Quote from: ExoExplorer on 07/11/2018 06:32 amQuote from: CuddlyRocket on 07/06/2018 07:59 amAn asteroseismic view of the radius valley: stripped cores, not born rocky (arXiv accepted paper)[Snipped abstract]It seems that things have rapidly moved on from the question as to whether there is a 'Fulton gap' to questions about the characterisation of that gap! I also note that the gap itself is being used to clearly delineate super-Earths from sub-Neptunes. Previously it seemed that people used these as synonyms for exoplanets with sizes between Earth and Neptune.Of course the use of Earth and Neptune in a classification scheme is, if not entirely arbitrary, somewhat anthropocentric. After all, there's no clear distinction between a super-Earth, Earth and, say, Venus, or between a sub-Neptune, Neptune and, say, Uranus. I suspect that sooner or later these terms will give way to classifications that span these objects and have the gap as their upper and lower bounds.There is something different between Earth and super-Earths, and Neptune and sub-Neptunes. The ambiguity of these dictions lead people to think super-Earths are just the scaled up Earth and sub-Neptunes are just simply the scaled down Neptune with no clear compositional or formational distinctions, defining the boundary is just the matter of time.In fact, they actually represent totally distinct planet populations which do not present in our solar system. Solar system planets can be compositionally categorized into three groups: rocky planets with little ice (<1%) and no gases (Mercury, Venus, Earth and Mars), gaseous (>80%) planets with little rocks and ice (Jupiter, Saturn), and icy (>50%) planets with little gases (<20%) and rocks (Neptune, Uranus). Based on the location of the gap and atmospheric escape models, now we have a good reason to suspect that the majority of planets with radius under 1.6 (the so-called super-Earths) is actually rocky planets with >1% gases and no ice, but the atmospheres were blown away during later evolution. This population implies a formation process of rocky planets that is complete different from that of solar system rocky planets. Most planets with radius between 1.6 and 3 might share similar formation process (mainly rock with higher mass fraction of gases) with super-Earths but are enveloped by higher mass fraction of gases which could not be blown away. That is exactly why we need ARIEL to show us how alien these planets are. Ah, the vagaries of astronomical terminology! It seemed to me (I could, of course, be under a misapprehension; but, that's how it seemed to me) that initially the term 'super-Earth' simply meant any planet with a mass bigger than Earth but less than Neptune and the term 'sub-Neptune' meant any planet with a mass less than Neptune but bigger than Earth. The overlap was obvious, but different astronomers preferred one or the other and as there was no scientific justification at the time to prefer one or the other both terms persisted. There was a tendency over time for some people to prefer 'super-Earth' for objects at the lower end of that mass range and 'sub-Neptune' for those at the upper, but nothing definitive until the demonstration of the Fulton or radius gap gave a clear(ish) boundary to hang such a distinction on. And that's where it seems to me the position is at present!(One wrinkle is that people initially defined these terms with reference to the planet's mass (as given by radial velocity detections) but this is giving way to defining them with reference to the radius (as given by transit detections). There is some correlation of course, but both definitions seem to be persisting and should ideally be sorted out! Perhaps the use of r and m subscripts? )I take your point about the different formation histories of the rocky planets of the solar system and those in the gap itself. Perhaps these should indeed be put into separate classes with (presumably!) the term super-Earth being reserved for the class which has the Earth as a member. And something similar for the term sub-Neptune? If so, this makes the mass or radius of the Earth and Neptune seem even more arbitrary as boundaries for these classes! What would be the real distinction between Venus, Earth and a super-Earth, etc?My one caveat in having different classification classes for such objects based on their formation history is that although the distinction is clear conceptually, in practice how easy is it to determine the formation history of a particular object?
