Exoplanet Discoveries and Updates

[sandcastles]

Discovery Alert: Ultra-hot 'Super-Earth' Could Have No Atmosphere

https://exoplanets.nasa.gov/news/1713/di...tmosphere/

[stevebowers]

In the NoLWoCS system this would probably be a Chthonian type world, which has lost any volatiles it once may have had. There still could be a vaporous atmosphere on such a world, since several normally solid elements would be near or above their melting or boiling point.

This planet has a mass of about 1.3 Earths, so would have higher gravity than our planet - that means any atmosphere that does form will last longer, despite the temperature.

[AstroChara]

A recent preprint, Trifonov et al. (2024), about GJ 581 was accepted for a journal was posted on arXiv yesterday.

Among its most important results is the inclination of its planetary system, at 47.0 degrees.

[AstroChara]

Today we have a news (LINK) about the direct imaging of Epsilon Indi A b by JWST, which returns a rather unexpected result.

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Epsilon Indi A b from Matthews et al. (2024)
Note: this orbital solution is only true if Epsilon Indi A b is dominates the perturbation of its star.
Semi-major axis: 28.4 +10 -7.2 AU
Eccentricity: 0.40 +0.15 -0.18
Mass: 6.31 +0.60 -0.56 Jupiter masses

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Based on radial velocity and astrometric data, Epsilon Indi A b was expected to be a planet with around 3 times Jupiter's mass which orbits in an eccentric orbit with semi-major axis ('average distance') of approximately 12 AU from the star. Its current description in EG reflects this, and the rest of the planetary system is essentially designed around it. With this new revision, we may need to look at what it implies about the stability of the system and, more importantly, the system's history, and whether it is still conducive for the current planet.

There are two known mechanisms that can send massive jovian planets into eccentric orbits, including planet-planet scattering and disk-planet interaction. Planet-planet scattering between such large jovians would likely cause chaos throughout the entire planetary system, and while disk-planet interaction may be less disruptive, I am not sure whether this is likely to produce the observed eccentricity, as the papers I have seen seem to imply rather mild eccentricities, and in one case, extreme eccentricity of 0.7-0.9, rather than 0.4.

[AstroChara]

Tau Ceti is probably one of the most important stars to spectrographs. It's bright and nearby, and stable, so it's often used to test spectrographs, and there's lots of radial velocity measurements on this star.

There have been some claims of planets around this star, ones that we gleefully adopted for our project: those planets claimed in Tuomi et al. 2013 and Feng et al. 2017, a system of superterrans and subneptunians. These planets were practically scraped out of the noise floor though, and after many years they remained as candidates.

Earlier, we have a new preprint (accepted for publication) posted on arXiv: A comprehensive study on radial velocity signals using ESPRESSO: Pushing precision to the 10 cm/s level. This paper notably does not detect the signal "e", and casts doubt on the signal "g", suggesting it may be stellar activity rather than a planet. The signal f, meanwhile, was considered dubious in an earlier poster from 2020, while signal "h" has a period similar to that of the star's rotation. Combined with Tau Ceti's low metallicity, I think the existence of the system as we currently described is probably unlikely.

Currently I have been working with a few others (non-Orion's Arm) to create a new layout for this system; I'll post the result of this in the Forums later. Discussing about this subject with Steve, the change probably shouldn't be difficult, and ties in neatly with our current initiative to change terraformed planets into something else; the early history is already independent of the planets. Stuff like the Kingdom of Eyre could be space hab-based polity — and we can make it dissolve at some point in the timeline to prevent yet another eternal, unchanging polity syndrome. The Corporate War may be fought over something else. If it needs to remain a planet, Nova Terra could either become a sunshaded, worldhoused small planet maybe between the size of Mercury and Mars, or a supraplanetary shell world around a subneptunian planet.

[Drashner1]

Looking forward to seeing it. Options all sound good to me.

