Two asteroid belts at Epsilon Eridani & constraints on planet b

SpaceRef: Solar System's Young Twin Has Two Asteroid Belts

Asteroid belts at 3 and 20 AU from the star, Kuiper belt at 35-100 AU.

The astrometric+RV orbit for Epsilon Eridani b with eccentricity=0.7 is ruled out.

Very strong evidence for at least another planet, in my honest opinion.

With a circular orbit, all this talk about "Well, let's wait until 2010 when Eps Eri b is farthest from the sun to image it" may be a moot point.

This is a very exciting find! Really, it represents the earliest stage of mapping our local neighborhood to a fairly accurate degree. Imagine, we are no detecting asteroid belts, and are able to draw some fairly substantive conclusions about their host systems based on those belts' appearance.

Epsilon Eridani has always been a favorite of mine, even after I realized that it was such a young system. And in a way, that is just as exciting. We are indeed looking at our own Solar System, as it was, when life first began to appear on the Earth. I wonder if, in the next few years, we won't discover some appropriately massed worlds in the HZ zone at Epsilon. If so... it would not be difficult to imagine it as a world wrapped in a thick cloud layer, beneath which lay rolling oceans and the earliest, barren continents. Another couple of billion years, and we'll be seeing that world's own Cambrian explosion!

I know that's optomistic. But it does make you wonder who looked at our System a few billion years ago, and wondered about our future....

Oh I love it when this happens. Here's the paper on arXiv.
http://arxiv.org/abs/0810.4564

Dynamical stability of the inner belt around Epsilon Eridani (pdf)

Seems like the orbital eccentricity has to be below about 0.1.

Near-circular planetary orbits... such a refreshingly radical idea...

(also makes you wonder whether Epsilon Eridani b has already been seen, but not picked up on because it wasn't where the RV or RV+astrometry orbit says it was)

The cold origin of the warm dust around epsilon Eridani
http://arxiv.org/abs/1011.4882

Quote :

Context: The K2V star eps Eri hosts one known inner planet, an outer Kuiper belt analog, and an inner disk of warm dust. Spitzer/IRS measurements indicate that the warm dust is present at distances as close as a few AU from the star. Its origin is puzzling, since an "asteroid belt" that could produce this dust would be unstable because of the known inner planet. Aims: Here we test the hypothesis that the observed warm dust is generated by collisions in the outer belt and is transported inward by Poynting-Robertson (P-R) drag and strong stellar winds. Methods: We simulated a steady-state distribution of dust particles outside 10AU with a collisional code and in the inner region (r<10AU) with single-particle numerical integrations. By assuming homogeneous spherical dust grains composed of water ice and silicate, we calculated the thermal emission of the dust and compared it with observations. We investigated two different orbital configurations for the inner planet inferred from RV measurements, one with a highly eccentric orbit of e=0.7 and another one with a moderate one of e=0.25. We also produced a simulation without a planet. Results: Our models can reproduce the shape and magnitude of the observed SED from mid-IR to sub-mm wavelengths, as well as the Spitzer/MIPS radial brightness profiles. The best-fit dust composition includes both ice and silicates. The results are similar for the two possible planetary orbits and without a planet. Conclusions: The observed warm dust in the system can indeed stem from the outer belt and be transported inward by P-R and stellar wind drag. The inner planet has little effect on the distribution of dust, so that the planetary orbit could not be constrained. Reasonable agreement between the model and observations can only be achieved by relaxing the assumption of purely silicate dust and assuming a mixture of silicate and ice in comparable amounts.

Interesting result, would be good to get some more constraints on what the orbit of the planet is. Not sure how this affects the results about the second "asteroid belt".

Unfortunately behind a paywall...

Greaves et al. (2014) "Extreme Conditions in a Close Analog to the Young Solar System: Herschel Observations of epsilon Eridani"

Resolves two belts, one at 12–16 AU, the other at 54–68 AU. The outer belt shows structures that may be attributable to a mildly eccentric planet ("c") near the belt.

Lestrade & Thilliez "MAMBO image of the debris disk around epsilon Eridani : robustness of the azimuthal structure"
http://arxiv.org/abs/1503.03097

Confirms the structure seen in the outer debris disc at 850 nm with new observations at 1.2 mm. Also indicates that the ring has a narrower relative width than the Solar System's Kuiper Belt.

Also on SpaceRef.

Deep exploration of ε Eridani with Keck Ms-band vortex coronagraphy and radial velocities: mass and orbital parameters of the giant exoplanet
https://arxiv.org/abs/1810.03794

Quote :

We present the most sensitive direct imaging and radial velocity (RV) exploration of ϵ Eridani to date. ϵ Eridani is an adolescent planetary system, reminiscent of the early Solar system. It is surrounded by a prominent and complex debris disk which is likely stirred by one or several gas giant exoplanets. The discovery of the RV signature of a giant exoplanet was announced 15 years ago, but has met with scrutiny due to possible confusion with stellar noise. We confirm the planet with a new compilation and analysis of precise RV data spanning 30 years, and combine it with upper limits from our direct imaging search, the most sensitive ever performed. The deep images were taken in the Ms band (4.7μm) with the vortex coronagraph recently installed in W.M. Keck Observatory's infrared camera NIRC2, which opens a sensitive window for planet searches around nearby adolescent systems. The RV data and direct imaging upper limit maps were combined in an innovative joint Bayesian analysis, providing new constraints on the mass and orbital parameters of the elusive planet. ϵ Eridani b has a mass of 0.78+0.38−0.12 MJup and is orbiting ϵ Eridani at about 3.48±0.02 AU with a period of 7.37±0.07 years. The eccentricity of ϵ Eridani b's orbit is 0.07+0.06−0.05, an order of magnitude smaller than early estimates and consistent with a circular orbit. We discuss our findings from the standpoint of planet-disk interactions and prospects for future detection and characterization with the James Webb Space Telescope.

Nice to see this one back again, seems to have ended up being a fairly decent Jupiter-analogue. Would have been interesting to see the astrometry included in the analysis as well.

Even better constraints.

Constraining the Orbit and Mass of ε Eridani b with Radial Velocities, Hipparcos IAD-{Gaia~DR2} Astrometry, and Multi-epoch Vortex Coronagraphy Upper Limits
https://arxiv.org/abs/2108.02305

Quote :

...We combine this data in a Bayesian framework. We find a new mass, Mb = 0.66+0.12−0.09~MJup, and inclination, i = 77.95∘+28.50−21.06, with at least a factor 2 improvement over previous uncertainties...

Re-analysis of Epsilon Eridani b HST/FGS astrometry taking into account the new RV data:

Benedict 2022 "Revisiting HST/FGS Astrometry of ε Eridani"
https://iopscience.iop.org/article/10.3847/2515-5172/ac5b6b

Result has an eccentricity of 0.16±0.02, inclination 45±8°