Extra-Solar Planets Planetary Physics Summer Term 2006 Lecture 10

Extra-Solar Planets  Since October 1995, more than 180 planets have been detected around more than 150 stars like the Sun – why the sudden success?  None has been seen directly: all found by ‘wobble’ of parent star caused by orbiting planet – how?  None is yet like the Earth: most have masses between Neptune and Jupiter – why?

Extra-Solar Planets Definitions:  Star: > 0.08 solar masses (80 jupiter masses), powered by H fusion; formed by gravitational collapse, occur singly or in multiples  Brown Dwarf: 13 jup < mass < 80 jup, some initial D fusion, then fade; formation and occurrence as normal stars  Planet: < 13 jup, no nuclear power source; formed by accretion from protoplanetary disc left behind from formation of parent star

In these HST pictures we see disks around stars, but also jets of material being blown out again, especially in the lowest picture (the ‘Rotten Egg’ nebula). Planets form from the disks.

Extra-Solar Planets Methods of detection:  Astrometry - long history, no detections  Radial velocity surveys - very successful  Brightness variations –planet passes in front of star: drop in brightness –gravitational lensing of star by planet: increase in brightness - only way to detect earth-mass planets –both becoming effective for detection and study  Interferometry - ground and space missions

Extra-Solar Planets Astrometry:  Very precise measurements of position of parent star, relative to inertial frame, repeated over many years  Centre of mass of system (CoM) moves in straight line  If planet exists, star’s motion will have slight ‘wobble’ about CoM motion - can find size and period of orbit, and mass of planet  Massive planets in wide, long-period orbits give largest wobble; nearby stars are best, but effects still too small to measure with present equipment

Extra-Solar Planets Radial velocity surveys:  Very precise measurements of radial velocity of parent star – motion in line of sight from observer to star  Single star will have constant velocity, but if companions are present their orbital motions will be reflected in motion of star about centre of mass – look for periodic oscillations in radial velocity, using doppler effect

Extra-Solar Planets Limits of radial velocity measurements:  Can find period, eccentricity and M P sin i, where i is inclination of orbit to line of sight  Can not measure i : need transits for this  Motion largest for large masses, short periods  Limit set by oscillations in star’s size (2-3 m/s)  Earth mass in 1-yr orbit gives only 0.1 m/s

Extra-Solar Planets Gravitational lensing:  Parent star (‘lens’) focuses light of background star as it passes in front of it: Observer Star Lens (and planet)  Planet causes blip in slow light variation time

Extra-Solar Planets History I:  : various false astrometric claims of Jupiter size companions, e.g. to Barnard’s star (van de Kamp)  1980s: pioneering radial velocity survey by Campbell & Walker - precision of 13 m/s, but no detections (small sample - only 21 stars)

Extra-Solar Planets History II:  Late 1980s, early 1990s: several large, high precision RV surveys began - Marcy & Butler (Lick), Mayor & Queloz (OHP), Cochran & Hatzes (McDonald)

Extra-Solar Planets 1995 October 6:  first extra-solar planet round a ‘normal’ star announced by Swiss team, Michel Mayor & Didier Queloz  (2 found earlier around a pulsar – but can’t be ‘normal’ planets)

Geoff Marcy and Paul Butler found this ‘wobble’ in the motion of the star 51 Pegasi, and were able to find a period of just over 4 days.

This shows the same observations, but now with all the different orbits superimposed to show the variation better.

Extra-Solar Planets What did we expect?  small mass planets (Earth-like) close to star: radiation should evaporate most abundant element, hydrogen, leaving small rocky planets  massive gaseous planets (Jupiter-like: mainly hydrogen) far enough out to avoid evaporation – so expect long periods  circular orbits, as in solar system  stars like the Sun

Extra-Solar Planets What did we find?  massive planets close to star!  no earth-like planets  many eccentric orbits!  stars generally richer in heavy elements (such as iron) than the Sun

Extra-Solar Planets Results for first 61 stars – later results confirm this trend

Extra-Solar Planets Update for 158 stars – red vertical line shows solar metallicity

The great majority of the planets are close to their star, although the systems with several planets do show a spread of distances

Extra-Solar Planets Current results (at 16/05/06):  188 planets with masses M jup (~0.3M nep or ~5 Earth masses) to 17.4 M jup  ~50 ‘hot Jupiters’ (~Jupiter mass, close to star: a < 0.4 AU)  ~83 ‘Jupiter analogues’ (‘ice giants’) (~Jupiter mass, far from star: P > 1 yr)  ~98 ‘eccentric’ planets (high eccentricity orbits: e > 0.2)  18 systems with multiple planets

Three planets around Upsilon Andromedae: first ‘solar system’

Extra-Solar Planets 55 Cancri system, as seen from near outermost planet (~4 jup). Neptune-mass planet is the black dot very close to the star.

