Ongoing: the EU-ESA Workshop on Size Determination of Potentially Hazardous Near-Earth Objects (https://indico.esa.int/event/530). Step one in “Planetary Defense” is, of course, to spot the Potentially Hazardous Objects (PHOs). But step two is also important: gauge the size of the threat object. If it turns out the body is only ten or so meters across (depending on composition), then it’s no threat at all- such bodies break up in Earth’s atmosphere before reaching the ground. Even thirty or forty meters is not much to worry about (again, assuming not a metal asteroid). At thirty or so meters, you get a light show in the sky and a hail of gravel on the ground. It’s the objects 100-140 meters across that we start to mobilize and prepare. Even then, at 100 meters, the defensive preparation may be to simply order an evacuation of the projected impact zone. The zone may not be that large. But how to gauge the size of these impactors? Let’s see…
Monday, 11/11/24
Photometric observations
Scattering and absorption of light by near-Earth-object surfaces: photometric and polarimetric phase effects Karri Muinonen (Dept of Physics, University of Helsinki), 2:15 PM
We consider scattering and absorption of light in planetary regoliths composed of sparsely or densely packed nonspherical particles. For the particles, we incorporate sizes and refractive indices and generate sample regolith geometries using varying packing algorithms for particles and their clusters. To ensure computational efficiency, we make use of average elementary scattering and…
NEO absolute magnitudes with H,G1,G2 photometric function
Antti Penttilä, Karri Muinonen (Dept of Physics, Univ. Helsinki), 2:40 PM
The photometric observations of an asteroid can be used to derive the reduced magnitudes at different phase angles, V(α). A photometric function can be used to fit the magnitudes at different phase angles and to predict the behavior into the exact backscattering geometry at V(0), giving the absolute magnitude H of the object. In 2012 IAU adopted the H,G1,G2 photometric function which is an…
Absolute magnitude determination from multi-filter all-sky photometric surveys
Benoit Carry (Lagrange, Observatoire de la Côte d’Azur), 3:05 PM
The absolute magnitude H of asteroids is a fundamental property.
It is a proxy to diameter, it is required to predict apparent magnitude, and it is the only way to measure colors whenever filters are not observed (near-)simultaneously.
Major ephemerides computation centers like the Minor Planet Center (MPC), the Jet Propulsion Laboratory (JPL), the Asteroid Dynamical Site (AstDyS), and…
Phase curves and the taxonomy of asteroids Max Mahlke, 3:30 PM
Asteroid phase curves provide insights into their surface properties. In particular, the surge of brightness towards low phase angles (opposition effect) & the change in brightness with change in phase angle (photometric slope) are function of the surface composition & particle properties. This dependence opens up phase curves to taxonomic classification of asteroids, a process that has…
ESA’s PDO Telescope Network: High-Precision Astrometry for Physical Characterization Marco Micheli (ESA NEOCC), Francisco Ocana (ESA NEOCC), 4:20 PM
ESA’s Planetary Defence Office has traditionally focused most of its observational activities to astrometry, in order to provide high-precision measurements for the orbit determination and impact monitoring processes that form a significant component of our activities.
Although most of our observations are still designed to optimize the astrometric output, during the last year we have…
Estimation of the H magnitudes of near-Earth asteroids with time-resolved photometric observations at La Silla and Ondrejov Observatory Petr Pravec (Astronomical Institute AS CR, Ondřejov, Czech Republic), 4:45 PM
We run a long-term project of time-resolved (lightcurve) photometric observations of near-Earth and main-belt asteroids. While our primary scientific interest is to determine other physical parameters of the studied objects (e.g., their spin rates and states, or binary nature), we also, as a by-product, obtain estimates of their absolute magnitudes. We run most of the observations at the…
Phase curve fitting in the context of large-scale photometric surveys Milagros Colazo
Nowadays, we are experiencing a revolution in astronomical surveys. Thanks to ground-based and orbiting telescopes, millions of observations of asteroids in various photometric filters are available. The main objective of our project is to develop tools for reading, processing, and analyzing large volumes of data. We’ve successfully determined phase curves for thousands of asteroids in orange…
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As you can see, there’s a big push for observations of lightcurves and phase (the changes in brightness as a body rotates, and as a body orbits the Sun relative to us). These observations are simple, using conventional (optical) telescopes. They’re also the observations that would happen anyway, since astronomy is in an era of sky surveys. Telescopes are now sweeping the skies, looking for supernovae (to gauge the scale and expansion of the universe), gamma-ray bursts (very interesting deaths of very interesting stars), cosmological shear and lensing (a complementary, backup way to measure the expanding universe), the optical counterparts to gravitational-wave events (yet another class of interesting stars), and now the counterparts of fast radio bursts (just what the heck are these FRBs?).
All the while, survey telescopes just happen to catch asteroids that are in the field of view. Known asteroids can be filtered out by computer, and their brightnesses logged in the relevant databases. We would then reassemble a light curve for a given asteroid, and see if we can deduce its rotation period, perhaps its rotation axis, and perhaps its phase effect. It turns out the phase brightening and darkening is an independent measure of a body’s albedo (darkness or shininess). Once we know an asteroid’s albedo, we can safely assume it’s either smaller and shinier, or larger and duller. Hence, size. Yes, it all sounds complicated, but again the telescopes are there and the data is ‘free.’
More to say…