Adam Hibberd
The asteroid 2024 YR4 will approach pretty close to Earth on 2032 December 22nd and we can't yet preclude a Tunguska-scale impact. Unlike Tunugska however, there would be quite a high likelihood of human fatalities, since its impact location could coincide with quite densely populated areas including India, for example, certainly a disaster which we should do our absolute utmost to avoid.
But 2024 YR4 is playing the devil's game in that its precise future path is proving annoyingly difficult to pin-down despite further observations. True the James Webb Space Telescope (JWST) which sees in infrared will be trained on the object between March and May of this year but its key purpose will be the determination of 2024 YR4's size and therefore the possible impact energy, and its orbital path might not be sufficiently refined to determine whether it will collide with Earth in 2032.
This means the determination of 2024 YR4's 'final destination' - an Earth strike or otherwise - might not happen until 2028 August, when the object returns from aphelion (point farthest from the Sun) and begins to get closer to the Earth once more. Its close approach to Earth towards the end of 2028, opens up many opportunities for flyby missions with extremely low launch performance requirement, i.e. characteristic energy (C3). In fact optimal trajectories tend to result in an encounter of the object at one of two points, the first in October, and the second in December of that year - go to my previous blog .
Recently however, I have been thinking beyond a simple flyby, and instead about a possible deflection mission. If we are to deflect this object, let's say to move it by a 1000 km distance when it comes around on 2032 December 22, what mass of impactor would we need?
It turns out that this depends on several pertinent parameters. Amongst these - and the most influential - are firstly the mass of 2024 YR4, and secondly the impactor's relative velocity. The latter we know since we can quite quite straight-forwardly calculate it for each launch date and flight duration combination. This allows us to determine the impactor's momentum. For the first of these we can adopt a mass for 2024 YR4 of 2.2e8 kg. The object's consequent change in momentum can thence be estimated using parameters similar to those measured by the DART collision. It turns out that DART offered plenty of insights into just such a scenario, since most of you will be aware that the DART mission entailed a spacecraft purposely impacting with an asteroid in order to study the target object's (in that case the asteroid Dimorphos), resulting change in momentum (which we now know).
So let us conduct precisely these investigations I've laid forth above. What results do we find? What mass of impactor would be needed? Refer below.
As you may observe, we find that required impactor masses on the order of tens to hundreds of kg would be quite sufficient to move 2024 YR4 by the amount required on 2032 December 22, especially with launch dates from the end of 2027 and for a majority of 2028 (with flight durations < 400 days). Launch windows subsequent to this are also eminently feasible, with opportunities arising in 2029/2030 and 2030/2031 and with impactor masses on the order of hundreds to thousands of kg.