Extra-Solar Planets The first planet to be found round a red dwarf star, GJ 436. Its mass is about 21 earth masses, or just larger than Neptune.

Extra-Solar Planets The second lowest mass planet so far discovered: the innermost planet of Gliese 876, which also has two Jupiter-mass planets. The mass of this planet is 5.9 M Earth, less than half of Neptune. Semi-amplitude is 4.1 m/s! Radial velocity amplitude is ~6 m s -1 !

Extra-solar Planets Catalog Including Candidates to be confirmed (sorted by increasing mass) From the Extrasolar Planets Encyclopaedia Extrasolar Planets Encyclopaedia Maintained by ©,1996 Jean Schneider Observatoire de Paris ©,1996 Jean Schneider Update: 10 May 2001 ( Warning: As there is no clear consensus about the definition criteria of planets, `super-planets' and brown dwarfs (mass, formation,...), this Catalog includes only (with a few exceptions) objects lighter than 13 M Jup (no deuterium burning)). The Catalog below contains four tables (the objects are sorted for each by increasing mass of the lightest planet in the system): 1.Confirmed planets around main sequence stars 1.HD update 2 Nov. 00HD HD update 22 Nov. 00HD HD update 4 May 00HD HD update 29 Mar. 00HD HD update 4 May 00HD HD update 16 Apr. 01HD Peg update 16 Apr Peg 8.BD update 27 Apr. 00BD HD 6434 update 22 Nov. 00HD HD update 6 Jul. 00HD HD update 25 Apr. 01HD upsilon And update 7 May. 01upsilon And 13.HD update 22 Nov. 00HD epsilon Eridani update 27 September 00epsilon Eridani 15.HD update 22 Nov. 00HD HD update 20 Apr. 01HD Cnc update 22 Nov Cnc 18.HD update 10 May. 01HD HD update 21 August 00HD HD update 22 Nov. 00HD HD update 30 Mar. 00HD rho CrB update 6 Apr. 01rho CrB 23.HD update 22 Nov. 00HD HD update 22 Nov. 00HD HD update 6 Jul. 00HD HD update 22 Nov. 00HD HD update 16 Dec. 00HD Cyg B update 18 Jan Cyg B 29.HD update 4 Apr. 01HD HD update 22 Nov. 00HD HD update 16 Dec. 00HD HD update 21 August 00HD Gliese 876 update 7 May. 01Gliese HD update 22 Nov. 00HD HD 8574 update 4 Apr. 01HD HR810 update 22 Nov. 00HR Uma update 22 Nov Uma 38.HD update 22 Nov. 00HD HD update 22 Nov. 00HD Her update 16 Apr Her 41.GJ 3021 update 22 Nov. 00GJ HD update 4 Apr. 01HD HD update 22 Nov. 00HD HD update 4 Apr. 01HD Gl 86 update 22 Nov. 00Gl tau Boo update 16 Dec. 00tau Boo 47.HD update 4 Apr. 01HD HD update 22 Nov. 00HD HD update 11 Jan. 01HD HD update 22 Nov. 00HD HD update 4 Apr. 01HD HD B update 4 Apr. 01HD B 53.HD update 22 Nov. 00HD Vir update 22 Nov Vir 55.HD update 4 Apr. 01HD HD update 22 Nov. 00HD HD update 4 Apr. 01HD HD update 22 Nov. 00HD Confirmed planets around pulsars 1.PSR update 28 Mar. 01PSR PSR B update 29 July 99PSR B Disks (potentially protoplanetary or associated to planets) (sorted by distance to the Sun) 1.Beta Pictoris update 2 Sep. 98Beta Pictoris 2.L 1551 update 2 Oct. 98L BD +31 o 643 (disk; to be confirmed) update 10 mar. 97BD +31 o Unconfirmed, doubtful, unpublished or invalidated objects. 1.W 3 (OH) update 28 Oct. 99W 3 (OH) 2.HR7875 update 15 Jul. 1998HR Geminga (invalidated) update 8 Sep. 99Geminga 4.PSR (Very doubtful) update 28 Apr. 99PSR PSR (unpublished data)PSR Q A (to be confirmed)Q A 7.Lalande (data unpublished) update 5 dec. 97Lalande CM Dra (to be confirmed) update 25 mar. 00CM Dra 9.Alpha Tau (to be confirmed) update 4 Dec. 97Alpha Tau 10.TMR-1C (invalidated) update 3 Apr. 2000TMR-1C BLG-35 (to be confirmed) update 7 mar BLG BLG-3 (to be confirmed) update 23 dec BLG BLG-41 (to be confirmed) update 4 nov BLG BLG-4 (to be confirmed) update 23 dec BLG stars with NO planet found (Walker et al.)NO planet found 1.- Confirmed planets (and/or brown dwarfs) (note 1: for planets detected by timing and radial velocity, only the product M x sini is known) 2.- Confirmed pulsar planets StarM[.sini] Jup. mass:(J) Earth mass:(E) (note 1) Semi- maj. Axis (AU) Period years(y) days(d) Ecc.Incli n. (deg) Radiu s (Earth rad.) PSR PSR ~ 300 pc (E) 3.4 (E) 2.8 (E) ~ 100 (E) ~ (d) (d) (d) ~ 170 (y) PSR B PSR B kpc 1.2 < M.sini < 6.7 (J) (y) Unconfirmed, doubtful or unpublished objects StarM[.sini] Jup. mass:(J) Earth mass:(E) (note 1) Semi-maj. Axis (AU) Period years(y) days(d) Ecc.Incli n. (deg) Radi us (Eart h rad.) HR7875 HR pc F8V V = (J)-42.5 (d) PSR PSR kpc 3 (E) 12 (E) 8 (E) (y) 1.35 (y) 2.71 (y) Q Q Gpc (z = 0.39) ~ a few (E) Lal Lal pc M2 V = (J) (y) 30 ? (y)--- CM Dra CM Dra 14.7 pc M4.5/M4. 5 V = Alpha Tau Alpha Tau pc K5III V = (J) (d)0.182 # ?- TMR-1C TMR-1C ~130 pc V = ? 2- 3 (J) ?> 1,500> 40,000 (y) ??~1 R J 98-BLG BLG- 35 ~ 5 kpc ~ (E) 1.5 or 2.3???- 95-BLG-3 95-BLG-3 ~ 5 kpc ~ 2 (J)> ? BLG-4 94-BLG-4 ~ 5 kpc ~ 5 (J)~ Beta Pic Beta Pic 18 pc A5V V = 3.8 -> (d)-< 1 o ~ 16 BD +31 o 643 BD +31 o pc B5V, B5V V = 8.5, 8.5 diskrad. disk: 6,600 --< 10 o - W 3 (OH) W 3 (OH) 3 kpc pc O8 star V = ? ? (E)2,000?---- Back to the Extra-solar Planets Encyclopedia The majority of the planets found so far have orbital radii less than 1 AU: 40% of them are less than 0.4 AU, although there is a growing number with larger radius, including four ‘beyond Jupiter’. (log scale)

