Opportunities in the Study of Extrasolar Planets

Peter R. McCullough, STScIPeter R. McCullough, STScI

Astrophysics Enabled by the Return to the MoonAstrophysics Enabled by the Return to the Moon

Nov 30, 2006Nov 30, 2006

Outline (also the summary)

1) Transiting planets are great science.

2) Somewhere in space is a good site for a 0.6-m telescope to monitor known transiting systems.

3) The Moon is in space.

4) Polarization may be more practical than spectra for physical characterization of exo-earths.

5) A 10-m diameter telescope with imaging polarization capability and more modest wavefront quality requirements than TPF-C can detect oceans if they exist on terrestrial exoplanets and nearly map continental boundaries.

6) Return to the Moon will inspire creative ways to overcome challenges and tap new opportunities.

Historical Precedent

Captain Cook’s International Expedition

Transit of Venus, 1769 in TahitiTransit of Venus, 1769 in Tahiti

Hoped to measure the physical scale of the solar Hoped to measure the physical scale of the solar system.system.

How much did it cost?How much did it cost?

Endeavor

Site Infrastructure lasts for

Generations

XO’s Site #1 is Haleakala’s Site #1, the SAO BakerNunn Building.

1957

www.ifa.hawaii.edu/users/steiger/post_cook.htm

1958

XO-1 telescope parade:

Exoplanets are relevant to these Satellites:

HubbleHubble SpitzerSpitzer MOSTMOST COROTCOROT KeplerKepler JWSTJWST TPF *TPF *

*Flight Opportunity for TPF is TBD.

HD 209458 with HST/STIS Spectrophotometry

Brown et al 2001

Ingress

Eclipse

Egress

Absorption Spectra of Planetary AtmosphereAbsorption Spectra of Planetary Atmosphere Precise photometry and timing of transitsPrecise photometry and timing of transits

Oblateness (rotation rate) of planetOblateness (rotation rate) of planet Rings, Satellites of planetRings, Satellites of planet Perturbations from TP: Perturbations from TP: TOA) ~ many secondsTOA) ~ many seconds Limb darkening and star spotsLimb darkening and star spots

Secondary EclipseSecondary Eclipse Temperature, Temperature, f/f ~ ( Tf/f ~ ( Tpp/T/Tss ) ( R ) ( Rpp/R/Rss ) )22 ~ 0.4% in IR ~ 0.4% in IR Eccentricity better than RV methodEccentricity better than RV method Albedo, Albedo, f/f ~ 0.02% x optical albedof/f ~ 0.02% x optical albedo

XO targets Bright Stars that allow …

An Extrasolar Planetary Atmosphere

Spectrophotometric observations of four planetary Spectrophotometric observations of four planetary transits taken in sodium doublet at 589.3nm.transits taken in sodium doublet at 589.3nm.

Charbonneau Charbonneau et. al.et. al. 2002, 2002, ApJApJ, , 568568, 377, 377

I (sodium/cont.):I (sodium/cont.): 2.32 2.32 (0.57) x 10 (0.57) x 10-4-4

Satellites of warm Jupiters Satellites of warm Jupiters Could be more Could be more

prevalent habitable prevalent habitable exoworlds than exoworlds than exoplanets (!?)exoplanets (!?)

Detectable by its Detectable by its gravitational influence gravitational influence on its host planet: on its host planet: transits arrive early and transits arrive early and late.late.

At some wavelengths, At some wavelengths, planet is much darker planet is much darker than its satellite(s).than its satellite(s).

There are ~10 transiting There are ~10 transiting Jupiters of stars V<12 Jupiters of stars V<12 and periods ~1 year; and periods ~1 year; they will be found they will be found before lunar sorties.before lunar sorties.

Habitable worlds

70 Vir, available from Extrasolar Visions Inc.

Lunar Deployable Telescope

Drake Deming (PI), Peter McCullough, and David Charbonneau

LDT’s terrestrial radius mass

diagram

Drake Deming (PI), Peter McCullough, and David Charbonneau

LDT’s terrestrial planet transit

Drake Deming (PI), Peter McCullough, and David Charbonneau

LDT as concept

Drake Deming (PI), Peter McCullough, and David Charbonneau

•By 2019 …

•Kepler will have completed its mission, detecting Earth-like planets orbiting solar-type stars from 100 to 300 pc distant.

