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I 'Oumuamua detection date and ramifications for a big asteroid collision with the Earth

  1. Dec 17, 2017 #1
    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.
     
    Last edited: Dec 17, 2017
  2. jcsd
  3. Dec 17, 2017 #2

    Drakkith

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    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.
     
  4. Dec 17, 2017 #3
    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.
     
    Last edited: Dec 17, 2017
  5. Dec 17, 2017 #4

    Drakkith

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    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.
     
  6. Dec 17, 2017 #5
    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.
     
  7. Dec 17, 2017 #6
    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.
     
  8. Dec 17, 2017 #7

    OmCheeto

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    I think that would make this topic a good homework problem.
    It's obviously true, but why?
     
  9. Dec 17, 2017 #8
    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.
     
    Last edited: Dec 17, 2017
  10. Dec 18, 2017 #9
    Radio telescopes which act in a similar way to radar can not detect at long enough range?
     
  11. Dec 18, 2017 #10
    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.
     
  12. Dec 18, 2017 #11
    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??
     
  13. Dec 18, 2017 #12
    Then nukes.
     
  14. Dec 18, 2017 #13
    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.
     
  15. Dec 18, 2017 #14

    Nugatory

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    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.
     
    Last edited: Dec 18, 2017
  16. Dec 18, 2017 #15

    Nugatory

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    It's really hard to see how that would work with the time parameters that @websterling is suggesting.
     
  17. Dec 18, 2017 #16
    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.
     
  18. Dec 18, 2017 #17

    mfb

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    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.
     
  19. Dec 18, 2017 #18

    russ_watters

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    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.
     
  20. Dec 18, 2017 #19
    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).
     
  21. Dec 19, 2017 #20

    mfb

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    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.
     
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