Japan’s Hayabusa2 spacecraft grabs close-up thirty feet above asteroid
cnet.com
cnet.com
Relative motion is smaller though: The gravitational force between the probe (660kg) and asteroid (4.5 * 10^11kg) is just 0.1 N. The probe has therefore to be circling the asteroid with about 0.25m/s or just 1km/h (0.57 mph for american readers).
And how else could it be: the asteroid was assumed to be a point mass and the probe in a circular orbit of 450m around it.
It depends on what you consider "dominates" to mean. For example, the corresponding value for the Earth and the Sun is 924,000 km, and the Moon is only 400,000 km from the Earth, but the Moon's orbit is still always concave towards the Sun.
If Earth wouldn't dominate the space in which the Moon moves, the Moon wouldn't be in orbit around Earth at all and the Sun couldn't perturbe this orbit (as you even stated yourself)?
My point is that "dominate" here could mean different things, and the Earth does not dominate all of them.
Specifically, the fact that the Moon's orbit is always concave to the Sun means that the "acceleration due to gravity" of the Sun on the Moon is larger than the "acceleration due to gravity" of the Earth on the Moon. In other words, the net "acceleration due to gravity" of the Moon is always towards the Sun, not towards the Earth. So the Earth does not dominate in this way.
The "sphere of influence" you mention is based on tidal forces: the tidal effect of the Earth on the Moon is larger than the tidal effect of the Sun on the Moon. So the Earth does dominate in this way.
> the Moon wouldn't be in orbit around Earth at all and the Sun couldn't perturbe this orbit (as you even stated yourself)?
No, that's not what I said. Whether you think of the Moon as orbiting the Earth or the Sun depends on how you define "orbit" and what you are trying to do. If you define "orbit" according to which body the Moon is accelerating towards, on net, then the Moon is orbiting the Sun, not the Earth (see above); in this sense, the Moon and the Earth are in two closely matched orbits about the Sun.
And my point about the Hayabusa spacecraft and the asteroid is that, if you calculate the "acceleration due to gravity", you find that it's similar to the Moon's--the spacecraft's net acceleration is towards the Sun, not towards the asteroid.
So sorry: it's not in that orbit. I should have made that clear instead of talking about the probe, circling, ... which sounds pretty concrete.
(The asteroid is not spherical or homogenous and is even supposed to be a "rubble pile" with large holes inside which makes it highly questionable at best to treat it as point mass (you could if the probe were far enough away from it ... which it is not at all), but hey ... ¯\_(ツ)_/¯)
TFA called it a cannonball, which is really quite amusing.
Yup, and you break my ability to zoom in or right click and view image on mobile.
Welcome to the future.
[0]https://www.cnet.com/videos/japans-hayabusa2-space-probe-fir...
Again ultra dark, so the camera needs to have an incredibly sensitive sensor.
And incredible motion, the spacecraft is whipping by the asteroid quickly.. so you'd need a fast shutter speed to get sharp detail. Which is made difficult by the lighting conditions.
No human photographer on the shutter button. Way too far away for that.
Incredibly challenging photographic environment.
No it's not. The whole point of the Hayabusa2 mission is to go to the asteroid and stay there. In fact it landed on it and grabbed a sample back in March.
Could the spacecraft—just in theory—introduce an atmosphere? Maybe not this spacecraft, but if we’re riding around in the starship Enterprise and want to get better snaps of asteroids, would it be a good idea to just send out a big pair of glass hemispheres, encapsulate the asteroid with them, pump them full of air, and then take a picture of the asteroid-capsule system?
Alternately, could you stick something really good at diffusing light—like a big block of aerogel—between the sun and the asteroid?
Science funding often needs some one's buyin.
Or just do the science with the camera you have and ignore the fact that human viewers don't like the results aesthetically.
Alternatively point a light strong light at yourself, so it is diffused back at the asteroid evenly. Photographers have used this trick for ages.
Is it so dark? IIUC the asteroids is almost at the same distance from the Sun than Earth (something like a 50% more) so the illumination should be similar (about a half, but a glass that blocks half the light looks totally transparent at sight, it's weird to measure it experimentally). Is the soil of the asteroid too dark? Like what? Grounded coffee?
