Why Should We Expect to Find Other Planets? Planetary system formation is a natural by-product of star formation

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1 1 Why Should We Expect to Find Other Planets? Planetary system formation is a natural by-product of star formation

2 2 Why Should We Expect to Find Other Planets? Observations show young stars are surrounded by accretion disks

3 3 Detecting Jupiter from Afar Consider our Solar System seen from a distance of 10 parsecs (a distance large enough that from the Earth's perspective there would be thousands of stars, and dozens of sun-like stars to examine). How separated (in an angular sense) would Jupiter be from our Sun. How bright would Jupiter be? How bright would the Sun be? Important numbers There are AU in a parsec. The Earth is 1 AU from the Sun, Jupiter is typically 5 AU from the Earth. One arcsecond separation at a distance of one parsec corresponds to 1AU physical separation 1 d ( pc) = parallax (")

4 4 Detecting Jupiter from Afar Consider our Solar System seen from a distance of 10 parsecs (a distance large enough that from the Earth's perspective there would be hundreds of stars, and dozens of sun-like stars to examine). How separated (in an angular sense) would Jupiter be from our Sun. How bright would Jupiter be? How bright would the Sun be? Important numbers There are AU in a parsec. The Earth is 1 AU from the Sun, Jupiter is typically 5 AU from the Earth. One arcsecond separation at a distance of one parsec corresponds to 1AU physical separation. 1 d ( pc) = parallax (") As seen from 10 parsecs away Jupiter would be 0.5 from the Sun.

5 5 Detecting Jupiter from Afar Consider our Solar System seen from a distance of 10 parsecs (a distance large enough that from the Earth's perspective there would be hundreds of stars, and dozens of sun-like stars to examine). How separated (in an angular sense) would Jupiter be from our Sun. How bright would Jupiter be? How bright would the Sun be? The Sun as seen from Earth is mag As seen from 10 parsecs the Sun would appear 4x1012 times fainter. 5 magnitudes is a factor of 100 in brightness 1012 corresponds to 30 magnitudes, plus another couple of magnitudes for the 4 The Sun would be a 5th or 6th magnitude star seen from 10 pc.

6 6 Magnitudes and You Two simple facts, no equations Magnitudes are a ranking system 2nd magnitude is brighter than 9th Five magnitudes difference corresponds to a factor of exactly 100 in flux. One magnitude is a factor of The difference in flux between a 2nd and 12th magnitude star is...

7 7 For the Equation Obsessed Two simple facts, no equations Magnitudes are a ranking system 2nd magnitude is brighter than 9th Five magnitudes difference corresponds to a factor of exactly 100 in flux. One magnitude is a factor of The difference in flux between a 2nd and 12th magnitude star is... Fa ma - mb = 2.5 log Fb ( ) If b is brighter than a does this equation make sense from a sign perspective.

8 8 Detecting Jupiter from Afar Consider our Solar System seen from a distance of 10 parsecs (a distance large enough that from the Earth's perspective there would be hundreds of stars, and dozens of sun-like stars to examine). How separated (in an angular sense) would Jupiter be from our Sun. How bright would Jupiter be? Jupiter is about -1 mag seen from 5 AU away here on Earth. 10 parsecs is 2 million AU.

9 9 Detecting Jupiter from Afar Consider our Solar System seen from a distance of 10 parsecs (a distance large enough that from the Earth's perspective there would be hundreds of stars, and dozens of sun-like stars to examine). How separated (in an angular sense) would Jupiter be from our Sun. How bright would Jupiter be? Jupiter is about -1 mag seen from 5 AU away here on Earth. 10 parsecs is 2 million AU. ( 2,000,000 5 ) 2 fainter

10 10 Detecting Jupiter from Afar Consider our Solar System seen from a distance of 10 parsecs (a distance large enough that from the Earth's perspective there would be hundreds of stars, and dozens of sun-like stars to examine). How separated (in an angular sense) would Jupiter be from our Sun. How bright would Jupiter be? Jupiter is about -1 mag seen from 5 AU away here on Earth. 10 parsecs is 2 million AU. ( 2,000,000 5 ) 2 fainter

11 11 Other Options - Barycentric Motion Two objects orbit their common center of mass. M A r A = M B rb ra MA rb MB The planet may be invisible but it displaces its star regularly both in position and in velocity. Binary Star Simulation

12 12 Directly See Stellar Displacement? Jupiter is 5 AU from the Sun and 1/1000th the Sun s mass. The Sun s motion due to Jupiter has an amplitude of 5/1000 th of an AU. Seen from 10 parsecs 5/1000th of an AU is 5/10,000th of an arcsecond! Barnard s Star

13 13 Detecting the Variable Doppler Shift of the Star Doppler Wobble The planet swings the star around as it orbits. We measure the velocity of the star spectroscopically via the Doppler shift.

