Pos(AASKA14)120

PoS(AASKA14)120 http://pos.sissa.it/ 35 currently known ∼ , & “Cradle of Life” WG 3 200 known stars and ∼ Caltech, Pasadena, CA, USA 3 , Gregg Hallinan JPL; 3 , 2 2 , T. Joseph W. Lazio 1 ∗ [email protected] Speaker. Planetary-scale magnetic fields are aplanet’s window atmosphere to and a surface planet’sets for interior of life. and the provide solar The shieldingnetic system of Earth, fields. all the Mercury, contain When Ganymede, internal coupled andmagnetosphere to dynamo the interaction energetic currents giant (keV) (compression that plan- electrons, or generate such magneticor planetary-scale as magnetosphere-satellite reconnection), mag- coupling, those magnetosphere-ionosphere the produced polar byof regions solar of intense, wind- a coherent, planetary circularly magnetic polarized fieldbe cyclotron are as radio the emissions. intense place as These solar emissionsMHz – ones range, that – and may are up produced toprovide constraints by 40 on all MHz the magnetized at thermal Jupiter. planets state,cult to composition, in Detection determine and the by of dynamics other solar of similar means system theirprocess – emissions as interior and in from well – of the as exoplanets the very an diffi- physics will improved of understandingDetailed star-planet of knowledge plasma the of planetary interactions. magnetospheric dynamo emissions fromexoplanets solar motivated system both planets theoretical and and observational theexoplanets. work discovery on of Scaling magnetospheric laws emissions and from theoreticalof-magnitude frameworks were predictions built of and frequencies extrapolated and topresent flux obtain stage densities order- of of the exoplanetary theory radioof suggests emissions. comparative that exo-magnetospheric The radio physics, detection but of alsosuch permit exoplanets as to will measure develop rotation exoplanetary the or parameters newdiscovery orbit field of inclination. the first exoplanet. Observational searchesWe review started the even scientific return before of the the detection confirmed of observational of searches, exoplanetary and radio discuss emissions, the the future current promiseLOW. status in To the the context of extent SKA, especially that SKA1- frequency Jupiter’s limit magnetic of field 50 MHz is implies not thatthe SKA1-LOW exceptionally currently will strong, planned likely detect sensitivity the Jovian-mass of current planets.detected SKA1-LOW, lower With we to about estimate 10 that pc. a Within this Jupiter-like volume planet there are could be exoplanets, and this number should increaseto substantially transits with and powerful coming ground-based space instruments. missions The dedicated if accessible volume scaling will laws be much derived increased in ourpermitting solar to system measure can lower mass be planets’ reliably dynamos extrapolated and to magnetospheres. exoplanetary systems, ∗ Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence. LESIA, CNRS – Obs. Paris, Meudon, France; c

E-mail: 1 Philippe Zarka Magnetospheric Radio Emissions from Exoplanets with the SKA Advancing Astrophysics with the Square KilometreJune Array 8-13, 2014 Giardini Naxos, Sicily, Italy PoS(AASKA14)120 [MHz] ce 150 MHz, ∼ Philippe Zarka ) detected by radial velocity www.exoplanet.eu 2 Planets appear to be the most favourable cradle of life in the context of present astrobiology. Experience from our solar system planets and theory tell us that the most intense electromag- In section 2, we summarize our observational and theoretical knowledge of solar system mag- The Earth, Mercury, Ganymede, and the giant planets of the solar system all contain internal Accelerated charged particles in a magnetic field generate radio emissions. The most intense With the growing number of exoplanets (>1800, cf. netic emissions from magnetospheres result fromelectrons coherent in cyclotron strong radiation, magnetic through fields which generate keV MHz intense, to circularly tens polarized, of sporadic MHz emissions range ina (synchrotron the much emission lower is also intensity). producedof at Measuring these higher the frequencies, cyclotron but dynamic emissions with spectrainclination can and in give the intensity presence access and of to satellites. (circular) the polarization above physical parameters,netospheres as and radio well emissions, as review orbit thewind-planet drivers interactions, for and magnetosphere-ionosphere electron or acceleration magnetosphere-satellite (star-planet coupling),extrapolate or and them stellar to various exoplanetarying conditions. observations. In Non section detections 3, put we summarize a past stringent and limit ongo- on planetary emission above dynamo currents that generatearise planetary-scale from magnetic differential rotation, fields. convection, compositionalobjects’ These dynamics, interiors. internal or Interaction a dynamo of combination currents thesea of magnetosphere, planetary-scale these a magnetic in cavity fields in with thecharged the wind particles solar dominated are wind by accelerated creates the to planet’stion keV-MeV magnetic at energies field. the by boundaries, Inside various interaction the processes with cavity, (magnetic embedded moons, reconnec- waves. . . ). ones are produced atthermal high coherent magnetic process latitudes well-identified (so-called today,Instability auroral, that (CMI) involves circumpolar (Treumann keV 2006). regions) electrons: This by process theare a widely Cyclotron thus operates non- Maser at strong all radio magnetized emitters planets,met which (Zarka by 1998). energetic electrons Emitted movingvalues frequencies along (a are magnetic few kHz) local field