Detecting Asteroid Collisions: 'Oumuamua & Radio Telescopes

[roineust]

A reasonably read and educated laymen, would response to a claim that science and technology still have no means to detect a big asteroid collision with earth, by saying that according to what he read and saw in communication channels reliable enough, an object of that size on course to hit earth, should be detected by radio telescopes around the world, in due time. Then comes into our solar system 'Oumuamua, which is detected only on 19 October 2017.

Please let me on your thoughts and knowledge regarding this subject.

 

[Drakkith]

I'm sorry, but are saying that we should have been able to detect it, or that we shouldn't have? I'm having some difficulty deciphering your post.

 

[roineust]

Saying that my impression was that any object of that size, would be detected by current technology at least several months ahead if not years ahead. But this looks like just weeks or days ahead. That is, hypothetically of course, 'Oumuamua is only an hypothetical example, i know that it will not ever hit Earth and that it is now on its way out of the solar system and that its distance from earth, is just getting bigger now at a very fast pace.

 

[Drakkith]

Detection by optical and near-optical telescopes depends on many different factors, including size, albedo, distance to the Sun, etc. Apparently Oumuamua is fairly dark and doesn't reflect much light, making it harder to detect. As for non-optical means, I can't say much. I only have an extremely limited amount of knowledge of radio telescopes and other methods.

In any case, our ability to detect objects before they are an immediate threat is obviously still limited. I wish I had more information for you.

 

[roineust]

i just read that Chicxulub impactor was 10-15 km in size and that ʻOumuamua is only estimated at 230 by 35 meters, this is significantly less. On the other hand, is it not still considered a huge size, in terms of impact possibility? For example, it is as big as Tunguska event asteroid, if not bigger.

 

[glappkaeft]

Saying that my impression was that any object of that size, would be detected by current technology at least several months ahead if not years ahead. But this looks like just weeks or days ahead. That is, hypothetically of course, 'Oumuamua is only an hypothetical example, i know that it will not ever hit Earth and that it is now on its way out of the solar system and that its distance from earth, is just getting bigger now at a very fast pace.

Our ability to detect faint objects in the daytime sky or close to the sun is almost non-existent. This is just not because of the sun blinding the sensors or the bright sky, the object itself will necessarily be poorly lit (back-lit) as seen from the Earth.

The full moon also severely limits the detection threshold of the rest of the sky during a large part of the time. On top of that the only truly sensitive all sky survey telescopes operational (PAN-Starrs) are located in one spot so it can only detect objects visible from Hawaii and local weather can shut them both down. Together they usually scan the available night sky four times a month and I believe that 'Oumuamua was actually detected rather soon after it became possible.

 

[OmCheeto]

...
In any case, our ability to detect objects before they are an immediate threat is obviously still limited. I wish I had more information for you.

I think that would make this topic a good homework problem.
It's obviously true, but why?

 

[|Glitch|]

i just read that Chicxulub impactor was 10-15 km in size and that ʻOumuamua is only estimated at 230 by 35 meters, this is significantly less. On the other hand, is it not still considered a huge size, in terms of impact possibility? For example, it is as big as Tunguska event asteroid, if not bigger.

In 2005 Congress tasked NASA with finding NEOs larger than 140 meters. That would put Oumuamua into that category. There are a few of issues with Oumuamua that made detecting it difficult.

The first issue was the angle which it entered our solar system. The overwhelming majority of planets, asteroids, and other objects in our solar are on or near the ecliptic plane, and that is where we focus the majority of our attention. Oumuamua entered our solar system almost perpendicular to the ecliptic plane, which is why it was not detected until it reached the ecliptic plane just after passing the sun.

Another issue that made detecting Oumuamua difficult was its speed. Just as it passed the sun Oumuamua was traveling 87.71 km/s. By the time it was discovered a month later the asteroid was traveling 49.67 km/s. By comparison Earth's orbital speed is 30 km/s, and Mercury (the fastest orbiting planet) has an orbital velocity of 47.36 km/s. By the time Oumuamua leaves our solar system sometime around the year 2430 it should be traveling at a speed of approximately 26.32 km/s.

As was previously mentioned, objects that approach Earth from the direction of the sun are in our visual and thermal "blind spot." Making the detection of such objects extremely difficult. The meteor that blew up over Chelyabinsk, Russia, in 2013 also approached Earth from the direction of the sun, which is why it was not detected. Further complicating matters is the fact that Oumuamua is not very bright. It is already too faint (with an apparent magnitude of ~23) and moving too fast to be studied by even the largest ground-based telescopes.

