Ferrone, Salvatore

English

Ithaca College

OSIRIS-REx,	an	asteroid	sample	return	mission,	is	the	third	project	of	NASA’s	New	Frontiers	program.	The	OSIRIS-REx	spacecraft	is	currently	on	its	outbound	cruise	to	asteroid	101955	Bennu	and	is	scheduled	to	rendezvous	in	November	of	2018.		Bennu	is	a	member	of	the	rare	B-class	asteroids	and	is	a	potentially	hazardous	object	(meaning	that	it	has	a	non-zero	probability	of	impacting	Earth	in	the	future).	B-type	asteroids	are	composed	of	carbon-rich	compounds,	potentially	including	organics	and	volatiles.		B-types	are	theorized	to	be	pristine,	unaffected	since	the	early	days	of	the	solar	system.	Obtaining	a	sample	from	Bennu	would	thus	provide	clues	to	the	early	composition	of	the	Earth,	and	insights	on	how	life	began	on	Earth.		The	OSIRIS-REx	science	team	will	have	about	1	Earth	year	to	explore	Bennu	before	selecting	a	sampling	site.		Of	highest	scientific	interest	is	an	organic-rich	sample,	and	hence	finding	organics	on	the	surface	of	Bennu	is	top	priority.		However,	because	Bennu	is	carbon-rich,	it	is	very	dark	such	that	all	3	compositional	spectrometers	on	the	spacecraft	have	relatively	large	fields-of-view,	and	this	will	result	in	low	spatial-resolution	spectral	maps.		In	fact,	the	highest	spatial	resolution	will	only	be	about	19	meters	in	diameter	per	observation.		It	is	therefore	of	primary	importance	to	understand	if	and	how	spectrometer	observations	can	be	combined,	using	spectral	super-resolution,	to	enhance	the	spatial	resolution	of	the	observations,	thus	improving	our	chances	of	detecting	the	subtle	spectral	signatures	of	organic	compounds	on	Bennu.			In	this	study,	we	conduct	original	research	to	explore	some	of	the	many	different	methods	of	creating	spectral	maps	and	determine	which	method	provides	spectral	maps	with	the	highest	fidelity	and	highest	spatial	resolution.		Our	goal	is	to	give	the	OSIRIS-REx	science	team	a	mapping	protocol	to	follow	during	the	Detailed	Survey	phase	of	the	mission	that	will	maximize	the	chances	of	detecting	organics.	Spectral	maps	are	maps	that	identify	the	surface	mineralogy	at	every	location	on	Bennu.		We	begin	by	designing	a	“Truth”	map	of	known	mineralogy	–	in	effect	a	simulated	Bennu	world	–	with	strategically	located	“outcrops”	of	organics	set	in	a	carbon-rich	non-organic	background	material.		We	simulate	visible-to-near-infrared	data	sets	using	this	Truth	map,	and	pass	these	data	through	our	mapping	routines.		Simulated	data	were	created	with	an	IDL	routine	“generate_test_data.pro”	written	by	Jonathan	Joseph	at	Cornell,	and	overlapping	observations	are	combined	on	a	per-facet	basis	with	a	MatLab	program	“makeMaps.m”	written	by	Luke	Hawley	at	the	University	of	Arizona.			We	then	analyze	the	maps	using	software	I	developed	at	Ithaca	College,	with	three	new	original	metrics:	Contrast,	Smear,	and	Obliteration	–	to	quantify	the	spatial	resolvability	of	a	spectral	map.	Because	our	mapping	routines	are	based	on	round	spectrometer	fields-of-view,	and	our	map	projections	use	tessellated	shape	models	of	the	asteroid	with	triangular	facets,	we	are	vulnerable	to	a	number	of	projection	effects.	We	investigated	maps	with	different	shape	model	facet	sizes,	maps	created	with	different	methods	of	assigning	spectral	data	to	facets,	and	maps	that	combine	data	from	several	global	surveys.	In	this	study,	we	investigated	seven	different	methods	of	combining	overlapping	spectrum	observations	to	assign	spectral	values	to	the	facets	of	a	shape	model,	we	utilized	three	different	shape	model	resolutions,	and	we	explored	three	different	global	survey	observation	plans.		Our	results	indicate	that	maps	created	by	assigning	data	from	the	nearest	spectrometer	observation	to	a	facet	replicates	our	Truth	map	with	highest	fidelity.	Maps	created	using	finer	shape	model	resolutions	are	of	the	highest	fidelity,	compared	to	maps	using	coarser	shape	model	resolutions.		We	tested	our	hypothesis	that	combining	the	data	from	three	different	global	surveys	of	the	asteroid	could	be	used	to	demonstrate	spectral	super-resolution,	however	the	results	were	inconclusive	due	primarily	to	problems	with	the	observation	plans	themselves.	These	findings	will	be	of	utmost	importance	to	the	OSIRIS-REx	science	team	when	creating	spectral	maps	of	Bennu,	starting	in	April	2019.						

Analysis of Spectral Mapping Techniques for the OSIRIS-REx Project

https://digitalcommons.ithaca.edu/cgi/viewcontent.cgi?article=1237&amp;context=whalen

Analysis of Spectral Mapping Techniques for the OSIRIS-REx Project

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