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Exoplanet Stuff

lpetrich

lpetrich

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Simulations explain giant exoplanets with eccentric, close-in orbits -- ScienceDaily
As planetary systems evolve, gravitational interactions between planets can fling some of them into eccentric elliptical orbits around the host star. Smaller planets should be more susceptible to this gravitational scattering, yet many gas giant exoplanets have been observed with eccentric orbits. In fact, the planets with the highest masses tend to be those with the most eccentric orbits. A new study explains these counter-intuitive observations.
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Signatures of a Planet–Planet Impacts Phase in Exoplanetary Systems Hosting Giant Planets - IOPscience
Exoplanetary systems host giant planets on substantially noncircular, close-in orbits. We propose that these eccentricities arise in a phase of giant impacts, analogous to the final stage of solar system assembly that formed Earth's Moon. In this scenario, the planets scatter each other and collide, with corresponding mass growth as they merge. We numerically integrate an ensemble of systems with varying total planet mass, allowing for collisional growth, to show that (1) the high-eccentricity giants observed today may have formed preferentially in systems of higher initial total planet mass, and (2) the upper bound on the observed giant planet eccentricity distribution is consistent with planet–planet scattering. We predict that mergers will produce a population of high-mass giant planets between 1 and 8 au from their stars.
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NASA Exoplanet Archive - ICE Plotter

That oddity is real. Of known exoplanets, their ranges of orbit eccentricities increase with increasing mass, with the champion having a projected mass of 1.5 Jupiter masses and an eccentricity of 0.95. That means that its maximum distance is 40 times its minimum distance. Some more details on that champion:

It is HD 20782 b, and it is the only known planet in its system. Its period is 1.635 (Earth) years, and its semimajor axis 1.36 AU. Its distance from its star thus ranges between 0.068 AU and 2.652 AU. The time it spends at less than twice its minimum distance is 4 days, and less than its s.m. axis distance 118 days or 0.323 years.

The star is HD 20782, and its mass is 1.07 solar masses, its radius 1.11 solar radii, its effective temperature 5790 K, and its spectral type G3V. Its metallicity index is -0.06 dex for Fe/H. Its luminosity I calculate to be 1.25 solar luminosities.

HD 20782 is almost a dead ringer for the Sun. Much like 51 Pegasi, the first "normal" star to be discovered to have an exoplanet.

The planet's equilibrium temperature thus ranges between 170 K and 1100 K.

The maximum period of that planet's moons, if any, is about 6.7 days (orbit period for the planet having a circular orbit at its closest distance). So the planet is not likely to have many moons.

The system is 36 parsecs / 117 light years away, and the star's apparent magnitude is +7.4. Its coordinates are RA = 03h20m03.58s Dec = -28d51m14.7s or RA = 50.014908, Dec = -28.854071.
 
The paper's authors propose that more than one Jovian planet can form, and that they can sideswipe each other or collide with each other, making the remaining planet(s) have high orbit eccentricity.

This brings to mind an oddity called the "Kepler dichotomy" - between single-planet systems and multiplanet systems. A big problem here is that transit detection requires a line-of-sight coincidence, and the method will thus be unable to detect the great majority of planets. It will even fail to detect many planets in systems where some planets could be observed. But there is a way out of that, to extrapolate to single planets from multiplanet observations. One finds something like twice as many single planets than what one might expect. Furthermore, the single planets' stars tend to have higher metallicity than average, giving support to the OP's scenario of planets too massive to easily coexist.

When Exoplanets Collide | NASA - evidence of collision of rocky planets in the form of interplanetary dust.


First exoplanet found around a Sun-like star (Nature magazine) - 51 Pegasi b, a hot Jovian planet, and the first of this weird kind of planet ever discovered.

Lessons from scorching hot weirdo-planets - "While these close-in, hefty worlds represent about 10 percent of the exoplanets thus far detected, it’s thought they account for just 1 percent of all planets." Because they are the easiest planets to detect.

