The yeast Saccharomyces cerevisiae and most eukaryotes carry two 5′ → 3′ exoribonuclease paralogs. In yeast, they are called Xrn1, which shuttles between the nucleus and the cytoplasm, and executes ...major cytoplasmic messenger RNA (mRNA) decay, and Rat1, which carries a strong nuclear localization sequence (NLS) and localizes to the nucleus. Xrn1 is 30% identical to Rat1 but has an extra ~500 amino acids C‐terminal extension. In the cytoplasm, Xrn1 can degrade decapped mRNAs during the last round of translation by ribosomes, a process referred to as “cotranslational mRNA decay.” The division of labor between the two enzymes is still enigmatic and serves as a paradigm for the subfunctionalization of many other paralogs. Here we show that Rat1 is capable of functioning in cytoplasmic mRNA decay, provided that Rat1 remains cytoplasmic due to its NLS disruption (cRat1). This indicates that the physical segregation of the two paralogs plays roles in their specific functions. However, reversing segregation is not sufficient to fully complement the Xrn1 function. Specifically, cRat1 can partially restore the cell volume, mRNA stability, the proliferation rate, and 5′ → 3′ decay alterations that characterize xrn1Δ cells. Nevertheless, cotranslational decay is only slightly complemented by cRat1. The use of the AlphaFold prediction for cRat1 and its subsequent docking with the ribosome complex and the sequence conservation between cRat1 and Xrn1 suggest that the tight interaction with the ribosome observed for Xrn1 is not maintained in cRat1. Adding the Xrn1 C‐terminal domain to Rat1 does not improve phenotypes, which indicates that lack of the C‐terminal is not responsible for partial complementation. Overall, during evolution, it appears that the two paralogs have acquired specific characteristics to make functional partitioning beneficial.
cRat1 can partially restore the cell volume, mRNA stability, proliferation rate, and 5′ → 3′ decay alterations that characterize xrn1Δ cells. In particular, cRat1 is not a good substitute for Xrn1, for not only initiating 5′ → 3′ decay but also for following the ribosome position during cotranslational mRNA decay. The use of the AlphaFold prediction of a cRat1–ribosome complex and the sequence conservation between cRat1 and Xrn1 suggest that the tight interaction with the ribosome observed for Xrn1 is not maintained in cRat1. It seems that the two paralogs acquire specific features to make functional partitioning beneficial.
Take‐away
Cytoplasmic Rat1 partly restores the general physiological defects of an xrn1∆ mutant.
cRat1 is very inefficient in cotranslational mRNA decay.
The C‐terminal domain of Xrn1 is not involved in 5′ → 3′ cotranslational decay.
Acoustics is new on Mars: it allows the characterization of turbulence at smaller scales than previously possible within the lowest part of the Planetary Boundary Layer. Sound speed measurements, by ...the SuperCam instrument and its microphone onboard the NASA Perseverance rover, allow the retrieval of atmospheric temperatures at 0.77 m above the ground, at 3 Hz, with a ∼10 ms response time that is 20–100 times shorter than for typical thermocouple sensors used on Mars. Here we report on the first measurements of the sound speed‐derived temperature and its fluctuations near the surface. Data highlight large and rapid fluctuations up to ±7 K/s, whose amplitude over such a timescale has never been reported, nor predicted by atmospheric models. These fluctuations follow the daytime pattern of the turbulence and highlight occasional high amplitude events that are likely due to the conjunction of low thermal inertia and strong winds.