14 14 Doppler Wobble Jupiter's motion displaces the Sun roughly by the Sun's diameter (once every 12 years - a Jupiter year) How much will this affect the Sun s velocity? This technique works best if - you have a lot of patience (12 years!) OR - the planet is quite massive (super-jupiters) - the planet is quite close to its star big velocity shift and very short orbital period

15 15 The First Exoplanetary Detections Doppler Wobble The planet swings the star around as it orbits. We measure the velocity of the star using the Doppler shift. Inventory

16 16 Planetary Transits The planet dims the star as it passes in front. Requires precise alignment solar system must be seen on edge

17 17 Two Indirect Detection Techniques The planet dims the star as it passes in front. Requires precise alignment solar system must be seen nearly on edge Pure Geometry rules!

18 18 The Kepler Mission Launched in March 2009, Kepler monitored 150,000 stars every 30 minutes for 4 years with the sensitivity to see earths transit their stars. Mission website

19 19 The Kepler Mission Launched in March 2009, Kepler monitored 150,000 stars every 30 minutes for 4 years with the sensitivity to see earths transit their stars. Mission website

20 20 The Kepler Mission The stability of space-based observation is far superior to that achieved on the ground.

21 21 The Kepler Mission The stability of space-based observation is far superior to that achieved on the ground. Animation Animation magnified

22 22 TRAPPIST - 1

23 23 TRAPPIST - 1

24 24 TRAPPIST - 1

25 25

26 26 Nooooooo!!!!!

27 27 Habitability of TRAPPIST-1 Planets

28 28 Wednesday Problem Set 7 is due Problem Set 8 will be out later today or early tomorrow. The Moon is close to New Exam 3 is Friday November 30

29 29 Detection Methods and Planetary Properties The transit method detects the dimming of the star caused by the passage of the planet. Inclination is guaranteed to be close to 90 degrees. Ingress and egress times directly measure the size of the planet given a good estimate of the star s size from spectroscopy / spectral type. The mass of the planet remains unknown as we do not see any effects of the planet s mass.

30 30 Detection Methods and Planetary Properties The radial velocity method detects the star s wobble in response to the planet(s) gravity. The star s mass is fairly well known given it s spectrum / spectral type. The radial velocity response of the star is proportional to the planet s mass. Since the Doppler effect is sensitive only to the radial component of motion, the inclination of the system is an unfortunate unknown. The method, in the absence of a known inclination, only provides an estimate of the minimum mass of the planet, Mplanet* sin(inclination) If a system is edge on (inclination = 90 degrees) this method gives the planet s mass. This method yields no information about a planet s size and thus it s density. Binary Star Simulation

31 31 Radial Velocity Reminder Doppler Wobble The planet swings the star around as it orbits. We measure the velocity of the star using the Doppler shift.

32 32 The Importance of Density There are a limited number of planetary building materials: Iron / metal 8 10 g/cm3 Silicate rock 3 g/cm3 Water / ice 1 g/cm3 Gas giant gas ~1 g/cm3 depending on state of compression. Bulk density is an easily measured quantity ( mass / volume ) The Earth has a density of 5.5 g/cm3, for example, suggesting a mix of rock and metal. Given a molten interior this density suggests a differentiated structure.

33 33 Earth Sized vs. Earth Like The radial velocity method can reveal (modulo sin(inclination)) Earth-mass planets. The transit method can reveal Earth-size planets. Neither turns up Earth-like planets! But What if we can find planets of similar size and density to Earth? What if we can probe their atmospheres?

34 34 The Context of the Drake Equation

35 35 fp

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37 37 The Kepler Mission Launched in March 2009, Kepler monitored 150,000 stars every 30 minutes for 4 years with the sensitivity to see earths transit their stars. Mission website

38 38 Kepler is Dead. Long Live TESS. The Transiting Exoplanet Sky Survey

39 39 Kepler is Dead. Long Live TESS. The Transiting Exoplanet Sky Survey Kepler TESS TESS is a wide-field full-sky survey for the nearest exoplanets.

40 40 Semi-major Axis and Habitability Both methods of detection yield the planet s orbital radius. Radial velocity also yields eccentricity. Knowing the orbital distance and the star s temperature we can estimate the surface temperature of the planet and ask whether liquid water is sustainable on it s surface.

41 41 Semi-major Axis and Habitability Both methods of detection yield the planet s orbital radius. Radial velocity also yields eccentricity. Knowing the orbital distance and the star s temperature we can estimate the surface temperature of the planet and ask whether liquid water is sustainable on it s surface.

42 42 Semi-major Axis and Habitability Both methods of detection yield the planet s orbital radius. Radial velocity also yields eccentricity. Knowing the orbital distance and the star s temperature we can estimate the surface temperature of the planet and ask whether liquid water is sustainable on it s surface.

43 43 Is the Habitable Zone a Red Herring? Radioactive and Tidal Heating can produce liquid water in unexpected places. Io extreme tidal heating.

44 44 Is the Habitable Zone a Red Herring? Radioactive and Tidal Heating can produce liquid water in unexpected places. Water is abundant in the outer Solar System. Many Jovian moons harbor oceans. Europa, the next moon out from Io.

45 45 Friday Problem Set 7 is history. Problem Set 8 is out there. Exam 3 is Friday November 30.

46 46 Bennu Not only has Hyabusa-2 arrived at and begun exploring Ryugu, but OSIRIS-Rex has arrived at Bennu another small nearearth asteroid. Official arrival is December 3.

