Astronomy and Planetary Science Thread

Flyaway

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About 66 million years ago, an estimated 6-mile-wide (9.6 kilometers) object slammed into Earth, triggering a cataclysmic series of events that resulted in the demise of non-avian dinosaurs.

Now, scientists think they know where that object came from.

According to new research, the impact was caused by a giant dark primitive asteroid from the outer reaches of the solar system's main asteroid belt, situated between Mars and Jupiter. This region is home to many dark asteroids — space rocks with a chemical makeup that makes them appear darker (reflecting very little light) compared with other types of asteroids.

Simulating over hundreds of millions of years, the model showed thermal forces and gravitational tugs from planets periodically slingshotting large asteroids out of the belt. On average, an asteroid more than 6 miles wide from the outer edge of the belt was flung into a collision course with Earth once every 250 million years, the researchers found. This calculation makes such an event five times more common than previously thought and consistent with the Chicxulub crater created just 66 million years ago, which is the only known impact crater thought to have been produced by such a large asteroid in the last 250 million years. Furthermore, the model looked at the distribution of "dark" and "light" impactors in the asteroid belt and showed half of the expelled asteroids were the dark carbonaceous chondrites, which matches the type thought to have caused Chicxulub crater.

 

Flyaway

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The recurrent nova RS Ophiuchi (RS Oph), located in the constellation of Ophiuchus, is in a rare outburst, its first for more than 15 years. RS Oph brightened rapidly on 8 August 2021 from around magnitude +12 to shine presently at about magnitude +4.8, a 600-fold in just a day. This is its first outburst since February 2006 and only five other eruptions have been observed since 1898.

 

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An international team of astronomers using data from NASA’s Juno spacecraft, the W.M. Keck Observatory and Japan’s Hisaki satellite was able to nail down the source of Jupiter’s surprising temperature, reporting their findings in the journal Nature.

“We found that Jupiter’s intense aurora, the most powerful in the solar system, is responsible for heating the entire planet’s upper atmosphere to surprisingly high temperatures,” said James O’Donoghue of the JAXA Institute of Space and Astronautical Science in Sagamihara, Japan.
View: https://youtu.be/pXTpL3DA6yY

 

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Rings around a black hole from X-ray echoes off interstellar dust

Some 7,800 light years from Earth, a black hole is actively sucking in material from a companion star with about half the mass of the Sun. The material forms a disc around the black hole, glowing in X-rays as particles crash together in a swirling inferno. The binary system is known as V404 Cygni and on 5 June 2015, the Swift space telescope detected an X-ray outburst that created a spectacular ring of “light echoes” as the high-energy radiation bounced off intervening clouds of smoke-like interstellar dust. In the composite image below, observations by the Chandra X-ray Telescope (shown in blue) were combined with optical imagery from the Pan-STARRS telescope in Hawaii. Eight concentric X-ray echoes can be seen as radiation reflects off dust at different distances.

 

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Saturn’s core is a big, diffuse, rocky slushball

The process should leave planets like Jupiter and Saturn with a solid, rocky core buried deep within the envelope of gas. But confirming that core composition has been difficult. Now, researchers have used features in Saturn's rings to detect subtle gravitational influences from the core. While not definitive, the results suggest that the core is large, and the solid, rocky portion is widely spread out across that area.

The new work relies on the features of the waves we've detected within Saturn's rings. In essence, the researchers built multiple models of what Saturn's core could look like and check whether the models would create the patterns we actually see. The real-world data is then used to put constraints on the possible elements of Saturn's core.

Overall, the models that fit the data place Saturn's core-envelope boundary a significant distance from the planet's center, roughly 60 percent of the way to the surface. That's a radius of nearly 60,000 kilometers, or over nine times Earth's radius.
The exact composition of the core is much harder to figure out, since the constraints are fairly wide. The total mass of heavier elements in the core is about 19 times Earth's mass, consistent with models of gas-giant formation that place rock and iron at the center, although a lot of this material could also be water ice. Yet the total mass of the core could be as high as 55 times the Earth's mass, indicating that there's a lot of other material there—likely metallic hydrogen and helium.


