Astronomy and Planetary Science Thread

Flyaway

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Venus’ clouds too dry, acidic for life


Here’s the related paper:


They also ruled out life in the Martian atmosphere and the upper atmosphere of Earth. But not some places in Jupiter’s atmosphere.
 

FighterJock

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Venus’ clouds too dry, acidic for life


Here’s the related paper:


They also ruled out life in the Martian atmosphere and the upper atmosphere of Earth. But not some places in Jupiter’s atmosphere.

A shame about Venus’s atmosphere not being suitable for life, it is also interesting about the possibility of life in some parts of Jupiter’s atmosphere.
 

Flyaway

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An Extreme Supernova Lit The Skies 1,000 Years Ago. We May Finally Know Its Type

Based on an analysis of a more recent supernova labeled SN 2018zd, astronomers think both SN 2018zd and the 1054 CE supernova are electron-capture supernovae – a rare third type of supernova alongside type I (thermonuclear) and type II (core collapse).

Experts have hypothesized about this third type of exploding star for decades at this point, though actual physical evidence of electron-capture supernovae has been difficult to come by. The unusual characteristics of SN 2018zd – a mere 31 million light-years away – may be the first one we've actually properly identified.


Here’s the related paper:

The electron-capture origin of supernova 2018zd

Abstract
In the transitional mass range (~8–10 solar masses) between white dwarf formation and iron core-collapse supernovae, stars are expected to produce an electron-capture supernova. Theoretically, these progenitors are thought to be super-asymptotic giant branch stars with a degenerate O + Ne + Mg core, and electron capture onto Ne and Mg nuclei should initiate core collapse1,2,3,4. However, no supernovae have unequivocally been identified from an electron-capture origin, partly because of uncertainty in theoretical predictions. Here we present six indicators of electron-capture supernovae and show that supernova 2018zd is the only known supernova with strong evidence for or consistent with all six: progenitor identification, circumstellar material, chemical composition5,6,7, explosion energy, light curve and nucleosynthesis8,9,10,11,12. For supernova 2018zd, we infer a super-asymptotic giant branch progenitor based on the faint candidate in the pre-explosion images and the chemically enriched circumstellar material revealed by the early ultraviolet colours and flash spectroscopy. The light-curve morphology and nebular emission lines can be explained by the low explosion energy and neutron-rich nucleosynthesis produced in an electron-capture supernova. This identification provides insights into the complex stellar evolution, supernova physics, cosmic nucleosynthesis and remnant populations in the transitional mass range.

 

Flyaway

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It’s Time To Retire The Super-Earth, The Most Unsupported Idea In Exoplanets

What came as a bit of a surprise to many, however, was where that transition point occurred. Many scientists working on exoplanets — based on no physical motivation in particular — had drawn an imaginary line at about two Earth radii in their minds: below that, and you’re likely to be rocky, above that, and you’re likely to be gas-rich. The simplest way to tell, of course, would be to look at the density of your planet. In our own Solar System, the rocky planets and the gas-rich planets possess enormously different densities, so if you’re two Earth radii and still rocky, you’d expect such a planet to have about eight times the mass of Earth.

But when the data came in, it showed something remarkable: there is a transition between rocky planets and gas-rich planets, but it occurs much, much earlier, at about two Earth masses, or just 1.2 to 1.3 Earth radii. There appears to be some variety in exoplanets above that size/mass, with most of them appearing to be miniature versions of Neptune, but with a few of them, perhaps all the way up to 1.5 or even 1.6 Earth radii, still being rocky. (The majority of those, interestingly enough, are extremely hot as well.)

There is no need, and in fact it’s harmful, to remain wedded to erroneous assumptions that were made in the early days of exploring a new scientific field. As it stands today, it’s already been some ~5 years since we recognized how exoplanet populations were actually distributed; we now have PhDs who entered graduate school when it was already known that almost everything we currently call a “super-Earth” is not a rocky planet at all. Although there’s still much to learn about these exoplanets, including what’s underneath those atmospheres, we know enough about them to know which worlds are rocky and which ones are more like the gas giants we have. Based on that, now is absolutely the proper time to retire the archaic, inaccurate term, “super-Earth.”

