Abstract
Biosignature gas research has been growing in recent years thanks to next-generation space- and ground-based telescopes. Methanol (CH
3
OH) has many advantages as a biosignature gas ...candidate. First, CH
3
OH’s hydroxyl group (OH) has a unique spectral feature not present in other anticipated gases in the atmospheres of rocky exoplanets. Second, there are no significant known abiotic CH
3
OH sources on terrestrial planets in the solar system. Third, life on Earth produces CH
3
OH in large quantities. However, despite CH
3
OH’s advantages, we consider it a poor biosignature gas in the atmospheres of terrestrial exoplanets due to the enormous production flux required to reach its detection limit. CH
3
OH’s high water solubility makes it very difficult to accumulate in the atmosphere. For the highly favorable planetary scenario of an exoplanet with an H
2
-dominated atmosphere orbiting an M5V dwarf star, we find that only when the column-averaged mixing ratio of CH
3
OH reaches at least 10 ppm can we detect it with the James Webb Space Telescope (JWST). The CH
3
OH bioproduction flux required to reach the JWST detection threshold of 10 ppm must be of the order of 10
14
molecules cm
−2
s
−1
, which is roughly three times the annual O
2
production on Earth. Considering that such an enormous flux of CH
3
OH is essentially a massive waste of organic carbon—a major building block of life, we think this flux, while mathematically possible, is likely biologically unattainable. Although CH
3
OH can theoretically accumulate on exoplanets with CO
2
- or N
2
-dominated atmospheres, such planets’ small atmospheric scale heights and weak atmospheric signals put them out of reach for near-term observations.
Abstract
About 2.5 billion years ago, microbes learned to harness plentiful solar energy to reduce CO
2
with H
2
O, extracting energy and producing O
2
as waste. O
2
production from this metabolic ...process was so vigorous that it saturated its photochemical sinks, permitting it to reach “runaway” conditions and rapidly accumulate in the atmosphere despite its reactivity. Here we argue that O
2
may not be unique: diverse gases produced by life may experience a “runaway” effect similar to O
2
. This runaway occurs because the ability of an atmosphere to photochemically cleanse itself of trace gases is generally finite. If produced at rates exceeding this finite limit, even reactive gases can rapidly accumulate to high concentrations and become potentially detectable. Planets orbiting smaller, cooler stars, such as the M dwarfs that are the prime targets for the James Webb Space Telescope (JWST), are especially favorable for runaway, due to their lower UV emission compared to higher-mass stars. As an illustrative case study, we show that on a habitable exoplanet with an H
2
–N
2
atmosphere and net surface production of NH
3
orbiting an M dwarf (the “Cold Haber World” scenario), the reactive biogenic gas NH
3
can enter runaway, whereupon an increase in the surface production flux of one order of magnitude can increase NH
3
concentrations by three orders of magnitude and render it detectable by JWST in just two transits. Our work on this and other gases suggests that diverse signs of life on exoplanets may be readily detectable at biochemically plausible production rates.
We report the discovery of TOI-172 b from the Transiting Exoplanet Survey Satellite (TESS) mission, a massive hot Jupiter transiting a slightly evolved G star with a 9.48-day orbital period. This is ...the first planet to be confirmed from analysis of only the TESS full frame images, because the host star was not chosen as a two-minute cadence target. From a global analysis of the TESS photometry and follow-up observations carried out by the TESS Follow-up Observing Program Working Group, TOI-172 (TIC 29857954) is a slightly evolved star with an effective temperature of Teff = 5645 50 K, a mass of M = M , radius of R = R , a surface gravity of log g = , and an age of . Its planetary companion (TOI-172 b) has a radius of RP = RJ, a mass of MP = MJ, and is on an eccentric orbit ( ). TOI-172 b is one of the few known massive giant planets on a highly eccentric short-period orbit. Future study of the atmosphere of this planet and its system architecture offer opportunities to understand the formation and evolution of similar systems.
Abstract
New sets of young M dwarfs with complex, sharp-peaked, and strictly periodic photometric modulations have recently been discovered with Kepler/K2 (scallop shells) and TESS (complex ...rotators). All are part of star-forming associations, are distinct from other variable stars, and likely belong to a unified class. Suggested hypotheses include starspots, accreting dust disks, corotating clouds of material, magnetically constrained material, spots and misaligned disks, and pulsations. Here, we provide a comprehensive overview and add new observational constraints with TESS and SPECULOOS Southern Observatory photometry. We scrutinize all hypotheses from three new angles: (1) We investigate each scenario’s occurrence rates via young star catalogs, (2) we study the feature’s longevity using over one year of combined data, and (3) we probe the expected color dependency with multicolor photometry. In this process, we also revisit the stellar parameters accounting for activity effects, study stellar flares as activity indicators over year-long timescales, and develop toy models to simulate typical morphologies. We rule out most hypotheses, and only (i) corotating material clouds and (ii) spots and misaligned disks remain feasible—with caveats. For (i), corotating dust might not be stable enough, while corotating gas alone likely cannot cause percentage-scale features and (ii) would require misaligned disks around most young M dwarfs. We thus suggest a unified hypothesis, a superposition of large-amplitude spot modulations and sharp transits of corotating gas clouds. While the complex rotators’ mystery remains, these new observations add valuable pieces to the puzzle going forward.