Quote from: CuddlyRocket on 07/06/2018 07:59 amAn asteroseismic view of the radius valley: stripped cores, not born rocky (arXiv accepted paper)[Snipped abstract]It seems that things have rapidly moved on from the question as to whether there is a 'Fulton gap' to questions about the characterisation of that gap! I also note that the gap itself is being used to clearly delineate super-Earths from sub-Neptunes. Previously it seemed that people used these as synonyms for exoplanets with sizes between Earth and Neptune.Of course the use of Earth and Neptune in a classification scheme is, if not entirely arbitrary, somewhat anthropocentric. After all, there's no clear distinction between a super-Earth, Earth and, say, Venus, or between a sub-Neptune, Neptune and, say, Uranus. I suspect that sooner or later these terms will give way to classifications that span these objects and have the gap as their upper and lower bounds.There is something different between Earth and super-Earths, and Neptune and sub-Neptunes. The ambiguity of these dictions lead people to think super-Earths are just the scaled up Earth and sub-Neptunes are just simply the scaled down Neptune with no clear compositional or formational distinctions, defining the boundary is just the matter of time.In fact, they actually represent totally distinct planet populations which do not present in our solar system. Solar system planets can be compositionally categorized into three groups: rocky planets with little ice (<1%) and no gases (Mercury, Venus, Earth and Mars), gaseous (>80%) planets with little rocks and ice (Jupiter, Saturn), and icy (>50%) planets with little gases (<20%) and rocks (Neptune, Uranus). Based on the location of the gap and atmospheric escape models, now we have a good reason to suspect that the majority of planets with radius under 1.6 (the so-called super-Earths) is actually rocky planets with >1% gases and no ice, but the atmospheres were blown away during later evolution. This population implies a formation process of rocky planets that is complete different from that of solar system rocky planets. Most planets with radius between 1.6 and 3 might share similar formation process (mainly rock with higher mass fraction of gases) with super-Earths but are enveloped by higher mass fraction of gases which could not be blown away. That is exactly why we need ARIEL to show us how alien these planets are.
An asteroseismic view of the radius valley: stripped cores, not born rocky (arXiv accepted paper)[Snipped abstract]It seems that things have rapidly moved on from the question as to whether there is a 'Fulton gap' to questions about the characterisation of that gap! I also note that the gap itself is being used to clearly delineate super-Earths from sub-Neptunes. Previously it seemed that people used these as synonyms for exoplanets with sizes between Earth and Neptune.Of course the use of Earth and Neptune in a classification scheme is, if not entirely arbitrary, somewhat anthropocentric. After all, there's no clear distinction between a super-Earth, Earth and, say, Venus, or between a sub-Neptune, Neptune and, say, Uranus. I suspect that sooner or later these terms will give way to classifications that span these objects and have the gap as their upper and lower bounds.
According to the standard tale, Earth’s water was imported. The region around the sun where the planet formed was too hot for volatile compounds like water to condense. So the nascent Earth started out dry, getting wet only after water-rich bodies from the distant solar system crashed into the planet, delivering water to the surface. Most of these were likely not comets but rather asteroids called carbonaceous chondrites, which can be up to 20 percent water by weight, storing it in a form of hydrogen like ringwoodite.But if there’s a huge stockpile of water in the transition zone, this story of water’s origin would have to change. If the transition zone could store 1 percent of its weight in water — a moderate estimate, Jacobsen said — it would contain twice the world’s oceans. The lower mantle is much drier but also voluminous. It could amount to all the world’s oceans (again). There’s water in the crust, too. For subduction to incorporate that much water from the surface at the current rate, it would take much longer than the age of the planet, Jacobsen said.
It may come as a surprise, then, that astronomers still find new moons orbiting the largest planet in the solar system. But 12 more moons were just discovered, bringing the total to 79, the most of any planet that orbits the sun. These small moons were not discovered by a spacecraft, but rather by powerful telescopes on Earth—and by a team, led by Carnegie Institution for Science astronomer Scott Sheppard, that didn't even set out to look for them."These moons are the last remnants of the objects that the planets were built from," Sheppard tells Popular Mechanics via email. "Most of the small objects that helped build the planets we see today were incorporated into the planets themselves, and these moons are all that remains."
There's something strange about the outer solar system — and that could be the signature of a long-ago visit to our neighborhood, according to a new study that looked to simulate how the outer solar system might have ended up so oddly arranged.