far cyclotron lines. from frequencies the Their planet, up range to extend the from maximum very surface cyclotron low frequency (f Radio Emissions from Exoplanets 1. Introduction or transits, which cover a broadsirable range to of sizes, determine masses the and physical orbital propertiesstudies. parameters, of Topics it exoplanetary of is systems interest increasingly to include de- carry magnetosphericplanetary in-depth dynamics, rotation, energetics comparative planetary of dynamos star-planet (large-scale interactions, planetaryin magnetic fields protecting play the an planet’s surface important role and atmosphere), etc. and hints of detections remainobservations, to from be early confirmed. science In operationsspecial section through attention 4, Phase to we 1 synergies, examine towavelengths. both the Phase prospects with 2. for other SKA In SKA section observations 5, and we with give observations a at2. other Background and Motivation 2.1 Solar system magnetospheres and radio emissions PoS(AASKA14)120 ) ) 6 τ − 10 ∼ Philippe Zarka ) or infrared ( 9 − 10 ∼ . The specific case of coronal 5 − 10 ∼ , as illustrated in Figure 2. This scaling 3 Jy at Earth (Zarka 2004)), as intense as − 7 10 10 × times weaker than the CMI. It is also much more ≥ 3 5 2 MHz. They are reflected off by the Earth’s iono- a few ∼ ∼ 1, much larger than in the visible ( K, flux density ∼ 19 10 T). For most solar system planets, planetary surface field magnitude is ≥ 4 − It was soon realized that due to the high brightness of the galactic radio background, Jupiter’s A scaling law was first found to relate the average magnetospheric radio output with the total The physical mechanisms underlying these scaling laws include magnetospheric compressions Due to the high efficiency of the CMI, Jupiter’s auroral radio emissions are extremely intense MeV electrons also produce synchrotron emission in Jupiter’s inner magnetosphere (so-called 1 G, thus emitted frequencies lie below solar ones (which arefavourable mostly planet-star due contrast to plasma radiation), as shown on Figure 1. Considering this decametric CMI emission cannot be detectedexisting at instruments. stellar The distances search (several pc) fortary even more directions: with intense (i) the planetary establishing largest emissions empiricalets scaling followed and laws two extrapolating for complemen- them radio to emissions exoplanets, fromemissions and solar and (ii) system identifying the plan- the regime primary of enginesions. parameters of which planetary allow radio this engine to produce more powerful emis- solar wind power input (dominatedsection by (Farrell the et solar al. wind 1999), ram with pressure) a on proportionality the constant magnetospheric cross by the solar wind or CME and associated shocks, magnetic reconnection between the magnetic ranges, observational searches for lowfore frequency the radio confirmed emission discovery from of any exoplanets exoplaneta started (Zarka difficult even 2011, task be- and and references therein). noery It unambiguous proved of detection to many has be exoplanets been by obtained radialobservational velocities yet work and (see on transit magnetospheric below). methods emissions has But from motivated the exoplanets. both discov- theoretical and mass ejections (CME) impacting aA magnetosphere second was scaling also law considered (Grießmeier wasconvected by et found the al. to solar wind relate 2007). on theal. the same magnetospheric 2007), cross radio with section output a (Zarka with proportionality etlaw al. constant the was 2001, incident found Grießmeier Poynting et to flux applyscaling law more based generally on to totaland any power at plasma input), least flow-obstacle including to interaction Io-Jupiter one(Zarka (contrary and documented 2010, to Ganymede-Jupiter and example interactions, the references of therein). magnetized binary star (the RS CVn system V711 (brightness temperature stable in time, showing variations at timescales longer than days/weeks. 2.2 Predictions for radio emissions from exoplanets radiation belts) (de Pater 2004). Its spectrumcies, extends up over to high several harmonics GHz. of The the synchrotronefficient cyclotron process than frequen- is the a CMI, nonthermal so incoherent that mechanism, this much emission less is 10 Radio Emissions from Exoplanets = 2.8 B [G] ;≤ 1 G = 10 sphere and thus cannot be detected fromfield the (up ground. to Jupiter, 14 having a G),sub-millisecond stronger emits dynamo to CMI and several surface radiation tens up of todiotelescopes. minutes. 40 MHz, These which bursts consists are of easily bursts detected of by duration ground-based from ra- PoS(AASKA14)120 6 to 10 3 900, so that × Philippe Zarka times larger than that of the solar 400, and Neptune’s by 6 × to 10 3 4 100, Uranus’ by × G), the exoplanet plays the role of Io and its parent star that of 2 − 1 20, Saturn’s by 10 × ≥ Spectra of astronomical radiosources detected from the Earth’s vicinity. Auroral planetary spectra For exoplanetary magnetospheres governed by internal processes (magnetosphere-ionosphere For exoplanets orbiting very close to their parent star, especially hot jupiters, it was found coupling), it was found that for giant planets orbiting at a few AU from their parent star, the auroral Jupiter. Extrapolating the above scalingtimes laws, that their of radio Jupiter. output Willes shouldorbits & accordingly around Wu be (2005) magnetic 10 studied white the dwarf particular stars,emission acting case with large as of flux a terrestrial densities. unipolar planets These inductor, inplanet systems and close surviving could generating the be CMI stellar remnants radio