93 research outputs found
The Carbon-Deficient Evolution of TRAPPIST-1c
Transiting planets orbiting M dwarfs provide the best opportunity to study
the atmospheres of rocky planets with current facilities. As JWST enters its
second year of science operations, an important initial endeavor is to
determine whether these rocky planets have atmospheres at all. M dwarf host
stars are thought to pose a major threat to planetary atmospheres due to their
high magnetic activity over several billion-year timescales, and might
completely strip atmospheres. Several Cycle 1 and 2 GO and GTO programs are
testing this hypothesis, observing a series of rocky planets to determine
whether they retained their atmospheres. A key case-study is TRAPPIST-1c, which
receives almost the same bolometric flux as Venus. We might, therefore, expect
TRAPPIST-1c to possess a thick, -dominated atmosphere. Instead,
Zieba et al. (2023) show that TRAPPIST-1c has little to no CO in its
atmosphere. To interpret these results, we run coupled time-dependent
simulations of planetary outgassing and atmospheric escape to model the
evolution of TRAPPIST-1c's atmosphere. We find that the stellar wind stripping
that is expected to occur on TRAPPIST-1c over its lifetime can only remove up
to bar of , less than the modern
inventory of either Earth or Venus. Therefore, we infer that TRAPPIST-1c either
formed volatile-poor, as compared to Earth and Venus, or lost a substantial
amount of during an early phase of hydrodynamic hydrogen
escape. Finally, we scale our results for the other TRAPPIST-1 planets, finding
that the more distant TRAPPIST-1 planets may readily retain atmospheres.Comment: 16 pages, 11 figures, 1 table, accepted to Ap
Report on the State of Available Data for the Study of International Trade and Foreign Direct Investment
This report, prepared for the Committee on Economic Statistics of the American Economic Association, examines the state of available data for the study of international trade and foreign direct investment. Data on values of imports and exports of goods are of high quality and coverage, but price data suffer from insufficient detail. It would be desirable to have more data measuring value-added in trade as well as prices of comparable domestic and imported inputs. Value data for imports and exports of services are too aggregated and valuations are questionable, while price data for service exports and imports are almost non-existent. Foreign direct investment data are of high quality but quality has suffered from budget cuts. Data on trade in intellectual property are fragmentary. The intangibility of the trade makes measurement difficult, but budget cuts have added to the difficulties. Modest funding increases would result in data more useful for research and policy analysis.
Mantle Degassing Lifetimes through Galactic Time and the Maximum Age Stagnant-lid Rocky Exoplanets can Support Temperate Climates
The ideal exoplanets to search for life are those within a star's habitable
zone. However, even within the habitable zone planets can still develop
uninhabitable climate states. Sustaining a temperate climate over geologic
(Gyr) timescales requires a planet contain sufficient internal energy to
power a planetary-scale carbon cycle. A major component of a rocky planet's
energy budget is the heat produced by the decay of radioactive elements,
especially K, Th, U and U. As the planet ages
and these elements decay, this radiogenic energy source dwindles. Here we
estimate the probability distribution of the amount of these heat producing
elements (HPEs) that enter into rocky exoplanets through Galactic history, by
combining the system-to-system variation seen in stellar abundance data with
the results from Galactic chemical evolution models. Using these distributions,
we perform Monte-Carlo thermal evolution models that maximize the mantle
cooling rate. This allows us to create a pessimistic estimate of lifetime a
rocky, stagnant-lid exoplanet can support a global carbon cycle and temperate
climate as a function of its mass and when it in Galactic history. We apply
this framework to a sample of 17 likely rocky exoplanets with measured ages, 7
of which we predict are likely to be actively degassing today despite our
pessimistic assumptions. For the remaining planets, including those orbiting
TRAPPIST-1, we cannot confidently assume they currently contain sufficient
internal heat to support mantle degassing at a rate sufficient to sustain a
global carbon cycle or temperate climate without additional tidal heating or
undergoing plate tectonics.Comment: Accepted to ApJ Letter
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