| 1. |
- Blanc, Michel, et al.
(author)
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Science Goals and Mission Objectives for the Future Exploration of Ice Giants Systems : A Horizon 2061 Perspective
- 2021
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In: Space Science Reviews. - : Springer Science and Business Media LLC. - 0038-6308 .- 1572-9672. ; 217:1
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Research review (peer-reviewed)abstract
- The comparative study of planetary systems is a unique source of new scientific insight: following the six “key science questions” of the “Planetary Exploration, Horizon 2061” long-term foresight exercise, it can reveal to us the diversity of their objects (Question 1) and of their architectures (Question 2), help us better understand their origins (Question 3) and how they work (Question 4), find and characterize habitable worlds (Question 5), and ultimately, search for alien life (Question 6). But a huge “knowledge gap” exists which limits the applicability of this approach in the solar system itself: two of its secondary planetary systems, the ice giant systems of Uranus and Neptune, remain poorly explored. Starting from an analysis of our current limited knowledge of solar system ice giants and their systems in the light of these six key science questions, we show that a long-term plan for the space exploration of ice giants and their systems will greatly contribute to answer these questions. To do so, we identify the key measurements needed to address each of these questions, the destinations to choose (Uranus, Neptune, Triton or a subset of them), the combinations of space platform(s) and the types of flight sequences needed. We then examine the different launch windows available until 2061, using a Jupiter fly-by, to send a mission to Uranus or Neptune, and find that: (1) an optimized choice of platforms and flight sequences makes it possible to address a broad range of the key science questions with one mission at one of the planets. Combining an atmospheric entry probe with an orbiter tour starting on a high-inclination, low periapse orbit, followed by a sequence of lower inclination orbits (or the other way around) appears to be an optimal choice. (2) a combination of two missions to each of the ice giant systems, to be flown in parallel or in sequence, will address five out of the six key questions and establish the prerequisites to address the sixth one: searching for life at one of the most promising Ice Giant moons. (3) The 2032 Jupiter fly-by window, which offers a unique opportunity to implement this plan, should be considered in priority; if this window cannot be met, using the 2036 Jupiter fly-by window to send a mission to Uranus first, and then the 2045 window for a mission to Neptune, will allow one to achieve the same objectives; as a back-up option, one should consider an orbiter + probe mission to one of the planets and a close fly-by of the other planet to deliver a probe into its atmosphere, using the opportunity of a future mission on its way to Kuiper Belt Objects or the interstellar medium; (4) based on the examination of the habitability of the different moons by the first two missions, a third one can be properly designed to search for life at the most promising moon, likely Triton, or one of the active moons of Uranus. Thus, by 2061 the first two missions of this plan can be implemented and a third mission focusing on the search for life can be designed. Given that such a plan may be out of reach of a single national agency, international collaboration is the most promising way to implement it.
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| 2. |
- Delrez, Laetitia, et al.
(author)
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Transit detection of the long-period volatile-rich super-Earth nu(2) Lupi d with CHEOPS
- 2021
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In: Nature Astronomy. - : Springer Science and Business Media LLC. - 2397-3366. ; :5, s. 775-787
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Journal article (peer-reviewed)abstract
- Exoplanets transiting bright nearby stars are key objects for advancing our knowledge of planetary formation and evolution. The wealth of photons from the host star gives detailed access to the atmospheric, interior and orbital properties of the planetary companions. nu(2) Lupi (HD 136352) is a naked-eye (V = 5.78) Sun-like star that was discovered to host three low-mass planets with orbital periods of 11.6, 27.6 and 107.6 d via radial-velocity monitoring(1). The two inner planets (b and c) were recently found to transit(2), prompting a photometric follow-up by the brand new Characterising Exoplanets Satellite (CHEOPS). Here, we report that the outer planet d is also transiting, and measure its radius and mass to be 2.56 +/- 0.09 R-circle plus and 8.82 +/- 0.94 M-circle plus, respectively. With its bright Sun-like star, long period and mild irradiation (similar to 5.7 times the irradiation of Earth), nu(2) Lupi d unlocks a completely new region in the parameter space of exoplanets amenable to detailed characterization. We refine the properties of all three planets: planet b probably has a rocky mostly dry composition, while planets c and d seem to have retained small hydrogen-helium envelopes and a possibly large water fraction. This diversity of planetary compositions makes the nu(2) Lupi system an excellent laboratory for testing formation and evolution models of low-mass planets.