A diffuse core in Saturn revealed by ring seismology

Abstract
The best constraints on the internal structures of giant planets have historically originated from measurements of their gravity fields1,2,3. These data are inherently mostly sensitive to a planet’s outer regions, stymieing efforts to measure the mass and compactness of the cores of Jupiter2,4,5 and Saturn6,7. However, studies of Saturn’s rings have detected waves driven by pulsation modes within the planet8,9,10,11, offering independent seismic probes of Saturn’s interior12,13,14. The observations reveal gravity-mode pulsations, which indicate that part of Saturn’s deep interior is stable against convection13. Here, we compare structural models with gravity and seismic measurements from Cassini to show that the data can only be explained by a diffuse, stably stratified core–envelope transition region in Saturn extending to approximately 60% of the planet’s radius and containing approximately 17 Earth masses of ice and rock. This gradual distribution of heavy elements constrains mixing processes at work in Saturn, and it may reflect the planet’s primordial structure and accretion history.

 

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Cool Worlds - Could Origami Be The Key to Detecting Exomoons?

View: https://youtu.be/2sXTNfU5pHc

Transit Origami: A Method to Coherently Fold Exomoon Transits in Time Series Photometry

One of the simplest ways to identify an exoplanetary transit is to phase fold a photometric time series upon a trial period - leading to a coherent stack when using the correct value. Such phase-folded transits have become a standard data visualisation in modern transit discovery papers. There is no analogous folding mechanism for exomoons, which would have to represent some kind of double-fold; once for the planet and then another for the moon. Folding with the planet term only, a moon imparts a small decrease in the surrounding out-of-transit averaged intensity, but its incoherent nature makes it far less convincing than the crisp stacks familiar to exoplanet hunters. Here, a new approach is introduced that can be used to achieve the transit origami needed to double fold an exomoon, in the case where a planet exhibits TTVs. This double fold has just one unknown parameter, the satellite-to-planet mass ratio, and thus a simple one-dimensional grid search can be used to rapidly identify power associated with candidate exomoons. The technique is demonstrated on simulated light curves, exploring the breakdown limits of close-in and/or inclined satellites. As an example, the method is deployed on Kepler-973b, a warm mini-Neptune exhibiting an 8 minute TTV, where the possibility that the TTVs are caused by a single exomoon is broadly excluded, with upper limits probing down to a Ganymede-sized moon.

 
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Interstellar objects outnumber Solar system objects in the Oort cloud

ABSTRACT
Here, we show that the detection of Borisov implies that interstellar objects outnumber Solar system objects in the Oort cloud, whereas the reverse is true near the Sun due to the stronger gravitational focusing of bound objects. This hypothesis can be tested with stellar occultation surveys of the Oort cloud. Furthermore, we demonstrate that ∼1 per cent
of carbon and oxygen in the Milky Way Galaxy may be locked in interstellar objects, implying a heavy element budget for interstellar objects comparable to the heavy element budget of the minimum mass Solar nebula model. There is still considerable uncertainty regarding the size distribution of the interstellar objects.

 

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Belatedly Habitable Planets

Abstract
Stars do not remain static, so their habitable zones evolve in time. Over a star's evolution, its habitable zone encompasses new planets, and it remains uncertain whether these planets can become habitable. We refer to this often overlooked class of planets as lying in the belatedly habitable zone, and stress that many planets found in the habitable zones of other stars will belong to this class. Future studies should take belated habitability into account and not implicitly assume that these planets are habitable.

 

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“Anomalous Stellar Acceleration: Causes and Consequences,” JBIS Vol. 74 (2021), pp. 269-275

Abstract:

As a successor to Hipparcus, an earlier European Space Agency (ESA) space telescope, the ESA Gaia space telescope was launched in December 2013 and is currently on-station at the Earth-Sun L2 Lagrange point, about 1.5 x 106km from Earth. The goal of this mission is accurate determination of position and motions for ~1 billion stars in the Milky Way galaxy [1].

 

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Release:


The researchers have identified a new class of habitable planets, dubbed ‘Hycean’ planets – ocean-covered planets with hydrogen-rich atmospheres – which are more numerous and observable than Earth-like planets.

At arXiv:


We investigate a new class of habitable planets composed of water-rich interiors with massive oceans underlying H2-rich atmospheres, referred to here as Hycean worlds. With densities between those of rocky super-Earths and more extended mini-Neptunes, Hycean planets can be optimal candidates in the search for exoplanetary habitability and may be abundant in the exoplanet population. We investigate the bulk properties (masses, radii, and temperatures), potential for habitability, and observable biosignatures of Hycean planets. We show that Hycean planets can be significantly larger compared to previous considerations for habitable planets, with radii as large as 2.6 Earth radii (2.3 Earth radii) for a mass of 10 Earth masses (5 Earth masses). We construct the Hycean habitable zone (HZ), considering stellar hosts from late M to sun-like stars, and find it to be significantly wider than the terrestrial-like HZ. While the inner boundary of the Hycean HZ corresponds to equilibrium temperatures as high as ~500 K for late M dwarfs, the outer boundary is unrestricted to arbitrarily large orbital separations. Our investigations include tidally locked `Dark Hycean' worlds that permit habitable conditions only on their permanent nightsides and `Cold Hycean' worlds that see negligible irradiation. Finally, we investigate the observability of possible biosignatures in Hycean atmospheres. We find that a number of trace terrestrial biomarkers which may be expected to be present in Hycean atmospheres would be readily detectable using modest observing time with the James Webb Space Telescope (JWST). We identify a sizable sample of nearby potential Hycean planets that can be ideal targets for such observations in search of exoplanetary biosignatures.
 