Plain Language Summary
The atmospheric surface layer of Mars, is prone to various interactions between the surface and the atmosphere, which control most of the climate and the weather of the red planet. There, large temperature gradients generate an intense turbulence during the daytime. Hence, the measurement of the air temperature variations close to the surface is important to understand the spatial and temporal scales of this turbulence. The SuperCam instrument onboard the NASA Perseverance rover enables the retrieval of the near‐surface atmospheric temperatures, and their fluctuations, at an unprecedented short timescale. Sound speed‐derived temperatures, also call sonic temperatures, collected over the Northern spring and summer of Martian Year 36 reveal large and rapid thermal fluctuations up to ±7 K/s, whose amplitude over such a timescale is not reported by any weather station sensors, nor predicted by models that simulate small‐scale eddies. These fluctuations follow the daytime pattern of the turbulence with a maximum amplitude early afternoon. Some occasional high temperature fluctuation events are observed, suggesting a complex effect of ground properties and local meteorological conditions on the turbulence. Overall, acoustics is a new and promising technique that records a unique view of atmospheric temperature variations near the surface of Mars.
Key Points
Sound speed derived temperature is used to study the microscale turbulence at an unprecedented short response time
Air temperature experiences fluctuations as high as ±7 K/s, which has never been reported in situ, nor resolved by mesoscale atmospheric models
Sonic temperature fluctuations follow the daytime turbulence pattern and find their origin in complex surface‐atmosphere interactions
The
Mars Regional Atmospheric Modeling System
(
MRAMS
) and a nested simulation of the
Mars Weather Research and Forecasting model
(
MarsWRF
) are used to predict the local meteorological conditions ...at the
Mars 2020 Perseverance
rover landing site inside Jezero crater (Mars). These predictions are complemented with the
COmplutense and MIchigan MArs Radiative Transfer
model (
COMIMART
) and with the local
Single Column Model
(
SCM
) to further refine predictions of radiative forcing and the water cycle respectively. The primary objective is to facilitate interpretation of the meteorological measurements to be obtained by the
Mars Environmental Dynamics Analyzer
(
MEDA
) aboard the rover, but also to provide predictions of the meteorological phenomena and seasonal changes that might impact operations, from both a risk perspective and from the perspective of being better prepared to make certain measurements. A full diurnal cycle at four different seasons (
L
s
0
∘
,
90
∘
,
180
∘
, and
270
∘
) is investigated. Air and ground temperatures, pressure, wind speed and direction, surface radiative fluxes and moisture data are modeled. The good agreement between observations and modeling in prior works Pla-Garcia et al. in Icarus 280:103–113,
2016
; Newman et al. in Icarus 291:203–231,
2017
; Vicente-Retortillo et al. in Sci. Rep. 8(1):1–8,
2018
; Savijärvi et al. in Icarus,
2020
provides confidence in utilizing these models results to predict the meteorological environment at
Mars 2020 Perseverance
rover landing site inside Jezero crater. The data returned by
MEDA
will determine the extent to which this confidence was justified.
The detection of methane at Gale crater by the Tunable Laser Spectrometer–Sample Analysis at Mars instrument aboard the Curiosity rover has garnered significant attention because of the implications ...for the presence of Martian organisms (Webster et al., 2015, https://doi.org/10.1126/science.1261713). Methane's photochemical lifetime is several centuries unless there is a fast, as‐yet‐unknown destruction mechanism (Lefèvre and Forget, 2009, https://doi.org/10.1038/nature08228). This is much longer than the atmospheric mixing time scale, and thus, the gas should be well‐mixed except when near a source or shortly after a release. Although most measurements report low background levels of ~0.4 parts per billion by volume, observed spikes of several parts per billion by volume or greater and a subsequent return to the background level are intriguing (Webster et al., 2015, https://doi.org/10.1126/science.1261713). The Mars Regional Atmospheric Modeling System is used to simulate, via passive tracers, the transport and mixing of methane released inside and outside of the crater from instantaneous and steady state releases, and to test whether the results are consistent with in situ observations made by the Mars Curiosity rover. The simulations indicate that the mixing time scale for air within the crater is approximately 1 sol. The timing of methane measurements within the crater is also important, because modeled methane abundance varies by ~1 order of magnitude over a diurnal cycle under all the scenarios considered. While the observed low background levels can be reproduced by the model under some circumstances, it is difficult to reconcile the measured peaks with the modeled transport and mixing. For periods of high methane abundance lasting longer than a few hours there must be a continuous release of methane inside the crater to counteract mixing, or there must be a large, methane‐rich air mass continually transported into the crater. The few scenarios that can produce peaks are problematic, because they would result in background methane values above what is observed.
