by BDanielMayfield » Thu Nov 22, 2018 6:17 am
MarkBour wrote: ↑Thu Nov 22, 2018 5:05 am
BDanielMayfield wrote: ↑Wed Nov 21, 2018 5:31 am
MarkBour wrote: ↑Wed Nov 21, 2018 2:34 am
\[Summary\]I would summarize my conjecture as "fortuitously-timed ejection of large dust, or gravel, or bigger chunks".
And I wondered about any detectable changes in rotational rate, which would presumably be the rate of change in the light curve.
Thanks for that extended treatment of my question Mark. One clarification I would seek in what you are saying is what you mean by "increase in velocity." This object has deviated somewhat from its projected path, but is it really moving away from the sun faster than it would have without the suspected outgassing, or has it just moved laterally off the expected trajectory? Naturally, it must in fact be slowing down as it climbs out of our system's gravity well.
However, I would naively expect a tumbling outgassing object to have the delta Vs it experiences largely cancel out due to its rotations and not cause a significant course alteration.
...
Bruce
Thanks, Bruce. I am pretty intrigued by Oumuamua. I was trying to sort out what possibilities could remain from the information in the APOD and directly-referenced sources. I can now add the following, though I am too "cheap" to buy access to the article in the first bullet point, at least for now.
- The source at the center of this is evidently:
"Non-gravitational acceleration in the trajectory of 1I/2017 U1 (‘Oumuamua)" Micheli, M., Farnocchia, D., Meech, K. J., et al. 2018, Nature, 559, 223
Accessible at: https://www.nature.com/articles/s41586-018-0254-4 ... if I want to pay for it.
- Oumuamua (as Art pointed out) was only observed past perihelion, on its outward journey, we have nothing before nor near perihelion. So, all of the discussion would have to involve only changes to its velocity on this outward journey.
- Oumuamua is no longer observable by any of our instruments. So, short of someone mounting a special mission, which seems highly unlikely, I guess all of the data-gathering on it is done.
- The sources I followed did consistently say it has higher outward velocity from the Sun than expected, not just a different angle or changing angle. You are correct in pointing out that overall, it is decelerating while moving away from the Sun. The deviation was not dramatic, but it was significant. Evidently it was just not decelerating quite as much as an inert rock ought to.
- One of the secondary references I found indicated that the trajectory was also inconsistent with a single added impulse, which would have been the case in my guess that a big chunk may have broken off and may have been thrown backward. I'd have to find out more before I could know why they say that.
Nice response Mark. It seems to me that this object is behaving somewhat like an out of control remnant of a designed lightsail might be expected to behave, being pushed by possibly both outgassing and solar wind/radiation pressure, or maybe just solar wind and radiation with no outgassing.
Note that I say it is behaving like an artifact might, not that it is an artifact. I still think this is a natural object, but there is a non-zero probability of it being a construction of some sort.
Bruce
[quote=MarkBour post_id=287537 time=1542863110 user_id=141361]
[quote=BDanielMayfield post_id=287508 time=1542778289 user_id=139536]
[quote=MarkBour post_id=287501 time=1542767688 user_id=141361]
\[Summary\]I would summarize my conjecture as "fortuitously-timed ejection of large dust, or gravel, or bigger chunks".
And I wondered about any detectable changes in rotational rate, which would presumably be the rate of change in the light curve.
[/quote]
Thanks for that extended treatment of my question Mark. One clarification I would seek in what you are saying is what you mean by "increase in velocity." This object has deviated somewhat from its projected path, but is it really moving away from the sun faster than it would have without the suspected outgassing, or has it just moved laterally off the expected trajectory? Naturally, it must in fact be slowing down as it climbs out of our system's gravity well.
However, I would naively expect a tumbling outgassing object to have the delta Vs it experiences largely cancel out due to its rotations and not cause a significant course alteration.
...
Bruce
[/quote]
Thanks, Bruce. I am pretty intrigued by Oumuamua. I was trying to sort out what possibilities could remain from the information in the APOD and directly-referenced sources. I can now add the following, though I am too "cheap" to buy access to the article in the first bullet point, at least for now.
[list=][*]The source at the center of this is evidently:
"Non-gravitational acceleration in the trajectory of 1I/2017 U1 (‘Oumuamua)" Micheli, M., Farnocchia, D., Meech, K. J., et al. 2018, Nature, 559, 223
Accessible at: https://www.nature.com/articles/s41586-018-0254-4 ... if I want to pay for it.
[*]Oumuamua (as Art pointed out) was only observed past perihelion, on its outward journey, we have nothing before nor near perihelion. So, all of the discussion would have to involve only changes to its velocity on this outward journey.
[*]Oumuamua is no longer observable by any of our instruments. So, short of someone mounting a special mission, which seems highly unlikely, I guess all of the data-gathering on it is done.
[*]The sources I followed did consistently say it has higher outward velocity from the Sun than expected, not just a different angle or changing angle. You are correct in pointing out that overall, it is decelerating while moving away from the Sun. The deviation was not dramatic, but it was significant. Evidently it was just not decelerating quite as much as an inert rock ought to.
[*]One of the secondary references I found indicated that the trajectory was also inconsistent with a single added impulse, which would have been the case in my guess that a big chunk may have broken off and may have been thrown backward. I'd have to find out more before I could know why they say that.[/list]
[/quote]
Nice response Mark. It seems to me that this object is behaving somewhat like an out of control remnant of a designed lightsail might be expected to behave, being pushed by possibly both outgassing and solar wind/radiation pressure, or maybe just solar wind and radiation with no outgassing.
Note that I say it is behaving like an artifact might, not that it is an artifact. I still think this is a natural object, but there is a non-zero probability of it being a construction of some sort.
Bruce