Planetary Defense Clues from Returning Samples from a Near Earth Asteroid (NEA) &#8211; Apophis Encounter as a Unique Chance
Authors: Stenzel Oliver J. , Renggli Christian J. , Hilchenbach Martin , Krupp Norbert , Walton Craig R. , Kleine Thorsten , Grundmann J. Thimo 
Published: July 2024

The upcoming passing of (99942) Apophis by Earth in 2029 within just a few ten thousand km presents a unique opportunity to study a potentially hazardous Near Earth Asteroid (PHA, NEA). This opportunity will be used by ground based observations and possibly two space missions, RAMSES and OSIRIS-APEX, by ESA and NASA, respectively [1,2], which will encounter Apophis shortly before respectively after the closest approach to Earth. RAMSES is a close derivate of Hera to be built quickly, and OSIRIS-APEX is the re-purposed OSIRIS-REx spacecraft already in space. More fly-by and rendezvous missions are proposed, including small spacecraft such as SATIS, re-purposing of the JANUS spacecraft pair currently in storage, as well as science payload sets carried on commercial platforms, e.g. DROID [3&#8211;5] In itself, this kind and spectrum of solutions is as close to those invoked in planetary defense exercises for short lead time PHAs as is the time left to implement planetary science missions to Apophis now [6]. However, except for a possible high-risk late phase of OSIRIS-APEX operations at Apophis, all these missions are limited in their instrumental setup to remote sensing. We strongly suggest to return samples from the surface of the asteroid to Earth to allow for extensive laboratory analysis, and thus propose APOSSUM, the APOphiS SUrface saMpler, a small separable sub-spacecraft to be included in the RAMSES mission [7]. Its concept of operations is directly applicable to PHAs in similar orbits that make a relatively close pass before a potential impact.Spectral analysis points at Apophis being an LL chondrite [8], which would put it in the same family and possible same parent body as the Chelyabinsk meteorite from 2013 (LL type). Results from [9] hint at an unresolved and therefore recent spallation event of Chelyabinsk parent body and would have likely formed other asteroids of the same composition as well. Such events can result in a multitude of hazardous objects and as the LL-type NEAs are abundant, they are of special interest for investigation[10,11]. As Apophis is an LL chondrite, it is possibly linked to the same parent body spallation as the Chelyabinsk meteorite. By analysis of samples from Apophis sampled and returned by APOSSUM we will be able to test this hypothesis. If they prove to be similar in their collision/breakup history, a closer look at LL asteroids as potential hazardous objects is warranted. Further, the interaction with the surface of Apophis during the sampling process will be highly instructive regarding its geotechnical properties. These are critical if and when an asteroid on collision course needs to be deflected, and also for the evaluation and possible development of asteroid mining[12]. Information on the interior and surface context of the samples collected can be provided by small instruments aboard APOSSUM, and a MASCOT derivative mobile nanolander can be delivered to the surface by APOSSUM for long-term observations including the closest approach to Earth, at and beyond the sampling site [13,14].[1]&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160; K&#252;ppers M, Martino P, Carnelli I, Michel P. 2024 3040, 1087.[2]&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160; DellaGiustina DN et al. 2023 Planet. Sci. J. 4, 198. (doi:10.3847/PSJ/acf75e)[3]&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160; Karatekin et al. Apophis T-5 Years. 2024[4]&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160; D.J. Scheeres, E.B. Bierhaus, C. McCaa, E. Kloska, D. Brack, J. Shoer. Apophis T-5 Years. 2024[5]&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160; C. A. Raymond et al. 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