Planetary Defense Experiment

[Shadowy Man]

Why would it blindside us? I think it’d be easier to see those objects coming from outside our orbit than those that would be coming from the sunward direction.

My (likely flawed) understanding is that we simply don't look there so much as we look within and near the plane of the ecliptic.

Observatories like the Sloan Digital Sky Survey and the upcoming Vera Rubin observatory are not limited to the ecliptic.

 

[barbos]

Why would it blindside us? I think it’d be easier to see those objects coming from outside our orbit than those that would be coming from the sunward direction.

My (likely flawed) understanding is that we simply don't look there so much as we look within and near the plane of the ecliptic.

The reason they were/are not looking there is because there are way objects to see inside asteroid belt. So yeah, they should start looking everywhere. But I think 10km asteroids from asteroid belt which intersect earth orbit are all discovered. Big asteroids is not the problem. Long period Comets have better potential for hitting the Earth on the first try, large asteroids can't do that.

 

[Elixir]

Observatories like the Sloan Digital Sky Survey and the upcoming Vera Rubin observatory are not limited to the ecliptic.

That's a small percentage of all observatories, and the ecliptic is but a small slice of the sky from which a killer object might come.
Barbos' comment "long period Comets have better potential for hitting the Earth on the first try" speaks to what I was thinking. Who knows what kind of things are lurking in the Kuyper Belt or the Oort Cloud... nobody knows.
If there is something like this 100+km diameter object (spotted in June of this year) headed for us, but only 1/100th its size, would we pick it up in time to do anything about it? I doubt it.

 

[Shadowy Man]

Observatories like the Sloan Digital Sky Survey and the upcoming Vera Rubin observatory are not limited to the ecliptic.

That's a small percentage of all observatories, and the ecliptic is but a small slice of the sky from which a killer object might come.

I don’t understand your response. These observatories doing sky surveys cover the whole night sky. If things are moving anywhere they can be detected, given the detection limits of the instruments. They can’t however look too close to the Sun.

 

[Shadowy Man]

Look, for example, at this paper:

A million asteroid observations in the Sloan Digital Sky Survey | Astronomy & Astrophysics (A&A)

Astronomy & Astrophysics (A&A) is an international journal which publishes papers on all aspects of astronomy and astrophysics

www.aanda.org

Entitled “A million asteroid observations in the Sloan Digital Sky Survey”.

The main SDSS imaging survey covered 7500 deg2 in the northern Galactic cap and 750 deg2in the southern Galactic cap, where each patch of the sky was imaged in five filters in a single visit. The 270 deg2 of Stripe 82 (a thin long area within 21 h < RA < 04 h and −1.25° < Dec < 1.25°; see Fig. 1) were repeatedly imaged (about 80 times) as a time-domain survey (Sako et al. 2008; Frieman et al. 2008). Both surveys include 80 common runs. We only kept 756 runs from DR16, rejecting the runs that were affected by bad weather (e.g., clouds, bad seeing) and thus had a quality score below 0.1. In total, we analyzed 938 unique runs, about twice as much as those listed in the ADR4.

The median 5σ depth of SDSS photometric observations, based on the formal uncertainties from point spread function (PSF) photometry on point sources, are, in AB magnitudes: u = 22.15, g = 23.13, r = 22.20, i = 22.20, and z = 20.71 (Ahumada et al. 2020). We thus set a brightness limit of 22.2 in r (0.7 magnitude fainter than the selection criterion of Ivezić et al. 2001).

Contrary to the ADR4 extraction we did not set an upper limit on the apparent velocity, to avoid the rejection of NEAs. Furthermore, as sources moving faster than 0.5° day−1 may appear trailed in the images, we did not restrict the object type to stars only, but allowed both stars (type=6) and galaxies (type=3). The larger number of runs, combined with our more relaxed selection criteria to maximize the completeness (the SQL (Structured Query Language) code is provided in Appendix B for reproducibility). leads to a dramatic increase in the number of SSO candidates compared to the ADR4: 4 804 003 in DR16 and 4 071 153 in Stripe 82.

 

[Elixir]

Observatories like the Sloan Digital Sky Survey and the upcoming Vera Rubin observatory are not limited to the ecliptic.

That's a small percentage of all observatories, and the ecliptic is but a small slice of the sky from which a killer object might come.

I don’t understand your response. These observatories doing sky surveys cover the whole night sky. If things are moving anywhere they can be detected, given the detection limits of the instruments. They can’t however look too close to the Sun.

I doubt that any Oort Cloud object would come at us "out of the sun" - unless it was on its return trip, in which case it would have been spotted on its way into the solar system.

An object coming "straight in" from the Oort cloud would not initially show up as a moving object in one of those broad sky search surveys, or so I am told.

 

[bilby]

If you have a way to make a nuke with a yield in the kg, rather than the kt range, call the Pentagon, they definitely want to talk to you.

I am not sure that this is even a problem.
most asteroids are piles of loosely attached boulders, perfect for blowing them up.
And even if it is solid, I doubt large fragments will be produced in the explosion.

Rubble pile - Wikipedia

en.wikipedia.org

You can doubt all you want, but there's a reason why mining companies don't save money and just put all the explosives into a single bore-hole when blasting.

 

[Shadowy Man]

Observatories like the Sloan Digital Sky Survey and the upcoming Vera Rubin observatory are not limited to the ecliptic.

That's a small percentage of all observatories, and the ecliptic is but a small slice of the sky from which a killer object might come.

I don’t understand your response. These observatories doing sky surveys cover the whole night sky. If things are moving anywhere they can be detected, given the detection limits of the instruments. They can’t however look too close to the Sun.

