aim-PALS PAYLOAD TO STUDY THE PHYSICS OF DART IMPACT IN DIDYMOON

1. aim-PALS PAYLOAD TO STUDY THE PHYSICS OF DART IMPACT IN DIDYMOON J. M. Trigo-Rodríguez, I. Lloro, J-E. Wahlund, E. Vinterhav, N. Ivchenko, and the AIM-PALS consortium.

2. OUTLINE • Introduction on the PALS team • Cubesat names • PALS science goals & P/L • PALS current status • Deep Impact legacy • Application of emission spectroscopy • Expected scientific outcome • Conclusions

3. PALS Project Team • Science • IRF, Uppsala & Kiruna • ICE (CSIC-IEEC), Barcelona • KTH, Stockholm • System Analysis and Design • ÅAC Microtec AB, Uppsala • Mission Analysis • DLR, Bremen

4. PALS CubeSat names • PALS = Payload of Advanced Little Satellites • PALS-1: Hugin (“thought”, “intuition”) • PALS-2: Munin (“memory”, “common sense”) • From old Viking Norse mythology: • Is the information gatherers of the one-eyed god of wisdom Odin • Hugin & Munin flies over the world and creates order and truth so that one can gain all the secrets of the universe.

5. ABOUT PALS • PALS is a deep space exploration mission in two 3U CubeSatsexploited to the limits to obtain close range measurements of the Didymosbinary asteroid system. • The cubesats carry two imagers (one working as emission spectrometer), a double fluxgate magnetometer (MAG) and a Volatile Composition Analyser (VCA). • The cubesatswill operate closer to the asteroids than the AIM spacecraft can, then producing an unique scientific outcome. • We briefly describe here the payload, focusing in the scientific interest behind the development of the video emission spectrometer (VES)

6. Status of PALS work • Work so far has been focused on: • Traceability, and complementarity to AIM objectives • Payload tasks & observation modes (mission scenario) • Results already given in TN-1 to ESA • CEF study (DLR) • Full mission scenario concept obtained at Bremen (DLR facility) • Successful integration of proposed P/L into 1U • CEF results documented as special report to ESA • The DLR, the German Space Agency is responsible for mission analysis and for preparing a conceptual attitude and orbit control system design to operate the spacecraft

7. PAYLOAD MAIN SCIENTIFIC GOALS • NAC: high-res mapping of the system from 100 m (Didymoon surface seen at a cm-sized resolution!): regolith characterization, DART impact recording from 2nd and 3rd vantage points to get insight of the impact plume evolution. • VES: video sequence up to 30 frames/s of the impact flare. Spectral measurements to infer ejecta temperature and derivation of bulk chemical composition of the gas by using the camera as emission spectrometer. • MAG will provide information about possible magnetization and metallic content of asteroids by measuring the magnetic environment: D1 and D2 magnetization and the solar wind interaction with asteroids magnetic fields and with the impact plume. • VCA will provide a continuous, lower resolution, ambient ion measurements in the vicinity of the binary system, also informing about the presence of sub-surface volatiles and solar wind interaction.

8. Impact luminosity will depend of the energy retained by the target porosity, and the efficiency to vaporize materials Due to the presumable chondritic nature of Dydimoon, we expect a significant vaporization of silicates and metals Shock melting will start short after the collision when T>1,600 K Light emission from impact plume: It will depend of the composition of the hot vapour Sinks of energy: IR and UV radiative mechanisms Fragmentation, quenching and sputtering processes STUDYING AN IMPACT PLUME ESA

9. THE RELEVANCE OF EMISSION SPECTROSCOPY • A brief history about emission spectroscopy: • Millman and Halliday (1961, 1963): NIR spectra in meteors • Harvey (1973): first bulk elemental abundance determinations • Modern meteor spectroscopy was born with a high-res fireball spectrum (Borovicka, 1993, 1994) • Bulk chem. abundances in meteoroids (Trigo-Rodríguez et al. (2003, 2004, 2007) • Jenniskens et al. on Leonid research: Astrobiology 4-1 (2004) • Video spectroscopy allow us to detect elusive lines and molecular bands • Know-how for direct application studying impact plumes! • DEEP IMPACT probe collided with comet 9P/Tempel 1 and recorded in mid-IR • Laboratory experiments • Now, our VES instrument onboard PALS will get emission spectra of the impact plume from UV to NIR in close-range observations (about 100 m)