Disc galaxies like our own Milky Way, characterized by a flattened disc of stars and gas (often with a central bulge of material as well) have a wide range of masses, spatial extents, and stellar content. Nonetheless all disc galaxies, both locally and in the distant Universe, share some strikingly similar properties. Most notable is that the star formation rate correlates tightly with the galaxy’s gas content, the gas motions (the "velocity dispersion"), and the dynamical lifetime (roughly, the time it takes for the galaxy to rotate once). Moreover, this curiously universal rate is remarkably small: only about one per cent of the gas in disc galaxies turns into stars over that timescale, with much of the activity concentrated in the galaxies’ central regions. Most simple models of star formation predict that gravity should be much more effective in forming stars as it compresses the gas in molecular clouds. Observations indicate that both the correlations and the inefficiency extend down to the scale of individual molecular clouds.
(Abstract)The Dharma Planet Survey (DPS) aims to monitor about 150 nearby very bright FGKM dwarfs (within 50 pc) during 2016−2020 for low-mass planet detection and characterization using the TOU very high resolution optical spectrograph (R≈100,000, 380-900nm). TOU was initially mounted to the 2-m Automatic Spectroscopic Telescope at Fairborn Observatory in 2013-2015 to conduct a pilot survey, then moved to the dedicated 50-inch automatic telescope on Mt. Lemmon in 2016 to launch the survey. Here we report the first planet detection from DPS, a super-Earth candidate orbiting a bright K dwarf star, HD 26965. It is the second brightest star (V = 4.4 mag) on the sky with a super-Earth candidate. The planet candidate has a mass of 8.47±0.47MEarth, period of 42.38 ± 0.01 d, and eccentricity of 0.04+0.05−0.03. This RV signal was independently detected by Diaz et al. (2018), but they could not confirm if the signal is from a planet or from stellar activity. The orbital period of the planet is close to the rotation period of the star (39−44.5 d) measured from stellar activity indicators. Our high precision photometric campaign and line bisector analysis of this star do not find any significant variations at the orbital period. Stellar RV jitters modeled from star spots and convection inhibition are also not strong enough to explain the RV signal detected. After further comparing RV data from the star’s active magnetic phase and quiet magnetic phase, we conclude that the RV signal is due to planetary-reflex motion and not stellar activity.
Every target will be initially observed ∼30 consecutive observable nights to target close-in low-mass planets detection. After that, each target will be observed an additional ∼70 times randomly spread over 420 days. The automatic nature of the 50-inch telescope and its flexible queue observation schedule are key to realizing this nearly homogenous high cadence.
Black holes aren’t surrounded by a burning ring of fire after all, suggests new research.Some physicists have believed in a “firewall” around the perimeter of a black hole that would incinerate anything sucked into its powerful gravitational pull.But a team from The Ohio State University has calculated an explanation of what would happen if an electron fell into a typical black hole, with a mass as big as the sun.
This paper explores the physics of the what-if question "what if the entire Earth was instantaneously replaced with an equal volume of closely packed, but uncompressed blueberries?" While the assumption may be absurd, the consequences can be explored rigorously using elementary physics. The result is not entirely dissimilar to a small ocean-world exoplanet.
It’s natural to assume even our 4.6 billion-year-old sun had a messy heyday in its youth, but without any hard evidence to prove this was case, the only thing many scientists had going for them were strong suspicions. New data, focused around a peculiar set of ancient blue crystals from space, seems to suggest the sun emitted a much higher flux of cosmic rays in its early history than we once thought.Those blue crystals are called hibonite, and they’ve arrived here on Earth by way of meteorite impacts. Hibonite are effectively some of the first minerals formed in the solar system, created by the cooling gas derived from the sun. The new study, published in Nature Astronomy, focuses on the Murchison meteorite, which fell in Australia in 1969, likely originating from an asteroid in the asteroid belt—and which possesses pieces of micron barely larger than the width of human hair.
There may be more habitable planets in the universe than we previously thought, according to Penn State geoscientists, who suggest that plate tectonics—long assumed to be a requirement for suitable conditions for life—are in fact not necessary.