Rebekah Dawson notes three theories about "hot Jupiters":
  • They formed close in
  • They formed farther out, then spiraled in by interacting with the protoplanetary nebula
  • They got kicked into very eccentric orbits, then their orbits got circularized by tidal friction caused by their stars
Another big trend is that hot Jupiters tend to be around stars that are more metal-rich. Astronomers refer to metals as any element heavier than hydrogen or helium. There’s more iron and other elements in the star, and we think that this may affect the disk of gas and dust that the planets formed out of. There are more solids available, and that could facilitate forming giant planets by providing material for their cores, which would then accrete gas and become gas giants.

Having more metals in the system could enable the creation of multiple giant planets. That could cause the type of gravitational interaction that would put the hot Jupiter onto a high eccentricity orbit.
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repoman said:
Speaking of Jovian planets, just found out about Simon Marius today who found the Galilean satellites a smidge before Galileo himself and named them (suggested by Kepler?)

https://en.wikipedia.org/wiki/Simon_Marius
Marian moons?
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There's also this:
He also concluded from his observations of the Galilean moons that they must orbit Jupiter while Jupiter orbits the Sun. Therefore, Marius concluded that the geocentric Tychonic system, in which the planets circle the Sun while the Sun circles the Earth, must be the correct world system, or model of the universe.
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So good that he got to name the moons but Galileo gets to claim them.
 
Building planets, piece by piece - on the "pebble accretion" theory, that protoplanets collected pebble-sized chunks.
Scientists used to think that planets formed as planetesimals collided and merged, like fistfuls of Play-Doh slapped together. But it turns out that that process would have taken too long. So astronomers recently proposed a new way to explain how baby planets grew.

Computer simulations show that small pebbles within the dusty disk would have glommed onto the growing protoplanets. Those tiny pebbles coalesced so rapidly that the protoplanets grew quickly into full-fledged planets — like a kid suddenly packing on enough pounds to become an adult.
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These so-called 'super-puff' worlds could be exoplanets with ring | Astronomy.com - "Astronomers investigate whether mysterious low-density planets are actually ringed planets that have been misunderstood."
Shreyas Vissapragada, a planetary astronomer at Caltech, started thinking about the possibility of super-puffs being ringed planets after another astronomer asked him about it.

“If an alien observed Saturn with the Kepler space telescope, how badly would they get the density wrong if they didn't realize it had rings?” Vissapragada said he asked himself. He did the math and found that they might calculate Saturn’s density to be only half of what it really is.

He teamed up with Anthony Piro, an astronomer at the Carnegie Institution for Science, to investigate what this could mean for Earth astronomers’ observations.

The pair considered what the ring systems would have to be like for known super-puffs to be ringed planets. For example, most known super-puffs are fairly close to their stars, so their rings would have to be rocky rather than icy. Some of the planets wouldn’t be able to have rocky rings wide enough to throw off density estimates, because rocky material that's too far from the planet would clump to form moons. For other super-puffs, rings might still be a possibility.
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The article had a picture of a simulated Saturn transit -- at maximum radial tilt, the planet's rings cover up as much of the Sun as the planet itself.
 
New Exoplanet Search Strategy Claims First Discovery | Quanta Magazine
noting
Coherent radio emission from a quiescent red dwarf indicative of star–planet interaction | Nature Astronomy
Back to Quanta.
Jupiter’s moon Io — the solar system’s most volcanic world — has inspired a new way to find distant exoplanets. As the moon orbits Jupiter, it tugs on the planet’s magnetic field, generating bright auroras in Jupiter’s atmosphere. Even if we couldn’t see Io itself, the enormous auroras, pulsing to the beat of a hidden orbiting body, would tell us that something was out there.
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The planet's discoverers used the LOFAR, the Low Frequency Array of radio telescopes. They found a star called GJ 1151, a red dwarf with unusually long-lived emissions, often longer than 8 hours, the available observing time per day. The emissions also looked more like aurora emissions than like flare emissions.

The discoverers infer that the planet has a period of 1 to 5 days. This planet has not been seen with radial velocity, however, giving its mass an upper limit of about 5 Earth masses.


