Radar reveals two moons orbiting asteroid Florence | Hacker News Reader

Radar reveals two moons orbiting asteroid Florence

astronomynow.com

211 pointsjapaget51 comments

Is the 'light' reflecting off the asteroid emitted from the sun? I had never seen or even knew radar could distinguish value like what is shown here.

I suppose terrestrial radar looks at much smaller objects and what it sees is emitted from the tower and bounced back in a straight line so that sort of makes sense.

More info on the observatory: https://en.wikipedia.org/wiki/Goldstone_Solar_System_Radar

> Is the 'light' reflecting off the asteroid emitted from the sun? I had never seen or even knew radar could distinguish value like what is shown here.

Yes it's emitted from the sun, it's clear given that the time-lapse shows "Inner moon eclipsed" when passing behind the site of the asteroid that is not lit.

I don't understand how the phrase 'inner moon eclipsed' tells the reader that the source of radiation for this radar measurement is the sun.

I don't either :) but sort of a silly question I guess. I presumed it was the sun due to the angle of illumination as well as common sense that the sun is probably the brightest object in the solar system along multiple bands of light; I was really just amazed at the relatively large amount of detail in the image.

Well, if the illumination was from the radio telescope, then the moon would be hidden behind the parent asteroid when it is eclipsed. We would not see it go dark, it would just be obscured.

That's just an artifact of the visualization; the point of view is above the north pole of Florence, which points decidedly away from Earth (probably +/- a few degrees from normal to the plane of the ecliptic).

I was always under the assumption that with Radar images that it didn't rely on a light source as technically the radar is the source. So that the impression that there is a light an dark side was based purely on the motion towards and away from the receiver.

But, you have pointed out something interesting and that would appear to indicate other wise. The clear rotation independent of source already shows that I am wrong on that.

Apparently I don't understand this very well.

You are correct, the "light" is the transmitted radar pulse from Goldstone, not from the sun.

They do all sorts of fancy signal processing to get this sort of resolution.

Because radar power received goes down with 1/(distance^4), the inverse square law, squared, this is hard to do at astronomical distances.

The power level differential between transmitted and received power can be in the order of ~10^15.

Goldstone transmits a 500kW radio pulse but will probably get nanowatts back, which is amplified millions of times by the big dish, amplifiers and signal processing.

This thread is very confused.

There are two things: the radar images are created with radio waves emitted by the radar installation. The second thing is that the visualisation shows a light source. They are unrelated to each other. I assume that the light source was added during rendering of the film and that it approximates the sun.

I don't think the visualisation shows any light source. The radar reflection from the asteroid just looks like it is "lit up"

The radar is the light source, just like shining a flashlight during the night at something.

The actual solar illumination of the asteroid at the time was likely significantly different from what we see in these images.

Yes. The radar illumination comes from the Sun.

No, that's not showing light reflected from the sun. In the still image, the radar source (aka Earth) is to the left; in the animation it's at the top.

In the still image, the vertical dimension is the bearing of the transmitted radar signal, while the horizontal dimension is distance away from Earth, as computed by the time of flight of the radar signals. In the animation those are swapped.

Phil Plait to the rescue! http://www.syfy.com/syfywire/close-encounter-by-the-big-aste...

Edit: I think it might be helpful to view this more like ultrasound image than a photograph. There is no "side" view. It has been reconstructed based upon the time it takes for the bounce to return.

Here's a good explainer on what you're actually seeing in the radar image: http://www.planetary.org/blogs/emily-lakdawalla/2011/3248.ht...

* The signal is emitted from a radar installation on the earth, and reflected back to another dish.

* Brightness is reflected signal strength. So surfaces that are perpendicular to us will reflect better. The less the surface normal points to us, the less reflection we see.

* Up/Down is Time axis. The points closer to us will return sooner than points farther away.

* Left/right is Doppler shift. Parts of the asteroid that are rotating away from us will show up on one side, parts rotating towards us will show up on the other side.

(this is the vertically oriented image).

Thank you very much! Awesome explanation.

How about we have satellites orbiting asteroids for a piggy back ride and then getting off the orbit when they are near a point of interest? My guess is the gravity would be too feeble.

You would need to first match the asteroid's velocity, and by then you do not really need the asteroid. But something very similar to your idea is used constantly for interplanetary travel - gravity assist which uses other bodies' gravity to accelerate and change direction.

Krastanov's answer is good, but it's worth adding that 'cyclers' are a similar but practical idea: https://en.m.wikipedia.org/wiki/Mars_cycler

How do the orbits of the moons, and the asteroid's axis of rotation match up to the ecliptic? Do both moons orbit in the same direction? How eccentric are the orbits of the moons?

What's the going theory on how such a small body can capture moons? It must not be too difficult, otherwise 3122 Florence wouldn't be the 3rd triplet spotted.

What's the surface gravity? https://en.wikipedia.org/wiki/3122_Florence

Mass isn't given, but could estimate from volume, and typical asteroid density?

A quick wolfram alpha suggests about 0.002 ms^-2, i.e. about 1/500 Earth gravity.

9.8 / 0.002 = 4900, so was that about 1/5000 Earth gravity?

Yes, sorry.

Imagine hijacking a 100-meter moon made of rare earth metals like gold, platinum, rhodium, ruthenium, iridium, etc. etc. More than enough to under write the mission and pay for a moon base.

Unless you did it very secretly and slowly you'd might crash the market though.

Imagine heating and spinning it into a thin foil disk, and then curving it into a slight parabola by gently accelerating the center point away from the sun. Solar-cooker death-ray for anyone who disputes your claim!

The trick is getting it through the atmosphere intact.

