Search Publications

Tropical to mid-latitude snow and ice accumulation, flow and glaciation on Mars

Jaumann, R.; Head, J. W.; Neukum, G. +11 more

Images from the Mars Express HRSC (High-Resolution Stereo Camera) of debris aprons at the base of massifs in eastern Hellas reveal numerous concentrically ridged lobate and pitted features and related evidence of extremely ice-rich glacier-like viscous flow and sublimation. Together with new evidence for recent ice-rich rock glaciers at the base o…

An X-Ray Study of Magnetic Field Strengths and Particle Content in the Lobes of FR II Radio Sources

Hardcastle, M. J.; Croston, J. H.; Birkinshaw, M. +3 more

We present a Chandra and XMM-Newton study of X-ray emission from the lobes of 33 classical double radio galaxies and quasars. We report new detections of lobe-related X-ray emission in 11 sources. Together with previous detections, we find that X-ray emission is detected from at least one radio lobe in ~75% of the sample. For all of the lobe detec…

Measurement of Spin-Orbit Alignment in an Extrasolar Planetary System

Butler, R. Paul; Vogt, Steven S.; Marcy, Geoffrey W. +10 more

We determine the stellar, planetary, and orbital properties of the transiting planetary system HD 209458 through a joint analysis of high-precision radial velocities, photometry, and timing of the secondary eclipse. Of primary interest is the strong detection of the Rossiter-McLaughlin effect, the alteration of photospheric line profiles that occu…

Radar Soundings of the Subsurface of Mars

Gurnett, Donald A.; Johnson, William T. K.; Stofan, Ellen R. +31 more

The martian subsurface has been probed to kilometer depths by the Mars Advanced Radar for Subsurface and Ionospheric Sounding instrument aboard the Mars Express orbiter. Signals penetrate the polar layered deposits, probably imaging the base of the deposits. Data from the northern lowlands of Chryse Planitia have revealed a shallowly buried quasi-…

Titan's Atmospheric Temperatures, Winds, and Composition

Strobel, D. F.; Showalter, M. R.; Lellouch, E. +42 more

Temperatures obtained from early Cassini infrared observations of Titan show a stratopause at an altitude of 310 kilometers (and 186 kelvin at 15°S). Stratospheric temperatures are coldest in the winter northern hemisphere, with zonal winds reaching 160 meters per second. The concentrations of several stratospheric organic compounds are enhanced a…

An upper limit to the masses of stars

Figer, Donald F.

There is no accepted upper mass limit for stars. Such a basic quantity eludes both theory and observation, because of an imperfect understanding of the star-formation process and because of incompleteness in surveying the Galaxy. The Arches cluster is ideal for investigating such limits, being large enough to expect stars at least as massive as ~5…

Reflections of Active Galactic Nucleus Outbursts in the Gaseous Atmosphere of M87

Churazov, E.; Vikhlinin, A.; Forman, W. +7 more

We combined deep Chandra, ROSAT HRI, and XMM-Newton observations of M87 to study the impact of active galactic nucleus (AGN) outbursts on its gaseous atmosphere. Many X-ray features appear to be a direct result of repetitive AGN outbursts. In particular, the X-ray cavities around the jet and counterjet are likely due to the expansion of radio plas…

The Foreshock

Eastwood, J. P.; Lucek, E. A.; Narita, Y. +4 more

Solar Wind Origin in Coronal Funnels

Wilhelm, Klaus; Marsch, Eckart; Wang, Jing-Xiu +4 more

The origin of the solar wind in solar coronal holes has long been unclear. We establish that the solar wind starts flowing out of the corona at heights above the photosphere between 5 megameters and 20 megameters in magnetic funnels. This result is obtained by a correlation of the Doppler-velocity and radiance maps of spectral lines emitted by var…

Helioseismological Implications of Recent Solar Abundance Determinations

Pinsonneault, Marc; Basu, Sarbani; Bahcall, John N. +1 more

We show that standard solar models are in good agreement with the helioseismologically determined sound speed and density as a function of solar radius, the depth of the convective zone, and the surface helium abundance, as long as those models do not incorporate the most recent heavy-element abundance determinations. However, sophisticated new an…