 

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Characteristics of the Basal Interface of the Martian South Polar Layered Deposits

Using radio waves, we investigated the properties of materials lying below the surface of Mars’ south polar regions (South Polar Layered Deposits; “SPLD”). We made maps of the buried surface below the SPLD (“basal interface”) and measured the radar energy reflected by this interface. From these maps, we measured the SPLD volume as 1.6 million cubic kilometers. Additionally, we found that there are multiple areas throughout the south polar region where the energy reflected from the basal interface is unexpectedly higher than that of the surface. Previous analyses of one such region suggested that these stronger reflections could be caused by the presence of an underground lake.

 

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Astronomers Thrill at Giant Comet Flying into Our Solar System

Efforts to study the object since it was announced have been swift. Already a team of astronomers has been able to detect signs of activity, most likely melting ices forming an atmosphere, or “coma,” around its solid nucleus, confirming it to be a comet. “Its brightness has increased a lot, which means that it’s active,” says Rosita Kokotanekova of the European Southern Observatory, who led the observations using a network of telescopes in the Southern Hemisphere. Getting continued rapid observations will be crucial in learning more about the comet. “There might still be a possibility we can see a rotational signal from the nucleus,” Kokotanekova says. “When the activity gets stronger, it will be completely obscured.”
Observing that activity will be enlightening, too, “because we’ve never observed a comet being active so far out [from the sun],” Kokotanekova says. This will allow researchers to probe the regions of the solar system where cometary activity begins. From the object’s initial apparition in DES optics in 2014 to 2018, it did not appear to show activity, meaning it likely “switched on” at some point in the past three years, Fitzsimmons says. “It’s going to give us a really nice ability to study what happens in this transition region—from being a frozen ice ball out in the Oort cloud to a fully active comet in the solar system.”

 

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A highly magnetized and rapidly rotating white dwarf as small as the Moon

Abstract
White dwarfs represent the last stage of evolution of stars with mass less than about eight times that of the Sun and, like other stars, are often found in binaries1,2. If the orbital period of the binary is short enough, energy losses from gravitational-wave radiation can shrink the orbit until the two white dwarfs come into contact and merge3. Depending on the component masses, the merger can lead to a supernova of type Ia or result in a massive white dwarf4. In the latter case, the white dwarf remnant is expected to be highly magnetized5,6 because of the strong magnetic dynamo that should arise during the merger, and be rapidly spinning from the conservation of the orbital angular momentum7. Here we report observations of a white dwarf, ZTF J190132.9+145808.7, that exhibits these properties, but to an extreme: a rotation period of 6.94 minutes, a magnetic field ranging between 600 megagauss and 900 megagauss over its surface, and a stellar radius of 2140+160−230
2140

230
+
160
kilometres, only slightly larger than the radius of the Moon. Such a small radius implies that the star’s mass is close to the maximum white dwarf mass, or Chandrasekhar mass. ZTF J190132.9+145808.7 is likely to be cooling through the Urca processes (neutrino emission from electron capture on sodium) because of the high densities reached in its core.

 

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Observational Evidence for a Thick Disk of Dark Molecular Gas in the Outer Galaxy

Abstract
We present the serendipitous discovery of an extremely broad (ΔVLSR ~ 150 km s−1), faint (Tmb < 10 mK), and ubiquitous 1667 and 1665 MHz ground-state thermal OH emission toward the second quadrant of the outer Galaxy (Rgal > 8 kpc) with the Green Bank Telescope. Originally discovered in 2015, we describe the redundant experimental, observational, and data quality tests of this result over the last five years. The longitude–velocity distribution of the emission unambiguously suggests large-scale Galactic structure. We observe a smooth distribution of OH in radial velocity that is morphologically similar to the H i radial velocity distribution in the outer Galaxy, showing that molecular gas is significantly more extended in the outer Galaxy than previously expected. Our results imply the existence of a thick (−200 pc < z < 200 pc) disk of diffuse (${n}_{{{\rm{H}}}_{2}}$ ~ 5 × 10−3 cm−3) molecular gas in the outer Galaxy previously undetected in all-sky 12CO surveys.


