000 years ago approached earth/sun 70,000 years ago then orbited back out to the Oort cloud where it was dislodged a SECOND TIME by say Scholtz's star or some other dwarf star which then accelerated it to a speed that is now escape velocity.

Agreed? I.e the only way Leonard could have visited us 70k years ago, and then comes back a second time at escape velocity is that it would have to been disrupted by a body twice. Once to remove it from Oort cloud and second time to accelerate it to escape velocity. Makes no sense to me.

Is it possible that the media reports are erroneous in saying that Leonard visited us 70k years ago?

Also not much of this is consistent with Oort cloud origin:

Leonard is said to be moving 25 miles/sec. So 1/8000 the speed of light. If its been moving 70,000 years that suggests it was like 9 light years away when it began. Which is quite further out than the Oort cloud (at 0.03 to 3 light years distance). That twice as far as Alpha Cenari.

That would suggest an interstellar origin for this comet. Yes?

 

[Helio]

OK I think we have to rethink whether this comet ever visited us in the past.

I read some of the article which was very informative. There are a number of possible origins for Leonard's comet:

1 interstellar space, quite possible
2 disrupted from the Oort Cloud by a passing body e.g. a dwarf star such as Scholt's star as you mention, questionable.

Both possible.

3. disrupted from the Kuiper belt by Neptune, maybe although the news report seem to rule this out. Should not be completely dismissed though as the alternatives might not be plausible.

4. a normal comet with normal trajectory that was disrupted by Jupiter or another planet. Apparently 4 has been ruled out from what I read. Because the trajectory of Leonards comet does not take it near Jupiter.

Both highly unlikely.

If Leonard was dislodged from the Oort cloud that would have to be a one time event. Its not like Oort cloud objects orbit, like comets, with a close approach to the sun.

One-time event for this object, though perhaps millions of other outer Oort objects were also affected in their lazy orbits.

...so it seems extremely unlikely that Leonard was dislodged from the oort cloud say 150,000 years ago approached earth/sun 70,000 years ago then orbited back out to the Oort cloud where it was dislodged a SECOND TIME by say Scholtz's star or some other dwarf star which then accelerated it to a speed that is now escape velocity.

Why introduce two events if one is sufficient? I doubt there is much evidence it had an earlier trip. Is there? That too would be interesting.

If something like Scholz’s star came into the Oort 70,000 years ago and slung Leonard our way then it may have originated from a region 20,000 to 30,000 AU distance. Free-fall time at 20,000 AU is 500,000 years, but given a nice push, perhaps 70,000 years is plausible. Only objects that had a near-perfect trajectory to the Sun would be seen. But if many thousands of these got similar kicks, then we might see more relatively soon.

Is it possible that the media reports are erroneous in saying that Leonard visited us 70k years ago?

You’re asking another good question.

Leonard is said to be moving 25 miles/sec. So 1/8000 the speed of light. If its been moving 70,000 years that suggests it was like 9 light years away when it began. Which is quite further out than the Oort cloud (at 0.03 to 3 light years distance). That twice as far as Alpha Cenari.

No. Comets start very slow then accelerate, so the average speed would be very slow.

 

[geminid]

Hello Helio: Thank you for all the information. I really do not know much about comets so I appreciate it.

Can you explain a little more how the comet speeds up during its trip?

I introduced two events because the news reports said Leonard had visited us 70k years before. Which I guess means that it has already reached perihelion back then and is now returning. So how is it escape velocity now? I dont see how it could have been at escape velocity if it reached perihelion 70k years before.

So perhaps the story I read is misunderstanding what happened 70k years ago.

thanks for your help.

 

[Helio]

Can you explain a little more how the comet speeds up during its trip?

Sure. What is true for comets, or any celestial object, is identical for falling objects we drop on Earth. The fall of an apple is how Newton began his famous gravity equation that became the first universal law -- a law that works throughout the universe.

So, since the Sun is so much more massive, objects will fall faster if they fall directly towards it. But their fall rate depends on how far away they are.

The strength of gravity determines how fast an object falls. This strength is strongest at the surface of a solid body like the Earth. But the farther you go, the weaker the gravitational field. It diminishes by the square of the distance. An object at 2x the Earth's radius, will feel only 1/4 the gravity as that at the surface.

I introduced two events because the news reports said Leonard had visited us 70k years before. Which I guess means that it has already reached perihelion back then and is now returning.

The farthest point in an elliptical solar orbit is aphelion; perihelion is the closest point. [It's easy to confuse these.]

