Asteroid 2024YR4 Threat

This object has been identified as a Type S (“stony”) or possibly a Type L object.  It would be a dry,  loose rubble pile of cobbles,  gravel,  sand,  and possibly some boulders,  just barely held together by vanishingly-weak gravity. 

This object was discovered after it had already passed by at closest approach.  So much for advanced warning.  It is currently headed out away from the sun (and us) on its approximately 4-year-long orbit,  that crosses Earth’s orbit two places.  Earth can be there when it is also there,  at only one of them,  apparently the outbound crossing in this case.  It will return for another close pass in late 2028,  and again in late 2032.

It is the 2032 close pass that is of concern for this object striking the Earth.  Its size is such that this is a “city buster”,  not an extinction event.  The initial estimate of the probability of a collision was in the neighborhood of 1%,  raised to around 2%,  then to about 3%,  then lowered again to near 1.5%.  The point:  we just do not really know anything,  except that there is a risk. 

As for deflection,  yes,  there are nuclear warheads,  and yes,  there are rockets that could send them to it.  But the guidance and control items,  and the warhead fuses,  do not yet exist for this purpose,  nor are they likely to,  in the next 4 years.  Most of the deflection methods we could use risk disrupting the rubble pile asteroid,  turning a single bullet strike into a widespread shotgun blast.

The close pass in 2028 offers an opportunity to find out more of what we need to know:  (1) better orbital data,  and (2) its physical properties.  Some sort of craft orbiting it could determine its mass with precision.  Some sort of impactor or explosive experiment might provide information about how easy it might be to disrupt this object versus deflecting it.  Time is very short to put “something” together!

The “brute force” mission is to launch right at the close pass,  so that upon achieving the right speed in the right direction,  you have already rendezvoused with the asteroid.  2028 would be the right time to do this.   2032 is too late,  in terms of the collision risk.  The figure shows the rough estimate I made for this mission.