I found an excellent Wikipedia page titled List of Asteroid close approaches to Earth:
https://en.wikipedia.org/wiki/List_of_asteroid_close_approaches_to_Earth
Looking at the table in the blue section there is identified an asteroid which will pass close to Earth on 26th June 2028. The size of the object is 610 to 1400m and it will pass within 0.65 of the distance to the moon. This table is clearly the result of an immense amount of work for which we should all be grateful.
It is important to find out the ultimate outcome of the trajectory of this asteroid. Will it ultimately hit the Earth or will it hit the moon and thus be no longer a threat? If we were to project forward the trajectory of this asteroid and the trajectory of the Earth and moon and found that in 1,000 years it will hit the Earth, is there anything we could do now to avoid this outcome? For example displacing the trajectory of the asteroid with rockets by even a tiny amount could over 1,000 years change the outcome so that it strikes the moon instead.
We would have to be sure that we had a really accurate identification of the current trajectory. Maybe precise observation from Earth and the JWST during its passage in 2028 would give an accurate enough reading.
It would also be worthwhile to make an honest assessment of the outcome of a direct impact by this object on Earth. Perhaps we should be making provision for the long term survival of the human species by preparing contingency plans for such an eventuality.
Richard
Richard,
'It is important to find out the ultimate outcome of the trajectory of this asteroid.'
Indeed.
But no ephemeris is accurate enough to make predictions over a millenium-scale that allow us to discriminate between an impact of the Earth and a miss by 100,000 km (say).
Regrettably.
ESA keeps a rather nice list of 'Risky' objects:
https://neo.ssa.esa.int/risk-list
James Garry That is very good to know the limitations of current astronomical predictions. Looking at Wikipedia about ephemeris it seems that they could be in the form of astronomical tables or in the form of computer based models.
It would be interesting to know where exactly the limitation lies in the prediction of future astronomical position. Is it in the limitation on the accuracy of measurement of the current position and trajectory or is it in the lack of knowledge of the precise gravitational conditions on all points on the future trajectory? One could imagine for a really accurate result one might have to take into account the position of all the other planets in the solar system at each future time. This would be hard to do to create general tables but for a computer model that is dealing with one specific object along its trajectory it would be feasible.
My point is that it could be really really important to be able to predict 1,000 years into the future because an adjustment of trajectory like crashing a space probe into the asteroid within the next decade could have a worthwhile effect after 1,000 years.
I know you said 100,000 km (say) as a rough figure but if we could just improve on that by a factor of 20 we are talking about 5,000 km which could be the difference between the survival or not of the human race.
Richard
Richard,
Looking at Wikipedia about ephemeris it seems that they could be in the form of astronomical tables or in the form of computer based models.
The limitations are principally in the measurement of the positions of planets. Time is trivially well-measured, but position in any reference frame is inevitably a matter of resolving an angle. And that's where most of the errors arise.
This paper speaks to that:
https://iopscience.iop.org/article/10.3847/1538-3881/abd414/pdf
Indeed, the locations of all of the known planets can be used to generate ephemerides - but I know of no ephemeris program that includes the motions of any asteroid when generating planetary ephemerides. Even Ceres and Vesta (which are charitably satellite-sized) are ignored.
See, the problem is that the asteroids are generally small, dark, and tumbling. Their variegated surfaces (look at Itokawa, or Bennu) means that they have an asymmetric Yarkovsky effect (heat/light is not emitted uniformly, and generates an unpredictable thrust). So smallish (km-scale) objects are inherently hard to track.
And the larger asteroids (Ceres, Vesta, etc) are so well-tracked that they pose *no* threat.
I grasp your concern, but our current ability to perturb those bodies that might (at a stretch) be considered worthy of modelling is very slight. I'd put more funding into the detection of long-period comets, personally. They (like Hyakutake and Hale-Bopp) can ruin one's day with relatively little notice.
James Garry I have looked at the link provided and it does include prediction tables going 17,000 + years into the future. I take your point that the accuracy diminishes the further you go into the future.
There seem to be two possible strategies for dealing with a potentially dangerous asteroid. One is to try to divert it so that it doesn’t hit the Earth. The other is to try to divert it so that it does hit the moon. I would favour the second approach.
So if we made a calculation that a specific really large asteroid was likely to hit the Earth in say 1,000 years then we could work out the optimum mission that would ensure that it hit the moon before that time.
We have lots of time to work on the problem and refine the orbital models and check them on each orbital pass. Also we could have a fairly accurate assessment of the effect of crashing a space probe into the asteroid directly in line with its centre of mass at a suitable direction and velocity. We have the time for many missions each adjusting the orbit of the asteroid by a small amount. A slight change in orbit should make a big difference after 1,000 years. The important thing seems to be to start planning now.
Richard
Richard,
I agree that the impacts from cosmic objects are unlikely but present terribly high hazards. But I suggest that the asteroidal population is not where the risks arise: their motions are periodic, and almost all of the potential Earth-crossers are known (evinced by the rapid fall in the number of 'new' objects found each year). The single problem that stymies any attempt at long-term modelling is the dynamical chaos that is present in n-body systems - no matter how the technology improves, we are at the mercy of the unpredictability of n-body motion.
No, I suggest that a significant (and even harder to predict) threat is from *unpredictable* objects such as long-period comets. You recall Hyakutake and Hale-Bopp? They arrived with barely five months notice - by virtue of having millenia-long orbits that precluded us from having seen them before.
Either of those bodes could have erased our civilization - and no amount of technology is going to radically change the difficulty of spotting a jet-black object at 20 AU.
There's an excellent book on this matter (impacts and how to avoid them) by Belton:
https://www.cambridge.org/ca/academic/subjects/physics/planetary-systems-and-astrobiology/mitigation-hazardous-comets-and-asteroids?format=HB&isbn=9780521827645
On the other hand:
https://files.givewell.org/files/DWDA%202009/Asteroids/Chapman.pdf
Chapman gives a good overview of the risks from asteroids. And I agree that the cometary population is small, but I suggest that the short warning period is the main problem - we're oblivious till the 'last minute'.
I'm with Nuth:
Article Defending the earth from long-period comets and sneaky aster...
Predicting the unpredictable is pointless without capability and agency.
We'd do well to focus on a robust cis-lunar industrial capability as soon as practicable.
James Garry I think there is a good solution to the n body problem which is through development of a precise computer model. We have to know the precise position of the larger planets and model all of their gravitational interactions. Then the gravitational effect of these planets on the asteroid can be precisely calculated.
It does seem to be a complex and highly interactive problem but not beyond the power of modern computers to achieve ever increasing precision. The availability of precise observational data on an ongoing basis should permit the fine tuning of the computer model.
Richard