47 47 A Strange Feeling of Déjà Vu... Not only has Hyabusa-2 arrived at and begun exploring Ryugu, but OSIRIS-Rex has arrived at Bennu another small nearearth asteroid. Official arrival is December 3.

48 48 A Strange Feeling of Déjà Vu... Not only has Hyabusa-2 arrived at and begun exploring Ryugu, but OSIRIS-Rex has arrived at Bennu another small nearearth asteroid. Official arrival is December 3. Ryugu

49 49 A Strange Feeling of Déjà Vu... Not only has Hyabusa-2 arrived at and begun exploring Ryugu, but OSIRIS-Rex has arrived at Bennu another small nearearth asteroid. Official arrival is December 3.

50 50 Ocean Worlds Europa isn t the only likely subsurface ocean in the outer solar system. Now that NASA has identified ocean worlds as an objective, just about everything has been classified (for good reason) as such.

51 51 Ocean Worlds - Enceladus Europa isn t the only likely subsurface ocean in the outer solar system. Now that NASA has identified ocean worlds as an objective, just about everything has been classified (for good reason) as such.

52 52 Ocean Worlds Ganymede and Titan Europa isn t the only likely subsurface ocean in the outer solar system. Now that NASA has identified ocean worlds as an objective, just about everything has been classified (for good reason) as such.

53 53 Ocean Worlds Even Pluto Europa isn t the only likely subsurface ocean in the outer solar system. Now that NASA has identified ocean worlds as an objective, just about everything has been classified (for good reason) as such.

54 54 TRAPPIST - 1 Not only is TRAPPIST-1 a remarkable 7 planet transit system, but the planets are so closely packed that they gravitationally interact with one another to produce detectable offsets in their transit times permitting measurement of their masses and thus densities.

55 55 Nooooooooo!!!

56 56 Nooooooooo!!!

57 57 TRAPPIST - 1

58 58 Semi-major Axis and Habitability Both methods of detection yield the planet s orbital radius. Radial velocity also yields eccentricity. Knowing the orbital distance and the star s temperature we can estimate the surface temperature of the planet and ask whether liquid water is sustainable on it s surface.

59 60

60 62 Transit Depth and Atmospheres Transits are geometric, so the attenuation of starlight depends only on the relative diameters of the star and planet (squared). Jupiter is 1/10th the size of the Sun. Transit depth = 0.01 or 1%. Earth is 1/100th the size of the Sun. Transit depth = or 0.01% Depth= r 2 planet 2 star r

61 63 Transit Depth and Atmospheres Transits are geometric, so the attenuation of starlight depends only on the relative diameters of the star and planet (squared). Jupiter is 1/10th the size of the Sun. Transit depth = 0.01 or 1%. Earth is 1/100th the size of the Sun. Transit depth = or 0.01% Given an atmosphere, the effective radius of the planet will be larger at wavelengths corresponding to strong molecular absorption. Depth= r 2 planet 2 star r

62 64 Atmospheres are Thin

63 65 Transit Spectroscopy Spectroscopy can reveal atmospheric composition.

64 69 Slide from a presentation by Heather Knutson (Caltech)

65 70 Exoplanetary Atmospheric Spectroscopy

66 72 Seeing the (Infrared) Light from Planets

67 75 Do these newly discovered worlds and solar systems fit in nicely with our knowledge of how the Solar System formed?

68 76 Metallicity and Planet Formation The presence of large Jovian exoplanets seems to correlate with stellar metal abundance.

69 77 Hot Jupiters

70 79 Planetary Migration The distribution of discovered exoplanets, particularly the position of Jupiter analogs is not consistent with our simple model of solar system formation. Jupiters are supposed to form beyond the ice line at several astronomical units. Planetary migration may be a viable mechanism for substantially changing the orbital radii of planets. Angular momentum must always be conserved. Planets couple to the disk mass, moving inward (or outward) while disk material moves outward.

71 80 Are We Biased? Most all planetary detection techniques benefit from the effects of close-in planets Both radial velocity variations and planetary transits are more easily detected if the happen frequently (days as opposed to years). Transits are more likely for close-in planets because the transits can be observed over a larger range of system tips relative to edge-on. Direct imaging is complementary Direct imaging is sensitive at large radii (>0.few arcseconds) However, contrast is a big problem. Recall Jupiter is about 20 magnitudes fainter than the Sun. Warm newly-formed planets can be self luminous and easier to detect.

72 81 Direct Detection Stellar glare hides the planets (which are more than a billion times fainter than their star) from view.

73 84 Infrared Improves Contrast

74 85 Direct Imaging of Infrared Luminous Planets Fomalhaut b (visible)

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76 90 LMIRcam

77 93 Will This Technology Reveal Other Earths? Eventually... Solar System Family Portraits

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79 102 The Next Step The James Webb Space Telescope

80 103 The Key to Detecting Life from a Distance

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83 107 Ultimately With several telescopes flying hundreds of kilometers apart and held in place to 1/100th the width of a human hair... Imaging another Earth becomes a possibility but is at least years away.