Super-puffs: Astronomers try to explain 'cotton candy' exoplanets - CNN - planets with lower density than one would expect from planetary-structure calculations. In particular, Jupiter is close to the largest possible cold object in our Universe, where "cold" means not hot enough for its internal temperature to contribute significantly to its internal pressure. But some exoplanets seem to be larger than Jupiter, making them "puffy planets". Some seem extra large, with an inferred density of 0.3 g/cm^3 as opposed to Jupiter's 1.33 g/cm^3.

Exploring Whether Super-puffs can be Explained as Ringed Exoplanets - IOPscience

The authors find that rings can explain many puffy planets, but they doubt that rings can explain all of them. Many "hot Jupiters" are close to their stars, making it necessary for rings to be rocky rather than icy. They also cannot extend very far out, because when the ring contents' orbit periods get close to the planet's orbit period, those particles' orbits become unstable. Tidal drag is also a problem, because this effect requires a significantly tilted spin axis, and tidal drag may untilt it.

Just for the heck of it, I calculated Saturn's apparent size when observed along its orbit. (Maximum observable tilt) / (edge-on) gives a projected area ratio of 2.25, or an apparent size increase of 1.5. For Jupiter's density of 1.33 g/cm^3, that gives about 0.4 g/cm^3.

So the ring hypothesis can work.
 
The  Spitzer Space Telescope was in operation from 2003 to 2020 Jan 30
NASA Spitzer Space Telescope - at Caltech
Spitzer Space Telescope | NASA
Looking Back at the Spitzer Space Telescope

It was an infrared telescope, and for much of its mission, its detectors were kept supercold to make them more sensitive.

It made many exoplanet-related observations, like observations of transits of TRAPPIST-1 by its seven known planets. Combined with other transit observations, one could find not only the planets' sizes, but also their masses, from how much they pull on each other. Some of these planets are low-density enough to have super oceans.
 
As Spitzer’s Mission Ends, First Light for CHEOPS
 CHEOPS - "CHaracterising ExOPlanets Satellite"
ESA - Cheops - "Characterising exoplanets known to be orbiting around nearby bright stars"
CHEOPS Mission Homepage

The satellite was launched 2019 Dec 18 from ESA's Kourou spaceport in French Guiana, atop a Soyuz booster rocket. It is in a Sun-synchronous orbit about 712-715 km in altitude. It has an orbit inclination of 98d, making it nearly polar and slightly retrograde. The Earth's equatorial bulge makes it precess forward so that it will always be illuminated by the Sun.

Its telescope cover was removed 2020 Jan 29, and its first-light image was taken on Feb 7. It was deliberately blurred so that each star's light would be spread over several pixels, thus getting greater precision. It should start science observations in April.


Its purpose is to look more closely at known exoplanets to determine their sizes and to get clues as to their atmospheres. Those tasks will be done by looking at their transits, and atmospheres that absorb more in some light wavelengths than others will seem larger in those wavelengths than in others. So by looking at apparent size as a function of observation wavelength, one can get clues as to the composition of whatever atmosphere a planet might have.
 
Transiting Exoplanet Survey Satellite Finds An Earth-Size Habitable-Zone World - Astrobiology

The planet is TOI 700 d, and it was confirmed with the Spitzer Space Telescope.
"TESS was designed and launched specifically to find Earth-sized planets orbiting nearby stars," said Paul Hertz, astrophysics division director at NASA Headquarters in Washington. "Planets around nearby stars are easiest to follow-up with larger telescopes in space and on Earth. Discovering TOI 700 d is a key science finding for TESS. Confirming the planet's size and habitable zone status with Spitzer is another win for Spitzer as it approaches the end of science operations this January."

...
TOI 700 is a small, cool M dwarf star located just over 100 light-years away in the southern constellation Dorado. It's roughly 40% of the Sun's mass and size and about half its surface temperature. The star appears in 11 of the 13 sectors TESS observed during the mission's first year, and scientists caught multiple transits by its three planets.

The star was originally misclassified in the TESS database as being more similar to our Sun, which meant the planets appeared larger and hotter than they really are. Several researchers, including Alton Spencer, a high school student working with members of the TESS team, identified the error.