I love how many deployable objects this spacecraft is carrying, the target markers included. The number of moving parts must be staggering! (I wonder if they charge over USB? :b). JAXA has really amazed me with how resilient their missions have been. (The first Hayabusa limped back with a sample after a bunch of engine failures; their Venus probe failed to enter Venus's orbit, spent 5 years orbiting the sun, then tried again and worked). There's clearly a mountain of potential over there, so it's a treat to see this one go so perfectly smoothly :)
Edit: Thank you to all the other posters who wrote way better answers with more information!
https://www.space.com/3332-nasa-finally-metric.html
I'm just as guilty as the next person when I post numbers. Occasionally, I'll also show metric. However, as an old(er) dog, my first instinct is to use feet, miles, etc.
Perhaps we should agree to use only the metric system on HN?
https://www.wired.com/2010/11/1110mars-climate-observer-repo...
It’s helpful when there’s only one system. In the US, it’s too costly to switch. HN readers are global and we’re technical so there’s no reason not to simply use metric.
What is the estimated cost out of curiosity?
https://www.cnbc.com/2015/06/04/why-the-us-hasnt-fully-adopt...
The cost of switching road signs alone was quite expensive. Exit numbers, for example, are often the mile marker number.
https://www.reddit.com/r/theydidthemath/comments/2cjiau/self...
Do they still teach the metric system in US schools? I learned it over 40 years ago. Metric is the official system for science.
It’s hard to believe that we’re so close but we still have holdouts. It’s not an arbitrary choice at this point.
It's not illegal to serve someone a "pint" if they ask for one, but it is illegal to offer a "pint" for sale.
Tucker Carlson: God bless you, and that's exactly what it is. Esperanto died, but the metric system continues, this weird, utopian, inelegant creepy system that we alone have resisted.
Japan's Hayabusa2 spacecraft grabs close-up 1/10th of an American football field above asteroid
It's only Americans who still use feet and other imperial units, which is why they lost a Mars probe.
I think us Brits are the worst of the worst when it comes to mixing units. Fuel is sold in litres but consumption measured in miles per gallon. Milk is sold in 1 pint or 2/4/6 litre bottles. Road signs to towns are in miles but in roadworks are in metres. And so on.
I wonder why the UK couldn't quite make the jump over?
At least the US has agreed that the Moon is a metric only zone! https://science.nasa.gov/science-news/science-at-nasa/2007/0...
McLaren recently failed to qualify for the Indy 500 (McLaren!) due in part to a unit conversion problem made prior to the last day of qualifying.
https://autoweek.com/article/indy-500/mclaren-ceo-zak-brown-...
It does seem that McLaren made a lot of boneheaded mistakes here, but this example just doesn't go with the "Brits are still using imperial units" theme of this thread at all.
(Part of the Mars orbiter fiasco was that it was being developed during the transition.)
It's funny how life fights with you though. My wife and I share a scale in the bathroom, it's a fitbit wifi thing and she finally laid down the law, it uses pounds now. Chasing 130lbs is somehow more satisfying than 58.9 or 59Kg. Our electronic outdoor thermometer is in Fahrenheit now too; this one sort of pisses me off, metric is simple, below 10 you need a coat, 10 to 20 probably want a light jacket, 30+ is shorts because it's hot. Mind you, she is an actual scientist, a real deal scientist that works on viruses and immunology, which is somewhat frustrating. You wouldn't believe the fit she had when our electronic human thermometer was found to be metric... When you call the doctor because your child has a fever, it is better to use whatever units the doctor uses.
I suspect that major new papers could probably start using metric units with translation in parens and only the wingnuts that think the papers already harbor a liberal bias would say anything about it. Other than temperature and like human height, you can toss out metric measurements to most folks when they ask something and they seem to absorb it well; from time to time you get a question or push-back, rarely I'll translate the unit for them. We're at the point where people just need to see it more. It would be an interesting experiment if some media organizations started to make metric more prominent. Hell the US military uses it, mostly for NATO reasons... we could probably somehow put a patriotic spin on it.
I mean, chasing 60kg is more satisfying than 132.2lbs. There's nothing intrinsically important about 130lbs except that it's a round number in base 10. In metric you just pick a different round number to chase.
Aviation also uses them (though they still fly above a sphere).