expansion of phase main and sequence back stars in with stable a orbit. Figure 1: lie below the Earth’smetric-decimetric ionospheric (synchrotron) cutoff, emissions. except Jupiter’s Normalizedspectrum must decametric to be the (CMI, upscaled same auroral by observer and distance Io-induced) of and 1 AU, Jupiter’s wind-Jupiter interaction (Zarka 2007). Inmagnetized the (surface unipolar field inductor case, the star needs to be strongly fields of the flow andductor” of interaction the of obstacle, a and conductingfield non-magnetized Alfvén lines body waves (of produced (the Jupiter). moon by Allradio Io) these the mechanisms moving so-called waves. lead across “unipolar to magnetic in- Jardine the accelerationsphere’s & of nose Cameron electrons through that (2008) a in proposed runaway turnmagnetosphere-ionosphere direct emit mechanism. coupling, independent electron Nichols of acceleration the (2011) solar at estimated wind. the the power magneto- dissipated by that star-planet magnetic/plasma interactions (SPIreconnection, – and incl. unipolar inductor) magnetospheric involve compression, a magnetic power 10 Radio Emissions from Exoplanets all are grouped within 2-3 orders of magnitude. PoS(AASKA14)120 Philippe Zarka ) the average value × (resp. 100 × 5 1” from their parent star), polarization and temporal modula- times that of Jupiter if the star has a strong X-UV output and the 5 discussed in the text. Insets sketch the types of interaction. τ to 10 4 . Note that planetary radio bursts can reach 10 3 − 10 × 1%) of the time. The thick bar extrapolates to hot jupiters the magnetospheric interaction 2 ∼ ∼ Scaling law relating magnetospheric (Earth, Jupiter, Saturn, Uranus and Neptune) and satellite- All theoretical predictions thus suggest that exoplanetary magnetospheric radio emissions Finally, it must be noted that CMI radiation is strongly circularly/elliptically polarized (syn- 10% (resp. Figure 2: induced (Io, Ganymede, Callisto) averageobstacle. radio power Dashed to line incident has Poyntinga slope flux coefficient 1, of emphasizing the the plasma proportionality flow between on ordinates the and abscissae, with tions should allow to discriminate stellarsimulations and exoplanetary presented radio in emissions, the as demonstrated nextidentification by section. of the CMI Theoretical radio predictions emission thus fromwhat exoplanets suggest do is that we possible, detection have so to and that learn it through is radio worth emission observing. detection But ? much stronger than Jupiter’slarge are enough likely instruments. to exist, SporadicCMI and radio further thus emission amplifications be generated may detectable withinlow occur frequencies at the e.g. (10’s stellar exoplanet’s of MHz, magnetosphere distances due depending istor with on to likely the driven scintillations. planetary to CMI field be emission, strength), restricted being whereashigher unipolar excited to frequencies induc- by (100’s MHz the to exoplanet a in few GHz). the stellar magnetic field,chrotron may emission reach from Jupiter’s radiation beltsso is that linearly it polarized), is and always beamedradiation anisotropically deeply is modulated essentially by unpolarized the andlution sporadic. planetary (known exoplanets rotation. Even orbit in at Conversely, solar/stellar the absence plasma of sufficient angular reso- planet has a fast rotation (P=1-3 hours). Radio Emissions from Exoplanets ∼ radio output may reach 10 (solid) and satellite-planet electrodynamic interactionsRS (dashed). CVn magnetic The binary orange V711 dot illustrates the case of the PoS(AASKA14)120 Philippe Zarka 6 ) (Berge & Gulkis 1976). Magnetospheric radio emissions ◦ 10 ∼ Each planetary magnetosphere – in our solar system – is a space plasma physics laboratory. The CMI theory provides a well-understood, quantitative framework for studying magneto- Similar to the question of solar system formation, which requires comparison of numerous Existence of a magnetosphere is also an essential ingredient in favour of the possibility to de- Planetary magnetic fields are a window to a planet’s interior, and magnetospheric radio emis- In-situ spacecraft exploration and remote electromagneticted (Radio, to UV, IR, infer their X) general observations properties, permit- butfield also amplitude, revealed tilt, numerous distance specificities to related to Sun,sition. the . presence . magnetic of embedded moons and rings, atmospheric compo- spheric radio emissions properties andronments using and them processes. as Recent a simulationsthe diagnostic in measurement that tool of framework of the (Hess planetary radio &tary plasma dynamic Zarka system, envi- spectrum 2011) in – showed addition in that to allowing intensitywould us and bring to the polarization discriminate following – between informations of (difficult stellar or and anthese impossible exoplanetary exoplane- to objects, emissions, determine as by other illustrated means)and about in tilt, Figure one will 3 be : ableing to tidal in measure spin-orbit addition the synchronization), planetary the to rotationmass), orbit the and inclination and revolution exoplanet’s (resolving identify periods magnetic the the (effectively ambiguity field test- primarytospheric on engine intensity compression, the of stellar planet’s the wind-magnetosphere electromagnetic magnetic reconnection, outputinteraction or of if “unipolar the inductor” the system: exoplanet SPImagnetospheric is (magne- processes weakly (magnetosphere-ionosphere magnetized or andporal magnetosphere-moon the modulations coupling). star different strongly from Tem- magnetized), thepresence or planetary of moons rotation internal or and the orbital