The discoverer, Leonard, thinks the aphelion point from its prior elliptical orbit (implied) was about 3700 AU. Knowing this distance yields a free-fall time of about 40,000 years, which was the time he gave. [80,000 years for one complete orbit (i.e. period).]

Had he been able to tell how long the comet was traveling (i.e. 40,000 years), then he could calculate the distance at aphelion. Since it's reasonable to assume he had no way to determine how much time has expired for the comet, then his time estimate comes from plotting the known trajectory it now has backwards in time.

So how is it escape velocity now?

Right, a great question that deserves an answer.

If we assume that he has been able to accurately compute the aphelion point for this, now, hyperbolic orbit, then something would have had to give the comet an extra approx. 1 kps push or bump. This is easy to calculate since the escape velocity at 3700 AU is about 0.7 kps. If Leonard is on an escape route it has to be traveling faster than this once it reaches 3700 AU.

But what would be out there at that distance? This region is expected to be short of the inner Oort Cloud somewhat, but very little is known of the Oort.

It seems to come down to how accurate the aphelion point can be determined. If the 3700 AU value is close, then perhaps a rogue planet shot by and triggered a wave of objects flying all about.

But if the real aphelion point is 20,000 AU or so, then Scholz's star may have something to do with it.

Your assumption that something has to explain the extra speed that it never had before, again, is correct. Just falling close to the Sun will not allow it to travel to a greater aphelion point. If, however, you're a fan of "flubber", then there's that.

 

[geminid]

well Im more confused now. Are we assuming that this comet had visited the earth and sun in a prior time? Some 70 or 80k years ago.

You said ", Leonard, thinks the aphelion point from its prior elliptical orbit (implied) was about 3700 AU."

So that says to me that we are both assuming there was a prior orbit around the sun reaching a PERIHELION POINT some 70k years ago. Correct?

If so that implies TWO EVENTS does it not? One event to trigger this comets PREVIOUS journey inward and a second event to kick it into escape velocity

I am totally confused because in your previous message you are asking me why I need to assume two events. Am i not explaining this correctly?

thanks again.

 

[Helio]

So that says to me that we are both assuming there was a prior orbit around the sun reaching a PERIHELION POINT some 70k years ago. Correct?

Yes, but the 70k years, IIRC, was the time for Scholz's star, not the comet period. The time from aphelion to the Sun he said was 40,000 years, so the period is twice that (80k years). But...

If so that implies TWO EVENTS does it not? One event to trigger this comets PREVIOUS journey inward and a second event to kick it into escape velocity

I don't think we should take any initial orbit seriously, or acitivity. Two trips, as he seems to suggest, likely comes from the view that the comet has a predicted aphelion of abut 3700 AU. This means its normal period would be 80,000 years, if we assume it ever had an orbit near the Sun, which is unlikely, IMO. An early pass isn't a reasonable circumstance because it had to have gotten a push at some point to make it have a speed greater than the escape velocity. It doesn't fly within the ecliptic so it very likely never got a bump from a known planet.

There's no way you can look at the comet and state what it was doing for a prior orbit, IMO. It's more of a math discussion on what the time would have been in a prior orbit, regardless how unlikely. If there's a better explanation, I'd love to see it.

My guess is that the comet was floating along in the innermost part of the Oort Cloud when something big flew by and sent it cascading down towards the Sun.

I'm assuming we can only address this current hyperbolic orbit, thus I ignore claims of any prior pass it may have had with the Sun, though I don't mind also doing math based on a what a prior orbit would have looked like. This is another example of valid math but invalid physics. There seems to me to be no physical argument for a prior pass.

 

[geminid]

I think we are pretty much in agreement. I havent studied everything you wrote there. Thanks again for your help. I know almost nothing of how they work.

 

[geminid]

There's no way you can look at the comet and state what it was doing for a prior orbit, IMO. It's more of a math discussion on what the time would have been in a prior orbit, regardless how unlikely.

Technically you can find meteor showers and stuff like that. But I agree in this case there does not seem to be any way to know what it was doing before this encounter.

So then we agree that it seems most likely : Leonard was kicked out of the Oort cloud by some passing celestial body that set it on a course to where it picked up enuf speed to reach escape velocity?

 

[Helio]

So then we agree that it seems most likely : Leonard was kicked out of the Oort cloud by some passing celestial body that set it on a course to where it picked up enuf speed to reach escape velocity?

Yep, that’s my best guess. But it’s very curious why a prior trip seemed so implied.