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do we have the means to slightly alter Comet Leonard's trajectory so it impacts Venus instead of 'grazing' it in December 2021??

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    $\begingroup$ You really want to shove a 10 billion tonne asteroid 4.3 million km to the side, in just 100 days? wow. I'll try to write an actual answer, but it will require just two letters, and they will be font size ~ 2.7km tall $\endgroup$ Sep 8, 2021 at 15:11
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    $\begingroup$ Ok, let's show it just in fuel. Using the very best chemical rocket engines we have, you need to burn 122643137028kg of hydrogen+oxygen to impart the needed motion change. That's 122.6 million tons of fuel. And you need to do that burn now. Delaying the burn by 50 days will increase your fuel need by 8.5 times. $\endgroup$ Sep 8, 2021 at 19:26
  • $\begingroup$ Useful information published in arXiv: Preview of Comet C/2021 A1 (Leonard) and Its Encounter with Venus $\endgroup$
    – uhoh
    Sep 8, 2021 at 23:54
  • $\begingroup$ DrSheldon says: (knock knock knock) Leonard (knock knock knock) Leonard (knock knock knock) Leonard $\endgroup$
    – DrSheldon
    Sep 9, 2021 at 3:52
  • $\begingroup$ The only practical ways we have now of diverting comets or asteroids is by tiny gravitational tugs over long periods of time. We would need to plan such a project decades in advance, and then you'd have to wonder why? Appreciably altering Venus' climate would take hundreds of comets much larger than Leonard (and thus farther from our ability to redirect). $\endgroup$
    – antlersoft
    Sep 9, 2021 at 12:55

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Lets just do some order of magnitude estimation:

4.3 million km / 100 days = 500 m/s

$\frac{1}{2}$(10 billion tonnes)(500m/s)2 = 1.25 × 1018 J to move the comet to Venus.

For comparison, the Tsar Bomba, the biggest nuclear bomb ever detonated, was only 2.4 × 1017 J, and even if it was teleported to the comet now, not all of that energy would go into moving the comet.

So the answer is as very definite no.

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