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Register a new userThe Need for Speed in Near-Earth Asteroid Characterization
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Added by
Jos\\'e Luis Galache
Publication date
2015
fields
Physics
and research's language is
English
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We have used Minor Planet Center data and tools to explore the discovery circumstances and properties of the currently known population of over 10,000 NEAs, and to quantify the challenges for follow-up from ground-based telescopes. The increasing rate of discovery has grown to ~1,000/year as surveys have become more sensitive, by 1mag every ~7.5 years. However, discoveries of large (H =< 22) NEAs have remained stable at ~365/year over the past decade, at which rate the 2005 Congressional mandate to find 90% of 140m NEAs will not be met before 2030. Meanwhile, characterization is falling farther behind: Fewer than 10% of NEAs are well characterized in terms of size, rotation periods, and spectra, and at current rates of follow-up it will take about a century to determine them even for the known population. Over 60% of NEAs have an orbital uncertainty parameter, U >= 4, making reacquisition more than a year following discovery difficult; for H > 22 this fraction is over 90%. We argue that rapid follow-up will be essential to characterize newly-discovered NEAs. Most new NEAs are found within 0.5mag of peak brightness and fade quickly, typically by 0.5/3.5/5mag after 1/4/6 weeks. About 80% have synodic periods of <3 years that bring them close to Earth several times a decade. However, follow-up observations on subsequent apparitions will be near impossible for the bulk of new discoveries, as these will be H > 22 NEAs that tend to return 100 times fainter. We show that for characterization to keep pace with discovery would require: Visible spectroscopy within days with a dedicated >2m telescope; long-arc astrometry, used also for phase curves, with a >4m telescope; and fast-cadence (<min) lightcurves obtained within days with a >= 4m telescope. For the already-known large (H =< 22) NEAs, subsequent-apparition spectroscopy, astrometry, and photometry could be done with 1-2m telescopes.
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In August 2002, the near-Earth asteroid 2002 NY40, made its closest approach to the Earth. This provided an opportunity to study a near-Earth asteroid with a variety of instruments. Several of the telescopes at the Maui Space Surveillance System were trained at the asteroid and collected adaptive optics images, photometry and spectroscopy. Analysis of the imagery reveals the asteroid is triangular shaped with significant self-shadowing. The photometry reveals a 20-hour period and the spectroscopy shows that the asteroid is a Q-type.
The Apollo-type near-Earth asteroid (155140) 2005 UD is thought to be a member of the Phaethon-Geminid meteor stream Complex (PGC). Its basic physical parameters are important for unveiling its origin and its relationship to the other PGC members as well as to the Geminid stream. Adopting the Lommel-Seeliger ellipsoid method and $H,G_1,G_2$ phase function, we carry out spin, shape, and phase curve inversion using the photometric data of 2005~UD. The data consists of 11 new lightcurves, 3 lightcurves downloaded from the Minor Planet Center, and 166 sparse data points downloaded from the Zwicky Transient Facility database. As a result, we derive the pole solution of ($285^circ.8^{+1.1}_{-5.3}$, $ -25^circ.8^{+5.3}_{-12.5}$) in the ecliptic frame of J2000.0 with the rotational period of $5.2340$ h. The corresponding triaxial shape (semiaxes $a>b>c$) is estimated as $b/a= 0.76^{+0.01}_{-0.01}$ and $c/a=0.40^{+0.03}_{-0.01}$. Using the calibrated photometric data of 2005 UD, the $H,G_1,G_2$ parameters are estimated as $17.19^{+0.10}_{-0.09}$ mag, $0.573^{+0.088}_{-0.069}$, and $0.004^{+0.020}_{-0.021}$, respectively. Correspondingly, the phase integral $q$, photometric phase coefficient $k$, and the enhancement factor $zeta$ are 0.2447, -1.9011, and 0.7344. From the values of $G_1$ and $G_2$, 2005 UD is likely to be a C-type asteroid. We estimate the equivalent diameter of 2005 UD from the new $H$-value: it is 1.30 km using the new geometric albedo of 0.14.
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