signature of periods the could stellar even wind reveal activity. the systems to infer general properties, therelies recent on field of a comparative corpus magnetospheric of physicswith (which 6 the detection very of different exoplanetary planetary radiorameters magnetospheres emissions, (star-planet distance, so that stellar will far) magnetic permit field will and tomagnetic considerably wind explore field, strength, expand a rotation, stellar large orbit X-UV range flux, inclination. . planetary of .study ), pa- better interactions understand between the plasma diversity flows of (magnetized planetaryvarious dynamos, or regimes, not) and and infer obstacles the (magnetizedlaws energy or will dissipation not) be involved in in confirmed SPI. and/orpredicting Furthermore, modified capability. the or above refined, scaling expanding their range of application and their are thus a unique tooldynamics for (including probing the exoplanet’s effect interior ofderstanding structure spin-orbit of (composition, locking the planetary for thermal dynamo hot state) process. jupiters), and leading to an improved un- sions are a proberadio of emission (Burke planetary & magnetic Franklin 1955) fields.ment provided the of first Ground-based the proof Jovian detection of magnetic existence ofits and field. interior, Jupiter’s the and Its first decametric to measure- monitoring discover the allowed existence onemagnetosphere of to a (Bigg define strong 1964). interaction accurately between the Maps the rotationfield moon of Io of relative the and to the synchrotron the Jovian emission rotation axis revealed ( the tilt of the magnetic Radio Emissions from Exoplanets 2.3 Motivations for the search for exoplanet’s radio emissions PoS(AASKA14)120 Philippe Zarka destruction by 3 orbit inclination, for emission of a orbit inclination, for emission of a ◦ ◦ and 0 ◦ 7 orbit inclination, for emission (a) of a full exoplanet’s auroral oval and (b) an auroral active sector Simulated dynamic spectra in intensity (a,b,d,g) and circular polarization (e,h) and associated ◦ Figure 3: parameters of the system that can beaxis determined: and (a,b,c) 0 exoplanetary magnetic field aligned with the rotation velop life: it ensures shielding of the planet’s atmosphere and surface, preventing O fixed in local time.full (d,e,f) auroral aligned oval. exoplanetary (g,h,i) magnetic exoplanetary fieldfull magnetic and auroral field oval. 15 tilted From by (Hess 15 & Zarka 2011). cosmic rays bombardment as well asits atmospheric erosion atmospheric by escape, the as stellar ionized wind(Grießmeier material or CMEs. et following It dipolar al. also field lim- lines 2004,ery returns tool, 2005). to complementary the to atmosphere Finally, radial radio velocitiesfinding or planets detection transit (giant may measurements or evolve terrestrial) because around it as active, is an magnetic more or independent adapted variable to discov- stars. Radio Emissions from Exoplanets PoS(AASKA14)120 ) υ And, υ exoplanet.eu Philippe Zarka 1 min., for which 100 mJy sensitivity ∼ ∼ Boo over the 40 hours of τ Jy near the position of the undetected planet. Boo at 74 MHz with µ τ 8 Boo field integrated over 40 hours. The crosshairs indicate τ 1 mJy level, setting this flux density level as an upper limit ∼ 15 and 30 MHz, specifically looking for pulses shorter than And or 55 Cnc. Other selection criteria included the existence of a strong stellar ∼ υ Boo, (left) 153 MHz GMRT image of the τ These non detections, summarized in Figure 5, can be due to the absence of significant emis- Most of the searches focussed on known exoplanetary systems discovered by radial velocity or Observations at the VLA provided no detection of Eri, HD 128311) (Winterhalter et al. 2006, George & Stevens 2007, 2008). A recent very Boo at GMRT, for 40 h (half of the exoplanet’s orbital period) covering all orbital/rotational ε significant negative result, shown inτ Figure 4, comes fromphases, that the provided deepest no 150 detection at MHzfor observation both of quiescent and2013). rotationally modulated No radio detection emission eitherUTR-2 from was between obtained a on hot a Jupiter dozenstatistical (Hallinan targets data et accumulation observed al. led during to a atarget few sensitivity (Zarka hours between et each 100 al. mJy at 1997, and Ryabov 1500 et mJy al. depending 2004). on the (Farrell et al. 2003,0.048 2004), mJy or of sensitivities HD (Lazio 80606obtained & with at Farrell the 330 2007, GMRT MHz at Lazio and 153,with et 1465 244 resp. MHz and al., 2.1 614 with 2010a). mJy, MHz resp. 2 on mJy Negative 1.7 HD and results 189733 mJy 0.16 (Lecavelier and were mJy et also sensitivities, al. and 2009, at 2011) 153 MHz on various targets ( transits measurements. Application of scaling laws to the exoplanet census (e.g. from observation. Time series at time resolutionmJy of respectively. 4 No sec evidence (red) of andFrom emission 17 (Hallinan is min et present (blue) al. at have 2013). any rms observed noise orbital/rotational of phase 65 of mJy the and 4 planet. 