We report the discovery of TOI 694 b and TIC 220568520 b, two low-mass stellar companions in eccentric orbits around metal-rich Sun-like stars, first detected by the Transiting Exoplanet Survey ...Satellite (TESS). TOI 694 b has an orbital period of 48.05131 0.00019 days and eccentricity of 0.51946 0.00081, and we derive a mass of 89.0 5.3 (0.0849 0.0051 ) and radius of 1.111 0.017 (0.1142 0.0017 ). TIC 220568520 b has an orbital period of 18.55769 0.00039 days and eccentricity of 0.0964 0.0032, and we derive a mass of 107.2 5.2 (0.1023 0.0050 ) and radius of 1.248 0.018 (0.1282 0.0019 ). Both binary companions lie close to and above the hydrogen-burning mass threshold that separates brown dwarfs and the lowest-mass stars, with TOI 694 b being 2 above the canonical mass threshold of 0.075 . The relatively long periods of the systems mean that the magnetic fields of the low-mass companions are not expected to inhibit convection and inflate the radius, which according to one leading theory is common in similar objects residing in short-period tidally synchronized binary systems. Indeed we do not find radius inflation for these two objects when compared to theoretical isochrones. These two new objects add to the short but growing list of low-mass stars with well-measured masses and radii, and highlight the potential of the TESS mission for detecting such rare objects orbiting bright stars.
Exploration of space has always held a certain fascination for humankind. Stepping foot on the Moon may have been the achievement of the century, and sending humans to Mars will be even more ...challenging and exciting. To achieve self-sufficiency off the Earth, humans will need a steady supply of food while also maintaining adequate mental health. We propose here a closed-loop ecosystem that accomplishes both while being feasible to transport, construct, and maintain on Mars. The resulting design, MarsGarden, is capable of providing a crew of four astronauts with all their dietary needs and also acting as a place of relaxation and restoration. MarsGarden is a scalable architecture that can be adapted to many deep space environments, or can be implemented on Earth as an agricultural solution for areas with land scarcity or extreme environments.
•Sustained life on Mars will require the ability to grow food.•A hydroponics-based greenhouse offers a viable option for food production on Mars.•MarsGarden is designed to maximize food production in a constrained space.•MarsGarden improves the psychological wellbeing of astronauts on Mars.
We produce light curves for all ∼34,000 targets observed with K2 in Campaign 17 (C17), identifying planet candidates, eclipsing binaries, and other periodic variables. The forward-facing direction of ...the C17 field means follow-up can begin immediately now that the campaign has concluded and interesting targets have been identified. The C17 field has a large overlap with C6, so this latest campaign also offers an infrequent opportunity to study a large number of targets already observed in a previous K2 campaign. The timing of the C17 data release, shortly before science operations begin with the Transiting Exoplanet Survey Satellite (TESS), also lets us exercise some of the tools and methods developed for identification and dissemination of planet candidates from TESS. We find excellent agreement between these results and those identified using only K2-based tools. Among our planet candidates are several planet candidates with sizes <4 R⊕ and orbiting stars with Kp 10 (indicating good RV targets of the sort TESS hopes to find) and a Jupiter-sized single-transit event around a star already hosting a 6 day planet candidate.
Venusian phosphine: a ‘wow!’ signal in chemistry? Bains, William; Petkowski, Janusz J.; Seager, Sara ...
Phosphorus, sulfur, and silicon and the related elements,
2022, Letnik:
197, Številka:
5-6
Journal Article
Recenzirano
Odprti dostop
The potential detection of ppb levels phosphine (PH3) in the clouds of Venus through millimeter-wavelength astronomical observations is extremely surprising as PH3 is an unexpected component of an ...oxidized environment of Venus. A thorough analysis of potential sources suggests that no known process in the consensus model of Venus’ atmosphere or geology could produce PH3 at anywhere near the observed abundance. Therefore, if the presence of PH3 in Venus’ atmosphere is confirmed, it is highly likely to be the result of a process not previously considered plausible for Venusian conditions. The source of atmospheric PH3 could be unknown geo- or photochemistry, which would imply that the consensus on Venus’ chemistry is significantly incomplete. An even more extreme possibility is that strictly aerial microbial biosphere produces PH3. This paper summarizes the Venusian PH3 discovery and the scientific debate that arose since the original candidate detection one year ago.
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