No two rocky bodies offer a better laboratory for exploring the conditions controlling interior dynamics than Venus and Earth. Their similarities in size, density, distance from the sun, and young ...surfaces would suggest comparable interior dynamics. Although the two planets exhibit some of the same processes, Venus lacks Earth’s dominant process for losing heat and cycling volatiles between the interior and the surface and atmosphere: plate tectonics. One commonality is the size and number of mantle plume features which are inferred to be active today and arise at the core mantle boundary. Such mantle plumes require heat loss from the core, yet Venus lacks a measurable interior dynamo. There is evidence for plume-induced subduction on Venus, but no apparent mosaic of moving plates. Absent plate tectonics, one essential question for interior dynamics is how did Venus obtain its young resurfacing age? Via catastrophic or equilibrium processes? Related questions are how does it lose heat via past periods of plate tectonics, has it always had a stagnant lid, or might it have an entirely different mode of heat loss? Although there has been no mission dedicated to surface and interior processes since the Magellan mission in 1990, near infrared surface emissivity data that provides information on the iron content of the surface mineralogy was obtained fortuitously from Venus Express. These data imply both the presence of continental-like crust, and thus formation in the presence of water, and recent volcanism at mantle hotspots. In addition, the study of interior dynamics for both Earth and exoplanets has led to new insights on the conditions required to initiate subduction and develop plate tectonics, including the possible role of high temperature lithosphere, and a renewed drive to reveal why Venus and Earth differ. Here we review current data that constrains the interior dynamics of Venus, new insights into its interior dynamics, and the data needed to resolve key questions.
Single seismometer structure
Because of the lack of direct seismic observations, the interior structure of Mars has been a mystery. Khan
et al.
, Knapmeyer-Endrun
et al.
, and Stähler
et al.
used ...recently detected marsquakes from the seismometer deployed during the InSight mission to map the interior of Mars (see the Perspective by Cottaar and Koelemeijer). Mars likely has a 24- to 72-kilometer-thick crust with a very deep lithosphere close to 500 kilometers. Similar to the Earth, a low-velocity layer probably exists beneath the lithosphere. The crust of Mars is likely highly enriched in radioactive elements that help to heat this layer at the expense of the interior. The core of Mars is liquid and large, ∼1830 kilometers, which means that the mantle has only one rocky layer rather than two like the Earth has. These results provide a preliminary structure of Mars that helps to constrain the different theories explaining the chemistry and internal dynamics of the planet.
Science
, abf2966, abf8966, abi7730, this issue p.
434
, p.
438
, p.
443
see also abj8914, p.
388
Data from the InSight mission on Mars help constrain the structure and properties of the martian interior.
For 2 years, the InSight lander has been recording seismic data on Mars that are vital to constrain the structure and thermochemical state of the planet. We used observations of direct (
P
and
S
) and surface-reflected (
PP
,
PPP
,
SS
, and
SSS
) body-wave phases from eight low-frequency marsquakes to constrain the interior structure to a depth of 800 kilometers. We found a structure compatible with a low-velocity zone associated with a thermal lithosphere much thicker than on Earth that is possibly related to a weak
S
-wave shadow zone at teleseismic distances. By combining the seismic constraints with geodynamic models, we predict that, relative to the primitive mantle, the crust is more enriched in heat-producing elements by a factor of 13 to 20. This enrichment is greater than suggested by gamma-ray surface mapping and has a moderate-to-elevated surface heat flow.
Pre-mission InSights on the Interior of Mars Smrekar, Suzanne E.; Lognonné, Philippe; Spohn, Tilman ...
Space science reviews,
02/2019, Letnik:
215, Številka:
1
Journal Article
Recenzirano
Odprti dostop
The Interior exploration using Seismic Investigations, Geodesy, and Heat Transport (InSight) Mission will focus on Mars’ interior structure and evolution. The basic structure of crust, mantle, and ...core form soon after accretion. Understanding the early differentiation process on Mars and how it relates to bulk composition is key to improving our understanding of this process on rocky bodies in our solar system, as well as in other solar systems. Current knowledge of differentiation derives largely from the layers observed via seismology on the Moon. However, the Moon’s much smaller diameter make it a poor analog with respect to interior pressure and phase changes. In this paper we review the current knowledge of the thickness of the crust, the diameter and state of the core, seismic attenuation, heat flow, and interior composition. InSight will conduct the first seismic and heat flow measurements of Mars, as well as more precise geodesy. These data reduce uncertainty in crustal thickness, core size and state, heat flow, seismic activity and meteorite impact rates by a factor of
3
–
10
×
relative to previous estimates. Based on modeling of seismic wave propagation, we can further constrain interior temperature, composition, and the location of phase changes. By combining heat flow and a well constrained value of crustal thickness, we can estimate the distribution of heat producing elements between the crust and mantle. All of these quantities are key inputs to models of interior convection and thermal evolution that predict the processes that control subsurface temperature, rates of volcanism, plume distribution and stability, and convective state. Collectively these factors offer strong controls on the overall evolution of the geology and habitability of Mars.