The Apollo module was 20,000-kg. We could do it in 50,000-lbs chunks but we would have to process it on the moon first so it wouldn't crater when it landed.

If the commodities market tanks, well, we'll value add it by selling it as "all weather platinum or gold siding" at Home Depot. ;-)

Apollo weight info: https://www.google.com/search?q=apollo+commad+module+weight&...

You can just make a flattish shape out of it and most likely it will enter just fine.

Your link says 5,500 kg for the Command module, which is the only part that re-entered.

And of that 5,500kg, maybe 300-400kg was actual payload (astronauts and samples).

Not a real problem, you'll only lose the outermost layers going through the atmosphere.

The biggest problem is what happens when it lands. And also what happens to whatever it lands on.

You can double selling asteroid insurance.

If we go grab a moon sized ball of gold, gold will lose most of its value. It'll be the next Aluminium.

That much gold would still be worth it for electronic and spaceflight applications. Gold's like a better copper or silver there. And let's not forget the most important application, stereo plug connectors.

For platinum or iridium, making it cheaper there would enable all sorts of catalytic chemical processes that are prohibitively expensive now. If abundant enough, new demand will keep the bottom of the market from falling out.

Gold is already not a major expense in electronics. Platinum is currently cheaper than gold. Most pgm catalysts are capable of ~< .1% catalyst loading (e.g. monsanto and cativa processes), and the catalytic metals are easily recovered.

I'd like to believe you about Pt and Ir catalysts, but I just had a chemistry PhD student complaining to me that some paper's processes were too uneconomical because of needing too many platinum atoms in the catalyst. The point was about new processes being viable, not existing techniques.

They actually just plate connectors typically, I think with around 7µm of gold. And no, gold is not a better copper or silver. Both silver and copper are more conductive than gold (then followed by aluminum).

Gold is excellent for contact points though as it does not tarnish.

Silver conducts heat and electricity the best of the three, but tarnishes the most easily, so it can have issues with high frequency signals as most of the signal travels on the outer surface.

If both silver and copper were the same price as copper, it'd probably be silver that would see the most increase in use in electrical applications. During the Manhattan project, there was a shortage of copper and cost was not an option. 430 million troy ounces of silver from the West Point Bullion Depository was melted down and used to make magnetic coils. At the end of the project, it was all returned, minus 120 oz.

https://en.wikipedia.org/wiki/Calutron

The stereo plug thing was a joke, but thanks for educating me on the Calutron. Very cool.

I got a chuckle out of the Hobbit movie, where Smaug's gold treasure was so enormous the dwarves would be rendered penniless if they tried to spend it :-)

There is precedent. When the Spanish extracted all that gold and silver from South America and shipped it back to Spain, all they got was inflation.

And a very large fleet of ships.

I never bought that argument. World gold production is about 100-200 billion per year. Just hold onto your meteor and sell 50 billion worth per year for the next 200 years.

You would need to do it in secret. Plot for the next James Bond movie?

1. Firstly they won't be sending it down a gravity well, unless of course there is need for it. And if they really do send it they will likely strictly control its supply. Economics today is quite well done. Even blood diamond miners restrict supply to ensure demands.

2. They will likely be using mined material from asteroids to build space stations and bases.

3. They will only mine as much as they need, given an how much of it is available.

Its like expansion of human cities you extract/mine as much as you need and when you need it.

Space economics is a crazy thing, once you start thinking about it. The first people to start building in space will ponder the vastness and almost a infinite space full of resources and real estate to occupy. Of course the concept of ownership will look ridiculous. This is at least until there is a rapidly growing and spreading population in space.

Beyond that its really how quickly you can spread out. And the economics of that is not money. But trading energy for longevity.

I can assure you we are a very long time away from spreading to the last inch of the universe.

Gold is peculiar in this sense, but generally speaking I think it’s worth separating value from price

If we doubled oil supply tomorrow, the price would drop drastically, probably to less than half. The total price of all the oil would be less than yesterday. But, that doesn’t mean we’re deriving less value from the oil. We’ll have more energy and materials, that’s more value. It probably isn’t twice the value (we’d probably be less energy efficient, for example) but it would definitely be more value.

Maybe if you do it.

If I do it, I don't think it's in my best interest to announce it like that.

Pet peeve:

> rare earth metals like gold, platinum, rhodium, ruthenium, iridium

Not one of those is a rare earth metal. The complete list of rare earth metals:

cerium (Ce), dysprosium (Dy), erbium (Er), europium (Eu), gadolinium (Gd), holmium (Ho), lanthanum (La), lutetium (Lu), neodymium (Nd), praseodymium (Pr), promethium (Pm), samarium (Sm), scandium (Sc), terbium (Tb), thulium (Tm), ytterbium (Yb), yttrium (Y).

Rare earths are also, despite the name of the group, not particularly rare or expensive, and it would never make sense to go mine for them in space. (The short-lived supply crunch that brought them into public eye was caused by the Chinese first effectively subsidizing supply to the point where all other suppliers had to close, and then restricting exports. Since mines take several years to spin up, this caused some disruption until production in the rest of the world caught up. Supplies of REE are found practically everywhere.)

I know that you didn't actually mean rare earths, you just meant rare metals in general. However, calling them rare earths is approximately as wrong as calling C# C or calling Javascript Java. It's really grating.

Well, that shows me! ;-) Thank you, some of these metals I have never heard of.

Well, they're quite rare :)

Peter Diamandis[0] has repeatedly predicted that the world's first trillionaire will be made by mining asteroids.

Planetary Resources[1] is at least one company that is attempting to do it.

[0]: https://en.wikipedia.org/wiki/Peter_Diamandis

[1]: http://www.planetaryresources.com/asteroids/

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