Abstract
Despite decades of scientific research on the subject, the climate of the first 1.5 Gyr of Mars' history has not been fully understood yet. Especially challenging is the need to reconcile ...the presence of liquid water for extended periods of time on the Martian surface with the comparatively low insolation received by the planet, a problem which is known as the Faint Young Sun paradox. In this paper, we use the Earth-like planet surface-temperature model (or ESTM), a latitudinal energy-balance model with enhanced prescriptions for meridional heat diffusion, and the radiative-transfer code EOS to investigate how seasonal variations of temperature can give rise to local conditions which are conducive to liquid-water runoffs. We include the effects of the Martian dichotomy, a northern ocean with either 150 or 550 m of global equivalent layer, and simplified CO
2
or H
2
O clouds. We find that 1.3–2.0 bar CO
2
-dominated atmospheres can produce seasonal thaws due to inefficient heat redistribution, provided that the eccentricity and the obliquity of the planet are sufficiently different from zero. We also studied the impact of different values for the argument of perihelion. When local favorable conditions exist, they nearly always persist for >15% of the Martian year. These results are obtained without the need for additional greenhouse gases (e.g., H
2
, CH
4
) or transient heat-injecting phenomena (e.g., asteroid impacts, volcanic eruptions). A moderate amount (0.1%–1%) of CH
4
significantly widens the parameter space region in which seasonal thaws are possible.
Aims.
We present new estimates of the brightness temperatures of Jupiter, Saturn, Uranus, and Neptune based on the measurements carried in 2009–2013 by
Planck
/LFI at 30, 44, and 70 GHz and released ...to the public in 2018. This work extends the results presented in the 2013 and 2015
Planck
/LFI Calibration Papers, based on the data acquired in 2009–2011.
Methods. Planck
observed each planet up to eight times during the nominal mission. We processed time-ordered data from the 22 LFI radiometers to derive planet antenna temperatures for each planet and transit. We accounted for the beam shape, radiometer bandpasses, and several systematic effects. We compared our results with the results from the ninth year of WMAP,
Planck
/HFI observations, and existing data and models for planetary microwave emissivity.
Results.
For Jupiter, we obtain
T
b
= 144.9, 159.8, 170.5
K
(± 0.2 K at 1
σ
, with temperatures expressed using the Rayleigh-Jeans scale) at 30, 44 and 70 GHz, respectively, or equivalently a band averaged
Planck
temperature
T
b
(ba)
= 144.7, 160.3, 171.2 K in good agreement with WMAP and existing models. A slight excess at 30 GHz with respect to models is interpreted as an effect of synchrotron emission. Our measures for Saturn agree with the results from WMAP for rings
T
b
= 9.2 ± 1.4, 12.6 ± 2.3, 16.2 ± 0.8 K, while for the disc we obtain
T
b
= 140.0 ± 1.4, 147.2 ± 1.2, 150.2 ± 0.4 K, or equivalently a
T
b
(ba)
= 139.7, 147.8, 151.0 K. Our measures for Uranus (
T
b
= 152 ± 6, 145 ± 3, 132.0 ± 2 K, or
T
b
(ba)
= 152, 145, 133 K) and Neptune (
T
b
= 154 ± 11, 148 ± 9, 128 ± 3 K, or
T
b
(ba)
= 154, 149, 128 K) agree closely with WMAP and previous data in literature.
Abstract
We present EOS, a procedure for determining the outgoing longwave radiation (OLR) and top-of-atmosphere (TOA) albedo for a wide range of conditions expected to be present in the atmospheres ...of rocky planets with temperate conditions. EOS is based on HELIOS and HELIOS-K, which are novel and publicly available atmospheric radiative transfer (RT) codes optimized for fast calculations with GPU processors. These codes were originally developed for the study of giant planets. In this paper we present an adaptation for applications to terrestrial-type, habitable planets, adding specific physical recipes for the gas opacity and vertical structure of the atmosphere. To test the reliability of the procedure, we assessed the impact of changing line opacity profile, continuum opacity model, atmospheric lapse rate, and tropopause position prescriptions on the OLR and the TOA albedo. The results obtained with EOS are in line with those of other RT codes running on traditional CPU processors, while being at least one order of magnitude faster. The adoption of OLR and TOA albedo data generated with EOS in a zonal and seasonal climate model correctly reproduces the fluxes of the present-day Earth measured by the CERES spacecraft. The results of this study disclose the possibility to incorporate fast RT calculations in climate models aimed at characterizing the atmospheres of habitable exoplanets.
Climate bistability of Earth-like exoplanets Murante, Giuseppe; Provenzale, Antonello; Vladilo, Giovanni ...
Monthly notices of the Royal Astronomical Society,
02/2020, Letnik:
492, Številka:
2
Journal Article
Recenzirano
Odprti dostop
ABSTRACT
Before about 500 million years ago, most probably our planet experienced temporary snowball conditions, with continental and sea ices covering a large fraction of its surface. This points to ...a potential bistability of Earth’s climate that can have at least two different (statistical) equilibrium states for the same external forcing (i.e. solar radiation). Here, we explore the probability of finding bistable climates in Earth-like exoplanets and consider the properties of planetary climates obtained by varying the semimajor orbital axis (thus, received stellar radiation), eccentricity and obliquity, and atmospheric pressure. To this goal, we use the Earth-like planet surface temperature model (ESTM), an extension of one-dimensional Energy Balance Models developed to provide a numerically efficient climate estimator for parameter sensitivity studies and long climatic simulations. After verifying that the ESTM is able to reproduce Earth climate bistability, we identify the range of parameter space where climate bistability is detected. An intriguing result of this work is that the planetary conditions that support climate bistability are remarkably similar to those required for the sustenance of complex, multicellular life on the planetary surface. The interpretation of this result deserves further investigation, given its relevance for the potential distribution of life in exoplanetary systems.
Having recently reported in Carraro et al. 2006. Astron. Astrophys. 460, L39 on the first light curve of the dwarf planet Eris (2003
UB
313
), we address here with more details the issue of the ...significance of the variability we found, and speculate on the possible origin of it. We present additional tests with respect to the quoted paper, making the variability detection more solid. Moreover, we discuss with more emphasis the possible role of Dysnomea, the recently discovered Eris satellite. We suggest that the presence of the satellite is not sufficient to account for the luminosity variation of Eris and propose other possible scenarios. At last we suggest the possibility to investigate the role of tidal interactions between Eris and Dysnomea.
In the context of current and future microwave surveys mainly dedicated to the accurate mapping of Cosmic Microwave Background (CMB), mm and sub-mm emissions from Solar System will represent a ...potential source of contamination as well as an opportunity for new Solar System studies. In particular, the forthcoming ESA
Planck
mission will be able to observe the point-like thermal emission from planets and some large asteroids as well as the diffused Zodiacal Light Emission (ZLE). After a brief introduction to the field, we focus on the identification of Solar System discrete objects in the
Planck
time ordered data.
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