3. Past and ongoing observations and results guided target selection (Lazio et al. 2004,such Grießmeier as et al. 2007, 2011), with promising candidates And), although the sporadicity ofet observed al. signatures makes 2008, them and references not therein). fully convincing (Shkolnik magnetic field, measured by(Farès Zeeman-Doppler et imaging al. (as 2010), for planets80606), the or with transiting planets a for planet very which HD elliptical SPI was 189733) orbit tentatively and detected via a optical periastron measurements very (HD 179949, close to the star (HD (right) Light curves for the right circularly polarized flux at the position of the position of the star (and planet). The rms noise in 400 Figure 4: Radio Emissions from Exoplanets PoS(AASKA14)120 15 ≤ sur f ace 150000 3.9 mJy ∼ ∼ Philippe Zarka upper limits between 100” resolution, σ ≤ 5 mJy/beam). The high- ≤ > 26 G at 74 MHz, B sur f ace 2 MHz bands, × 120” resolution, ≤ 9 2 MHz bands, × 120, 28, 19, and 18 mJy respectively (Sirothia et al. 2014). For the latter ∼ 20-80 MHz), in full polarization. HJUDE relies on a relatively small instrument ∼ Boo) (Hartman et al. 2013). UTR-2 has the advantage of a large effective area ( τ More encouraging results were obtained at two occasions with the GMRT: (i) a Ongoing targeted searches are carried on (by the authors of this chapter) with UTR-2 and We are thus in a situation where efforts intensify, both for targeted observations (still at a Systematic searches in survey data will continue in the next releases of the TGSS, and is ) and observes at the lowest frequencies accessible from the ground (10-32 MHz), but measures 2 two, detection is marginalfurther and observations should are be needed to confirmedThe exclude authors by do possible not deeper coincidence claim observations. any with unambiguous detection,up. a but For For background this the may all radio other be source. 171 the four top exoplanetary ones, of systems, the TGSS iceberg non showing detection provides 3 LOFAR, several tens of hours beingrecently distributed on 32 a hours few dozen on targets 55frame (a Cnc). of few hours the More per HJUDE target, extensive project, and (incl. observations aiming are at carried thousands out of observing with hours the distributed LWA in on the a few targets modest level with large instruments) and systematic searches in sky surveys (that become available Radio Emissions from Exoplanets sion from these targets (permanentmagnetic of dipole moments at of observation the epochs, observedpermitting exoplanets due too CMI to weak emission to their to generate occur intrinsic a at variability),> surface the magnetic observed to 54 field frequencies (B G atemission 150 at MHz. . the . ), time or ofangles observation to relative to (CMI the the indeed magnetic Earth field produces lying inemission narrowly the outside as beamed source a the ; emission function this at beaming of beaming time). specific strongly patternemission affects In from of the the Jupiter visibility the case but of of planet’s the the UTR-2, sensitivity radio the was frequency moderate. range matches the decametric emission was detected in 2009P-11 at that 153 includes MHz a atan Neptune-mass <1 eclipse transiting when FWHM exoplanet, the beam and planet distance passedrepeated the in from behind light 2010 the the did curve star not system was detect (Figure HAT- any consistent 6)suggesting significant ; a signal with in but variable the an planetary radio equally light emission sensitiveet curve or observation near al. the a same 2013). false position, positive (ii)encompasses (5% The 175 probability) first exoplanetary in published 2009 systems; part (Lecavelier 164509) for of TGSS 4 the radio sources of ongoing were them GMRT found sky coincidingwith (61 with survey flux Vir, or (TGSS) densities 1RXS1609, located at of very HD close 150 86226, to MHz their and coordinates, HD 8.7 mJy and 136 mJy. m a single linear (EW) polarizationlargest and present has radio to telescope deal (interferometer)to with in 10 a the MHz polluted range with radio 30-250 reducedits spectrum. MHz, sensitivity low (van that band LOFAR Haarlem may is ( et extend the al. down 2013). Exoplanet search is conducted in frequency part is near complete whereas the low-frequency part is ongoing. (256 dipoles) in the 10-88at MHz exoplanet’s band, orbital periods) but and with fullcases. a polarization large measurements. duty Data cycle analysis (searching is for ongoing periodic in signals all starting in LOFAR’s Multifrequency Snapshotnorthern sky Sky survey Survey in (Heald the spectral et ranges al. 30-75 MHz (8 2014). The latter is a mJy/beam) and 120-160 MHz (8 PoS(AASKA14)120 Philippe Zarka 10 Time series of the 150 MHz flux density measured on July 16, 2009, in the direction of the radio Summary of previous attempts to detect radio emissions from exoplanets. Blue symbols are from Figure 6: source near HAT-P-11. Measurements havethe been right rebinned and to left 36 circular min.of polarizations. Triangles the The and planet’s two squares eclipse vertical correspond behindcurve – to the fitted dashed host to lines the star. indicate data The the points. beginning dashed From and horizontal (Lecavelier et the lines al. end show 2013). the box-shaped eclipse light Figure 5: the VLA, red from thevarious GBT, orange targeted from observations. the The GMRT, and bluethe cyan diamond average from emission is UTR-2. from the Arrows potential statistical are planetsdetection upper upper in from limit the limits Lecavelier from et solar from Lazio al. neighbourhood. et (2013). The al. orange star (2010b) is on the unconfirmed Radio Emissions from Exoplanets PoS(AASKA14)120 × 3 10 ≥ Jy across the Philippe Zarka µ Jy at 10 pc range, µ rather than × 1 − 0 10 ≥ ) between 70 and 7 σ Jy at Earth, i.e. 40 7 10 to 30 with respect to LOFAR in the ∼ 11 1” for SKA1-SUR and SKA1-MID at 0.5-1 GHz), it will ∼ 1 hour integration (Figure 7). Confusion noise affecting deep × 150 MHz are rare. It is thus needed to explore a large sample of ≥ Being little dependent on extrapolations of the scaling laws of section 2.2 to high-power ranges Experience from LOFAR, that uses elementary dipole antennas seeing a large fraction of the Jupiter bursts in the 30-40 MHz range can exceed 10 The result of past