We only have 2 examples, but both this and the Rosetta mission object were rubber-duck-shaped. Is this very common?
It's pretty common. Based on radar data about 10-15% of Near Earth asteroids (larger than 200 meters) are contact binaries (or contact-binary shaped at least). We don't have enough data on main belt asteroids, trojan asteroids, and especially TNOs/KBOs to say what the percentages look like for those populations but it's a fair likelihood that the proportions are at least as high if not higher among KBOs.
the development of double precision floating point, and the kalman algorithm, were two major improvements. Basically there is a computer at JPL that, given a location in the solar system and a current location of a ship, will give you instructions on when to burn. After you burn fuel to move, you update based on visual locations of known stars, fit a model, and do incremental burns until convergence. The book Digital…
> the development of double precision floating point So refreshing to hear that a double is good enough for JPL when repeatedly told it's not good enough for mere dollars and cents.
JPL also has PhD applied mathematicians on staff to ensure numerical stability of their algorithms at double precision. Most developers do not have the ability to do that sort of non-trivial analysis. They are not just blindly saying "a double is good enough."
I find it truly amazing that New Horizons was able to take photos of a 20 mile object whilst flying past at ~8 miles/sec - that’s an incredibly small space and time window within which to capture the images. Does anyone know how NASA manages to pilot spacecraft with this level of precision? What kind of engineering processes do you need to enable this?
> two of its three degrees of orbital freedom Three? > I know these things because I used to work at JPL Ok, I don't. What are the three DoFs and how do they relate to 6DoFs or six Keplerian elements? Some background-fixing?
Brain wedgie. I meant six. And direct observations give you four of the six. I guess I was just thinking about 3-d location and just forgot about the time derivatives. Sorry.
Each line is the same star viewed from a different point on Earth. They arranged for telescopes in a long line North to South to all observe UT at the same time, just as it was predicted to pass in front of the star. Then they precisely timed the apparent blinks of the star. The North-South offset meant the star bisected UT across different sections for each telescope.
Then they just worked out the parallax difference and mapped out the blink times on a chart to see the silhouette.
Absolutely amazing that they nailed the shape so well based on the occlusion data. That is super impressive.
From /r/space: Image of the occultation profile vs actual shape: https://i.imgur.com/PNh4nmX.png Each line is the same star viewed from a different point on Earth. They arranged for telescopes in a long line North to South to all observe UT at the same time, just as it was predicted to pass in front of the star. Then they precisely timed the apparent blinks of the star. The North-South offset meant the star bisected…
From that pic it looks like they were able to measure accurately to within meters of the actual shape at this distance! That is incredible
No, that's actually not true. Hitting Ultima-Thule is much harder. For starters, just figuring out where U-T actually is is very difficult. The observations we have only constrain two of its three degrees of orbital freedom. The third has to be inferred via orbital mechanics. Likewise, figuring out where the spacecraft is is also non-trivial. By way of contrast, figuring out where you are relative to New York to with…
I wonder how much would it cost to build a GPS-like network for the whole solar-system... The good thing is that, for such a thing to be really useful, we'd have to invent better propulsion systems which would, in turn, make the network much cheaper to build.
Pulsars can be used to arrive at celestial positioning accurate to ±5 km. There is a test rig on the ISS that has validated this. No need to build human made beacons when the universe has so graciously provided us with them.
What's exciting to me is, both the first interstellar object we've observed visiting our solar system (Oumuamua) and the first Kuiper Belt Object we've visited have been "unusual". That strongly suggests to me that the unusual is more usual than we would have suspected, which means there's probably a great deal of opportunity to increase our understanding of the universe!
It's easier to observe bigger objects than smaller objects. Bigger objects have greater gravity than smaller objects, therefore are more spheroid. As we get better at observing, we'll see more objects that are less spheroid.
At least in the case of Oumuamua though, being non-spheroid wasn't really the weird thing about it. It was that it exhibited comet-like acceleration, without any visible off-gassing, and without breaking up as it passed the sun, as a comet would be expected to do. Also the fact that from our current understanding, it is much more likely for a comet to be ejected from a solar system than an asteroid, so it's surprising (not impossible, certainly, but unlikely) that the first interstellar object was more like an asteroid.
As this is the first Kuiper Belt Object we've visited, it's hard to draw much about the statistics of the thing.
Re: first Kuiper Belt Object we've visited Pluto may be a KBO also. Further, it's possible some moons of the gas-giant planets are captured KBO's. The unusual thing about Ultima Thule is that it's in a nearly circular and "flat" orbit, which many experts interpret to mean it's mostly undisturbed from its point of origin. It's a prime "fossil". Pluto has a "disturbed" orbit such that its origin is currently unknown. S…
> Pluto has also been turned inside-out, perhaps multiple times, by a still unidentified force.
Whoa, come again? How do we know this? What does it mean for a planet-like object to be turned inside out?