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Fastest-moving asteroid flies closer to Sun than Mercury

Astronomers using the 570-megapixel Dark Energy Camera have found the fastest-moving asteroid yet discovered, a 1-kilometre-wide (0.6-mile-wide) body that crosses the orbits of Venus and Mercury and passes within just 20 million kilometres (12 million miles) of the Sun every 113 days. The asteroid, catalogued as 2021 PH27, heats up to almost 500 Celsius (about 900 Fahrenheit) during close approach, hot enough to melt lead.

The asteroid, catalogued as 2021 PH27, may have originated in the main asteroid belt between Mars and Jupiter, subsequently dislodged by gravitational interactions with the inner planets. But its orbit is tilted 32 degrees to the Sun’s equatorial plane, indicating it could be an extinct comet that ended up in a short-period orbit after passing by a terrestrial planet.

 

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A quarter of Sun-like stars eat their own planets, according to new research

The relatively calm history of our Solar System has favoured the flourishing of life here on Earth. In the search for alien worlds that may contain life, we can narrow down the targets if we have a way to identify systems that have had similarly peaceful pasts.

Our international team of astronomers has tackled this issue in research published in Nature Astronomy. We found that between 20% and 35% of Sun-like stars eat their own planets, with the most likely figure being 27%.


Here’s the related paper:

Chemical evidence for planetary ingestion in a quarter of Sun-like stars

Abstract
Stellar members of binary systems are formed from the same material, and therefore they should be chemically identical. However, recent studies have unveiled chemical differences between the two members of binary pairs composed of Sun-like stars. These chemically inhomogeneous binaries represent one of the most contradictory examples in stellar astrophysics and a source of tension between theory and observations. It is still unclear whether the abundance variations are the result of inhomogeneities in the protostellar gas clouds or are due to planet engulfment events that occurred after the stellar formation. The former scenario undermines the general belief that the chemical makeup of stars provides the fossil information of the environment in which they formed, whereas the second scenario would shed light on the possible evolutionary paths of planetary systems. Our study provides compelling evidence in favour of the planet engulfment scenario. We also establish that planet engulfment events occur in Sun-like stars with a 20–35% probability. Therefore, an important fraction of planetary systems undergo very dynamical evolutionary paths that critically modify their architectures, unlike our calm Solar System. This study opens the possibility of using chemical abundances of stars to identify which ones are the most likely to host Solar System analogues.

 

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Radio evidence of a stellar merger

Core collapse supernovae occur when a massive star exhausts its fuel and explodes. Theorists have predicted that a similar explosion could occur if an evolved massive star merges with a compact companion, such as a neutron star. Dong et al. have identified a radio source that was not present in earlier radio surveys. Follow-up radio and optical spectroscopy show that it is an expanding supernova remnant slamming into surrounding material, probably ejected from the star centuries before it exploded. An unidentified x-ray transient occurred at a consistent location in 2014, suggesting an explosion at that time that produced a jet. The authors suggest that the most likely explanation is a merger-triggered supernova. —KTS


Source: https://www.eurekalert.org/news-releases/927166
 

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First time we’ve had an update in this planet nine business in what feels like ages.

Planet 9 may be closer and easier to find than thought—if it exists
A new study's "treasure map" suggests that a planet several times more massive than Earth could be hiding in our solar system, camouflaged by the bright strip of stars that make up the Milky Way.


Here’s the new paper:
 

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We already have a Planet 9, Pluto, even if it is currently 'unpersoned', in a manner of speaking.

Can we double-like a post? First victim of cancel culture! Content enough for Eris, Sedna et al to be dwarf planets but would personally have "grandfathered in" Pluto.

Pluto was a planet for quite some time. I don't think that history should be discarded so lightly!
 