The majority of planets (~53%) still have masses between 1 and 8 Jupiter masses, but there is a growing number (~38%) with masses less than that of Jupiter (down to jup ~5.4  ). But only lower limits are known without knowing i: needs transits. ‘Mass’ really means M sin i 10 with masses > 10 Mj

7 November 1999: first-ever planetary transit observed for sun-like star HD by Henry, Marcy, Butler and Vogt

The radial velocity group of Marcy, Butler and Vogt found this evidence of a wobble in the motion of the star and alerted Greg Henry to observe its brightness.

This is the 0.8m Automatic Photoelectric Telescope of the Tennessee State University’s Fairborn Observatory in southern Arizona, which was used by Greg Henry to observe the planetary transit. An attempt to verify the result on November 14 was clouded out, but other groups later verified it.

Average of four HST transit observations

This is the light curve for the second transit to be detected, in July Nine transits are now known, four found (like this one) by a gravitational lensing survey. This planet is the second closest to its parent star so far (less than 5 solar radii away!).

Extra-Solar Planets The Future - I:  Continuing radial velocity searches (lower mass planets – now down to ~5 Earth masses; more multiple systems – now 18 known)  Transits – now 9 definite cases, and lensing surveys are producing many new candidates  Gravitational lensing proper – statistical only, but the best hope of detecting Earth- mass planets at Earth-like distances (~1AU)

Extra-Solar Planets The Future - II:  Direct imaging? Difficult from the ground  Space-based imaging (e.g. DARWIN)

An artist’s impression of the proposed 6-spacecraft Darwin mission, due to fly in about Each craft contains a large IR telescope, and they are spread over distances of 40 to 500 metres.

Extra-Solar Planets The Future - III:  Ground-based astrometry – very hard  Space-based astrometry (e.g. GAIA)

Due to fly about 2015

Extra-Solar Planets Where next? Who knows! THE END

Extra-Solar Planets