"When we corrected the star's parameters, the sizes of its planets dropped, and we realized the outermost one was about the size of Earth and in the habitable zone," said Emily Gilbert, a graduate student at the University of Chicago. "Additionally, in 11 months of data we saw no flares from the star, which improves the chances TOI 700 d is habitable and makes it easier to model its atmospheric and surface conditions."
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The star is  TOI 700, and it is about 102 light years / 31 parsecs away.
The innermost planet, called TOI 700 b, is almost exactly Earth-size, is probably rocky and completes an orbit every 10 days. The middle planet, TOI 700 c, is 2.6 times larger than Earth -- between the sizes of Earth and Neptune -- orbits every 16 days and is likely a gas-dominated world. TOI 700 d, the outermost known planet in the system and the only one in the habitable zone, measures 20% larger than Earth, orbits every 37 days and receives from its star 86% of the energy that the Sun provides to Earth. All of the planets are thought to be tidally locked to their star, which means they rotate once per orbit so that one side is constantly bathed in daylight.
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NASA Exoplanet Archive - from analyzing the data from TESS, 42 confirmed planets and 1,737 candidates.

Home - TESS - Transiting Exoplanet Survey Satellite - the satellite's home page

It has finished year 1 of observations, of the southern ecliptic hemisphere, and it is now 2/3 of the way through year 2, doing the northern hemisphere. In year 3, it will observe the southern hemisphere again.
 
New Planets from Old Data - from a spectrographic survey of 33 nearby red-dwarf stars, 5 planets and 8 candidates. Two of them are in the habitable zone, planets of stars GJ180 and GJ229A. So we may be seeing more of those stars.

Exoplanets Data Visualizer - Jupyter Notebook Viewer
Introduction: Recently, a new gold rush in the form of exo-planet hunting has seized the Internet. A major astrology enthusiast myself, I want to take the opportunity to learn as much about these distant objects as possible. What better way to complement reading than to see the data for myself!

The purpose of this notebook is both an exploration and a tutorial. We will dwell into the NASA exo-planet database to understand the planet data first hand while learning the basic coding of Python for data analysis. Enjoy!
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Jupyter is Mathematica-like software that uses Python and that is all open-source. It's all-numeric, however.


Giant Planets in a Post-Apocalyptic Solar System
noting
Cold Giant Planets Evaporated by Hot White Dwarfs - IOPscience
It’s nearly eight billion years in the future.

The Sun, having exhausted its source of fuel, has dramatically expanded into a red giant and then puffed off its outer layers, leaving its dense, scalding hot core exposed. This core — a white dwarf — initially clocks in at nearly 100,000 K (180,000 °F), bathing its surroundings in harsh extreme-ultraviolet (EUV) radiation at levels that are up to a million times brighter than the present-day Sun.
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It would erode the outer planets, and some of their substance would fall onto the Sun.

About 1/3 of hot white dwarfs are known to have evidence of this sort of contamination in their spectra. This agrees with calculations for at least 1/2 of hot white dwarfs having at least one giant planet.
 
News | NESSI Emerges as New Tool for Exoplanet Atmospheres
Since February 2018, scientists have been testing an instrument at the Hale Telescope called the New Mexico Exoplanet Spectroscopic Survey Instrument, or NESSI. A collaboration between NASA's Jet Propulsion Laboratory in Pasadena, California, and the New Mexico Institute of Mining and Technology, NESSI was built to examine the atmospheres of planets that orbit stars beyond our Sun, or exoplanets, providing new insights into what these worlds are like.

So far, NESSI has checked out two "hot Jupiters," massive gas giants orbiting close to their stars and too scorching to sustain life. One, called HD 189773b, has such extreme temperatures and winds that it may rain glass sideways there. The other, WASP-33b, has a "sunscreen" layer of atmosphere, with molecules that absorb ultraviolet and visible light.
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News | For Hottest Planet, a Major Meltdown, Study Shows
Called KELT-9b, the planet is an ultra-hot Jupiter, one of several varieties of exoplanets - planets around other stars - found in our galaxy. It weighs in at nearly three times the mass of our own Jupiter and orbits a star some 670 light-years away. With a surface temperature of 7,800 degrees Fahrenheit (4,300 degrees Celsius) - hotter than some stars - this planet is the hottest found so far.

