So astronomers really don't have an idea about density of asteroids?

[swampwiz]

This article about an "Armageddon" scenario says that astronomers don't have a very good idea about the density of asteroids.

https://slate.com/technology/2019/05/international-planetary-defense-conference-asteroid-impact.html
I had thought that they had a much better idea about it. Can't the material be surmised from observation?

 

[russ_watters]

This article about an "Armageddon" scenario says that astronomers don't have a very good idea about the density of asteroids...

I had thought that they had a much better idea about it. Can't the material be surmised from observation?

I don't see that in the article at all - that wasn't even the purpose of the conference. Can you give a quote where it says that and discusses it? And what of your own research have you done into this question? It's pretty provocatively worded... Heck, I'm not even sure it is really the question you mean to ask!

 

[swampwiz]

It's the Slate article. I'll post the highlights here:

Imagine this: Scientists have just detected an asteroid hurtling toward Earth. According to their calculations, the damage would be catastrophic, and we don’t have long to prepare. Experts determine that the best plan of action would be to launch armed spacecraft , perhaps with nukes, to rendezvous with the asteroid.


Though this sounds suspiciously like the plot of Armageddon, it’s also the plot of the sixth International Academy of Astronautics Planetary Defense Conference. Representatives from NASA, the Federal Emergency Management Agency, the European Space Agency, the U.N., and other international space experts have gathered in College Park, Maryland, this week to do a cosmic fire drill. The premise of this role-play universe begins with an imaginary asteroid called 2019 PDC, which has a 1 in 100 chance of striking Earth in 2027. According to NASA, those odds were selected for this drill because experts worldwide generally agree that that’s the threshold for when we should take collective action.

< snip >

A great deal of discussion has focused on how best to deflect the asteroid’s path. Some suggested deploying kinetic impactors, launched to collide with the asteroid and knock it into a different path, as well as launching nuclear weapons. The problem is that scientists aren’t yet sure exactly how each method would move the asteroid because they’re not sure of the asteroid’s mass, which, as you may guess, matters a lot when it comes to physics. The logistics of this exercise assume that humankind will send a probe up to study the asteroid more closely, but given the lag in how long it takes for spacecraft to reach the asteroid, scientists will need to make a decision about their deflection method before the probe sends back additional data.

I presume that the problem is ascertaining the asteroids' density since the size can be ascertained.

 

[JLowe]

This article about an "Armageddon" scenario says that astronomers don't have a very good idea about the density of asteroids.

https://slate.com/technology/2019/05/international-planetary-defense-conference-asteroid-impact.html
I had thought that they had a much better idea about it. Can't the material be surmised from observation?

I'm assuming they can estimate the mass to a pretty good degree, but when you're trying to deflect it's path, you need to be almost exact, which they can't be without closer inspection. They do say humankind would send a probe to investigate more closely, although it might be too late by the time they get the data.

 

[fresh_42]

This article about an "Armageddon" scenario says that astronomers don't have a very good idea about the density of asteroids.

This means that the variety of possible densities is large, so given a certain one you can't know without further information (orbit data, size, behavior in sun wind etc.) whether it is Ni-Fe rock or an icy dust ball. To claim astronomers have no idea about densities is wrong. Neither can such a general statement be seriously made, nor is your reference an acceptable source. Pop science publications are chasing headlines, not facts.

This thread will be closed until you can specify your question and provide a serious reference.

This article about an "Armageddon" scenario says that astronomers don't have a very good idea about the density of asteroids.

... is wrong and only proves the ignorance of the authors and not of astronomers. You show me a rock and I'll tell you the mass is not how science works.