searches suggest that magnetospheric radio emissions much stronger than 11” for SKA1-LOW at 110 MHz, ∼ for reaching detectable emission levels (we will need emissions band 50-350 MHz, with 4images MHz will be a few timescomputed larger from in (Condon total intensity 2005)). atwill the Detection be lowest of less frequencies severely time-variable (dashed affected. and/or line Thus, circularly Jupiter-like infrom exoplanets Fig. polarized distances will 7, become emission of detectable several for parsecs. the(Ryabov first Even time et al. if bursts 2004) will are permit intrinsically to shorter, reach statistical long accumulation integration times without diluting the signal. the average flux densitylower. of SKA1-LOW, consisting the of some emission 250000 at dipoleswill in hour a bring radio-quiet timescale an site being (Dewdney improvement et aboutrange al. in one 2013), 50-250 sensitivity order MHz. by of a SKA1-LOW magnitude factor will have a sensitivity (1 Jupiter), and needing exoplanetary magnetic fields50 only MHz, slightly it larger is than highly Jupiter’s likely to that emit SKA1-LOW above will detect exoplanetary radio signals. sky at any time, taughtleast at us the that initial imaging – detection willaround – be stage, the because more target it powerful and allows than to tothermal better beamformed obtain remove noise. high observations the contribution dynamic at Beamformed of range observations sources will images,tational be cost reaching very – a useful the sensitivity targets to of detected monitorincluding order by predictor/estimator – of schemes imagery. at such the New as much imaging Kalman lower techniques filtersimaging compu- (Tasse are 2014), process also or on being decomposition the of developed, the Fourierthe transform efficiency of of the variable observation source time, imaging that in may the considerably future. improve 4.1 SKA Phase 1 targets with highest possible continuum sensitivity,lar preferably at inductor low driven frequencies CMI (although emission unipo- ( may reach hundreds ofgenerally MHz). not be At possible the to resolve SKAto exoplanet-star angular the systems. exoplanet’s resolution Once magnetosphere, a to signal an isto exoplanet-induced detected, exoplanet-independent attributing signal stellar it into activity the should star’s betemporal magnetic relatively modulations field, easy of or on the the basis signalor of (see full polarization section polarization and 2.3). (4-Stokes)Such are Thus measurements measurements should required, be in over wealy circular affected longsmooth by (V-Stokes) and or confusion, stable provided repeated with that time. observations the beam for shape each remains target. Jupiter’s and at frequencies Radio Emissions from Exoplanets for the first time atunambiguous. low enough frequencies). First hints of detection are encouraging4. but not Science yet outcome enabled by SKA PoS(AASKA14)120 Philippe Zarka 200 are known or ∼ larger than Jupiter’s for a Jovian-like × 12 1 to 10 times stronger than Jupiter’s up to a distance ∼ 35 exoplanets are currently known, and about 2500 known stars within 30 pc, ∼ 400 stars and white and brown dwarfs within 10 pc, out of which ∼ Predicted maximum emission frequency and expected radio flux for known exoplanets (in 2011, The search strategy should significantly evolve as compared to previous targeted searches. But it remains correct to assume that exoplanets closer to their parent star, or orbiting stars There are exoplanet at 1 AU fromorbiting a strongly magnetized solar-type stars. star), Thus and aemitting that systematic exoplanets. search unipolar should These inductor reveal detections a SPI will large give do numbermagnetic access of exist fields, radio- to for rotation numerous periods, exoplanets measurements orbits of inclinations, exoplanetary the and field SPI of regimes and comparative powers.around (exo-)planetary They exoplanets magnetospheric will (generating open physics, Io-Jupiter maysystems like allow to CMI study to radiation), further discover in and search moons will for life help signatures. to select favourable observable, and with about 200 currently knownsurvey planets. of It all will stars be (visible possible frompc, with the allowing SKA SKA to to site) detect conduct within any an 10of radio pc authoritative 10 emission and pc, a and large any fraction emissionall of known one those exoplanets order within should of 30 be magnitude monitored stronger (>1800 up planets to are a known distance today of within 30 >1100 pc. systems In parallel, with large X-UV flux, should emit stronger signals (e.g. 20 Figure 7: indicated by triangle symbols) for a rotation-independent2. planetary The magnetic field approximate and sensitivity the of scalingof several law instruments 4 of Fig. is MHz, shown or (for an 1line. equivalent h combination). of Frequencies integration below Confusion time 10 limit and(Grießmeier MHz for a et are bandwidth al. SKA1-LOW is not 2011). indicated observable by from the the dashed ground red (ionospheric cutoff). Adapted from Radio Emissions from Exoplanets PoS(AASKA14)120 exo- ), multi- 2 λ Philippe Zarka 1 sec to 1 min. ' t δ at 110 MHz, scaling as 2 ◦ 5 × 5 ∼ 1 MHz spectral channels) and 13 ∼ 1% (or ' f/f δ 50% of SKA1-LOW capabilities, SKA1-LOW will already be a powerful in- ∼ Jy across the SKA1-LOW band ((Condon 2005) and Fig. 7). Extending SKA- µ ). Further emphasis may be put on systems for which the stellar magnetic field is ), searching for coincidences (as for the GMRT and LOFAR sky surveys), that may guide The imaging observations in search for exoplanetary signals conducted in Phase 1 will be Finally, all survey-type