Now, a team of astronomers using NASA's Spitzer space telescope has found evidence that the heat is too much even for molecules to remain intact. Molecules of hydrogen gas are likely ripped apart on the dayside of KELT-9b, unable to re-form until their disjointed atoms flow around to the planet's nightside.
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A Wrecking Ball in the HR 5183 System | News | Astrobiology
noting
In the Presence of a Wrecking Ball: Orbital Stability in the HR 5183 System - IOPscience
for
The Extrasolar Planet Encyclopaedia — HR 5183 b

The "wrecking ball" is planet HR 5183 b, a Jovian planet with a mass at least 3.23 Jupiter masses. It orbits with a period of 75 years, and it was discovered in 2019 using some 20 years of spectroscopic radial-velocity data. Its semimajor axis and eccentricity are 18.0 AU and 0.84, giving a distance range of 2.88 to 33.12 AU. The distance for the Earth's light flux is 1.54 AU.

Another planet in that system will not have a long-term stable orbit if it orbits too close to that Jovian planet's orbit, but that research suggests that the inner part of the habitable zone may allow a stable orbit.


Discovery of TESS Mission’s First Circumbinary Planet - TOI 1338 b
TESS Discovers Its 1st Planet Orbiting 2 Stars | NASA
The Extrasolar Planet Encyclopaedia — TOI-1338

The planet orbits a binary star with a period of 71.4 days and has an apparent radius of 1.6 Jupiter radii. Those stars orbit each other with a period of 15 days. They have masses 1.20 and 0.3250 solar masses.


News | A New Tool for 'Weighing' Unseen Planets - NEID, a spectroscope that can go as good as 1/3 m/s, as opposed to nowadays typical 1 m/s. That will improve radial-velocity detection and radial-velocity masses.
 TOI 1338
 
Possibly Impossible Planets

There is a curious gap in known exoplanets along a line between (period = 0, mass = 19 ME) and (period = 21 d, mass = 0). ME = Earth mass. This gap is likely due to photoevaporation, a planet's star evaporating its volatile content.

Related is the "hot Neptune desert": Hot Neptune Desert Data Visualization [image] | EurekAlert! Science News - a shortage of "hot Neptunes" between hot Earth-sized planets and hot Jupiter-sized ones. This is likely from being close to their stars -- evaporation is relatively slow at first, then picks up, until all the volatiles are gone. That leaves behind an Earthlike planet, and such a planet does not shrink any further. Thus one sees most a close-to-beginning state and an end state.

Astronomers Just Found The First Ever Exoplanet That Swoops Outside The Galactic Plane - it's well outside the "thin disc", where the Sun is, though inside the "thick disc" of relatively old stars, at least 10 billion years old.

exoplanets on Reddit - lots of stuff on exoplanet research.
 
The Skies of Mini-Neptunes | The Planetary Society
These planets are called super-Earths or mini-Neptunes. They populate an unfamiliar regime of worlds. They are larger than Earth, the Sun’s biggest rocky world, yet smaller than Neptune or Uranus, which are about 4 Earths in diameter. In fact, an exoplanet detected as it transits across the disk of its host star is 4 times more likely to have a size in the super-Earth/mini-Neptune regime than to be bigger than Neptune. These discovery statistics are telling us something—but what?

Here in our own solar system, there’s an interesting trend among the outer planets: an atmosphere’s proportion of heavy elements increases as the planet’s mass decreases. For example, compared to their relative abundance in the Sun, Jupiter has 4 times more heavy elements, Saturn has 10 times, and Neptune and Uranus have about 100 times. If we use water vapor in an exoplanet’s atmosphere to estimate the abundance of oxygen (and thus all heavy elements), then we can determine whether this trend applies in other planetary systems.

The first definitive measurement of this type was conducted on WASP-43b, a world with twice the mass of Jupiter. Its heavy elements have relative abundances matching the Sun’s, fitting the expected trend.

Subsequent observations with Hubble revealed water vapor in the atmospheres of smaller exoplanets, such as the Saturn-mass world WASP-39b and the Neptune-mass worlds HAT-P-11b and HAT-P-26b. However, these planets didn’t fit the solar system pattern. The “warm Saturn” WASP-39b has an atmosphere with, proportionately, 150 times more heavy elements than the Sun. Meanwhile, the atmosphere of Neptune-mass HAT-P-26b comes in at between 1 times and 30 times the Sun’s value, but that of the somewhat smaller world HAT-P-11b has anywhere between 90 times and 700 times the solar abundance of heavy elements!
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That's just plain weird.

