33 research outputs found
Valuing life detection missions
Recent discoveries imply that Early Mars was habitable for
life-as-we-know-it; that Enceladus might be habitable; and that many stars have
Earth-sized exoplanets whose insolation favors surface liquid water. These
exciting discoveries make it more likely that spacecraft now under construction
- Mars 2020, ExoMars rover, JWST, Europa Clipper - will find habitable, or
formerly habitable, environments. Did these environments see life? Given finite
resources (\$10bn/decade for the US ), how could we best test the hypothesis of
a second origin of life? Here, we first state the case for and against flying
life detection missions soon. Next, we assume that life detection missions will
happen soon, and propose a framework for comparing the value of different life
detection missions:
Scientific value = (Reach x grasp x certainty x payoff) / \$
After discussing each term in this framework, we conclude that scientific
value is maximized if life detection missions are flown as hypothesis tests.
With hypothesis testing, even a nondetection is scientifically valuable.Comment: Accepted by "Astrobiology.
Thermodynamic Limits on Magnetodynamos in Rocky Exoplanets
To ascertain whether magnetic dynamos operate in rocky exoplanets more
massive or hotter than the Earth, we developed a parametric model of a
differentiated rocky planet and its thermal evolution. Our model reproduces the
established properties of Earth's interior and magnetic field at the present
time. When applied to Venus, assuming that planet lacks plate tectonics and has
a dehydrated mantle with an elevated viscosity, the model shows that the dynamo
shuts down or never operated. Our model predicts that at a fixed planet mass,
dynamo history is sensitive to core size, but not to the initial inventory of
long-lived, heat-producing radionuclides. It predicts that rocky planets larger
than 2.5 Earth masses will not develop inner cores because the
temperature-pressure slope of the iron solidus becomes flatter than that of the
core adiabat. Instead, iron "snow" will condense near or at the top of these
cores, and the net transfer of latent heat upwards will suppress convection and
a dynamo. More massive planets can have anemic dynamos due to core cooling, but
only if they have mobile lids (plate tectonics). The lifetime of these dynamos
is shorter with increasing planet mass but longer with higher surface
temperature. Massive Venus-like planets with stagnant lids and more viscous
mantles will lack dynamos altogether. We identify two alternative sources of
magnetic fields on rocky planets: eddy currents induced in the hot or molten
upper layers of planets on very short period orbits, and dynamos in the ionic
conducting layers of "ocean" planets with ~10% mass in an upper mantle of water
(ice).Comment: Accepted to The Astrophysical Journa
A roadmap to the efficient and robust characterization of temperate terrestrial planet atmospheres with JWST
Ultra-cool dwarf stars are abundant, long-lived, and uniquely suited to
enable the atmospheric study of transiting terrestrial companions with JWST.
Amongst them, the most prominent is the M8.5V star TRAPPIST-1 and its seven
planets, which have been the favored targets of eight JWST Cycle 1 programs.
While Cycle 1 observations have started to yield preliminary insights into the
planets, they have also revealed that their atmospheric exploration requires a
better understanding of their host star. Here, we propose a roadmap to
characterize the TRAPPIST-1 system -- and others like it -- in an efficient and
robust manner. We notably recommend that -- although more challenging to
schedule -- multi-transit windows be prioritized to constrain stellar
heterogeneities and gather up to 2 more transits per JWST hour spent.
We conclude that in such systems planets cannot be studied in isolation by
small programs, thus large-scale community-supported programs should be
supported to enable the efficient and robust exploration of terrestrial
exoplanets in the JWST era
The Importance of Thermal Emission Spectroscopy for Understanding Terrestrial Exoplanets
The primary objective of this white paper is to illustrate the importance of the thermal infrared in characterizing terrestrial planets leveraging our experience in characterizing extra-solar jovian worlds
The 16th Data Release of the Sloan Digital Sky Surveys: First Release from the APOGEE-2 Southern Survey and Full Release of eBOSS Spectra
This paper documents the 16th data release (DR16) from the Sloan Digital Sky Surveys (SDSS), the fourth and penultimate from the fourth phase (SDSS-IV). This is the first release of data from the Southern Hemisphere survey of the Apache Point Observatory Galactic Evolution Experiment 2 (APOGEE-2); new data from APOGEE-2 North are also included. DR16 is also notable as the final data release for the main cosmological program of the Extended Baryon Oscillation Spectroscopic Survey (eBOSS), and all raw and reduced spectra from that project are released here. DR16 also includes all the data from the Time Domain Spectroscopic Survey and new data from the SPectroscopic IDentification of ERosita Survey programs, both of which were co-observed on eBOSS plates. DR16 has no new data from the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey (or the MaNGA Stellar Library "MaStar"). We also preview future SDSS-V operations (due to start in 2020), and summarize plans for the final SDSS-IV data release (DR17)
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The 16th Data Release of the Sloan Digital Sky Surveys: First Release from the APOGEE-2 Southern Survey and Full Release of eBOSS Spectra
This paper documents the 16th data release (DR16) from the Sloan Digital Sky Surveys (SDSS), the fourth and penultimate from the fourth phase (SDSS-IV). This is the first release of data from the Southern Hemisphere survey of the Apache Point Observatory Galactic Evolution Experiment 2 (APOGEE-2); new data from APOGEE-2 North are also included. DR16 is also notable as the final data release for the main cosmological program of the Extended Baryon Oscillation Spectroscopic Survey (eBOSS), and all raw and reduced spectra from that project are released here. DR16 also includes all the data from the Time Domain Spectroscopic Survey and new data from the SPectroscopic IDentification of ERosita Survey programs, both of which were co-observed on eBOSS plates. DR16 has no new data from the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey (or the MaNGA Stellar Library "MaStar"). We also preview future SDSS-V operations (due to start in 2020), and summarize plans for the final SDSS-IV data release (DR17)