As you yourself have identified, size is also an issue in early detection. NASA knows the orbits of 98%+ of all the NEOs that are 1 km or larger in our solar system, however, NASA knows less than 1% about the orbits of the NEOs that are 140 meters in diameter. So size does matter. Radio telescopes are not used to discover NEOs because NEOs typically do not emit radio frequencies that a radio telescope can detect. Only infrared and optical telescopes are used. The overwhelming majority of these telescopes are ground-based, but there are a few satellites that are also used.


Oumuamua passing through our solar system

If you want to see what the effects of an asteroid like Oumuamua would have if it were to impact Earth, I would recommend that you visit Impact Earth!, an interactive website by Purdue University that calculates the effects of asteroid impacts.

 

[roineust]

Radio telescopes which act in a similar way to radar can not detect at long enough range?

 

[websterling]

Radio telescopes which act in a similar way to radar can not detect at long enough range?

Radio telescopes configured as radar are routinely used to study near Earth objects. They are useful for determining, for example, rotational rates and surface properties. They are also useful for refining the orbit of an object.

They are not useful as instruments for discovering such objects. Large radio telescopes have a very narrow beamwidth so they only see a very small area of the sky. And you have to consider the round trip time of a radar pulse. At its detection Oumuamua was about 2 light minutes from Earth giving a round trip time of 4 minutes. So you would have to transmit a pulse and wait for at least 4 minutes to see if you got a return before you could move the antenna to try again in a different area of the sky.

 

[websterling]

Since a collision of an object like Oumuamua with the Earth is part of the discussion, here are a few thoughts.

Assume the parameters of the discovery are essentially the same and that the object is on a collision course with Earth. When the object was discovered it was about 33,000,000 km from Earth and traveling ~50 km/sec. At this rate it would hit the Earth in about 7.5 days. The discovery image wouldn't fix the object's orbit so it might be the next night before there was a rough orbit indicating a chance of a collision. This would expedite follow up observations, both optical and radar. So within 3 or 4 days we would know the basis characteristics of the object, where and when it would impact, and probably have a rough idea of what to expect from the collision.

Then what??

 

[nikkkom]

Since a collision of an object like Oumuamua with the Earth is part of the discussion, here are a few thoughts.

Assume the parameters of the discovery are essentially the same and that the object is on a collision course with Earth. When the object was discovered it was about 33,000,000 km from Earth and traveling ~50 km/sec. At this rate it would hit the Earth in about 7.5 days. The discovery image wouldn't fix the object's orbit so it might be the next night before there was a rough orbit indicating a chance of a collision. This would expedite follow up observations, both optical and radar. So within 3 or 4 days we would know the basis characteristics of the object, where and when it would impact, and probably have a rough idea of what to expect from the collision.

Then what??

Then nukes.

 

[DrStupid]

Then nukes.

That might not be sufficient, even if we would be able to lauch them in time and intercept such a fast object with the required accuracy.

 

[Nugatory]

At this rate it would hit the Earth in about 7.5 days. ... So within 3 or 4 days we would know the basis characteristics of the object, where and when it would impact...

Then what??

In very round numbers, the impact of an object 230 meters by 35 moving at 50 km/sec would release about as much energy as several hundred one megaton hydrogen bombs. That's comparable to the energy released by a major hurricane, an earthquake hitting ten on the Richter scale, or a Tambora-sized volcanic eruption. On the scale of events like Chicxulub it's a mere fleabite, but if the impact happens at the wrong place and time it would be a catastrophe unprecedented in human history..

With only a few days to respond, we would be trying to evacuate the at-risk areas. A projected ocean impact would require evacuating many thousands of miles of coastline because of the tsunami threat; a land impact would affect a smaller area but the damage within that area would be more complete.

 

[Nugatory]

Then nukes.

It's really hard to see how that would work with the time parameters that @websterling is suggesting.

 

[nikkkom]

It's really hard to see how that would work with the time parameters that @websterling is suggesting.

I don't know what capabilities exist ready-to-use now. If there are secret plans how to fit a nuke on a SM-3 or a GBI, I know nothing about them.

But in 1975 US had an ABM system with 5Mt interceptor warhead capable of reaching 500+ km altitude. It was tested (sans actual warhead explosion, of course). ~40 years later, we should be able to do better with relative ease.

5Mt would reduce that rock to rubble.

