M. Wong

Impact flux on Jupiter: From superbolides to large-scale collisions

Context. Regular observations of Jupiter by a large number of amateur astronomers have resulted in the serendipitous discovery of short bright flashes in its atmosphere, which have been proposed as being caused by impacts of small objects. Three flashes were detected: one on June 3, 2010, one on August 20, 2010, and one on September 10, 2012. Aims. We show that the flashes are caused by impacting objects that we characterize in terms of their size, and we study the flux of small impacts on Jupiter. Methods. We measured the light curves of these atmospheric airbursts to extract their luminous energy and computed the masses and sizes of the objects. We ran simulations of impacts and compared them with the light curves. We analyzed the statistical significance of these events in the large pool of Jupiter observations. Results. All three objects are in the 5−20 m size category depending on their density, and they released energy comparable to the recent Chelyabinsk airburst. Model simulations approximately agree with the interpretation of the limited observations. Biases in observations of Jupiter suggest a rate of 12−60 similar impacts per year and we provide software tools for amateurs to examine the faint signature of impacts in their data to increase the number of detected collisions. Conclusions. The impact rate agrees with dynamical models of comets. More massive objects (a few 100 m) should impact with Jupiter every few years leaving atmospheric dark debris features that could be detectable about once per decade.

The Robo-AO-2 facility for rapid visible/near-infrared AO imaging and the demonstration of hybrid techniques

We are building a next-generation laser adaptive optics system, Robo-AO-2, for the UH 2.2-m telescope that will deliver robotic, diffraction-limited observations at visible and near-infrared wavelengths in unprecedented numbers. The superior Maunakea observing site, expanded spectral range and rapid response to high-priority events represent a significant advance over the prototype. Robo-AO-2 will include a new reconfigurable natural guide star sensor for exquisite wavefront correction on bright targets and the demonstration of potentially transformative hybrid AO techniques that promise to extend the faintness limit on current and future exoplanet adaptive optics systems.

The Gas Composition and Deep Cloud Structure of Jupiter's Great Red Spot

We have obtained high-resolution spectra of Jupiters Great Red Spot (GRS) between 4.6 and 5.4 microns using telescopes on Mauna Kea in order to derive gas abundances and to constrain its cloud structure between 0.5 and 5~bars. We used line profiles of deuterated methane CH3D at 4.66 microns to infer the presence of an opaque cloud at 5+/-1 bar. From thermochemical models this is almost certainly a water cloud. We also used the strength of Fraunhofer lines in the GRS to obtain the ratio of reflected sunlight to thermal emission. The level of the reflecting layer was constrained to be at 570+/-30 mbar based on fitting strong ammonia lines at 5.32 microns. We identify this layer as an ammonia cloud based on the temperature where gaseous ammonia condenses. We found evidence for a strongly absorbing, but not totally opaque, cloud layer at pressures deeper than 1.3 bar by combining Cassini/CIRS spectra of the GRS at 7.18 microns with ground-based spectra at 5 microns. This is consistent with the predicted level of an NH4SH cloud. We also constrained the vertical profile of water and ammonia. The GRS spectrum is matched by a saturated water profile above an opaque water cloud at 5~bars. The pressure of the water cloud constrains Jupiters O/H ratio to be at least 1.1 times solar. The ammonia mole fraction is 200+/-50ppm for pressures between 0.7 and 5 bar. Its abundance is 40 ppm at the estimated pressure of the reflecting layer. We obtained 0.8+/-0.2 ppm for PH3, a factor of 2 higher than in the warm collar surrounding the GRS. We detected all 5 naturally occurring isotopes of germanium in GeH4 in the Great Red Spot. We obtained an average value of 0.35+/-0.05 ppb for GeH4. Finally, we measured 0.8+/-0.2 ppb for CO in the deep atmosphere.

Jupiter’s Synchrotron Radiation Throughout the Comet P/Shoemaker-Levy 9 Impact Period

Jupiter’s microwave emission was observed throughout the SL9 impact period by many different telescopes, among which the NRAO 140-foot telescope in Green Bank (21 cm), Westerbork (92 cm), Effelsberg (6, 11 cm), Parkes (21 cm), NASA DSN (13 cm), and the Very Large Array (22, 90 cm). We determined the “average” total nonthermal flux density from the planet after having subtracted the thermal contribution, following the formulation by de Pater and Klein, (1989) and Klein et al., (1989). The flux density increased typically by 40-50% at 6 cm wavelength, 27% at 11-13 cm, 22%at 21 cm and 10-15% at 90 cm. Thus the radio spectrum hardened considerably during the week of cometary impacts. Following the week of cometary impacts, the flux density began to subside at all wavelength. VLA images show the brightness distribution of the planet; a comparison of images taken before and during the week of impacts show marked changes in the brightness distribution. At a central meridian longitude λ III ≈ 110°, the left side of the belts increased considerably and moved inwards by ~ 0.2 R J. This suggests that the increase in flux density is caused by energization of the resident particle population.