Plain Language Summary
The in situ detection of methane at Gale crater by the Tunable Laser Spectrometer–Sample Analysis at Mars instrument aboard the Mars Science Laboratory Curiosity rover has garnered significant attention because of the potential implications for the presence of indigenous Martian organisms. There are many major unresolved questions regarding this detection: (1) Where is the release location? (2) How spatially extensive is the release? (3) For how long is methane released? In an effort to address the release location of methane, the spatial extensivity, and the magnitude and duration of the release, atmospheric circulation studies of Gale crater (where the Mars Science Laboratory Curiosity rover landed in 2012) were performed with the Mars Regional Atmospheric Modeling System Martian meteorological model using tracers to study transport and mixing of methane from potential source locations. The aim of this work is to test whether methane releases inside or outside of Gale crater are consistent with Tunable Laser Spectrometer–Sample Analysis at Mars observations.
Key Points
Crater mixing time scales are ~1 sol during all seasons
Methane abundances vary by at least an order of magnitude over a diurnal cycle under all the scenarios considered
It is difficult to reconcile measurements with the modeled transport and mixing
•The meteorology is controlled by interacting circulations and dynamical instabilities from the planetary scale down to the microscale.•The northern winter season is unique; the air mass in the ...crater mixes with external crater air due to the breaking of large amplitude mountain waves.•At other seasons, the mixing between the air in the floor of Gale Crater and air external to the crater may be more limited.•It is difficult to reconcile the putative methane detection with the Gale Crater circulation.
Numerical modeling results from the Mars Regional Atmospheric Modeling System are used to interpret the landed meteorological data from the Rover Environmental Monitoring Station onboard the Mars Science Laboratory rover Curiosity. In order to characterize seasonal changes throughout the Martian year, simulations are conducted at Ls 0, 90, 180 and 270. Two additional simulations at Ls 225 and 315 are explored to better understand the unique meteorological setting centered on Ls 270. The synergistic combination of model and observations reveals a complex meteorological environment within the crater. Seasonal planetary circulations, the thermal tide, slope flows along the topographic dichotomy, mesoscale waves, slope flows along the crater slopes and Mt. Sharp, and turbulent motions all interact in nonlinear ways to produce the observed weather. Ls 270 is shown to be an anomalous season when air within and outside the crater is well mixed by strong, flushing northerly flow and large amplitude, breaking mountain waves. At other seasons, the air in the crater is more isolated from the surrounding environment. The potential impact of the partially isolated crater air mass on the dust, water, noncondensable and methane cycles is also considered. In contrast to previous studies, the large amplitude diurnal pressure signal is attributed primarily to necessary hydrostatic adjustments associated with topography of different elevations, with contributions of less than 25% to the diurnal amplitude from the crater circulation itself. The crater circulation is shown to induce a suppressed boundary layer.
We utilize SuperCam's Mars microphone to provide information on wind speed and turbulence at high frequencies on Mars. To do so, we first demonstrate the sensitivity of the microphone signal level to ...wind speed, yielding a power law dependence. We then show the relationship between the microphone signal level and pressure, air and ground temperatures. A calibration function is constructed using Gaussian process regression (a machine learning technique) taking the microphone signal and air temperature as inputs to produce an estimate of the wind speed. This provides a high rate wind speed estimate on Mars, with a sample every 0.01 s. As a result, we determine the fast fluctuations of the wind at Jezero crater which highlights the nature of wind gusts over the Martian day. To analyze the turbulent behavior of this wind speed estimate, we calculate its normalized standard deviation, known as gustiness. To characterize the behavior of this high frequency turbulent intensity at Jezero crater, correlations are shown between the evaluated gustiness statistic and pressure drop rates/sizes, temperature and energy fluxes. This has implications for future atmospheric models on Mars, taking into account turbulence at the finest scales.