With 2
years of tracking data collection from the MRO spacecraft, there is noticeable improvement in the high frequency portion of the spherical harmonic Mars gravity field. The new JPL Mars gravity ...fields, MRO110B and MRO110B2, show resolution near degree 90. Additional years of MGS and Mars Odyssey tracking data result in improvement for the seasonal
J
¯
3
gravity changes which compares well to global circulation models and Odyssey neutron data and Mars rotation and precession (
ψ
˙
=
-
7594
±
10
mas
/
year
). Once atmospheric dust is accounted for in the spacecraft solar pressure model, solutions for Mars solar tide are consistent between data sets and show slightly larger values (
k
2
=
0.164
±
0.009, after correction for atmospheric tide) compared to previous results, further constraining core models. An additional 4
years of Mars range data improves the Mars ephemeris, determines 21 asteroid masses and bounds solar mass loss (
dGM
Sun
/
dt
<
1.6
×
10
−13
GM
Sun
year
−1).
The questions of whether Venus is geologically active and how the planet has resurfaced over the past billion years have major implications for interior dynamics and climate change. Nine ..."hotspots"--areas analogous to Hawaii, with volcanism, broad topographic rises, and large positive gravity anomalies suggesting mantle plumes at depth--have been identified as possibly active. This study used variations in the thermal emissivity of the surface observed by the Visible and Infrared Thermal Imaging Spectrometer on the European Space Agency's Venus Express spacecraft to identify compositional differences in lava flows at three hotspots. The anomalies are interpreted as a lack of surface weathering. We estimate the flows to be younger than 2.5 million years and probably much younger, about 250,000 years or less, indicating that Venus is actively resurfacing.
•2-D model of corona formation on Venus.•Corona topography is generated by buoyant magmatic intrusions in or below the lithosphere.•Corona topography spreads laterally and grows vertically as melt ...spreads and accumulates.•Corona rim topography is generally created in 105 to 106 year timescales.•Corona rim topography not created in earth-like model due to increased viscosities from cooler temperatures.
Coronae are volcanic-tectonic features seemingly unique to the surface of Venus. As such they offer potential insights into differences in geodynamic processes on Venus and Earth. Largely due to limitations in processing power and computational complexity, models of corona formation generally ignore the effect of melt and magmatism despite the presence of volcanic features like domes and lava flows. Here we present a new model of corona formation integrating visco-plastic rheology with two-phase flow melt migration. Additionally, we model brittle failure of surface material, viscous flow of partially molten material at depth, and cracking of solid rock from fluid pressure in one model. The model consists of a two-dimensional half space with a round plume body ascending through an asthenosphere and interacting with a Venusian lithosphere and crust. The size and temperature of the plume body, lithosphere thickness, crustal thickness, and regional strain rate are all varied over 20 model runs. Most models show deflection of the plume as it rises due to the increased viscosity of the base of the lithosphere. As the plume spreads and rises against the base of the lithosphere, melting occurs. Melt rises and accumulates in the lithosphere which supports surface topography. Brittle failure occurs at the surface due to the induced stress of the migrating plume body and rising melt. Increased temperatures and sizes of initial plumes result in larger topographies occurring over smaller timescales. Decreased temperatures and sizes of initial plumes result in smaller topographies over larger timescales. Increased lithosphere thickness generates smaller topographies. Thinner crusts result in more viscous lithosphere and more strain accumulation, creating surface depressions seen in approximately half of real corona. Both thicker crusts and increased regional strain result in lower viscosities at the base of the lithosphere, preventing the deflection of the plume body, which instead rises through the lithosphere relatively unimpeded. The varied model parameters generally result in an evolutionary sequence of topographies and fracture patterns which resemble actual corona, without requiring a collapsing dome to create outer rims, as is often invoked for corona formation via upwelling plumes. Corona rim topography is generally created within 105 and 106 year timescales, while multiple rims or central depressions are generally observed over 106 year timescales. Observed topography is actively supported by partially molten regions in the lithosphere, supporting the notion of an active squishy-lid Venus. These partially molten regions are not centrally located and may provide a source for observed lava flows away from corona centers.
