Radar Soundings of the Ionosphere of Mars Gurnett, D. A; Kirchner, D. L; Huff, R. L ...
Science (American Association for the Advancement of Science),
12/2005, Letnik:
310, Številka:
5756
Journal Article
Recenzirano
Odprti dostop
We report the first radar soundings of the ionosphere of Mars with the MARSIS (Mars Advanced Radar for Subsurface and Ionosphere Sounding) instrument on board the orbiting Mars Express spacecraft. ...Several types of ionospheric echoes are observed, ranging from vertical echoes caused by specular reflection from the horizontally stratified ionosphere to a wide variety of oblique and diffuse echoes. The oblique echoes are believed to arise mainly from ionospheric structures associated with the complex crustal magnetic fields of Mars. Echoes at the electron plasma frequency and the cyclotron period also provide measurements of the local electron density and magnetic field strength.
The height of mountain ranges reflects the balance between tectonic rock uplift, crustal strength and surface denudation. Tectonic deformation and surface denudation are interdependent, however, and ...feedback mechanisms—in particular, the potential link to climate—are subjects of intense debate. Spatial variations in fluvial denudation rate caused by precipitation gradients are known to provide first-order controls on mountain range width, crustal deformation rates and rock uplift. Moreover, limits to crustal strength are thought to constrain the maximum elevation of large continental plateaus, such as those in Tibet and the central Andes. There are indications that the general height of mountain ranges is also directly influenced by the extent of glaciation through an efficient denudation mechanism known as the glacial buzzsaw. Here we use a global analysis of topography and show that variations in maximum mountain height correlate closely with climate-controlled gradients in snowline altitude for many high mountain ranges across orogenic ages and tectonic styles. With the aid of a numerical model, we further demonstrate how a combination of erosional destruction of topography above the snowline by glacier-sliding and commensurate isostatic landscape uplift caused by erosional unloading can explain observations of maximum mountain height by driving elevations towards an altitude window just below the snowline. The model thereby self-consistently produces the hypsometric signature of the glacial buzzsaw, and suggests that differences in the height of mountain ranges mainly reflect variations in local climate rather than tectonic forces.
Abstract
Wide-field surveys for transiting planets are well suited to searching diverse stellar populations, enabling a better understanding of the link between the properties of planets and their ...parent stars. We report the discovery of HAT-P-69 b (TOI 625.01) and HAT-P-70 b (TOI 624.01), two new hot Jupiters around A stars from the Hungarian-made Automated Telescope Network (HATNet) survey that have also been observed by the
Transiting Exoplanet Survey Satellite
. HAT-P-69 b has a mass of
M
Jup
and a radius of
R
Jup
and resides in a prograde 4.79 day orbit. HAT-P-70 b has a radius of
R
Jup
and a mass constraint of
M
Jup
and resides in a retrograde 2.74 day orbit. We use the confirmation of these planets around relatively massive stars as an opportunity to explore the occurrence rate of hot Jupiters as a function of stellar mass. We define a sample of 47,126 main-sequence stars brighter than
T
mag
= 10 that yields 31 giant planet candidates, including 18 confirmed planets, 3 candidates, and 10 false positives. We find a net hot Jupiter occurrence rate of 0.41 ± 0.10% within this sample, consistent with the rate measured by
Kepler
for FGK stars. When divided into stellar mass bins, we find the occurrence rate to be 0.71 ± 0.31% for G stars, 0.43 ± 0.15% for F stars, and 0.26 ± 0.11% for A stars. Thus, at this point, we cannot discern any statistically significant trend in the occurrence of hot Jupiters with stellar mass.