News | Cooking up Alien Atmospheres on Earth - H2 and CO at 1000 C - to see what goes on in a hot Jovian planet's atmosphere.

An Earth-sized Planet for TESS - it orbits HD 21749 with a period of 7.8 days.  HD 21749 - 23 Earth masses, 2.8 Earth radii - a mini-Neuptune?

Super-Earth Smackdowns May Explain Diverse Worlds | Space
Catastrophic collisions may explain differences in giant rocky planets around other stars.

A new study suggests that the heat generated by material smashing into a planet plays an important role in removing some or all of a planet's atmosphere. A wide variety of sizes for these deadly asteroids would explain differences seen in the more massive rocky worlds.
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Like differences in how much atmosphere -- a giant collision can strip off much of a planet's atmosphere.

The best theory so far for the origin of the Moon is such an impact.
 
“Goldilocks” Stars May Be “Just Right” for Finding Habitable Worlds - spectral class K
Why? First, K stars live a very long time — 17 billion to 70 billion years, compared to 10 billion years for the Sun — giving plenty of time for life to evolve. Also, K stars have less extreme activity in their youth than the universe’s dimmest stars, called M stars or “red dwarfs.”

...
But the turbulent youth of M stars presents problems for potential life. Stellar flares – explosive releases of magnetic energy – are much more frequent and energetic from young M stars than young Sun-like stars. M stars are also much brighter when they are young, for up to a billion years after they form, with energy that could boil off oceans on any planets that might someday be in the habitable zone.

“I like to think that K stars are in a ‘sweet spot’ between Sun-analog stars and M stars,” said Giada Arney of NASA’s Goddard Space Flight Center in Greenbelt, Maryland.
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Noting
The K Dwarf Advantage for Biosignatures on Directly Imaged Exoplanets - IOPscience
Proposing that methane can coexist better with oxygen in planets of K stars than of G stars like the Sun - because the stars' light has less ultraviolet radiation from their surfaces not being as hot.

Tilted Exoplanets Could Explain Odd Orbits - Sky & Telescope - Sky & Telescope - orbits just out of resonance. Tilted spins could cause enough precession to make a different. Tilted spins with rings could also make "puffy planets".

Planet Formation: How Ocean Worlds Happen - a star exploded not long before the Solar System form, salting its protoplanetary nebula with aluminum-26. That heated the protoplanetary bodies and kept them from having much water. Al-26 likely accounts for the melting of Vesta early in its history.

But where it was absent, planets could get huge oceans with layers of high-pressure ice beneath them.
 
Doomed Exoplanet Sets Record for Shortest Orbit Around a Star - NGTS-10b is a Jovian planet with a period of 18.4 hours.
The researchers also determined that NGTS-10b is slowly inching closer to its star — in fact, they believe it’ll cut about seven seconds off its orbit over the next 10 years.

Within 38 million years, they say it’ll pass the Roche limit and be torn to shreds by its star — meaning the exoplanet’s days as the universal record holder for shortest orbit are already numbered.
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Its outer layers will become pulled off, and its core will be left behind. That is a likely explanation for may Earth-sized planets orbiting very close to their stars.

This Is Why Earth, Surprisingly, Is The Densest Object In Our Solar System
What Makes Something A Planet, According To An Astrophysicist?

Discusses protoplanetary nebulae, and mentions the soot and frost lines. The soot line is where polycyclic aromatic hydrocarbons can form - that's how carbon condenses out. The frost line is where water can condense as ice. Inside the soot line, only metals and metal silicates can condense - metal silicates are typical rocky materials.

Ancient stars shed light on Earth’s similarities to other planets | UCLA
noting
Oxygen fugacities of extrasolar rocks: Evidence for an Earth-like geochemistry of exoplanets | Science

It's hard for me to tell what they were actually doing, since a white dwarf's surface is hot enough to make nearly molecules disintegrate. Did they measure the oxygen content?
 