Source: https://www.google.co.uk/amp/s/www....alactic-structure-discovered-by-accident/amp/
 

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Alien Technosignature? The Mysterious Star VVV-WIT-08:

As he says with trying to fit an alien explanation you’re always going to run in the issue of “aliens of the gaps”.

View: https://youtu.be/OgZtPIo-hKE
The Great Daylight Fireball of 1972 (Teton event) stayed in atmosphere for 1,500 km. The grainy Super-8 film of it showed no fragmentation like that from Chelyabinsk or Peekskill. The de facto aerobrake was such that it was to make a resonant return in the 1990’s. In 1993, SMU recorded a linear earthquake that suggested the passage of a strangelet through the Earth. I wonder if there has been any trajectory works suggesting a link, and/or if another return might be had. Seismologists and volcanologists don’t often talk to each other—as per Galeras—so I expect seismologists and astronomers cross pollinate even less. But calculating the orbit of such contraterrene objects might give us potential new missions. Vela, Tunguska are still being looked at…but the SMU linear earthquake.. could that have been Teton?
 

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Study Projects a Surge in Coastal Flooding, Starting in 2030s

In the mid-2030s, every U.S. coast will experience rapidly increasing high-tide floods, when a lunar cycle will amplify rising sea levels caused by climate change.

 

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The problem with this theory isn’t just that it requires active volcanoes on Venus, but explosive active ones at a high level in the recent past to get the phosphides in the amounts where they need to be in the atmosphere.


Biosignature Spotted on Venus Could Be From Volcanoes, Not Life

“The phosphine is not telling us about the biology of Venus,” said Jonathan Lunine, a planetary scientist at Cornell University and co-author of the paper, in a university press release. “It’s telling us about the geology. Science is pointing to a planet that has active explosive volcanism today or in the very recent past.”

But the mystery of whether Venus has phosphine or not, and what might have produced it, is far from settled. “I sadly remain unconvinced by this latest argument,” said Clara Sousa-Silva, a quantum astrochemist at the Center for Astrophysics | Harvard and Smithsonian, in an email. “The reaction of mineral phosphides with concentrated sulfuric acid will not necessarily generate phosphine. ... A likely outcome of reacting phosphides with concentrated sulfuric acid would be an oxidation reaction and not production of phosphine.”

Sousa-Silva’s previous work has examined the atmospheres of Venus and other planets for potential signs of life like phosphine. She added, “we have known (and stated as much, repeatedly) that there are abiotic routes for the formation of phosphine, including volcanism. It’s just that these routes are extremely rare and inefficient.”

 

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A Single-Year Cosmic Ray Event at 5410 BCE Registered in 14C of Tree Rings

Plain Language Summary
The 14C data of tree rings register extreme storms of solar energetic particles (SEPs), far larger than the largest SEP event ever observed in the Space Era. So far, three extreme SEP events have been reported as a rapid 14C increase in tree rings and 10Be and 36Cl increases in ice cores. In this study, we found a new rapid 14C increase in 5410 BCE using annual 14C content in ring samples from California, Switzerland, and Finland. The 14C signature of 5410 BCE event ties the origin of this 14C excursion to an extreme SEP event similar to three other extreme SEP events (774/775 CE, 992/993 CE, and ∼660 BCE) confirmed with radionuclides of ice cores.


Source: https://phys.org/news/2021-07-tree-newly-extreme-solar-event.html
 

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A hot subdwarf–white dwarf super-Chandrasekhar candidate supernova Ia progenitor

Abstract
Supernovae Ia are bright explosive events that can be used to estimate cosmological distances, allowing us to study the expansion of the Universe. They are understood to result from a thermonuclear detonation in a white dwarf that formed from the exhausted core of a star more massive than the Sun. However, the possible progenitor channels leading to an explosion are a long-standing debate, limiting the precision and accuracy of supernovae Ia as distance indicators. Here we present HD 265435, a binary system with an orbital period of less than a hundred minutes that consists of a white dwarf and a hot subdwarf, which is a stripped core-helium-burning star. The total mass of the system is 1.65 ± 0.25 solar masses, exceeding the Chandrasekhar limit (the maximum mass of a stable white dwarf). The system will merge owing to gravitational wave emission in 70 million years, likely triggering a supernova Ia event. We use this detection to place constraints on the contribution of hot subdwarf–white dwarf binaries to supernova Ia progenitors.