We have successfully reproduced the Ozone ENSO Index (OEI) in the Goddard Earth Observing System (GEOS) chemistry‐climate model (CCM) forced by observed sea surface temperatures over a 25‐year ...period. The vertical ozone response to ENSO is consistent with changes in the Walker circulation. We derive the sensitivity of simulated ozone to ENSO variations using linear regression analysis. The western Pacific and Indian Ocean region shows similar positive ozone sensitivities from the surface to the upper troposphere, in response to positive anomalies in the Niño 3.4 Index. The eastern and central Pacific region shows negative sensitivities with the largest sensitivity in the upper troposphere. This vertical response compares well with that derived from SHADOZ ozonesondes in each region. The OEI reveals a response of tropospheric ozone to circulation change that is nearly independent of changes in emissions and thus it is potentially useful in chemistry‐climate model evaluation.
Key Points
We have successfully reproduced the Ozone ENSO Index in GEOS CCM
The vertical ozone response is consistent with changes in Walker and Hadley cell
OEI response is independent of changes in emissions and useful in CCM evaluation
ABSTRACT
We report the discovery of HD 110113 b (TESS object of interest-755.01), a transiting mini-Neptune exoplanet on a 2.5-d orbit around the solar-analogue HD 110113 (Teff = 5730 K). Using TESS ...photometry and High Accuracy Radial velocity Planet Searcher (HARPS) radial velocities gathered by the NCORES program, we find that HD 110113 b has a radius of 2.05 ± 0.12 R⊕ and a mass of 4.55 ± 0.62 M⊕. The resulting density of $2.90^{+0.75}_{-0.59}$ g cm−3 is significantly lower than would be expected from a pure-rock world; therefore HD 110113 b must be a mini-Neptune with a significant volatile atmosphere. The high incident flux places it within the so-called radius valley; however, HD 110113 b was able to hold on to a substantial (0.1–1 per cent) H–He atmosphere over its ∼4 Gyr lifetime. Through a novel simultaneous Gaussian process fit to multiple activity indicators, we were also able to fit for the strong stellar rotation signal with period 20.8 ± 1.2 d from the RVs and confirm an additional non-transiting planet, HD 110113 c, which has a mass of 10.5 ± 1.2 M⊕ and a period of $6.744^{+0.008}_{-0.009}$ d.
The detection of low-mass transiting exoplanets in multiple systems brings new constraints to planetary formation and evolution processes and challenges the current planet formation theories. ...Nevertheless, only a mere fraction of the small planets detected by Kepler and K2 have precise mass measurements, which are mandatory to constrain their composition. We aim to characterise the planets that orbit the relatively bright star K2-138. This system is dynamically particular as it presents the longest chain known to date of planets close to the 3:2 resonance. We obtained 215 HARPS spectra from which we derived the radial-velocity variations of K2-138. Via a joint Bayesian analysis of both the K2 photometry and HARPS radial-velocities (RVs), we constrained the parameters of the six planets in orbit. The masses of the four inner planets, from b to e, are 3.1, 6.3, 7.9, and 13.0 M⊕ with a precision of 34, 20, 18, and 15%, respectively. The bulk densities are 4.9, 2.8, 3.2, and 1.8 g cm−3, ranging from Earth to Neptune-like values. For planets f and g, we report upper limits. Finally, we predict transit timing variations of the order two to six minutes from the masses derived. Given its peculiar dynamics, K2-138 is an ideal target for transit timing variation (TTV) measurements from space with the upcoming CHaracterizing ExOPlanet Satellite (CHEOPS) to study this highly-packed system and compare TTV and RV masses.
We report the discovery and tomographic detection of WASP-174b, a planet with a near-grazing transit on a 4.23-d orbit around a V= 11.9, F6V star with Fe/H = 0.09 ± 0.09. The planet is in a ...moderately misaligned orbit with a sky-projected spin-orbit angle of λ = 31° ± 1°. This is in agreement with the known tendency for orbits around hotter stars to be misaligned. Owing to the grazing transit, the planet's radius is uncertain with a possible range of 0.8-1.8 RSUBJup/SUB. The planet's mass has an upper limit of 1.3 MSUBJup/SUB. WASP-174 is the faintest hot-Jupiter system so far confirmed by tomographic means.
Context.
The sub-Jovian, or Neptunian, desert is a previously identified region of parameter space where there is a relative dearth of intermediate-mass planets with short orbital periods.