10. “DeepImpact” experienceonTempel 1 Tempel 1 size The spacecraft records the impactor approach and impact flare Impact on July 4th, 2005 Deep impact observation of the impact flare from far away

11. REDUCTION OF SEQUENTIAL SPECTROSCOPY • Each video frame will provide unique information about the temperature, density and composition of the hot gas: • VES window in between 400 to 1.000 nm • QE is 30% in VIS, and 15% in NIR • Discrete emission from elemental and molecular lines (e.g. OH Meinel band at 780 nm) • Plus a thermal background. • First steps: • Instrumental sensitivity can be calibrated by using a standard (experiments) • Identification of main spectral lines to calibrate the wavelength • Intensity calibration Sporadic fireball (Trigo-Rodriguez et al., 2003).

12. DETERMINING CHEMICAL ABUNDANCES • Following Borovicka (1993) procedure the synthetic spectrum vs. the observed one (discontinuous) • Assuming thermal equilibrium the brightness of the lines is computed using 4 free parameters to fit the emission spectra: • Density of atoms in column relative to Fe • Temperature (K) • Radiating area • Damping constant () • Chemical abundances by matching the synthetic to the observed spectrum. (Trigo-Rodriguez., 2002).

13. Trigo-Rodriguez et al., 2008, MNRAS VIDEO SPECTROSCOPY • A mid resolution spectrum allows the determination of chemical abundances for the main rock-forming elements • It has a chondritic composition • The synthetic spectrum fit (purple) to the observed one (blue)

14. AVERAGING THE CHEMICAL ABUNDANCES • In a similar way as we averaged the chemical abundances from different segments, video observations also alllow frame to frame modeling • Trigo-Rodríguez et al. (2003) in MAPS: 15 emission spectra of cm-sized meteoroids • Bulk chemistry results, and overall behavior consistent with rock-forming minerals

15. Ca • This element is generally inside refractory phases (e.g. CAIs, oxides) resistant to ablation: • Not all Ca contributes to the production of meteor light. • Probably it survives as grains of anorthite, Ca-pyroxene or Ca-Al oxides (CAIs). • The derived Ca column abundance will depend on the available energy: • Underabundance is evidence of incomplete evaporation (Plane, 2003). (Trigo-Rodriguez, 2002)

16. SOME RESULTS IN METEOROIDS • Na relative abundance plotted as a function of the geocentric velocity (Vg). • Na/Si higher than expected in cometary meteoroids. • Cometary meteoroids have higher Na abundance than the chondrites (organics/hydrated minerals)? • A result recently cited by Rosetta science papers (Trigo-Rodriguez. et al., 2004, MNRAS)

17. TERNARY Fe-Mg-Si DIAGRAM • From the elemental ratios is also possible obtaining clues • Fe-Mg-Si are the main constituents of silicates so very relevant in cosmochemical studies. • The location in the diagram can be lined up with the average for IDPs and chondrites. (Trigo-Rodriguez. et al., 2003, MAPS).

18. CONCLUSIONS • Our AIM-COPINS PALS mission is envisioned to work at far ranges from the Earth inside the sphere of influence of a low gravity system • PALS CubeSats are designed for high autonomy and high reliability using state-of-the-art instrumentation and packaging technology • Feasible mission architecture and concept has been demonstrated to ESA • The studies to be performed by the imagers onboard the AIM-PALS mission will provide a significant scientific outcome in our knowledge about crater excavation, luminous efficiency and momentum transfer: • NAC can provide a high resolution mapping of the secondary asteroid of the system at a cm-sized resolution, and also the impact plume • VES spectral measurements on the ejecta T and composition of the hot gas by using emission spectroscopy. Insight on the physical mechanisms at work in light production • A successful AIM-PALS mission will enhance significantly our understanding of the asteroids in general and Didymos in particular