Todd

[AstroChara]

Earlier today, a preprint on direct imaging attempts of planets around at Ran / Epsilon Eridani was released: Searching for Planets Orbiting ε~Eridani with JWST/NIRCam. They failed to detect planets in the outer system, setting a mass constraint that rules out at least Saturn-massed planets orbiting beyond around 16 au (according to current models of planet evolution and brightnesses). As for Ægir / Epsilon Eridani b, they did have a possible detection of an object at the expected location with expected brightness, but it happened to land in a noisy area, and hence they couldn't confirm the detection of this planet.

As an additional paper observing the debris discs of this star is projected to be released later, I will continue to wait for this paper to inform my decisions, and my rework of the Ran system in Orion's Arm will not begin yet.

[sandcastles]

I mentioned this planet a few years ago and looked at Wikipedia, and it has updated information.

https://en.wikipedia.org/wiki/Gliese_367
The star's mass is .454 solar mass and its age is about 7,95 billion years.

The star's name is Añañuca and its innermost planet is named Tahay, after names for the endemic Chilean wildflowers Phycella cyrtanthoides and Calydorea xiphioides.

The article gives masses for two more planets.
Mass Period
≥4.13±0.36 M? 11.5301±0.0078
≥6.03±0.49 M? 34.369±0.073

If I did the math right, the distances of the other two planets would be about .07 AU and about .15 AU, but I notice the article doesn't give estimates for the distances.

[AstroChara]

Today a preprint about the star system Eta Cassiopeiae (specifically the A component, or Achird) appears on arXiv. It does not detect a planet signature, and also failed to detect a candidate previously proposed by a preceding paper.

The gist is that the paper finds that a combination of radial velocity measurements and dynamical stability studies suggest the lack of giant planets in this system. Figure 3 shows the RV detection completeness, while Figure 4 shows the survivability of a planet orbiting at a given distance from star A, as well as (maximum) eccentricity induced by the companion star. Note that the binary orbit from Giovinazzi et al. (2025), a previous paper that investigated this system, finds inclination of ~35 degrees, implying that if its planetary system is coplanar to this binary orbit, then the true mass of any planet around these stars would be almost twice the mass found from RV.

As for my thoughts...while the combination of this work, planet occurrence rates in binary systems, and our understanding of giant planet formation would point to this system likely not having a giant planet, it is good to keep in mind that Gamma Cephei A b and Nu Octantis A b exist, and even Alpha Centauri A might be orbited by a giant planet as well (though I personally doubt), so it is not perfectly settled in stone. That said, I'd be comfortable with us removing any giant planet from this system, though what should orbit around these two stars is anyone's guess.

[AstroChara]

Today's arXiv day brings us a preprint of the 55 Cancri system. It refined the properties of the known planets around the primary star (A; Copernicus), and proposed a sixth planet which doesn't look that stable when placed next to Lipperhey...but then again Lipperhey is a dubious planet, and this paper came out too soon to cite the earlier preprint that doubted it.

More interestingly, this work also checked RV data of the secondary star in this system (B), and found two planets: 55 Cancri B b and B c, superterran/subneptunian worlds with the following parameters:

55 Cancri B b
- Semi-major axis: 0.044 au
- Orbital period: 6.7994 days
- Mass: 3.5 ± 0.8 MEarth

55 Cancri B c
- Semi-major axis: 0.13 au
- Orbital period: 33.747 days
- Mass: 5.3 ± 1.4 MEarth
Notably, this planet appears to receive about as much sunlight as Mars does.

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Honestly, I like the idea that we have a LHS 1140 b here in 55 Cancri B c, though I wouldn't get my hopes too high up; certainly it could also be a neptunian, although I think I wouldn't expect a bare rock here.

In Orion's Arm, the star B is named Rheticus, orbited by three planets: Metius, Huygens, and Bayer. The naming theme follows that of Copernicus system. This naming theme will be kept, although I might attempt to find more fitting names.