NASA’s Dawn Probe has finally reached the vicinity of the protoplanet Vesta, the second largest asteroid at about 500km across, and will enter orbit on Saturday. Here is the first good quality image, taken from a distance of 26,000 miles.
Looking at the approach images, it seems likely Vesta will be classified as a dwarf planet in the future. It appears to be a gravitationally rounded body, albeit one that has taken a pounding from impacts. One crater close to the south pole is nearly the full width of Vesta itself.
Yes, for example the much smaller asteroid Ida has a tiny moon, Dactyl. 0.022g may not be a lot compared to Earth, but Vesta has a Hill sphere tens of thousands of kilometers across, where it’s gravitational attraction dominates.
The real question is, can you throw a baseball in one direction and have it come over the horizon from the other direction and hit you in the back of the head? What kind of orbital velocities are we talking about around it?
The wikipedia link on Vesta (where I got my surface gravity info) says that “escape velocity” is estimated at .35 km/sec. (1260 kph, or 782.9 mph)
Earth’s EV is 11.186 km/sec. (31.96 times greater than Vesta.)
I was thinking that spacecraft typically travel at thousands of miles per hour, and is going to have to slow waaay the hell down to drop into a stable orbit around Vesta.
While true, it doesn’t precisely address the baseball question.
For the sake of not making myself completely crazy, I made some assumptions (Vesta is spherical, mass distribution is uniform, and so forth). The simplest way I could think of looking at this was to look at the mechanics of a circular orbit right at the surface, and try to calculate the orbital velocity required for an object in such an orbit. Technically, it should be around 1.5 meters above the surface, but since that’s only about 0.0006% of Vesta’s radius, it gets lost in the noise.
This is fairly silly, but it should give us some idea of how fast the baseball needs to be going.
The formula for orbital velocity in a circular orbit is
Would the reduced gravity mean I could throw a ball significantly faster than on Earth? Not 579 mph certainly, but noticeably faster? I’m sure the lack of atmospheric drag would help a bit.
I doubt that atmospheric drag on your arm makes much difference to a pitch…certainly not as much as having that arm encumbered by a space suit. You might also have trouble because of a lack of traction.
If you took a world-class pitcher who could snap off a 100mph pitch angled upward at 45 degrees, and gave him a magic ring that let him breathe in a vacuum and get traction on bare rock when he weighs almost nothing, he could probably throw the ball several miles. Vesta is no little speck of rock, though–its circumference is around a thousand miles.
The 579mph figure doesn’t even really work, except to illustrate a sort of bare minimum–it’s how fast you’d have to throw the ball if Vesta itself weren’t in the way. That is, if you were hanging in orbit 265km from a black hole with Vesta’s mass, you could fire off a projectile at that speed, and it could conceivably whack you in the back of the head a bit under two hours later.
I guess I wasn’t clear; I meant less atmospheric drag on the ball might allow it to travel faster when I throw it. But I suppose the only real effect would be to make the ball decelerate more slowly, not leave my hand at a higher velocity.
I would be able to throw it faster than on Earth due to the lower gravity, is that right?
Edit: Without throwing it in an arc, but throwing it “parallel” to the ground.
These numbers are consistent, since the escape velocity should be the square root of two times the orbital velocity at the same distance from the center of mass. If I use the Wikipedia value for the escape velocity, the orbital velocity at the surface of the object should be ~550 mph.
Yeah, I didn’t really put a lot of thought into it before I posted my question. I could see being able to throw a ball farther in lower gravity, or higher if I threw it at an angle as Balance suggested. Faster, not so much.
As neat as having two moons would be, it might be more useful if we dragged it to Mars. The spinning gravity interaction could kick start the planet core and generate a magnetic field.
Except it’s relative velocity (of course, all velocity is relative). I imagine it would be theoritically possible to launch from Earth at just the right velocity to slide into orbit (presumably not very round) around Vesta without any boost at all.
At some point in their respective orbits, I’d think that the RV between Earth and Vesta would exactly negative Earth escape velocity (not that that would be useful information).