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| 3. |
- Georgieva, Iskra, 1987, et al.
(author)
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TOI-733 b : A planet in the small-planet radius valley orbiting a Sun-like star
- 2023
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In: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 674
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Journal article (peer-reviewed)abstract
- We report the discovery of a hot (Teq ≈ 1055 K) planet in the small-planet radius valley that transits the Sun-like star TOI-733. It was discovered as part of the KESPRINT follow-up program of TESS planets carried out with the HARPS spectrograph. TESS photometry from sectors 9 and 36 yields an orbital period of {equation presented} days and a radius of {equation presented}. Multi-dimensional Gaussian process modelling of the radial velocity measurements from HARPS and activity indicators gives a semi-amplitude of K = 2.23 ± 0.26 m s-1, translating into a planet mass of {equation presented}. These parameters imply that the planet is of moderate density ({equation presented}) and place it in the transition region between rocky and volatile-rich planets with H/He-dominated envelopes on the mass-radius diagram. Combining these with stellar parameters and abundances, we calculated planet interior and atmosphere models, which in turn suggest that TOI-733 b has a volatile-enriched, most likely secondary outer envelope, and may represent a highly irradiated ocean world. This is one of only a few such planets around G-type stars that are well characterised.
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| 4. |
- Persson, Carina, 1964, et al.
(author)
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TOI-2196 b: Rare planet in the hot Neptune desert transiting a G-type star
- 2022
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In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 666
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Journal article (peer-reviewed)abstract
- The hot Neptune desert is a region hosting a small number of short-period Neptunes in the radius-instellation diagram. Highly irradiated planets are usually either small (R less than or similar to 2 R-circle plus) and rocky or they are gas giants with radii of greater than or similar to 1 R-J. Here, we report on the intermediate-sized planet TOI-2196 b (TIC 372172128.01) on a 1.2 day orbit around a G-type star (V = 12.0, [Fe/H] = 0.14 dex) discovered by the Transiting Exoplanet Survey Satellite in sector 27. We collected 41 radial velocity measurements with the HARPS spectrograph to confirm the planetary nature of the transit signal and to determine the mass. The radius of TOI-2196 b is 3.51 +/- 0.15 R-circle plus, which, combined with the mass of 26.0 +/- 1.3 M-circle plus, results in a bulk density of 3.31(-0.43)(+0.51) g cm(-3). Hence, the radius implies that this planet is a sub-Neptune, although the density is twice than that of Neptune. A significant trend in the HARPS radial velocity measurements points to the presence of a distant companion with a lower limit on the period and mass of 220 days and 0.65 M-J, respectively, assuming zero eccentricity. The short period of planet b implies a high equilibrium temperature of 1860 +/- 20 K, for zero albedo and isotropic emission. This places the planet in the hot Neptune desert, joining a group of very few planets in this parameter space discovered in recent years. These planets suggest that the hot Neptune desert may be divided in two parts for planets with equilibrium temperatures of greater than or similar to 1800 K: a hot sub-Neptune desert devoid of planets with radii of approximate to 1.8-3 R-circle plus and a sub-Jovian desert for radii of approximate to 5-12 R-circle plus. More planets in this parameter space are needed to further investigate this finding. Planetary interior structure models of TOI-2196 b are consistent with a H/He atmosphere mass fraction between 0.4% and 3%, with a mean value of 0.7% on top of a rocky interior. We estimated the amount of mass this planet might have lost at a young age and we find that while the mass loss could have been significant, the planet had not changed in terms of character: it was born as a small volatile-rich planet and it remains one at present.
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