ICBM apogee is higher (~1200km) and they, of course, also _are_ nukes. Redesigning them to perform interception is non-trivial, but technically quite possible.

 

[mfb]

It doesn't help to have a nuclear weapon explode near the object. What do you expect? First, the weapon is missing its most destructive component, the shock wave, as there is no atmosphere in space. You get a lot of radiation, some of it evaporates the surface layer of the asteroid, and most of the energy is wasted.
Even if we assume you manage to break the asteroid apart: So what? Now you have several smaller components that still fly towards Earth with the same combined energy. But instead of one area with a massive impact crater you get many impact craters scattered over a large area. You might even increase the damage it does.

Evacuate the most likely impact area as good as possible, let it hit, then rebuild the areas that are worth rebuilding.

NASA knows the orbits of 98%+ of all the NEOs that are 1 km or larger in our solar system, however, NASA knows less than 1% about the orbits of the NEOs that are 140 meters in diameter.

In 2012 NASA estimated that 20% to 30% of the Earth-crossing objects larger than 100 meters have been found. We don't know most of them, but we know a relevant fraction, and that should increase significantly within the next 10 years. As comparison: In 1998 only about 10% of the objects larger than 1 km were known (source).
Everything smaller than 100 meters can still destroy towns and smaller regions, but it won't destroy a large country.

 

[russ_watters]

In ver y round numbers, the impact of an object 230 meters by 35 moving at 50 km/sec would release about as much energy as several hundred one megaton hydrogen bombs. That's comparable to the energy released by a major hurricane, an earthquake hitting ten on the Richter scale, or a Tambora-sized volcanic eruption. On the scale of events like Chicxulub it's a mere fleabite, but if the impact happens at the wrong place and time it would be a catastrophe unprecedented in human history..

With only a few days to respond, we would be trying to evacuate the at-risk areas. A projected ocean impact would require evacuating many thousands of miles of coastline because of the tsunami threat; a land impact would affect a smaller area but the damage within that area would be more complete.

As you say, the internet tells me the 2011 Japan earthquake released an energy of about 500 megatons, killing 15,000 people. Depending on how the energy was focused (it would be higher intensity and lower surface area), having 2 days to get ready for such an event could make a huge difference in the death toll, if not the damage. A land impact/airburst would have a pretty small heavy damage radius; perhaps a hundred miles. An ocean impact would cause damage over a much wider area, but it is tough to be sure how big of a tsunami it would cause (100 feet? 500 feet?). Still, most people killed in Japan were people who didn't evacuate before the tsunami. So two days notice would make a big difference.

 

[|Glitch|]

It doesn't help to have a nuclear weapon explode near the object. What do you expect? First, the weapon is missing its most destructive component, the shock wave, as there is no atmosphere in space. You get a lot of radiation, some of it evaporates the surface layer of the asteroid, and most of the energy is wasted.
Even if we assume you manage to break the asteroid apart: So what? Now you have several smaller components that still fly towards Earth with the same combined energy. But instead of one area with a massive impact crater you get many impact craters scattered over a large area. You might even increase the damage it does.

Evacuate the most likely impact area as good as possible, let it hit, then rebuild the areas that are worth rebuilding.

In 2012 NASA estimated that 20% to 30% of the Earth-crossing objects larger than 100 meters have been found. We don't know most of them, but we know a relevant fraction, and that should increase significantly within the next 10 years. As comparison: In 1998 only about 10% of the objects larger than 1 km were known (source).
Everything smaller than 100 meters can still destroy towns and smaller regions, but it won't destroy a large country.

It was in 1998 that Congress tasked NASA with locating NEOs 1 km and larger. So they weren't specifically looking for them until after 1998. Furthermore, the NEOWISE project you reference was an after-thought by NASA to use the WISE satellite to spot NEOs for the few remaining months it was still capable of functioning.

You are also comparing two different things. While all PHAs are NEOS, not all NEOs are PHAs. The NASA source you provided refers to PHAs, not NEOs. I specifically stated NEOs, not PHAs.

The NEOWISE project located 600 NEOs (not PHAs), of which about 135 of which were newly discovered, during the 11 months it operated in 2011 and 2012. NASA is using that as their sample data to estimate the number of PHAs. As of November 14, 2017, there have been 17,155 NEOs discovered, while NASA estimates only 4,700 PHAs exist (your source).

 

[mfb]

This is a thread about impact risks, so I focused on asteroids with impact risk.
The trend is the same for both categories. We discovered most of the larger ones, and the discoveries are shifting towards the smaller ones as the detection methods get better and we run out of large objects to discover.

