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Class events: week 12. Goals: learn about extrasolar planets Methods of detection Planets observed Towards detecting life Solar system creation theories The Rare Earth Hypothesis Extra readings: Challenges in detection. - PowerPoint PPT Presentation


  • *Class events: week 12Goals: learn about extrasolar planets

    Methods of detectionPlanets observedTowards detecting lifeSolar system creation theoriesThe Rare Earth Hypothesis

    Extra readings:

  • *Challenges in detectionVisual detections of planets are difficult because their photons are swamped by the central star.

    L /LEarth=1.5109L/LJupiter=4.1108

  • *Direct observationsImagery of the object itself This has been achieved using speckle interferometry or other modern methods for only a few planets.

    Spectral data of the object While brightness differences of suns and their planets are huge (i.e., 109 difference for Jupiter vs. our Sun in optical), they can be less overwhelming in infrared (i.e., a 105 difference in IR).

  • *Astrometric detectionsLooking for tiny shifts in stellar position

    Seeking planets because of their gravitational influence on the central star is possible, but difficult because of the mass difference.

    With some algebra

    For Earth-Sun system, X* = 310-6 a.u., 450 km, 0.00065 RFor Jupiter-Sun system, X* = 1.0 R.

  • *The Doppler effect and radial velocityWaves emitted by approaching [receding] objects are shifted to shorter [longer] wavelengths. This is called the Doppler effect, with blueshifts and redshifts.

    By analyzing the Doppler shifts of photons, the line-of-sight component of an objects velocity can be measured.

  • *Radial velocity detections of planetsLook for Doppler shifts exhibited by the central star in a planetary system.

    Highly effective (pre-Kepler, the vast majority of exoplanets were found this way, including 51 Pegasi, the first star with an exoplanet discovered).Asymmetries in the stellar motions can indicate orbital parameters such as eccentricities, as in 70 Virginis.In some cases, even multiple planet systems can be analyzed.

  • *Doppler detectionsHOWEVEROrbital tilts mean we only measure some, and not all, of the orbital velocity.

    Therefore, we only measure a portion of the Doppler shift from the planet, and the star may be getting yanked about harder than we know.

    This method only gives us a lower limit for the planets. (The value is distorted by cos .)

    Fortunately, while we cannot correct a single planets mass for this effect, on average, it is not too bad for a sample of exoplanets:Only a 33% chance of a planet being more than 2 the inferred mass; Only a 13% chance of a planet being more than 5 the inferred mass; Only a 6% chance of a planet being more than 10 the inferred mass; BUT a 0.6% chance of a planet being more than 100 the inferred mass!

  • *Transit detectionsLooking for stellar eclipses...This method is effective only if the orbital plane is closely aligned with the Earth.This alignment does not have to be as highly coincidental for cases where the planet is very close to the star.Jupiter would cause a 1.1% brightness drop for the Sun.The Earth would cause a 0.008% drop for the Sun.

    Many stars have brightness variations that exceed this. Therefore, the job is to look for highly periodic brightness changes.

  • *Stellar transits detected by KeplerKepler was launched in 2009.10.5 square field of view150,000 stars, every 30 minutes!

    As of Feb 2014About 1800 planet confirmed candidates;About 1800 planet confirmed candidates;23% Jupiter to super-Jupiters (6-22 REarth);40% Neptune-sized (2-6 REarth);26% super-Earth (1.25-2 REarth);10% Earth-sized (R< 1.25 REarth).

    Most (76%) are Neptune-sized or smaller.Many are within the habitable zone.

    (More at

  • *Gravitational lensingOGLE-2005-BLG-390Lb: 5.5 MEarth, T~50 K, 2.1-4 a.u. from a (red dwarf?) star. Detected at a range of about 7000 parsecs!General relativity shows us that gravity can bend beams of light.

    One manifestation of this is to make stars wink brightly, as their light is focused towards us.

  • *Future missionsTransiting Exoplanet Survey Satellite (TESS) 500, 000 G-K stars.Plans to focus on Earthlike planets August 2017 SpaceX Falcon launch date

  • *The planetary zooMany of the planets detected are huge, and very close to their stars.

    The most extreme of these are more massive than Jupiter, but are closer than about 0.05 a.u. (Mercury is at 0.4 a.u.).

    These are called hot Jupiters. Smaller versions are called hot Neptunes

    Our detection methods would tend to preferentially detect these planets.

  • *The planetary zooWASP-12b

    An extreme Hot Jupiter.

    1.4 MJupiter1.74 RJupiter1.09 day orbital periodHome star: G

    Surface T: 2500K

    It will be vaporized in about 10 million years.

  • *The planetary zooHD 96167bAn eccentric Jupiter.

    0.68 MJupiter498 day orbital periodHome star: G5e=0.710

    7% of all systems have eccentric Jupiters. They are more common than hot Jupiters!

    It is unlikely that other planets can share the system with an eccentric Jupiter!

  • *The planetary zooHD 189733bThe azure planet

    1.16 MJupiter2.2 day orbital periodHome star: K1-2 V

    Despite being a hot Jupiter, its color has beenmeasured as being deep blue.