Source: http://www.sci-news.com/astronomy/hd-265435-type-ia-supernova-progenitor-09857.html
 

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Not sure if I've posted this before, but its Shostakovich and I'll take any excuse to bring him up. I like the rough imagery - this one's all editing, no CGI. As a young man, DSCH earned money playing the piano at cinemas, so I can imagine him under the flickering black and white imagery. The Kubrickian reference is canny too - in the original drafts of 2001, Discovery was to go to Saturn (the monolith would be on Iapetus) and this remained so in the novel, but Mr K was not happy with the special effects. Doug Trumbull later went on to use Saturn as a backdrop for Silent Running. As for the waltz, Kubrick used it in Eyes Wide Shut. So it goes, round and round.
View: https://www.youtube.com/watch?v=VnyuQjegeFk
 

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Methane in the plumes of Saturn's moon Enceladus: Possible signs of life?

An unknown methane-producing process is likely at work in the hidden ocean beneath the icy shell of Saturn's moon Enceladus, suggests a new study published in Nature Astronomy by scientists at the University of Arizona and Paris Sciences & Lettres University.


Related paper:

Bayesian analysis of Enceladus’s plume data to assess methanogenesis

Abstract
Observations from NASA’s Cassini spacecraft established that Saturn’s moon Enceladus has an internal liquid ocean. Analysis of a plume of ocean material ejected into space suggests that alkaline hydrothermal vents are present on Enceladus’s seafloor. On Earth, such deep-sea vents harbour microbial ecosystems rich in methanogenic archaea. Here we use a Bayesian statistical approach to quantify the probability that methanogenesis (biotic methane production) might explain the escape rates of molecular hydrogen and methane in Enceladus’s plume, as measured by Cassini instruments. We find that the observed escape rates (1) cannot be explained solely by the abiotic alteration of the rocky core by serpentinization; (2) are compatible with the hypothesis of habitable conditions for methanogens; and (3) score the highest likelihood under the hypothesis of methanogenesis, assuming that the probability of life emerging is high enough. If the probability of life emerging on Enceladus is low, the Cassini measurements are consistent with habitable yet uninhabited hydrothermal vents and point to unknown sources of methane (for example, primordial methane) awaiting discovery by future missions.

 

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EHT Pinpoints Dark Heart of the Nearest Radio Galaxy

In a new paper published Monday in Nature Astronomy, data from the 2017 Event Horizon Telescope (EHT) observations have been analyzed to image Centaurus A in unprecedented detail.

"This allows us for the first time to see and study an extragalactic radio jet on scales smaller than the distance light travels in one day. We see up close and personal how a monstrously gigantic jet launched by a supermassive black hole is being born,” says astronomer Michael Janssen of the Max Planck Institute for Radio Astronomy and Radboud University.

The researchers predict that future observations at an even shorter wavelength and higher resolution will be able to photograph the central black hole of Centaurus A. This will require the use of space-based satellite observatories.

“These data are from the same observing campaign that delivered the famous image of the black hole in M87. The new results show that the EHT provides a treasure trove of data on the rich variety of black holes and there is still more to come”, says Heino Falcke, EHT board member and professor for astrophysics at Radboud University.