 

[|Glitch|]

This is a thread about impact risks, so I focused on asteroids with impact risk.
The trend is the same for both categories. We discovered most of the larger ones, and the discoveries are shifting towards the smaller ones as the detection methods get better and we run out of large objects to discover.

Yet you cite projects that search for NEOs, and not just PHAs. The only reason NASA is looking for NEOs larger than 140 meters is because they were told to do so by Congress in 2005. Just as they were told to locate NEOs larger than 1 km by Congress in 1998. Without that direction from Congress NASA wouldn't be tracking any NEOs. It is not as if NASA found all the large NEOs and are now looking for smaller ones, as you seem to be claiming. They are locating NEOs of a certain size because that is what they were specifically told to do by their funding authority.

 

[mfb]

I cite projects relevant for finding potentially hazardous asteroids. If these projects find other asteroids as well: so what?

“Congress tells NASA -> NASA does it” is clear, but your claim of the reverse would need a citation. How can you be sure NASA wouldn’t look for PHAs (and other NEOs: Again, not the topic here) without that congress order?
Also: How exactly does that matter if we discuss how many we know today?

 

[nikkkom]

It doesn't help to have a nuclear weapon explode near the object. What do you expect?

I expect attempting to achieve surface blast. (Subsurface would be even better, but it requires development of a penetrating warhead).

Ivy Mike's 10Mt explosion on a small coral reef island resulted in 1.9km diameter, 50m deep crater. You can fit about a hundred Oumuamua's into a crater of these dimensions.

 

[|Glitch|]

I cite projects relevant for finding potentially hazardous asteroids. If these projects find other asteroids as well: so what?

“Congress tells NASA -> NASA does it” is clear, but your claim of the reverse would need a citation. How can you be sure NASA wouldn’t look for PHAs (and other NEOs: Again, not the topic here) without that congress order?
Also: How exactly does that matter if we discuss how many we know today?

You misrepresented the project you cited, claiming it was to search for PHAs when it was actually searching for NEOs. As for a citation, how about your own post?

As comparison: In 1998 only about 10% of the objects larger than 1 km were known (source).

NASA was established in 1958, and yet 40 years later they had only discovered ~10% of the NEOs larger than 1 km. Yet since Congress ordered NASA to locate NEOs larger than 1 km NASA has managed to find more than 98% of them in less than 20 years. Which clearly demonstrates that NASA was not specifically looking for NEOs (of any size) until ordered to track them by Congress.

 

[nikkkom]

NASA was established in 1958, and yet 40 years later they had only discovered ~10% of the NEOs larger than 1 km. Yet since Congress ordered NASA to locate NEOs larger than 1 km NASA has managed to find more than 98% of them in less than 20 years. Which clearly demonstrates that NASA was not specifically looking for NEOs (of any size) until ordered to track them by Congress.

Consider that finding NEOs efficiently requires robotic telescopes and software/hardware capable of processing thousands of images every day.

 

[|Glitch|]

Consider that finding NEOs efficiently requires robotic telescopes and software/hardware capable of processing thousands of images every day.

It also helps if you are actually looking for them, which NASA wasn't prior to being given a congressional directive in 1998.

 

[DrStupid]

Ivy Mike's 10Mt explosion on a small coral reef island resulted in 1.9km diameter, 50m deep crater.

Ivy Mike exploded at ground level. That's not easy with a speed of 50 km/s.

 

[nikkkom]

Ivy Mike exploded at ground level. That's not easy with a speed of 50 km/s.

I don't think so. Military have 100+ years of experience in developing contact fuses.

 

[websterling]

Military have 100+ years of experience in developing contact fuses

I don't think a contact fuse would do it. Even with a direct hit and the fuse being activated, with the speeds involved (50 km/sec for the target and another 5-10 km/sec for the warhead) the warhead would probably be destroyed before it detonated.

 

[roineust]

Radio telescopes configured as radar are routinely used to study near Earth objects. They are useful for determining, for example, rotational rates and surface properties. They are also useful for refining the orbit of an object.

They are not useful as instruments for discovering such objects. Large radio telescopes have a very narrow beamwidth so they only see a very small area of the sky. And you have to consider the round trip time of a radar pulse. At its detection Oumuamua was about 2 light minutes from Earth giving a round trip time of 4 minutes. So you would have to transmit a pulse and wait for at least 4 minutes to see if you got a return before you could move the antenna to try again in a different area of the sky.

