PROXIMA CENTAURI B: DISCOVERY AND HABITABILITY XIANG ZHANG

Transcription

1 PROXIMA CENTAURI B: DISCOVERY AND HABITABILITY XIANG ZHANG

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3 Discovery methods of exoplanets Discovery Method Number Astrometry 1 Imaging 44 Radial Velocity 621 Transit 2707 Transit timing variations 15 Eclipse timing variations 8 Microlensing 44 Pulsar timing variations 5 Pulsation timing variations 2 Orbital brightness modulations 6 Total 3453 Data from NASA exoplanet Archive. Updated 22/02/2017.

4 Discovery methods of exoplanets Bennet, Jeffrey, et al. The essential cosmic perspective. Addison-Wesley, 2008.

5 Discovery method: Transit Bennet, Jeffrey, et al. The essential cosmic perspective. Addison-Wesley, 2008.

6 The Kepler Mission Objective: Determining the frequency of Earth-sized planets in and near the habitable zone of Sun-like stars. Observation: Monitoring about 150,000 main sequence stars for several years Confirmed planets: 2330 (up to 16/02/2017) Borucki, William J., et al. "Kepler planet-detection mission: introduction and first results." Science (2010): Koch, David G., et al. "Kepler mission design, realized photometric performance, and early science." The Astrophysical Journal Letters (2010): L79.

7 Discovery method: Radial velocity K is the amplitude of radial variations of a star of mass M_* that are introduced by an orbiting planet of mass M_p. Lissauer, Jack J., and Imke De Pater. Fundamental planetary science: physics, chemistry and habitability. Cambridge University Press, 2013.

8 High Accuracy Radial velocity Planet Searcher (HARPS) A fibre-fed, cross-dispersed echelle spectrograph installed on the ESO's 3.6m telescope at La Silla Observatory in Chile. Precision: 1 m/s Has discovered over 130 exoplanets Mayor, M. et al. "Setting new standards with HARPS." The Messenger 114 (2003): 20.

9 The Alpha Centauri System Closest star system to the Solar system. Distance: 4.37 light years Composed of three stars: Alpha Centauri A Alpha Centauri B Alpha Centauri C (also known as Proxima Centauri)

10 A planet discovered in 2012? Exoplanets down to the size of Earth have been found, but not in the habitable zone. Dumusque, Xavier, et al. "An Earth-mass planet orbiting Alpha Centauri B." Nature (2012):

11 And then there were none The 3.24 d signal observed in the Alpha Cen B data almost certainly arises from the window function of the original data. Rajpaul, Vinesh, Suzanne Aigrain, and S. Roberts. "Ghost in the time series: no planet for Alpha Cen B." Monthly Notices of the Royal Astronomical Society: Letters (2016): L6-L10.

12 Proxima Centauri b discoverd Anglada-Escudé, Guillem, et al. "A terrestrial planet candidate in a temperate orbit around Proxima Centauri." Nature (2016):

13 Proxima Centauri b discoverd Discovery method: Radial velocity Instruments: HARPS and the Ultraviolet and Visual Echelle Spectrograph (UVES), both at ESO Doppler semi-amplitude: 1.4 m/s Signal period: 11.2 day Anglada-Escudé, Guillem, et al. "A terrestrial planet candidate in a temperate orbit around Proxima Centauri." Nature (2016):

14 Some properties of Proxima b Anglada-Escudé, Guillem, et al. "A terrestrial planet candidate in a temperate orbit around Proxima Centauri." Nature (2016):

15 Possible internal structures Possible radius: R_Earth Minimum radius: A Mercury-like planet with 65% core mass fraction Maximum radius: An ocean planet with 50% water in mass Brugger, B., et al. "Possible Internal Structures and Compositions of Proxima Centauri b. The Astrophysical Journal Letters (2016): L16.

16 Orbital resonance

17 Orbit of Proxima b -- 1:1 or 3:2? Proxima b s obliquity is likely null and its spin is either synchronous or in a 3:2 spin-orbit resonance, depending on the planet s eccentricity and level of triaxiality. Ribas, Ignasi, et al. "The habitability of Proxima Centauri b-i. Irradiation, rotation and volatile inventory from formation to the present." Astronomy & Astrophysics 596 (2016): A111.

18 Temperature Turbet, Martin, et al. "The habitability of Proxima Centauri b-ii. Possible climates and observability." Astronomy & Astrophysics 596 (2016): A112.

19 Turbet, Martin, et al. "The habitability of Proxima Centauri b-ii. Possible climates and observability." Astronomy & Astrophysics 596 (2016): A112.

20 Turbet, Martin, et al. "The habitability of Proxima Centauri b-ii. Possible climates and observability." Astronomy & Astrophysics 596 (2016): A112.

21 Proxima Centauri: a star with flares Davenport, James RA, et al. MOST Observations of our Nearest Neighbor: Flares on Proxima Centauri. The Astrophysical Journal Letters (2016): L31.

22 Proxima Centauri: a star with flares Observational instrument: microsatellite Microvariability and Oscillations of STars (MOST) Flare occurrence rate: 63 flares per day Superflares with energies 10^33 erg occur about 8 times per year Davenport, James RA, et al. MOST Observations of our Nearest Neighbor: Flares on Proxima Centauri. The Astrophysical Journal Letters (2016): L31.

23 Stellar wind from Proxima Centauri Garraffo, Cecilia, Jeremy J. Drake, and Ofer Cohen. The Space Weather of Proxima Centauri b. The Astrophysical Journal Letters (2016): L4.

24 High-energy irradiation Ribas, Ignasi, et al. "The habitability of Proxima Centauri b-i. Irradiation, rotation and volatile inventory from formation to the present." Astronomy & Astrophysics 596 (2016): A111.

25 Proxima Centauri, a history Barnes, Rory, et al. "The Habitability of Proxima Centauri b I: Evolutionary Scenarios." arxiv preprint arxiv: (2016).

26 The evolution of its habitable zone The habitable zone moved inwards, while the planet Barnes, Rory, et al. "The Habitability of Proxima Centauri b I: Evolutionary Scenarios." arxiv preprint arxiv: (2016).

27 XUV flux evolution for Proxima Ribas, Ignasi, et al. "The habitability of Proxima Centauri b-i. Irradiation, rotation and volatile inventory from formation to the present." Astronomy & Astrophysics 596 (2016): A111.

28 Any water left for Proxima b? Barnes, Rory, et al. "The Habitability of Proxima Centauri b I: Evolutionary Scenarios." arxiv preprint arxiv: (2016).

29 Conclusions: is Proxima b habitable? Aspects Internal structure Orbital resonance Stellar flare Space weather Evolution history Habitability Possible Possible Maybe not Maybe not Possible

30 The Trappist-1 system Gillon, Michaël, et al. "Seven temperate terrestrial planets around the nearby ultracool dwarf star TRAPPIST-1." Nature 542 (2017),

31 The Trappist-1 system Gillon, Michaël, et al. "Seven temperate terrestrial planets around the nearby ultracool dwarf star TRAPPIST-1." Nature 542 (2017),