1. Earth-like planets in habitable zones around L (and T) dwarfs José A. Caballero /xó-se ka-ba-jé-ro/ Departamento de Astrofísica Universidad Complutense de Madrid Detecting planets around low- mass stars (and brown dwarfs): the gateway to terrestrial planets

2. Earth-like planets in habitable zones around L (and T) dwarfs  The Sun has planets  Solar-like stars have planets (51 Peg 1.11 M sol, HD 209458 1.01 M sol...)  M-type stars have planets (HO Lib/GJ 581 0.31 M sol, GJ 317 0.24 M sol, OGLE-05-390L 0.22 M sol...)  And in between? (~0.08-0.01 M sol )  Jupiter has giant satellites (0.001 M sol )

3. “There are things known and there are things unknown and in between are the Doors” (William Blake) “There are things known and there are things unknown and in between are the L (and T) dwarfs” (José A. Caballero) L spectral type: T ~ 2200-1300 K T spectral type: T ~ 1300-700 K T Leuchars (July, 1971-2000) = 292.2 K T Jupiter (1 bar) = 165 K ChaHa8 (M6.5, ~3 Ma) ( 0.085 ± 0.015 M sol ) Joergens & Müller (2007, ApJ, 666, 113) MOA-2007-BLG-192-L (?, ?) ( 0.060 +0.028 -0.021 M sol ) Bennet et al. (2008, ApJ, in press, arXiv:0806.0025)

4. Earth-like planets in habitable zones around L (and T) dwarfs: a reasonable idea! Very young (1-10 Ma), M-type low- mass stars and brown dwarfs in star- forming regions (Chamaeleon,  Orionis): * have (protoplanetary?) discs [disc fraction ~50%] * will be L and T dwarfs 1 Ga later [age typical of field ultracool dwarfs] Masses of 1 Ga-old field ultracool dwarfs: M = 0.075-0.040 M sol (L) M = 0.040-0.015 M sol (T)

5. HZ (1): “a region of space where conditions are favourable for life (as it may be found on Earth)” HZ (2): “an interval of orbital separations to a star where liquid water can exist (at a normal pressure)” T surf = 273-373 K [but: runaway greenhouse] Kasting et al. (1993): HZ in FGK stars... Joshi et al. (1997): HZ in M stars... HZ in L stars and brown dwarfs? Variability in brown dwarfs: atmospheres and transits ( Caballero & Rebolo 2002, ESA SP-485, 261) In: Proceedings of the First Eddington Workshop on Stellar Structure and Habitable Planet Finding, 11-15 June 2001, Córdoba, Spain

6. The radiative energy balance equation: (1-A)  R 2 p S = 4  R 2 p  T 4 eff,p A, R p, T eff,p : planetary albedo, radius, and effective temperature S = L/4  a 2 (power per surface area) L: luminosity of central object a: average separation (semi-major axis) Planetary surface temperature, T surf,p : T 4 surf,p = T 4 eff,p (1+2  /3)  : effective optical thickness Effective vs. surface planetary temperatures: the effective optical thickness Surface pressure Greenhouse gases (CO 2 ) Oceanic and eolic global patterns (orbital locking, ocean-land distribution... Tropospheric adiabatic gradient,  Deviations of the energy balance equation (internal energy source –tides-, non-unity atmospheric emissivity, flux factor for a slow- rotating, thin-atmosphere planet) Planet  Venus160 Earth0.80 Mars0.38

7. Low orbital eccentricity e = 0 (high-amplitude) stable tides Lower albedoes  closer planets  easier detection No appreciable activity found in field ultracool dwarfs Peak of photosynthetic efficiency of Bacterioclorophyll a (Chloracidobacterium thermophilum) at 750-800 nm The habitable zones around L (and T) dwarfs: astrobiological restrictions Synchronous rotation (global circulation vs.  T surf in both hemispheres) Relative indetermination of the nIR planetary albedo (theoretical models predict very low albedoes) Ultraviolet emission and magnetic fields (flares in M-type dwarfs, Jupiter-Io) Photosynthesis in the near-infrared ?

8. A new complication: the Roche radius (from Aggarwal & Oberbeck 1974) R Roche,AO74 = 1.38 (  * /  p ) 1/3 The habitable zones around L (and T) dwarfs: a toy model Theoretical isochrones of the Lyon group Orbital separation a  Orbital period P (Kepler’s third law) Albedo A = 0.10 Effective optical thickness  = 1.0 M p = 5 M Earth

9. Detectability of earth-like planets in habitable zones around L (and T) dwarfs: Transits Caballero (2006, PhD, thesis) Blake et al. (2008): Near infrared monitoring of ultracool dwarfs: prospects for searching for transiting companions Search for transits  Search for atmosheric variability (CLOUDS: Continuous Longitude Observations of Ultracool DwarfS)

10. Detectability of earth-like planets in habitable zones around L (and T) dwarfs: Radial velocity Desidera (1999) Caballero (2006, PhD, thesis) Viki Joergens Hugh Jones Jamie Lloyd Cullen Blake A high-resolution near-infrared spectrograph with resolution of 5 m/s would detect 5 M Earth exoplanets around L0-7 dwarfs in less than two nights

11. The planet hunters: NAHUAL @ 10.4 Gran Telescopio Canarias, JHK, High Resolution + Image Slicer R = 61500 (2nd generation instrument) CARMENES @ 3.5 Calar Alto Teleskop, JH, High Resolution R = 60000? (Phase A)