How fundamental is that narrow beam width limitation, in terms of being a current technological barrier? Isn't it possible to develop a radar-radio-telescope, which encodes its transmitter signals just like internet packets and then not waiting with the whole apparatus for the round trip time, rather having a receiver that listens somehow to a wider range of returning signals, so any signal that returns is already encoded and thus will be known, to what region of transmission that signal belongs?

 

[websterling]

How fundamental is that narrow beam limitation, in terms of being a current technological barrier? Isn't it possible to develop a radar-radio-telescope, which encodes its transmitter signals just like internet packets and then not waiting with the whole apparatus for the round trip time, rather having a receiver that listens at a much wider returning beam-width, so any signal that returns is already encoded and thus will be known, to what region of transmission that signal belongs?

It's not uncommon to have the receiver and transmitter on different antenna. And they could be separated by some distance- radars for observing meteors are typically done this way. I think any encoding would probably be scrambled by a reflection from an irregular surface. You might be able to use different frequencies rather than an encoding. Still, considering transmitted power and beamwidth constraints, I don't think you could make a very efficient system.

 

[roineust]

It's not uncommon to have the receiver and transmitter on different antenna. And they could be separated by some distance- radars for observing meteors are typically done this way. I think any encoding would probably be scrambled by a reflection from an irregular surface. You might be able to use different frequencies rather than an encoding. Still, considering transmitted power and beamwidth constraints, I don't think you could make a very efficient system.

If some new SETI collaboration programs claim, that they will be able to hear an encoded signal as low as 100W in power, from a distance of up to 50 light years, isn't it possible to have Earth transmitters strong enough, to decode an asteroid hit round trip of up to a few hours?

 

[websterling]

they will be able to hear an encoded signal as low as 100W in power, from a distance of up to 50 light years

In the article they're talking about a signal from a 100W laser; entirely different physics involved.

With radar I think the limit for just detection of a 1km object is less than 1 AU, less than a 15 minute round trip time. For an object like Oumuamua it would be far less.

 

[roineust]

In the article they're talking about a signal from a 100W laser; entirely different physics involved.

With radar I think the limit for just detection of a 1km object is less than 1 AU, less than a 15 minute round trip time. For an object like Oumuamua it would be far less.

Yes, sorry, i read the whole article but missed the laser part when returned to quote, what about laser scanning then? (-:

It looks like LIDAR telescopes are used for atmospheric research. In what ways would it be different to scan much further away to a distance and object size of an asteroid 2 light hours from earth?

 

[mfb]

You misrepresented the project you cited, claiming it was to search for PHAs when it was actually searching for NEOs.

Uh, what?
"They looked for A and B."
"How often did they find A?"
"I said they looked for A and B, not only for A!"

Here A=PHAs, B=NEOs that are not PHAs just in case it was not clear.

NASA was established in 1958, and yet 40 years later they had only discovered ~10% of the NEOs larger than 1 km. Yet since Congress ordered NASA to locate NEOs larger than 1 km NASA has managed to find more than 98% of them in less than 20 years. Which clearly demonstrates that NASA was not specifically looking for NEOs (of any size) until ordered to track them by Congress.

No it does not demonstrate this, and even if it would, it would miss the point because I was asking about a different time frame. Telescopes and data analysis are improving rapidly, with or without congress orders.

Gaia alone is expected to roughly double the number of known asteroids in the solar system (and measure most of the discovered ones as well, of course). Without any congress order, and without NASA at all, because it is an ESA mission.

Yes, sorry, i read the whole article but missed the laser part when returned to quote, what about laser scanning then? (-:

You can't "laser scan" for asteroids. They are not nice retroreflectors that would reflect the lasers. Even with the Moon, which is nearby and where we have actual retroreflectors, we just get something like 1 photon per shot back with the best combination of ground stations and mirrors. You have to know precisely where the mirror is and you need a good estimate for the distance already, otherwise you wouldn't even find the Moon with that approach.
To get a detectable signal back from radar astronomy, the beam has to be very narrow. You cannot scan the whole sky, or even a relevant fraction of it, like that.

I expect attempting to achieve surface blast. (Subsurface would be even better, but it requires development of a penetrating warhead).

Ivy Mike's 10Mt explosion on a small coral reef island resulted in 1.9km diameter, 50m deep crater. You can fit about a hundred Oumuamua's into a crater of these dimensions.

You are still missing the atmosphere.