programs that will be conducted with SKA1-LOW during SKA Phase At a fraction For each target, several observations of several hours each should be performed to account for exoplanet.eu limited by confusion rather thanto by hundreds thermal of noise. Confusion noise will actually be several tens strument to detect radio emissionsvations from at exoplanets. an There early is phase thus oflisted interest the above, to i.e. project, start stars concentrating intensive within on obser- 5 the(Lazio to most et 10 favourable al. pc, targets known among 2004, exoplanets those for Grießmeierexist which (Lecavelier et a et al. large al. radio 2007, 2013, flux Sirothia 2011,tized is et predicted Nichols stars. al. 2012), The 2014), or commensal and for searches knownthe which exoplanets mentioned beginning orbiting a in strongly of hint the magne- the previous of section operations. detection observations should at More be other carried generally, wavelengths, on advantage as from should describedproject. be in taken section from 5.2 synergies below, from with the early phases4.3 of Science the outcome anticipated from SKA Phase 2 LOW to a less compact array configuration, with baselines e.g. up to 200 km as for SKA1-MID, 1 (e.g. transients searches) should have their data correlated with the exoplanet catalog ( Finer resolutions are temporary required forThe the large purpose number of of RFI mitigation targets beforeview. to post-integration. observe In several times order requires to largebeam increase duty observations cycles the are and SKA1-LOW very large FoV desirable. fieldsrestricting ( the of As beam emissions bandwidth (e.g. are to moresystem 50 likely capabilities. MHz) can to The allow occur availability to at of formfor many as low beams exoplanet many frequencies, at search, beams little as as cost possible on forare the will searches slow be transients). or a any significant other advantage transient signals (exoplanetary radio emissions planet.eu follow-on observations. More generally,exoplanets the should search be for systematically performed emission commensally at to the all coordinates SKA1-LOW observations. 4.2 of all Early known science operations of SKA Phase 1 phase effects (combined to the narrow beaming ofsensitivity CMI is emission) needed or at intrinsic all variability. Maximum times,observations. implying Modest the temporal use and of spectral the resolutions fulltives are array, described and needed above, circular typically for or meeting full-polarization the physical objec- Radio Emissions from Exoplanets – measured and large, the phase ofmagnetic strongest field extrapolations radio (Farès signals et being al. predictable 2010)the in (and comparison unique that between information case observational can from results thus stellar be anddeduced obtained predictions). from from Kepler Exoplanet-rich observations fields and the of new vieware generation (e.g. also ESO-VLT instruments targets – of see particular section interest, 5.2) any where periodic it signal will matching be an possible exoplanet’s to rotation search or in orbital long period. observations series PoS(AASKA14)120 Philippe Zarka 10 pc. ≥ 3” at 110 MHz) will make ≤ Jy in the range 50-350 MHz, µ K. They have been attributed to CMI 15 14 emission in kGauss magnetic fields. Therence period. duration of This the justifies the bursts large isthe duty-cycle a detection required few for of percent their exoplanetary of detection, radio the and signals.from recur- similarly brown for Tracing dwarfs magnetic fields to and planetsfor radio will radio flux bring emission densities scaling unique laws. constraints for dynamo theories as well as Stellar flares and mass ejectionsbursts – – such can excite as magnetospheric solar planetary CMEs emissions and (and associated cause atmospheric solarSome loss). “type stellar II” radio flares couldunipolar actually induction or be magnetic reconnection). induced by an orbitingThere is close-in probably exoplanet a continuum (through ofcreasing physical rotational conditions period, increasingly from cool brown and dwarfs neutralstable to atmosphere, magnetic exoplanets transition (de- field to large-scale topologies, withized weaker periodic magnetic bursts field have magnitude). beenal. discovered Circularly from 2007, polar- the 2008), former with at brightness GHz temperatures frequencies > (Hallinan 10 et SKA2 will also extend and deepen large surveys started with SKA1. This will make increas- Detection of stellar radio flares with SKA will have similar instrumental requirements as exo- But there are also deep physical connections between stellar physics and activity and exoplanet • • • ingly relevant the systematic search of exoplanetaryexoplanet signals catalog. in Increased these angular surveys resolution by of correlation the with observations the (to planet radio detection (sensitivity, circular polarization,example, detection SKA1-LOW of will bursts, be large able duty to cycles). detect For the brightest solar bursts out to making Jupiter-like emission easily detectable at >10systematic pc range. searches. Increased field The of view higher willradio signal-to-noise improve emissions ratio with will which be dynamicdetailed measured, quantitative spectra interpretation beyonf of of exoplanet’s the theZarka few observations 2011) in dB (see the section required frame 2.3). for of the mere simulations detection, of will (Hess & enable coincidences more robust, less likely to beof due SKA1-SUR to and background SKA1-MID, radio searches sources. forsuch periodic With the higher as development frequency predicted unipolar inductor by emission dwarfs, Willes following & a Wu (2004, strategy(known 2005) that magnetic should will field, be depend angular targeted ofbe distribution, at the very distance. . known . useful. statistics ). (magnetic) of More white below), Multi-beam known synergies as capability white well will will as dwarf become with undoubtly properties relevant, observations at with other other wavelengths SKA (section 5.2). observations (section 5.1 5. Synergies 5.1 Synergies with other SKA observations search: Radio Emissions from Exoplanets would reduce the confusion tothermal values noise close because to of the increased thermal collecting noise area), (and down at to a the few same time reduce the PoS(AASKA14)120 Philippe Zarka 50 MHz and down to 10 MHz) radiotele- ≤ 15 Finally, Kepler has shown(Dressing that & Charbonneau lower 2013), mass and(although close-in planets habitability planets may are may need be to more located be frequent in redefined the based around on habitable magnetic M zone activity). dwarfs Thanks to our experience of solar system magnetospheres and radio emissions, and extensive Provided that complex time domain voltage data from tied array beams can be exported in As already mentioned above, measurements of stellar magnetic fields by Zeeman-Doppler The number of known planets in the solar neighbourhood should increase substantially thanks Finally, LOFAR will continue to provide observations within part of the SKA1-LOW range in • theoretical studies, the interpretation frame ofthe exoplanetary radio first observations confirmed is detections ready, and waiting for several measurements exoplanet’s of parameters, dynamic including spectra. the Beyond magneticand the field habitability) measurement (with and of rotation, implications radio on detections dynamo will theory open the new field of comparative exoplanetary scopes UTR-2, NenuFAR, OLWA, will perform follow-on observations(in of the SKA1-LOW overlapping candidates part of the sky) or vice-versa. 6. Conclusion parallel with imaging or beamformed spectralmensally observations, performed sensitive SETI with exoplanetary searches observations, could in be spectral com- SETI ranges searches little (see or not corresponding explored chapter). by past 5.2 Synergies with observations at other wavelengths imaging (with instruments suchCFHT/Spirou in as the CFHT/Espadons infrared in and the near-future)emission TBL/Narval are will a in be key visible ingredient measured to with light, assessof SKA. SPI CMEs and whose Magnetic and associated topology with in can turn influencewill their the also impact motivate direction SKA on of observations orbiting emission in exoplanets.in search principle for Measurements predicted unipolar of along inductor large the emissions, magnetic planet’s whoseXMM-Newton, orbit level Chandra, fields can (Farès and in be et the al. future 2010). bylar the outputs UV Athena+ and and X-ray allow X observatory to will observations identify characterize by bestcoupling stel- exoplanet HST, (Nichols candidates for 2011, enhanced 2012). magnetosphere-ionosphere Observationsradio of emissions large flares triggered can by also these motivateexoplanet’s flares atmosphere), specific (in as searches parallel was of with done successfully spectroscopic to studies detect of Uranus’ their aurorae impact (Lamy on etto al. the 2012). missions PLATO (Planetaryoplanet Transits Survey and Satellite), Oscillations whereas of SpirouThe JWST stars) will will and find be TESS Earth-like able to (Transiting planetsspheric characterize Ex- studies around the with nearby atmospheres SKA of red will these bring dwarfs. will nearby constraints planets, also to whereas provide their magneto- habitability. insights Studies toVLT of instruments different lower NGTS mass regimes (Next-Generation planets Transit of Survey) planetary andfor ESPRESSO dynamos. Rocky (Echelle SPectrograph Exoplanet New and surveys Stableconfirmed by exoplanets the Spectroscopic up ESO- Observations) to several will tens likely per increase field of the view number of SKA1-LOW. of the northern hemisphere, whereas the lower frequency ( Radio Emissions from Exoplanets PoS(AASKA14)120 Philippe Zarka Jy, full Stokes measurements) µ 10 pc, independent of any extrapolation of ≥ 16 Jupiter’s will be detectable within 10 pc, where all stars should × The context of these searches will be favoured by the expected rapid growth in the number Such synergies with observations at different wavelengths will be important, but also syner- Part of this research was carried out at the Jet Propulsion Laboratory, California Institute of Up to now, detecting the signal is the most difficult step. But the characteristics of SKA1-LOW number SKA-TEL-SKO-DD-001, Rev. 1 Dressing, C. D., & Charbonneau, D.Farès, 2013, R., Astrophys. Donati, J., J.-F., 767, Moutou, 95 C.,Farrell, et W. al. M., 2010, Desch, MNRAS, M. 406, D., 409 & Zarka, P. 1999, J. Geophys. Res., 104, 14025 of known exoplanets due toEXPRESSO. new . . instruments ) and space that missionsto could (PLATO, take result TESS, full in JWST, NGTS, advantage tens ofvations), of for this exoplanets which context, per a large SKA1-LOW multi-beam fieldtargeted duty-cycles searches, capability of are commensal will view. needed observations, and be (repeated, In correlation extremelyalog. hours-long of order useful. Radio surveys obser- flux to densities up-to-date Observations of exoplanet will 1-10 cat- include gies with other SKA observations,the especially field concerning topology, the dynamo, “star-planet and connection”:may radio evolve a output as study a from of discovery dwarfs tool,magnetic to e.g. or planets. variable adapted stars. 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