'Oumuamua

[halfeye]

That's the name they've eventually settled on for this:

http://www.syfy.com/syfywire/breakin...ote-not-aliens

I do like that we've spotted it at all, and it is kinda cool.

However, it was spotted leaving the solar system.

It was discovered just last week <this is an old quote>, on October 19, in observations made by the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS).

A/2017 U1 <old name> passed the Sun inside the orbit of Mercury in early September, curving sharply due to the Sun’s gravity, and is now on its way out.

So, how much mass would an object like this need to make a Chicxulub sized mess?

We've been looking for these for a very short time, and we found one. How many are there in a millenium? Obviously this one is now past the danger point, it was already past that when it was spotted, and the odds must be billions to one against one hitting Earth at random.

It seems to me that the Pan STARRS system failed in not spotting this on its way in, we need a better lookout ASAP.

[wumpus]

That's the name they've eventually settled on for this:

http://www.syfy.com/syfywire/breakin...ote-not-aliens

I do like that we've spotted it at all, and it is kinda cool.

However, it was spotted leaving the solar system.





So, how much mass would an object like this need to make a Chicxulub sized mess?

We've been looking for these for a very short time, and we found one. How many are there in a millenium? Obviously this one is now past the danger point, it was already past that when it was spotted, and the odds must be billions to one against one hitting Earth at random.

It seems to me that the Pan STARRS system failed in not spotting this on its way in, we need a better lookout ASAP.

I was pushing for "Rama".

Wiki says Chichxulub was "10 to 15 kilometres (6 to 9 miles) in diameter". Of course I suspect that this is based on a body orbiting the Sun with Earth (and hitting with roughly Earth escape velocity ~11km/s). Since Oumuamua is going 44km/s, it would only need a mass 1/16 of that: I think it has that (and would probably keep more mass and velocity since it appears pretty aerodynamic).

Note 44km/s might only be near Mercury and it might have been less out by Earth.

[gomipile]

One hundred years ago, the object was 561±0.6 AU (84 billion km) from the Sun and traveling at 26 km/s (58,000 mph) with respect to the Sun. The object continued to speed up until it went through perihelion, where it peaked at 87.7 km/s (196,000 mph). By the discovery date it had slowed down to 46 km/s (100,000 mph) and will continue to slow down until it reaches a speed of 26 km/s (58,000 mph) relative to the Sun.

So, 44 km/s is the speed at time of publishing the article, probably.

[halfeye]

I was pushing for "Rama".

Wiki says Chichxulub was "10 to 15 kilometres (6 to 9 miles) in diameter". Of course I suspect that this is based on a body orbiting the Sun with Earth (and hitting with roughly Earth escape velocity ~11km/s). Since Oumuamua is going 44km/s, it would only need a mass 1/16 of that: I think it has that (and would probably keep more mass and velocity since it appears pretty aerodynamic).

Note 44km/s might only be near Mercury and it might have been less out by Earth.

Nope, 44km/s was when it was spotted. It'll be less now, but it's still not coming back. It must have been faster at perihelion, I wonder how fast?

<edit> Thanks gomipile, interesting stuff, I must recheck Wikipedia. </edit>

is now on its way out. It’s already farther away from the Sun than Earth is, moving at a very brisk 44 km/sec.

It's spinning now, but was it spninning on its way in?

[wumpus]

It's spinning now, but was it spninning on its way in?

Angular momentum needs to be conserved. If one side is a different color or otherwise spun off something (perhaps a micrometeroite hit it) would be the only way to change the rotational speed. Of all the possible rotation speeds it might have picked up over the course of several billion years (it is likely a bit older than the solar system), zero wouldn't be one I'd expect. It might have been banged around and had its rotation changed a bit, but I doubt it was zero when it came in.

- note I don't just mean "absolutely zero", I mean "it doesn't appear to be moving as a fuzzy image to the naked eye". Zero is still a fairly small range of possible motion.

[halfeye]

Angular momentum needs to be conserved.

Yeah, but it just pulled off a 120 degree turn. That might well throw it's rotation off. Being a long thin shape wouldn't hinder that.

There's this titbit from Larry Niven's "Tales of Known Space":

I keep meeting people who have done mathematical treatments of the short story "Neutron Star," ... Alas and dammit, Shaeffer can't survive. It turns out that his ship leaves the star spinning, and keeps the spin.

Spoiler: Neutron Star

Show

The ship in question was nose toward the star because of tides on its passage through, with rotational controls ruined by previous attempts to change that orientation.

The Sun is quite a bit bigger and more diffuse than a neutron star, but it's in the same mass range, and the object did turn a lot on its way through the system.

[Lord Torath]

Angular momentum of the object still needs to be conserved. Bending the trajectory by 120 degrees (or whatever) does not affect the angular momentum at all. Linear momentum is conserved by accelerating the sun ever-so-slightly toward the perihelion of 'Oumuamua's trajectory.

Edit: For a real-world analogy, look at an air-hockey puck. If you put it on the table, it starts floating, and (on a good table) will stay put. If you give it a gentle shove, it starts floating away, but is still not rotating unless your shove was off-center. Eventually the puck hits the wall. If it hits straight on (at a 90^o angle, it bounces straight back at you, and is still not spinning, despite the fact that its trajectory has been bent 180 degrees.

Tidal forces could affect the rotation of an oblong object, but they fall off at the cube of the distance between the objects (for comparison, gravity falls of at the square of the distance). You have to get really close to the center of mass for tidal forces to affect you on a short time frame. You can get much closer to the center of mass of a neutron star than you can to the sun, which is, as you noted, far more diffuse than a neutron star.