Orbital period change of Dimorphos due to the DART kinetic impact.

The Double Asteroid Redirection Test (DART) spacecraft successfully performed the first test of a kinetic impactor for asteroid deflection by impacting Dimorphos, the secondary of near-Earth binary asteroid (65803) Didymos, and changing the orbital period of Dimorphos. A change in orbital period of approximately 7 min was expected if the incident momentum from the DART spacecraft was directly transferred to the asteroid target in a perfectly inelastic collision1, but studies of the probable impact conditions and asteroid properties indicated that a considerable momentum enhancement (ß) was possible2,3. In the years before impact, we used lightcurve observations to accurately determine the pre-impact orbit parameters of Dimorphos with respect to Didymos4-6. Here we report the change in the orbital period of Dimorphos as a result of the DART kinetic impact to be -33.0 ± 1.0 (3σ) min. Using new Earth-based lightcurve and radar observations, two independent approaches determined identical values for the change in the orbital period. This large orbit period change suggests that ejecta contributed a substantial amount of momentum to the asteroid beyond what the DART spacecraft carried.

Detection of interstitial oxygen contents in Czochralski grown silicon crystals using internal calibration in laser-induced breakdown spectroscopy (LIBS).

We use an internal calibration approach in laser-induced breakdown spectroscopy (LIBS) for quantitative detection of dead load interstitial oxygen contents (Oi) in industrial-grade silicon (Si) crystal ingots. Si crystal samples were grown via Czochralski technique and supplied by SunEdison Semiconductor Ltd. with known Oi contents measured via gas fusion analysis (GFA) and Fourier transform infrared (FTIR) spectroscopy. The LIBS analyses reported here use and compare a direct approach based on the known oxygen atomic emission line at 777. 19 nm and an indirect approach based on an internal calibration technique using an emission line at 781 nm associated to Si I. Unlike the first direct approach, the latter exhibited much higher sensitivity, reliability and less error. In this approach, an internal calibration uses systematic variations in the 781 nm emission line in conjunction with observed changes in plasma excitation temperatures as a quantitative measure of changes in plasma conditions and laser-matter interactions due to varying Oi contents in the analyte matrix. Using this technique, we establish the detection limit of LIBS in measuring Oi in Si crystal ingots down to 8 ±â€¯1 ppma level. The approach assists to overcome the limitations of common industrial techniques such as FTIR that cannot provide accurate quantitative measurements for heavily doped Si crystals and GFA that is significantly cumbersome to be an online technique. Our results establish LIBS at the forefront of alternative industrial analytical tools heretofore not considered for rapid, potential on-line monitoring of dead loads in commercial grade Si wafers during their growth processes.

Direct detection of the asteroidal YORP effect.

The Yarkovsky-O'Keefe-Radzievskii-Paddack (YORP) effect is believed to alter the spin states of small bodies in the solar system. However, evidence for the effect has so far been indirect. We report precise optical photometric observations of a small near-Earth asteroid, (54509) 2000 PH5, acquired over 4 years. We found that the asteroid has been continuously increasing its rotation rate omega over this period by domega/dt = 2.0 (+/-0.2) x 10(-4) degrees per day squared. We simulated the asteroid's close Earth approaches from 2001 to 2005, showing that gravitational torques cannot explain the observed spin rate increase. Dynamical simulations suggest that 2000 PH5 may reach a rotation period of approximately 20 seconds toward the end of its expected lifetime.

Spin rate of asteroid (54509) 2000 PH5 increasing due to the YORP effect.

Radar and optical observations reveal that the continuous increase in the spin rate of near-Earth asteroid (54509) 2000 PH5 can be attributed to the Yarkovsky-O'Keefe-Radzievskii-Paddack (YORP) effect, a torque due to sunlight. The change in spin rate is in reasonable agreement with theoretical predictions for the YORP acceleration of a body with the radar-determined size, shape, and spin state of 2000 PH5. The detection of asteroid spin-up supports the YORP effect as an explanation for the anomalous distribution of spin rates for asteroids under 10 kilometers in diameter and as a binary formation mechanism.