This drives me nuts because 'affect' as a verb means something closer to causing an 'effect', while 'affect' as a noun doesn't. Because of that, on the surface, it feels like 'effect' as verb would make more sense than 'affect' when describing the action of causing an effect on something.
Anecdotally, I pronounce them the same way and have never heard anyone making much of a distinction (northeastern US), with the exception of the rarely used "to put on appearances" ("Dude, this intellectual affect is too much, stop it with the scarves!") which I'd generally put more of a distinct "a" sound at the front.
If it's so fundamental and obvious, then why wouldn't these world-class astroscientists say anything about any estimations of deviation after such surprising success?
Your toenail is affecting the asteroid's trajectory, by laws of physics. That adds nothing to this conversation.
They don't have a radar gun pointing at the asteroid which measures velocity. Instead, they have to measure position after a period of time to measure velocity. The smaller the change in velocity -- and this is a very tiny change -- the longer the time needed to measure the change.
There! That's what I was looking for. So they were expecting a miniscule change, and instead they were pleasantly surprised by the evidence and are now expecting a very tiny change?
It is a small value, but its a measurable fraction of the the velocity of its orbit around the primary (about 12h).
They know the momentum that the impacter had. They had an estimate of the mass of Didymoon and its velocity. They are interested in how much of that momentum was transfered to Didymoon and how much was carried away from ejecta.
I mean, they quote Ian Carnelli in the article, saying that he expects a "much bigger deflection than (he) had planned". That said, the article also mentions that it will take Earth-bound telescopes/radars at least a week to get initial estimates in regard to the change of the asteroid's orbit, and then three to four weeks before getting precise measurements.
I think the real takeaway here is just that something unexpected happen. They're monitoring as they would have regardless, and results will come in time. Expecting results and/or a conclusion this early is, well, jumping the gun.
You know, I have my doubts about the practical benefits of this whole operation given that there aren't any planet killers lurking in the asteroid belt for at least a century, and so I suspect this was sold with a planetary defense angle because a bit of a scare is a good way to loosen the pocket book. That said, maybe we could justify rebuilding Arecibo along similar lines. I believe they were in fact using it as a near Earth radar gun and it was even initially constructed as a defense project.
1. We have absolutely no certainty that no planet-killers are there. All we know is that none mapper are.
2. China has an Arecibo-class device. Actually bigger than Arecibo. Do we need two? Considering that the whole Free World could not scratch together enough money just to maintain Arecibo, building it again seems beyond possibility.
The astronomers I've seen lecture say that they have a pretty good mapping of the asteroid belt and they know that there are no planet killers in there anytime soon which seems to intuitively make sense since we only get planet killers on the order of every 100 million years or so. Of course there are tons of smaller asteroids out there that can be problematic as well. I wouldn't want to be around when Berringer Crater was created, but that was still a few 10's of thousands of years ago if I'm remembering right. (I'd recommend stopping by if you're ever in the American Southwest).
I'm not all that familiar with any of the big radio telescopes, but I thought that China's didn't have the active radar capabilities that Arecibo did. That said, I find it sad that something like Arecibo was possible to build and maintain in the 60's but not now. I suppose that has to do with the perception of it moving from defense project to science project.
There's a fair amount of chaos/uncertainty in orbital mechanics, so perfection may be impossible. Also, the smaller "city killers" can be very hard to spot, especially if they're in the wrong position relative to the sun, but those aren't extinction level.
That said, I would think runaway climate change or nuclear war are much greater threats to civilization (though humanity would probably survive in some form), so those are probably where the effort should go if survival of human civilization is your thing.
We have orbital predictions for all the asteroids above a certain size, but only a fraction of tens of thousands of smaller bodies entirely sufficient to end civilization and very possibly drive us to extinction.
One struck the ice sheet in Canada only 12,800 years ago that wiped out 30+ genera in North America including camels, horses, cheetahs, mammoths, mastodons, giant ground sloths, dire wolves, sabertooth cats, a giant beaver, and a giant bear. Their bones, and Clovis spear points, appear only below a thin stratum with massively elevated platinum concentration.
Radar is just a matter of putting the right antenna horn on the focal carriage, wired to appropriate gadgetry.