Event Horizon Telescope observations of the jet launching and collimation in Centaurus A

Abstract
Very-long-baseline interferometry (VLBI) observations of active galactic nuclei at millimetre wavelengths have the power to reveal the launching and initial collimation region of extragalactic radio jets, down to 10–100 gravitational radii (rg ≡ GM/c2) scales in nearby sources1. Centaurus A is the closest radio-loud source to Earth2. It bridges the gap in mass and accretion rate between the supermassive black holes (SMBHs) in Messier 87 and our Galactic Centre. A large southern declination of −43° has, however, prevented VLBI imaging of Centaurus A below a wavelength of 1 cm thus far. Here we show the millimetre VLBI image of the source, which we obtained with the Event Horizon Telescope at 228 GHz. Compared with previous observations3, we image the jet of Centaurus A at a tenfold higher frequency and sixteen times sharper resolution and thereby probe sub-lightday structures. We reveal a highly collimated, asymmetrically edge-brightened jet as well as the fainter counterjet. We find that the source structure of Centaurus A resembles the jet in Messier 87 on ~500 rg scales remarkably well. Furthermore, we identify the location of Centaurus A’s SMBH with respect to its resolved jet core at a wavelength of 1.3 mm and conclude that the source’s event horizon shadow4 should be visible at terahertz frequencies. This location further supports the universal scale invariance of black holes over a wide range of masses5,6.

 

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Chunk of an ancient supercontinent discovered under New Zealand

As the California heat blazed outside in the summer of 2018, Rose Turnbull sat in the cool confines of a windowless basement sorting through grains of fine sand. A geologist based in New Zealand, Turnbull was in a colleague’s lab at California State University, Northridge, trying to find tiny crystals of zircon, which she hoped would help unravel secrets of the mysterious eighth continent of Zealandia, also known by its Māori name Te Riu-a-Māui.

The task required a practiced hand and a bit of elbow grease—or rather, nose grease. Turnbull demonstrates over Zoom, raising the closed tweezers to the outside of her nose to pick up a bit of oil, which prevents the grains from zinging across the room when plucked.

The crystals hailed from rocks that were collected from the islands of New Zealand, which are among the few bits of Zealandia's nearly two million square miles that poke above the sea. Only recently recognized by scientists, Zealandia is the most submerged, thinnest, and youngest continent yet found. Turnbull, who works at the research and consulting group GNS Science in New Zealand, and her colleagues wanted to know more about the processes that shaped this unusual landmass.


A hidden Rodinian lithospheric keel beneath Zealandia, Earth’s newly recognized continent

We present a data set of >1500 in situ O-Hf-U-Pb zircon isotope analyses that document the existence of a concealed Rodinian lithospheric keel beneath continental Zealandia. The new data reveal the presence of a distinct isotopic domain of Paleozoic–Mesozoic plutonic rocks that contain zircon characterized by anomalously low δ18O values (median = +4.1‰) and radiogenic εHf(t) (median = +6.1). The scale (>10,000 km2) and time span (>>250 m.y.) over which plutonic rocks with this anomalously low-δ18O signature were emplaced appear unique in a global context, especially for magmas generated and emplaced along a continental margin. Calculated crustal-residence ages (depleted mantle model, TDM) for this low-δ18O isotope domain range from 1300 to 500 Ma and are interpreted to represent melting of a Precambrian lithospheric keel that was formed and subsequently hydrothermally altered during Rodinian assembly and rifting. Recognition of a concealed Precambrian lithosphere beneath Zealandia and the uniqueness of the pervasive low-δ18O isotope domain link Zealandia to South China, providing a novel test of specific hypotheses of continental block arrangements within Rodinia.

 

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A peculiarly short-duration gamma-ray burst from massive star core collapse

Abstract
Gamma-ray bursts (GRBs) have been phenomenologically classified into long and short populations based on the observed bimodal distribution of duration1. Multi-wavelength and multi-messenger observations in recent years have revealed that in general long GRBs originate from massive star core collapse events2, whereas short GRBs originate from binary neutron star mergers3. It has been known that the duration criterion is sometimes unreliable, and multi-wavelength criteria are needed to identify the physical origin of a particular GRB4. Some apparently long GRBs have been suggested to have a neutron star merger origin5, whereas some apparently short GRBs have been attributed to genuinely long GRBs6 whose short, bright emission is slightly above the detector’s sensitivity threshold. Here, we report the comprehensive analysis of the multi-wavelength data of the short, bright GRB 200826A. Characterized by a sharp pulse, this burst shows a duration of 1 second and no evidence of an underlying longer-duration event. Its other observational properties such as its spectral behaviours, total energy and host galaxy offset are, however, inconsistent with those of other short GRBs believed to originate from binary neutron star mergers. Rather, these properties resemble those of long GRBs. This burst confirms the existence of short-duration GRBs with stellar core-collapse origin4, and presents some challenges to the existing models.