    Spectroscopy has detected atmosphericmolecule information! K, Na, CO2, H2O, O2, CH4

  • *The planetary zooKepler-10b

    One of the first rocky planets verified.

    4.55 MEarth1.39 REarth0.84 day orbital periodT=2800 KHome star: GKepler-10c

    One of the biggest super-Earths known.

    17 MEarth2.35 REarth45 day orbital periodT=584 KHome star: G

  • *The planetary zooGliese 1214b (super-Earth)

    Based upon its mass and radius, estimates can be made about its composition and structure.

    Its spectrum has been detected and is featurelessone explanation is that its atmosphere is water-steamy. Its overall composition may be 25% rock, 75% water.

    6.36 MEarth2.69 REarth1.58 day orbital periodHome star: M

  • *The planetary zooHabitable super-Earth

    Kepler-22b11-30 MEarth2.4 REarth(g=2-3gEarth)289 day orbital periodHome star: G5

  • *The planetary zooVery EarthlikeGliese 581d HD 85512b

    ~6.04 Mearth~3.50 MEarth66 day orbital period54 day orbital periodHome star: M2.5Home star: K5Triple planet system

  • *The planetary zoo: Earthlike and in the habitable zone!Kepler 186 f~1.13 RearthHome star: M1130 day orbital periodFive-planet system

  • *The planetary zooKepler-20e, KOI-961: The smallest planets detected so far.

    Kepler-20eKOI-961 0.4-1.7 MearthSub-Earth?0.87 REarth6.1 day orbital period0.45, 1.2, 1.9 dayHome star: G8M star

  • *The planetary zooPlanets in binary/multiple star systems.

    Kepler-16 (AB)b0.33 MJupiter0.74 RJupiter228.78 day orbital periodHome star: K, MAlpha Cen Bb1.13 MEarth3.23 day orbital periodHome star: K1

    This case is one where the planet orbits a single star, which is in a multiple system with a G2 and M5 star.

    The azure planet is in a similar double system

  • *The planetary zooHD 10180 - A planetary system around a G1V star

    HD10180b(?) 1.4 MEarth1.18dHD10180c 13.1 MEarth5.76dHD10180d 11.8 MEarth16.36dHD10180e 25.1 Mearth49.74dHD10180f 23.9 MEarth122.76dHD10180g 21.4 MEarth 601.20dHD10180h(?) 63.6 MEarth 2222.0d

  • *The planetary zooGliese 667- A complicated systemGliese 667A (K3V, 0.12 LSun) orbits Gliese 667B (K5V, 0.05 LSun) in 42 yGliese 667C (M1V, 0.014 LSun) orbits the pair in xx days

    Gliese 667Cb 4-7 MEarth7.2dGliese 667Ch(?) 1-3 MEarth~17dGliese 667Cc 3-5 MEarth28.1d (Habitable zone)Gliese 667Cf 2-4 Mearth39.1d (Habitable zone)Gliese 667Ce 1-4 MEarth62.3d (Habitable zone)Gliese 667Cd 3-7 MEarth91.6dGliese 667Cg(?) 3-8 MEarth 256d

  • *The planetary zooPSR J1719-1438b (the diamond planet)

    Formerly a red giant star, and then a white dwarf in a binary. (Its companion already converted itself into a pulsar.)

    The pulsar blew away nearly all the white dwarf star, and the remaining residual carbon-rich core is now considered a diamond planet.

    1.02 MJupiter0.4 RJupiter (4 REarth) 2.18 h orbital periodHome star: pulsar

  • *Some (soft) planetary statsEstimates of planetary numbers still varies widely from team to team. However, all are suggesting that planets are common

    Analyses of Kepler data suggest that stars in the galaxy have, on average, 1.6 planets. Therefore, about 160 billion planets exist in the galaxy.

    11 billion of these planets may orbit within the habitable zone of sunlike stars.

    1.42.7% of all sunlike star systems are expected to have an Earthlike planet within the habitable zone.

    Oversized planets, orbiting in the habitable zone, may have habitable moons!

    Planets in unbound orbits may number in the trillions (1012)!

  • *Detecting exoplanetary lifeThe heat is on for detecting Earth-size planets in habitable zones...

    If one is found, how could Earthbound scientists look for exoplanetary life?

    Look for oxygen, methane, or other suspicious compounds in the atmosphere. So far, we have detected atmospheric K, Na, CO2, H2O, O2, CH4 in the azure planet and others.

    Like the Martian meteorite ALH84001, however, evidence would have to be very, very strong.

    Turning the tablesthese lines of evidence are present in abundance in the Earths atmosphere. Curious alien astronomers that point their telescopes towards Earth would easily detect our signatures of life

  • *Hot Jupiters and solar system theoriesRecall our theory of solar system formation.

    Hydrogen planets would not form close to the central star, because the proto-planetary disk would have been so hot that hydrogen, helium, and hydrogen-rich compounds would have been in gas f