Plain Language Summary
The NASA Perseverance mission sent microphones to the surface of Mars. This microphone has recorded signals due to the wind. We examine how these recorded signals vary with other sensor data from Perseverance, which shows a link between the microphone signal, the dedicated wind speed sensor and air temperature. Based on this finding, we develop a way to predict the wind speed from the microphone data using a machine learning technique. The microphone records data at a very high rate compared with sensors so far sent to Mars. This means that the wind speed predicted from the microphone data can be used to study the chaotic and variable wind behavior on Mars to a level never seen before. We show that this chaotic and variable behavior has links to temperature and the number of whirlwinds observed. This will lead us to better weather models for Mars.
Key Points
Wind‐induced noise is observed by the SuperCam Mars microphone on Perseverance
Microphone and air temperature data are used to estimate the wind speed at high frequencies, using a machine learning model
The wind speed estimate is used to examine the relationships between turbulent intensity, pressure drops, temperature, and energy flux
We report new measurements of atmospheric methane by the Curiosity rover’s Tunable Laser Spectrometer that is part of the Sample Analysis at Mars suite (TLS-SAM), finding nondetections during two ...daytime measurements of average value 0.05 ± 0.22 ppbv (95% confidence interval CI). These are in marked contrast with nighttime background levels of 0.52 ± 0.10 (95% CI) from four measurements taken during the same season of northern summer. This large day-night difference suggests that methane accumulates while contained near the surface at night, but drops below TLS-SAM detection limits during the day, consistent with the daytime nondetection by instruments on board the ExoMars Trace Gas Orbiter. With no evidence for methane production by the rover itself, we propose that the source is one of planetary micro-seepage. Dynamical modeling indicates that such methane release is contained within the collapsed planetary boundary layer (PBL) at night due to a combination of nocturnal inversion and convergent downslope flow winds that confine the methane inside the crater close to the point where it is released. The methane abundance is then diluted during the day through increased vertical mixing associated with a higher altitude PBL and divergent upslope flow that advects methane out of the crater region. We also report detection of a large spike of methane in June 2019 with a mean
in situ
value over a two-hour ingest of 20.5 ± 4 ppbv (95% CI). If near-surface production is occurring widely across Mars, it must be accompanied by a fast methane destruction or sequestration mechanism, or both.
The Mars2020 Perseverance Rover landed successfully on the Martian surface on the Jezero Crater floor (18.44°N, 77.45°E) at Martian solar longitude, Ls, ∼5° in February 2021. Since then, it has ...produced highly valuable environmental measurements with a versatile scientific payload including the MEDA (Mars Environmental Dynamics Analyzer) suite of environmental sensors. One of the MEDA systems is the PS pressure sensor system, which weighs 40 g and has an estimated absolute accuracy of better than 3.5 Pa and a resolution of 0.13 Pa. We present initial results from the first 414 sols of Martian atmospheric surface pressure observations by the PS, whose performance was found to meet its specifications. Observed sol‐averaged atmospheric pressures follow an anticipated pattern of pressure variation in the course of the advancing season and are consistent with data from other landing missions. The observed daily pressure amplitude varies by ∼2%–5 % of the sol‐averaged pressure, with absolute amplitude 10–35 Pa in an approximately direct relationship with airborne dust. During a regional dust storm, which began at Ls ∼ 135°, the daily pressure amplitude roughly doubled. The daily pressure variations were found to be remarkably sensitive to the seasonal evolution of the atmosphere. In particular, analysis of the daily pressure signature revealed diagnostic information likely related to the regional scale structure of the atmosphere. Comparison of Perseverance pressure observations with data from other landers reveals the global scale seasonal behavior of Mars' atmosphere.