Discovery and confirmation of the shortest gamma-ray burst from a collapsar

Abstract
Gamma-ray bursts (GRBs) are among the brightest and most energetic events in the Universe. The duration and hardness distribution of GRBs has two clusters1, now understood to reflect (at least) two different progenitors2. Short-hard GRBs (SGRBs; T90 < 2 s) arise from compact binary mergers, and long-soft GRBs (LGRBs; T90 > 2 s) have been attributed to the collapse of peculiar massive stars (collapsars)3. The discovery of SN 1998bw/GRB 980425 (ref. 4) marked the first association of an LGRB with a collapsar, and AT 2017gfo (ref. 5)/GRB 170817A/GW170817 (ref. 6) marked the first association of an SGRB with a binary neutron star merger, which also produced a gravitational wave. Here, we present the discovery of ZTF20abwysqy (AT2020scz), a fast-fading optical transient in the Fermi satellite and the Interplanetary Network localization regions of GRB 200826A; X-ray and radio emission further confirm that this is the afterglow. Follow-up imaging (at rest-frame 16.5 days) reveals excess emission above the afterglow that cannot be explained as an underlying kilonova, but which is consistent with being the supernova. Although the GRB duration is short (rest-frame T90 of 0.65 s), our panchromatic follow-up data confirm a collapsar origin. GRB 200826A is the shortest LGRB found with an associated collapsar; it appears to sit on the brink between a successful and a failed collapsar. Our discovery is consistent with the hypothesis that most collapsars fail to produce ultra-relativistic jets.


Source: https://www.google.co.uk/amp/s/scit...igh-energy-radiation-racing-toward-earth/amp/
 

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A neighbouring Planetary system reveals its secrets (ESO cast 242 Light):

View: https://youtu.be/BfnlIoapky0
A team of astronomers have used ESO’s Very Large Telescope in Chile to shed new light on planets around a nearby star that resemble those in the inner Solar System. This video summarises what they found about the planetary system, called L 98-59.
 

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One Year in the Life of Young Suns: Data Constrained Corona-Wind Model of kappa1 Ceti

The young magnetically active solar-like stars are efficient generators of ionizing radiation in the form of X-ray and Extreme UV (EUV) flux, stellar wind and eruptive events. These outputs are the critical factors affecting atmospheric escape and chemistry of (exo)planets around active stars. While X-ray fluxes and surface magnetic fields can be derived from observations, the EUV emission and wind mass fluxes, Coronal Mass Ejections and associated Stellar Energetic Particle events cannot be directly observed. Here, we present the results of a three-dimensional magnetohydrodynamic (MHD) model with inputs constrained by spectropolarimetric data, HST/STIS Far UV, X-ray data data and stellar magnetic maps reconstructed at two epochs separated by 11 months. The simulations show that over the course of the year, the global stellar corona had undergone a drastic transition from a simple dipole-like to a tilted dipole with multipole field components, and thus, provided favorable conditions for Corotating Interaction Events (CIRs) that drive strong shocks. The dynamic pressure exerted by CIRs are 1300 times larger than those observed from the Sun and can contribute to the atmospheric erosion of early Venus, Earth, Mars and young Earth-like exoplanets. Our data-constrained MHD model provides the framework to model coronal environments of G-M planet hosting dwarfs. The model outputs can serve as a realistic input for exoplanetary atmospheric models to evaluate the impact of stellar coronal emission, stellar winds and CIRs on their atmospheric escape and chemistry that can be tested in the upcoming JWST and ground-based observations.

 

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