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The Enigmatic Brown Dwarf WISEA J153429.75-104303.3 (a.k.a. "The Accident")

Abstract
Continued follow-up of WISEA J153429.75−104303.3, announced in Meisner et al., has proven it to have an unusual set of properties. New imaging data from Keck/MOSFIRE and HST/WFC3 shows that this object is one of the few faint proper motion sources known with J − ch2 >8 mag, indicating a very cold temperature consistent with the latest known Y dwarfs. Despite this, it has W1−W2 and ch1−ch2 colors ∼1.6 mag bluer than a typical Y dwarf. A new trigonometric parallax measurement from a combination of WISE, Spitzer, and HST astrometry confirms a nearby distance of ${16.3}_{-1.2}^{+1.4}$ pc and a large transverse velocity of 207.4 ± 15.9 km s−1. The absolute J, W2, and ch2 magnitudes are in line with the coldest known Y dwarfs, despite the highly discrepant W1−W2 and ch1−ch2 colors. We explore possible reasons for the unique traits of this object and conclude that it is most likely an old, metal-poor brown dwarf and possibly the first Y subdwarf. Given that the object has an HST F110W magnitude of 24.7 mag, broadband spectroscopy and photometry from JWST are the best options for testing this hypothesis.

 

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ESO captures best images yet of peculiar “dog-bone” asteroid

Using the European Southern Observatory’s Very Large Telescope (ESO’s VLT), a team of astronomers have obtained the sharpest and most detailed images yet of the asteroid Kleopatra. The observations have allowed the team to constrain the 3D shape and mass of this peculiar asteroid, which resembles a dog bone, to a higher accuracy than ever before. Their research provides clues as to how this asteroid and the two moons that orbit it formed.


Accompanying video:

View: https://youtu.be/3TUjPyDeZec
 

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A search of the full six years of the Dark Energy Survey for outer Solar System objects

We present the results of a search for outer Solar System objects in the full six years of data (Y6) from the Dark Energy Survey (DES). The DES covered a contiguous 5000 deg2 of the southern sky with ≈80,000 3 deg2 exposures in the grizY optical/IR filters between 2013 and 2019. This search yielded 815 trans-Neptunian objects (TNOs), one Centaur and one Oort cloud comet, with 461 objects reported for the first time in this paper. We present methodology that builds upon our previous search carried out on the first four years of data. Here, all DES images were reprocessed with an improved detection pipeline that leads to an average completeness gain of 0.47 mag per exposure, as well as an improved transient catalog production and optimized algorithms for linkage of detections into orbits. All objects were verified by visual inspection and by computing the sub-threshold significance, the total signal-to-noise ratio in the stack of images in which the object's presence is indicated by the orbit fit, but no detection was reported. This yields a highly pure catalog of TNOs complete to r≈23.8 mag and distances 29<d<2500 au. The Y6 TNOs have minimum (median) of 7 (12) distinct nights' detections and arcs of 1.1 (4.2) years, and will have grizY magnitudes available in a further publication. We present software for simulating our observational biases that enable comparisons of population models to our detections. Initial inferences demonstrating the statistical power of the DES catalog are: the data are inconsistent with the CFEPS-L7 model for the classical Kuiper Belt; the 16 ``extreme'' TNOs (a>150 au, q>30 au) are consistent with the null hypothesis of azimuthal isotropy; and non-resonant TNOs with q>38 au, a>50 au show a highly significant tendency to be sunward of the major mean motion resonances, whereas this tendency is not present for q<38 au.


Source: https://www.sciencealert.com/over-4...-in-the-cold-dark-reaches-of-the-solar-system
 

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Physicists at the University of Sussex have discovered that black holes exert a pressure on their environment, in a scientific first.

In 1974 Stephen Hawking made the seminal discovery that black holes emit thermal radiation. Previous to that, black holes were believed to be inert, the final stages of a dying heavy star.

The University of Sussex scientists have shown that they are in fact even more complex thermodynamic systems, with not only a temperature but also a pressure.


Quantum gravitational corrections to the entropy of a Schwarzschild black hole

ABSTRACT
We calculate quantum gravitational corrections to the entropy of black holes using the Wald entropy formula within an effective field theory approach to quantum gravity. The corrections to the entropy are calculated to second order in curvature and we calculate a subset of those at third order. We show that, at third order in curvature, interesting issues appear that had not been considered previously in the literature. The fact that the Schwarzschild metric receives corrections at this order in the curvature expansion has important implications for the entropy calculation. Indeed, the horizon radius and the temperature receive corrections. These corrections need to be carefully considered when calculating the Wald entropy.

 

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