Plain Language Summary
Mars2020 Perseverance Rover successfully arrived on Mars in February 2021. It landed in an early Martian spring afternoon in a crater north of Mars' equator called Jezero crater. The rover is equipped with meteorological instruments that have so far produced extensive and valuable data for understanding the Martian atmosphere. One of the meteorological instruments is an accurate and precise pressure sensor. The pressure sensor has revealed large changes in the pressure over the seasons that are related to large changes in the actual mass of the Martian atmosphere. This is in line with seasonal pressure changes measured during previous Mars missions and can be explained as the condensation of the atmosphere onto the Martian poles and its subsequent sublimation. On a shorter time scale, the pressure sensor revealed complex pressure changes over a Martian day. These variations are thought to be related to atmospheric dust, whose ubiquitous nature is known to have a strong influence on the Martian climate. As the seasons progressed, the daily pressure variations morphed to exhibit different patterns likely related to the large‐scale regional changes in the atmosphere. Comparison of Perseverance pressure observations with other landers revealed the global nature of the atmosphere.
Key Points
The atmospheric pressure observations by Perseverance Rover have proved to be of excellent quality fulfilling expectations
Jezero crater pressure exhibits significant differences to other Martian areas likely due to varying regional geography and solar forcing
Overall, the diurnal and seasonal atmospheric pressure cycles at Jezero Crater follow an anticipated pattern of pressure variation
•Line-of-sight and column extinction suggest little atmospheric mixing in Gale Crater.•Gale Crater not a dusty place on Mars.•Mars rover has clear view of crater rim due to lack of low-down dust.
We ...report on line-of-sight extinction in northern Gale Crater, Mars as seen by the Mars Science Laboratory (MSL) rover, Curiosity from sol 100 to sol 900; a little more than an entire martian year. Navcam images oriented due north, which show the distant crater rim, the near ground and the sky allow the extinction due to dust within the crater to be determined. This line-of sight extinction is compared to a complementary dataset of column extinctions derived from Mastcam. The line-of-sight extinction within the crater is less than the column extinction for the majority of the martian year. This implies that the relatively low mixing ratio of dust within the crater as compared to the atmosphere above the crater rim persists through most of the year. This suggests relatively little mixing between the atmosphere above the crater and the atmosphere inside the crater and suggests that northern Gale Crater is a net sink of dust in the current era. The data does however show a yearly convergence of the line-of-sight extinction and the column-averaged extinction around Ls=270–290°. This suggests that air above the crater mixes with air in the crater at this time, as predicted by mesoscale models. Matching line-of-sight and column extinction values are also seen around Ls≈135°, a season that has only been observed once in this dataset, this is particularly interesting as the Rover Environmental Monitoring Station onboard Curiosity reports increased convective boundary layer heights in the same season.
Abstract
We use a spectral approach to analyze the pressure and wind data from the InSight mission and investigate the diurnal and seasonal trends. Our analyses show that the daytime pressure and ...wind spectra have slopes of approximately −1.7 and −1.3 and, therefore, do not follow the Kolmogorov scaling (as was also previously reported for a reduced data set in Banfield et al.). We find that the nighttime pressure spectral slope is close to −1 (as reported in Temel et al.), and that the wind speed spectral slope is close to −0.5, flatter than the theoretical slope expected for the shear-dominated regime. We observe strong nocturnal (likely shear-generated) turbulent behavior starting around
L
s
= 150° (InSight sol 440) that shifts to progressively earlier local times before reaching the “5th season” (InSight sols 530–710) identified by Chatain et al.. The diurnal spectral slope analyses indicate an asymmetry in the diurnal behavior of the Martian boundary layer, with a slow growth and fast collapse mechanism. Finally, the low-frequency (5–30 mHz) pressure data exhibit large spectral slope oscillations. These occur particularly during the periods with a highly stable atmosphere and, therefore, may be linked to gravity wave activity.
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