I doubt that any Oort Cloud object would come at us "out of the sun" - unless it was on its return trip, in which case it would have been spotted on its way into the solar system.

An object coming "straight in" from the Oort cloud would not initially show up as a moving object in one of those broad sky search surveys, or so I am told.

Who told you that?

Anything within the solar system will have noticeable parallax at least.

Aren’t long-period comets with high eccentricities essentially coming from the Oort Cloud in the way you describe? Isn’t that what instigated the hypothesis of the Oort Cloud in the first place?

 

[Elixir]

Aren’t long-period comets with high eccentricities essentially coming from the Oort Cloud in the way you describe? Isn’t that what instigated the hypothesis of the Oort Cloud in the first place?

I think that's right, but they were well into the inner solar system before being detected and their orbits extrapolated.
Which is also when parallax becomes useful.

 

[Jimmy Higgins]

Why not?
Pressure from the weight is equivalent to few meters on the earth.
You can literally dig yourself inside like into the sand.
You will need a power source - some kind of nuclear reactor.
In fact, chemical power source may be enough.

You planning some sort of autonomous mini-TBM?

 

[Shadowy Man]

Aren’t long-period comets with high eccentricities essentially coming from the Oort Cloud in the way you describe? Isn’t that what instigated the hypothesis of the Oort Cloud in the first place?

I think that's right, but they were well into the inner solar system before being detected and their orbits extrapolated.
Which is also when parallax becomes useful.

And we have much better tools now for discovering these now, especially worth the advent of these surveys like the upcoming Rubin observatory will execute. Just look at the magnitude limits in the SDSS paper I cited.

 

[Loren Pechtel]

And this begs the question of how we might break apart a 10km asteroid into chunks no larger than 20meters. How much energy would that take?

We have the firepower to do it. The problem is distributing it evenly. Big booms tend to blow rocks into large chunks, not little bits.

Yup. You need lots of little explosions to pulverise rock.

Nukes need not apply. Amatol or similar is ideal for the job - the tricky part is getting it in place, distributed throughout the target rock.

Against a dinosaur killer chemical explosives need not apply--there's simply no way even SpaceX can lift enough.

That leaves deflection--Orion.

 

[Loren Pechtel]

Check your math. You're looking at the ballpark of 1 MJ/kg.

I checked, still 10MJ per ton of atmosphere.

10km is the dinosaur killer. You're way low on it's impact energy.

 

[Loren Pechtel]

If you have a way to make a nuke with a yield in the kg, rather than the kt range, call the Pentagon, they definitely want to talk to you.

Why would the Pentagon care? They would be too expensive.

 

[Loren Pechtel]

If you have a way to make a nuke with a yield in the kg, rather than the kt range, call the Pentagon, they definitely want to talk to you.

I am not sure that this is even a problem.
most asteroids are piles of loosely attached boulders, perfect for blowing them up.
And even if it is solid, I doubt large fragments will be produced in the explosion.

Rubble pile - Wikipedia

en.wikipedia.org

The problem is that it's not all the same size rubble. You'll blow off small bits very fast and large chunks slowly.

 

[Loren Pechtel]

In any case, 10 km asteroids on short notice are astronomically rare.
The one which killed dinosaurs had tens of millions of years notice. Dinosaurs did not have NASA.

What is our level of confidence that there are no "earth crossers" of that size that have yet to be cataloged?
If a new one were discovered today, how much notice would be required to do anything about it?

Seems to me that an object from the asteroid belt would be detected a lot earlier than say, a Kuyper Belt object whose orbit was somehow perturbed by collision or whatever, and took up an earth-crossing orbit in an orientation 60-90 degrees off the ecliptic. Such an object would probably blindside us.

Why would it blindside us? I think it’d be easier to see those objects coming from outside our orbit than those that would be coming from the sunward direction.

That's assuming someone is looking at the right place and the right time and looking for unknown objects. Most telescopes are going to be looking at known objects, one more point of light in the sky would go unnoticed. Only those looking for new objects are likely to notice a new dot in the sky and until they find it three separate times it won't mean anything.

 

[Loren Pechtel]

Observatories like the Sloan Digital Sky Survey and the upcoming Vera Rubin observatory are not limited to the ecliptic.

That's a small percentage of all observatories, and the ecliptic is but a small slice of the sky from which a killer object might come.

I don’t understand your response. These observatories doing sky surveys cover the whole night sky. If things are moving anywhere they can be detected, given the detection limits of the instruments. They can’t however look too close to the Sun.

I doubt that any Oort Cloud object would come at us "out of the sun" - unless it was on its return trip, in which case it would have been spotted on its way into the solar system.

An object coming "straight in" from the Oort cloud would not initially show up as a moving object in one of those broad sky search surveys, or so I am told.

Who told you that?

Anything within the solar system will have noticeable parallax at least.

Aren’t long-period comets with high eccentricities essentially coming from the Oort Cloud in the way you describe? Isn’t that what instigated the hypothesis of the Oort Cloud in the first place?

Parallax measurements require multiple observatories, or they require observation over a long period.

 

[barbos]

You can doubt all you want, but there's a reason why mining companies don't save money and just put all the explosives into a single bore-hole when blasting.

20 meters fragments are considered small

 

[barbos]

Parallax measurements require multiple observatories, or they require observation over a long period.

That's how asteroids are being detected

 

[barbos]

Check your math. You're looking at the ballpark of 1 MJ/kg.

I checked, still 10MJ per ton of atmosphere.

10km is the dinosaur killer. You're way low on it's impact energy.

How do you know I am way low? Have you calculated or you use gut feelings?