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Thread: At what distance can we track asteroids and comets which can wipe out humanity?

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    At what distance can we track asteroids and comets which can wipe out humanity?

    Hi,

    I would be realy grateful if you could answer a couple of questions.

    NASA and many volunteers are discovering and tracking asteroids and comets, Near Earth Objects (NEOs). A great job, but what regarding the 'far away' objects?
    I've read that there are many comets in the Oort Cloud, but as far I know we are not able to track this comets at this distance. For this reason I'm wondering at what distance we can track comets as big or bigger as the dinosaurus killer and how much time do we have in that case if the comet is on a collision course to hit Earth? Let suppose we can track this kind of comets at a distance of 365,000,000 miles and the speed of the comet is 42,926 miles per hour in that case we only have 8,503 hours, so 354 days to protect all human beings and animals/nature. A too short time? How does it work?

    Furtheremore, is it possible that an asteroid as big or bigger as the Dinosaur-Killing Asteroid can enter our solar system originally coming from another star system? Like the interstellar asteroid: https://www.nasa.gov/planetarydefense/faq/interstellar If yes, at what distance are we able to track this asteroid and how much time do we have in that case to prepair?

    Summarizing:
    1) At what distance can we track real human killer comets (as big or bigger as the dinosaur-killer) comming directly from the Oort Cloud? And how much time do we have in that case to protect all humanity and animals/nature?
    is it possible that an asteroid as big or bigger as the Dinosaur-Killing Asteroid can enter our solar system originally coming from another star system? If yes, at what distance are we able to track this size asteroids and how much time do we have in that case to protect all human beings and nature?

    Maybe stubid questions from a 'noob' I look forward your comments and thank you in advance.


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    Last edited by jo92; 2019-Sep-01 at 05:54 PM.

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    Just a quick answer, others will probably reply with more detail. Currently, there are a few obstacles to tracking such objects: the biggest is that we don't really watch the whole sky with our best instruments. It is my understanding that we have imaged Halley's Comet near its aphelion (somewhere between the orbits of Uranus and Neptune), but only because we knew exactly where to look, and take a long exposure. At the moment, that's probably about the limit for something slightly larger than the Chicxulub object.
    In a few years, the LSST will be active, doing large fraction of the sky surveys every couple of days, but that will miss things hidden by the Sun, and probably wouldn't detect 10km diameter objects much further out than Saturn.

    Concerning Interstellar asteroids, yes. They are rare, but there is no reason that one couldn't be big enough, and be on course to hit us.

    As to how long do we have to prepare, if we are lucky and find it early, perhaps a few years. In the worst case a few months.
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    Yes, I would be realy grateful if someone can explain in more detail, how we can discover and track comets (big enough to wipe out humanity) coming from the Oort Cloud and how we can discover and track interstellar asteroids (big enough to wipe out humanity).

    In additional, will a comet (big enough to wipe out humanity) and asteroid (big enough to wipe out humanity) always swing near Earth before it hits? How does it work?

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    Quote Originally Posted by jo92 View Post
    In additional, will a comet (big enough to wipe out humanity) and asteroid (big enough to wipe out humanity) always swing near Earth before it hits? How does it work?
    No, it doesn't. If it is on a hyperbolic trajectory (so that it won't enter orbit), then it would need to be on a direct course to hit earth. If it is something that is gravitationally bound to the sun, then I think it is likely that it will make some passes by the earth before happening to get on a direct path.

    And about the first question, the basic way is to compare photographs taken at different times, and find something that moves compared to other stars. That means it is close-by, so would have to be an asteroid or comet.

    I don't know about future plans, but it seems that you could have an automated system, using AI, where a telescope would be constantly scanning the whole sky, from orbit somewhere, and then the program would examine the data and find moving things.

    The problem with the sun is that if the object is coming at us from the sun, the light is behind it, so it is dark, and in addition the sun is very bright, making it hard to see things.
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    And to add one thing, it is also possible to use active observations, i.e. radar, to observe asteroids. The advantage is that it is very accurate, but the problem is that it takes a lot of power to reach faraway objects, so it's not very practical for all-sky surveys, and is mostly used get good measurements for asteroids that are already known about, rather than for discovering new ones.
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    The flipside is that the more threatening it is, the easier it is to spot.

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    Hi jo92.

    I can't give you precise numbers, but I can give you some resources on this. NASA/JPL have CNEOS (Center for Near Earth Object Studies). There are lots of resources on their website.

    The Sentry link on that webpage gives a table of objects that they are tracking that have the potential for future impacts, their probability, and the possible damage.

    I think that as you explore this, you will find that people don't talk in exact numbers, because they can't be that precise. We can't say "we will see every object bigger than x meters at a distance of y million kilometers". What you will see are probabilities: "we are 90% certain we can track objects bigger than x meters at a distance of y million kilometers, and assign a probability that they hit the Earth".

    This CNEOS page gives some good background.

    In terms of orbital elements, NEOs are asteroids and comets with perihelion distance q less than 1.3 au . Near-Earth Comets (NECs) are further restricted to include only short-period comets (i.e., orbital period P less than 200 years). The vast majority of NEOs are asteroids, referred to as Near-Earth Asteroids (NEAs). NEAs are divided into groups (Atira, Aten, Apollo and Amor) according to their perihelion distance (q), aphelion distance (Q) and their semi-major axes (a).

    Potentially Hazardous Asteroids (PHAs) are currently defined based on parameters that measure the asteroid's potential to make threatening close approaches to the Earth. Specifically, all asteroids with an Earth Minimum Orbit Intersection Distance (MOID) of 0.05 au or less and an absolute magnitude (H) of 22.0 or less are considered PHAs. In other words, asteroids that can't get any closer to the Earth (i.e., MOID) than 0.05 au (roughly 7,480,000 km or 4,650,000 mi) or are smaller than about 140 m (~500 ft) in diameter (i.e., H = 22.0 with assumed albedo of 14%) are not considered PHAs.
    As I understand it, the hardest ones to track are not interstellar or Oort cloud objects, but ones that are in orbits very close to Earth's orbit. And among these, very small objects are very difficult to track (these are the ones that occasionally surprise observers when they pass by unexpectedly). These objects are too small for extinction level events, but would really ruin someone's day if they hit.
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  8. #8
    Quote Originally Posted by Jens View Post
    The problem with the sun is that if the object is coming at us from the sun, the light is behind it, so it is dark, and in addition the sun is very bright, making it hard to see things.
    Leaving aside the issue of whether it's worthwhile or not, could telescopes parked at the earth's Lagrange points deal with that issue?

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    Quote Originally Posted by 21st Century Schizoid Man View Post
    Leaving aside the issue of whether it's worthwhile or not, could telescopes parked at the earth's Lagrange points deal with that issue?
    I think it would be better if they were at Venus' Lagrange points, but yes, that would substantially reduce the number of unknown big rocks in elliptical orbits close to the Sun.
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