Aims.
We ...present the discovery of a new transiting planetary system within the Neptunian desert, NGTS-14.
Methods.
Transits of NGTS-14Ab were discovered in photometry from the Next Generation Transit Survey (NGTS). Follow-up transit photometry was conducted from several ground-based facilities, as well as extracted from TESS full-frame images. We combine radial velocities from the HARPS spectrograph with the photometry in a global analysis to determine the system parameters.
Results.
NGTS-14Ab has a radius that is about 30 per cent larger than that of Neptune (0.444 ± 0.030
R
Jup
) and is around 70 per cent more massive than Neptune (0.092 ± 0.012
M
Jup
). It transits the main-sequence K1 star, NGTS-14A, with a period of 3.54 days, just far away enough to have maintained at least some of its primordial atmosphere. We have also identified a possible long-period stellar mass companion to the system, NGTS-14B, and we investigate the binarity of exoplanet host stars inside and outside the Neptunian desert using
Gaia
.
ABSTRACT
We present the discovery and characterization of two transiting planets observed by TESS in the light curves of the young and bright (V = 9.67) star HD73583 (TOI-560). We perform an ...intensive spectroscopic and photometric space- and ground-based follow-up in order to confirm and characterize the system. We found that HD73583 is a young (∼500 Myr) active star with a rotational period of 12.08 ± 0.11 d, and a mass and radius of 0.73 ± 0.02 M⊙ and 0.65 ± 0.02 R⊙, respectively. HD 73583 b (Pb = $6.3980420 _{ - 0.0000062 } ^ { + 0.0000067 }$ d) has a mass and radius of $10.2 _{ - 3.1 } ^ { + 3.4 }$ M⊕ and 2.79 ± 0.10 R⊕, respectively, which gives a density of $2.58 _{ - 0.81 } ^ { + 0.95 }$ ${\rm g\, cm^{-3}}$. HD 73583 c (Pc = $18.87974 _{ - 0.00074 } ^ { + 0.00086 }$ d) has a mass and radius of $9.7 _{ - 1.7 } ^ { + 1.8 }$ M⊕ and $2.39 _{ - 0.09 } ^ { + 0.10 }$ R⊕, respectively, which translates to a density of $3.88 _{ - 0.80 } ^ { + 0.91 }$ ${\rm g\, cm^{-3}}$. Both planets are consistent with worlds made of a solid core surrounded by a volatile envelope. Because of their youth and host star brightness, they both are excellent candidates to perform transmission spectroscopy studies. We expect ongoing atmospheric mass-loss for both planets caused by stellar irradiation. We estimate that the detection of evaporating signatures on H and He would be challenging, but doable with present and future instruments.
Preoperative chemoradiation in patients with locally advanced rectal cancer has no impact on overall survival (OS) and distant recurrences. The aim of the study was to evaluate local downstaging, ...toxicity and long-term outcome in patients with locally advanced rectal cancer after induction therapy with capecitabine and oxaliplatin (CAPEOX) followed by radiotherapy concomitant with capecitabine chemoradiotherapy (CRT) before total mesorectal excision (TME).
Patients with T4 tumors, all T3N+ tumors or T3 tumors involving or with a distance ≤1 mm to the mesorectal fascia were included. Patients were planned for two cycles of CAPEOX followed by radiotherapy concomitant with capecitabine. TME was carried out 6 weeks after the completion of CRT.
Of 84 consecutively admitted patients starting induction CAPEOX, 77 patients underwent surgery. R0 resection was seen in 94% and T downstaging in 69%. In the intention-to-treat group, pathological complete response was seen in 23%. Five-year disease-free survival (DFS) and OS were 63% 95% confidence interval (CI), 52.2% to 73.7% and 67% (95% CI, 56.1% to 77.3%), respectively. Grade 3/4 toxicity was seen in 18%, and four deaths occurred within 2 months of therapy.
Induction chemotherapy before CRT and surgery showed a high local control rate and promising long-term outcome as OS and DFS.
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