The analysis of Venus’ gravity field and topography suggests the presence of a small number of deep mantle plumes (∼9). This study predicts the number of plumes formed at the core–mantle boundary, ...their characteristics, and the production of partial melt from adiabatic decompression. Numerical simulations are performed using a 3D spherical code that includes large viscosity variations and internal heating. This study investigates the effect of several parameters including the core–mantle boundary temperature, the amount of internal heating, and the mantle viscosity. The smallest number of plumes is achieved when no internal heating is present. However, scaling Earth’s radiogenic heating to Venus suggests a value of ∼16
TW. Cases with internal heating produce more realistic lid thickness and partial melting, but produce either too many plumes or no plumes if a high mantle temperature precludes the formation of a hot thermal boundary layer. Mantle viscosity must be reduced to at least 10
20
Pa
s in order to include significant internal heating and still produce hot plumes. In all cases that predict melting, melting occurs throughout the upper mantle. Only cases with high core temperature (>1700
K) produce dry melting. Over time the upper mantle may have lost significant volatiles. Depending on the water content of the lower mantle, deep plumes may contribute to present-day atmospheric water via volcanic outgassing. Assuming 50
ppm water in mantle, 10 plumes with a buoyancy flux of 500
kg/s continuously erupting for 4
myr will outgas an amount of water on the order of that in the lower atmosphere. A higher level of internal heating than achieved to date, as well as relatively low mantle viscosity, may be required to achieve simulations with ∼10 plumes and a thinner lid. Alternatively, if the mantle is heating up due to the stagnant lid, the effect is equivalent to having lower rates of internal heating. A temperature increase of 110
K/byr is equivalent to −13
TW. This value along with the internal heating of 3
TW used in this study may represent the approximate heat budget of Venus’ mantle.
The Mars Reconnaissance Orbiter (MRO) is the latest addition to the suite of missions on or orbiting Mars as part of the NASA Mars Exploration Program. Launched on 12 August 2005, the orbiter ...successfully entered Mars orbit on 10 March 2006 and finished aerobraking on 30 August 2006. Now in its near‐polar, near‐circular, low‐altitude (∼300 km), 3 p.m. orbit, the spacecraft is operating its payload of six scientific instruments throughout a one‐Mars‐year Primary Science Phase (PSP) of global mapping, regional survey, and targeted observations. Eight scientific investigations were chosen for MRO, two of which use either the spacecraft accelerometers or tracking of the spacecraft telecom signal to acquire data needed for analysis. Six instruments, including three imaging systems, a visible‐near infrared spectrometer, a shallow‐probing subsurface radar, and a thermal‐infrared profiler, were selected to complement and extend the capabilities of current working spacecraft at Mars. Whether observing the atmosphere, surface, or subsurface, the MRO instruments are designed to achieve significantly higher resolution while maintaining coverage comparable to the current best observations. The requirements to return higher‐resolution data, to target routinely from a low‐altitude orbit, and to operate a complex suite of instruments were major challenges successfully met in the design and build of the spacecraft, as well as by the mission design. Calibration activities during the seven‐month cruise to Mars and limited payload operations during a three‐day checkout prior to the start of aerobraking demonstrated, where possible, that the spacecraft and payload still had the functions critical to the science mission. Two critical events, the deployment of the SHARAD radar antenna and the opening of the CRISM telescope cover, were successfully accomplished in September 2006. Normal data collection began 7 November 2006 after solar conjunction. As part of its science mission, MRO will also aid identification and characterization of the most promising sites for future landed missions, both in terms of safety and in terms of the scientific potential for future discovery. Ultimately, MRO data will advance our understanding of how Mars has evolved and by which processes that change occurs, all within a framework of identifying the presence, extent, and role of water in shaping the planet's climate over time.
The Marsquake catalogue from InSight, sols 0–478 Clinton, John F.; Ceylan, Savas; van Driel, Martin ...
Physics of the earth and planetary interiors,
January 2021, 2021-01-00, 2021-01, Letnik:
310
Journal Article
Recenzirano
Odprti dostop
The InSight (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) mission began collecting high quality seismic data on Mars in February 2019. This manuscript documents the ...seismicity observed by SEIS, InSight's seismometer, from this time until the end of March 2020. Within the InSight project, the Marsquake Service (MQS) is responsible for prompt review of all seismic data collected by InSight, detection of events that are likely to be of seismic origin, and curation and release of seismic catalogues. In the first year of data collection, MQS have identified 465 seismic events that we interpret to be from regional and teleseismic marsquakes. Seismic events are grouped into 2 different event families: the low frequency family is dominated by energy at long period below 1 s, and the high frequency family primarily include energy at and above 2.4 Hz. Event magnitudes, from Mars-specific scales, range from 1.3 to 3.7. A third class of events with very short duration but high frequency bursts have been observed 712 times. These are likely associated with a local source driven by thermal stresses. This paper describes the data collected so far in the mission and the procedures under which MQS operates; summarises the content of the current MQS seismic catalogue; and presents the key features of the events we have observed so far, using the largest events as examples.
•The Marsquake Service is providing updated catalogues of Martian seismicity as recorded on InSight.•465 distant marsquakes have been identified in the first 478 martian days (sol) since InSight landed.•This version of the catalogue includes an additional 712 events that may be due to local cracking from thermal forcing.
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