Climates of Distant Terrestrial Worlds
The authors show that M-dwarf planets absorb more of their hosts’ radiation, both in their atmospheres and their surfaces, whereas F-dwarf planets absorb less. As a result, a planet can have a climate similar to that of modern-day Earth if it’s receiving current solar amounts of incoming radiation from a G-dwarf star — but to achieve the same climate around an M-dwarf star, it would need to receive 12% less incoming radiation. Around an F-dwarf star, it would need to receive 8% more.

What about rotation? The above models assumed that the planets all had 24-hour rotation rates, but Shields and collaborators also test how this compares to a tidally locked planet that always shows the same face to its host. For an M-dwarf host, a tidally locked planet has lower minimum and maximum dayside temperatures when compared with a planet with a 24-hour rotation period; the average dayside temperature is around 37 K colder on the tidally locked planet.
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noting
Energy Budgets for Terrestrial Extrasolar Planets - IOPscience


Will Humans Ever Walk on Exoplanets? - mentions the great difficulty of interstellar spaceflight


Mass-ive Implications for Exoplanetary Atmospheres
A planet’s mass plays an important role in how far its atmosphere extends. This has prompted studies on whether a planet’s mass could be inferred from its transmission spectrum alone. In some cases, this approach works. But in other cases, the transmission spectra of very different planets can appear to be alike.
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A White Dwarf’s Giant Planet - a partially-stripped one
 
Why Are There so Many Sub-Neptune Exoplanets? - there is a "radius cliff" at about 3 Earth radii where sub-Neptune planets became much rarer. Neptune and Uranus are both at 4 Earth radii.

Hypothesis: the planets' cores soak up much of the hydrogen that was originally in the planets' outer layers, leaving them with heavier elements.


TESS Reveals HD 118203 b Transits After 13 Years - it was first discovered with the radial-velocity method 13 years ago, and being seen with both methods gives us both its mass and its radius.

[1911.05150] TESS Reveals HD 118203 b to be a Transiting Planet (arxiv preprint) Its numbers:
  • The Star:
    • Distance: 93 pc / 302 ly
    • Mass: 1.257 Msun
    • Radius: 2.103 Rsun
    • Luminosity: 4.18 Lsun
    • Temperature: 5692 K
  • The Planet:
    • Period: 6.134980 days
    • Mass: 2.173 Mjup
    • Radius: 1.133 Rjup
    • Semimajor axis: 0.0782 AU
    • Eccentricity: 0.316
    • Equilibrium temperature: 1496 K
    • Est. circularization timescale: 12.7 Gyr
Yet another "hot Jupiter", hot enough to glow in visible light over all of its orbit.
 
Discovery Alert: This Four-planet System is Leaking – Exoplanet Exploration: Planets Beyond our Solar System
A team of scientists led by Carole Haswell and Daniel Staab of the U.K.'s Open University tried out their new search method using a 3.6-meter telescope in Chile. Relying on an instrument called a spectrograph, they zeroed in on a star about 200 light-years away. The spectrograph can reveal what types of gases are present in a planetary system, and in this case, found evidence of a possible "circumstellar gas shroud" – a diffuse cloud of gas orbiting the star, likely bleeding into space from one or more of the inner, "super Earth" planets. The team used radial velocity measurements, which track the wobbles of a star caused by the gravity of orbiting planets, to estimate the size and number of planets in this system.
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Exoplanet Archive: DMPP-1

The star has mass 1.21 Msun, radius 1.26 Rsun, luminosity 2.07 Lsun, temperature 6196 K, spectral type F8V

The planets have:
  • d: P = 2.882 d, a = 0.0422 AU, Teq = 1632 K, M*sin(i) = 3.35 Me
  • e: P = 5.516 d, a = 0.0651 AU, Teq = 1314 K, M*sin(i) = 4.13 Me
  • c: P = 6.584 d, a = 0.0733 AU, Teq = 1239 K, M*sin(i) = 9.600 Me
  • b: P = 18.57 d, a = 0.1462 AU, Teq = 877 K, M*sin(i) = 24.27 Me
Increasing size going outward.
 
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