From the EU-ESA Workshop on Size Determination of Potentially Hazardous Near-Earth Objects:
Wednesday, 11/13/24
( … see also Monday and Tuesday)
Polarimetric observations
Double Trouble: Polarimetric Insights into the Didymos- Dimorphos post-DART Evolution Zuri Gray
On September 26, 2022, the NASA DART (Double Asteroid Redirection Test) spacecraft struck Dimorphos, the moonlet of Didymos, to test near-Earth object deflection via impact for planetary defence [1]. As well as causing a change in Dimorphos’ orbital period [2], the impact caused a massive dust cloud to be ejected from the surface, e.g. [3,4]. By studying the characteristics and behaviour of…
Polarimetry as a tool for physical characterization of potentially hazardous NEOs
Maxime Devogele (ESA NEOCC)
The degree of linear polarization of sunlight scattered by an asteroid contains valuable information for rapid characterization of the surface properties of Near-Earth objects (NEOs). In the case of atmosphereless bodies the state of linear polarization varies as a function of the phase angle (α) and is described using the so-called Pr parameter.
The properties of the phase-polarization…
Cross validation of albedo determination for 1627 Ivar from three different techniques Elena Selmi
Near Earth Objects, with their perihelia < 1.3 AU, represent both a potential hazard and a valuable asset for the foreseeable in-space resource utilization, and are hence of great interest to the scientific community. Their physical parameters, such as diameter, albedo and thermal inertia, can be constrained by a number of techniques, with different types of input requirements and levels of…
Rapid-Defender: A New Polarimeter for Planetary Defense
Estela Fernández-Valenzuela (Florida Space Institute, UCF)
Polarization observations are a key tool for swiftly determining the size of a NEO, and consequently, their potential threat to Earth. The degree of linear polarization is inversely proportional to the albedo of the scattering surface of an asteroid. This relation is better constrained at high phase angles at which NEOs are usually observed and where polarization is more significant. This…
Asteroid polarization at near-infrared wavelengths Joseph Masiero
The polarization of light reflected by asteroids can be used to constrain the albedo of the asteroid’s surface, and probe mineralogical surface properties such as grain size and index of refraction. Depending on the specific mineral components of the body these surface properties are expected to change with wavelength, and so observations of the polarization beyond the visible provide…
Miscellaneous observations of NEOs
Stellar occultations for NEA high-accuracy astrometry and size determination
Damya Souami
The powerful method of stellar occultations is an unbeatable technique uniquely approaching, in some aspects, the performances of planetary space missions. It allows km-level accuracies on the determination of shapes and sizes of objects, and down to a couple of hundred meters for sum-km sized NEAs.
Furthermore, it allows to derive, from ground using small aperture telescopes, asteroid…
Asteroid size determination from photometric/spectroscopic observations at the IAC (REMOTE) Julia De León (Instituto de Astrofísica de Canarias, Tenerife; Departamento de Astrofísica, Universidad de La Laguna, Tenerife, Spain)
Determining the size of an asteroid is scientifcally interesting, but also particularly relevant in the case of those objects that are considered as potential impactors: together with the distance to Earth, is one of the two criteria used to classify an asteroid as Potentially Hazardous. There are several ways to compute this physical property, some of them based on the acquisition of…
ESA’s Flyeye telescopes
Dora Föhring (ESA Near-Earth Coordination Center), Dr Ernesto Doelling (ESA)
The European Space Agency’s Flyeye telescopes will play a crucial role in global efforts to detect and track near-Earth objects (NEOs). Inspired by the compound vision of a fly, the unique design of Flyeye-1 divides its field of view into 16 subfields, enabling the telescope to scan a wide area of the sky every night.
This talk will explore the design and development of the Flyeye-1, focusing…
Observations of NEOs with the TRAPPIST telescopes in support of size determination using polarimetry and radar Elisabeth Petrescu (Space Sciences, Technologies & Astrophysics Research (STAR) Institute University of Liège, Belgium)
Photometric observations of near-Earth asteroids (NEAs) using the TRAPPIST telescopes are regularly performed notably to support shape modeling using radar data as well as an effort to calibrate the relation between the albedo and the polarization displayed by NEAs. These two methods allow to obtain accurate size determination for these objects.
The TRAPPIST telescopes are two twin 60-cm…
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This, the third and final day of the meeting, we continued polarimetry. There’s a lot of prior art, yet still a lot of promise to be seen. It was mentioned briefly that Hayabusa 1 attempted polarized imaging at Itokawa, but as a secondary investigation the team never made things work out. Well, that was a generation ago. Groups around the world are now tackling polarimetry.
As a brief but welcome tangent, the occultation method was covered by Damiya Souami. (If you aren’t familiar, occultometry is the measurement of “micro eclipses,” by asteroids passing in front of stars. If several observers log an occultation, their eclipse times can be ganged into a footprint of the asteroid shadow.) Professional and amateur and mixed teams around the world have been, and will be, ganged to catch these occultations, with good results shown in the Souami presentation. Of course, weather and mechanical and logistical issues all have to work, but on the whole this method can give accuracies measured in a few meters when everything works.
Ideally, we would like a spectrum of an asteroid, to search for minerals. But short of a literal spectroscopic measurement, a color (‘medium resolution spectrophotometry’) can still give us an asteroid type (broadly, S-Type or C-Type, maybe better), which hints at albedo and thus size. The Canarias telescopes in Spain are doing colors- and quickly, for some small, fleeting NEOs that might impact. Of course, the derived albedos are categoric estimates. Other attendees were quick to point out that there need to be error bars on the measurements, as with all field measurements. But given that just a few percent of asteroids (certainly the Near-Earth Ones) have colors, we’ll take them.
Status update: the European Flyeye telescope (properly, NEOSTEL) has its prime components built, and subassemblies are now in checkout. The mountaintop site has been prepared. But we are still over a year from first light, and more like two years until normal operations. It’s a new optical design, with lots to iron out. How new? Based on lessons learned, the Flyeye-2 design (yes, #2 is moving forward) will drop some optical features, instead replacing them with new silicon. The second telescope will complement the first from a Southern-Hemisphere location; a third unit is also a possibility. The data pipeline, regardless of unit number, is now being demo’ed; rapid response and follow-up are in test, because this is a planetary defense resource.
Even before Flyeye, or Vera Rubin, we are living in an era of surveys. Asteroid researchers are not islands, asteroid telescopes do not exist in vacuum. The greater world of astronomy is pushing forward on exoplanets, including the funding of many exoplanet telescopes. These telescopes are still usable on asteroids, and chance asteroids enter the field of view of exoplanet researchers. The TRAPPIST project, scouring the night for exoplanets, reported its chance asteroids.
We closed with a (now) heated topic. If surveys feed databases, who maintains databases and ensures quality control? Getting back to error bars, what keeps a researcher from looking up archival data, and getting out an entry that was only slightly more than a broad estimate? Ultimately, a spreadsheet can have hundreds of columns, so some of them can be sorted into a ‘broad estimate’ bin. Or we can use data flags to warn others. But we need to form a consistent accounting system, since Big Data databases are already Big, and just getting bigger every night.
Good meeting all, keep watching the skies!