But it was your scenario. That's why I responded to it.
But stellar speeds do not.
Good discussion all around.
I am of the opinion that for all the highfalutin' mathematics and continuously evolving technology of the last few centuries?
It still remains a viable rule of thumb "That all action produces an equal and opposite reaction".
r8chard, was this the thread you intended to post this to?
I've been trying to understand what you meant by that, but couldn't. No matter how I look at the graph in post #37, I see low speeds in the most likely range.
Same when I look at the W velocity dispersion from the presentation linked to in post #33.
Maybe I'm missing something obvious here.
The difference here is between speed and velocity.
As an example, consider a uniform velocity distribution from -20 km/s to +20 km/s in both directions. What is the speed distribution for speeds below 20 km/s?
It is a linearly increasing function. Regions of fixed speed are circles, and the circle corresponding to 1 km/s is much smaller than the circle corresponding to 10 km/s. Slower speeds are less likely. This stays true even if the velocity distribution is not completely uniform. The probability that both velocities are very close to zero at the same time is very small.
Ok, I can appreciate how there would be a dip around the zero point. But if the distribution in the x-y plane is such that 50% of the population falls within a circle of radius 20, then any speed of less than 20 still makes the star fall within that 50% range, no?
In that case 20 km/s is the median speed, sure. The mean can be higher.
This asteroid, now called ʻOumuamua, is thought to be about 150 meters across.
If it was a red dwarf star instead, with a mass of 0.1 solar masses, it would have perturbed all the planets' orbits.
Earth would have a semi-major axis of over 7 AU.
Here is a simulation of our new solar system:
Nice! (Pun intended)
At 7 AU global warming becomes something we aspire to.
What happens to the moon in this scenario?
Why does A2017U1 keep coming back? I thought its orbit was hyperbolic.
Did you run this with a Jupiter-sized object? Anything interesting happen?
The Moon stays with the Earth, but its eccentricity is nearly quadrupled.
In the simulation, the "camera" is in an unrealistically-fast orbit around the solar system just to show it to you from all sides. That makes it appear as if A2017U1 keeps coming back. If you check "Trails" and run it, you will see that's its spiraling away in this rotating frame of reference.
With a Jupiter-mass, it wasn't nearly as interesting. Earth's orbit got ever-so-slightly rounder. The Moon's eccentricity jumped from about 0. 55 to about 0.1.
As this object continues to get observed, its trajectory gets refined. The good news is that with the latest data, Earth only gets pushed out to 2.6 AU.
The IAU posted an announcement on 2017-Nov-14 concerning the newly discovered interstellar object that explained its discovery circumstances, its naming and the new designation system. The new object is now officially known as 1I/2017 U1 and named 'Oumuamua which in Hawaiian means “a messenger from afar arriving first”. This was approved by the IAU Executive Committee. It is being called a prototype of a new class of objects, an “interstellar asteroid” which is
not gravitationally bound to the Solar System. https://www.iau.org/news/announcements/detail/ann17045/
A search on "2017 U1" in arxiv will find the recently submitted papers on 1I/2017 U1
Today I find 10 such new papers.
The orbit of 1I/2017 U1 was updated on 2017-Nov-13 with the issuance of
MPEC 2017-V63 (2017 Nov. 13) 1I/`OUMUAMUA
The latest value of the eccentricity e = 1.1992920
The values of the orbital parameters are only changing out at the 4th or 5th decimal place.
Observers W. H. Ryan and E. V. Ryan. submitted astrometry on 1I/2017 U1 with magnitude near 24 using the 2.4-m f/8.9 reflector telescope at Magdalena Ridge Observatory, Socorro.
Karen Meech is PI of Hubble Space Telescope proposal 15405 titled "Which way home? Finding the origin of our Solar System's first interstellar visitor".
Hubble is going to be used to observe 1I/2017 U1 possibly until 2018-Jan-01 when it will have faded to magnitude 27.5
Details of the observing plan can be found online at
When observations are completed, they will show up under the HST Archive link.
They will be used to extend the observation arc and orbit and gather light curve data.
Spitzer Space Telescope has an approved plan to observe 1I/2017 U1.
I know it's not possible but it sure would be interesting to get a probe to it,
To see if it's composition is similar or not to solar system asteroids.
Apparently, it's a spindle - more than five times longer than it is wide.
The article (or is it Wiki) says that some suggestions are that it is a contact binary.
How would 2 (or more) smaller asteroids manage to make contact (and then stay in contact long enough to adhere) in such an arrangement?
Seems to me, it's essentially two (or more) long, thin asteroids balancing on their tips against gravity.
I've also read that it's possible those long spindles are created by molten rock being flung out from an impact and frozen like that.
An object with a trajectory never seen before and a shape never seen before? That's like winning the lottery 2 weeks in a row. Folks, this is an alien craft.
Press release from ESO on 1I/2017 U1: http://www.eso.org/public/unitedkingdom/news/eso1737/
Separate names with a comma.