•Ground- and space-based transit surveys, augmented by precise radial velocities, will have detected 100 hot Jupiters transiting Sun-like stars and some terrestrial planets transiting nearby K- and M-dwarfs.

•Spitzer measurements of thermal emission from exoplanets will have carried over to JWST, which will have measured thermal emission spectra of hot Jupiters and hot Neptunes. JWST will be pushing toward measuring the thermal spectrum of a close-in Earth-like planet around a lower main sequence star, using the secondary eclipse technique.

•The most important requirement for transiting planet studies is a site in space, free of the terrestrial atmosphere, and with the capability to observe a given transiting planet system with photon-limited photometric precision for long durations (multiple transits).

•LDT will be deployable by two astronauts and operate autonomously. It will …

•Observe planets transiting bright, nearby, stars.

•Stare at a given star for weeks to months.

•Discover additional terrestrial planets of known transiting systems based upon:

•Transits of the terrestrial planets: the premise (unproven) is the inclination is favorable.

•Timing giant-planet transits.

•Measure accurate sizes for terrestrial planets orbiting the nearest stars and measure their visible reflected light (at secondary eclipse).

Drake Deming (PI), Peter McCullough, and David Charbonneau

Much BiggerLight Buckets…

Transiting Planet Spectroscopy (1 of 2)

• Proven technique: V=8, Jovian planet HD 209458b orbiting sun-like star, observed with HST STIS, Na etc detected.

• Earth-Sun at 10 pc: Absorption-lines due to transiting planet atmosphere feasible with 10-m steerable light bucket in vacuum plus spectrograph. (Gilliland, p.c.)

• PSF FWHM = 1 arcmin is ok

Transiting Planet Spectroscopy (2 of 2)• Emission spectrum of planet disappearing behind star.

planet atmosphere.

• Proven technique: V=8, Jovian planet HD 209458b, etc provides spectral energy distributions of planet in Spitzer bands.

• JWST will get true spectra of hot Jupiters by this technique – but probably not terrestrial exoplanets.

Imaging Stars with Transits

Does this help?Size of error bar ~ 1/(A t)1/2

Water… needs more than a

bucket

McCullough (2006 astroph 2007 ApJ)

A few others independently working on this concept also: Ford, Hough, Williams, Stam, Schmid

Unpolarized Light

Satellite images

Simulations

Polarized Light

S-pol

P-pol

10-m or 20-m precision-surface (but not TPF-C) steerable telescope required.

Total flux

2x flux difference

What’s great about this? Speckle pattern (think JWST-like PSF) can be designed Speckle pattern (think JWST-like PSF) can be designed to be nearly identical in the two polarizations, so the to be nearly identical in the two polarizations, so the glare of the star can be suppressed not only by glare of the star can be suppressed not only by coronagraphy but also by subtracting one polarized coronagraphy but also by subtracting one polarized image from the other. The unpolarized star cancels image from the other. The unpolarized star cancels out; the polarized planet doesn’t.out; the polarized planet doesn’t.

Spectra imply dividing light into 100+ bins; linear Spectra imply dividing light into 100+ bins; linear polarization implies two bins.polarization implies two bins.

Rayleigh scattering is very blue; glint from oceans is Rayleigh scattering is very blue; glint from oceans is achromatic. (so four bins: 2 polarization; 2 achromatic. (so four bins: 2 polarization; 2 wavelengths)wavelengths)

Glint is very localized (~15 degrees of “longitude”).Glint is very localized (~15 degrees of “longitude”).

The glint’s flux difference in the two polarizations is The glint’s flux difference in the two polarizations is 0.15 photons per second for a 10-m telescope 0.15 photons per second for a 10-m telescope observing Earth-Sun system at 10 pc. Long integrations observing Earth-Sun system at 10 pc. Long integrations (days) can pick out the polarized light from an oceanic (days) can pick out the polarized light from an oceanic planet in the glare of the star. One hour integration planet in the glare of the star. One hour integration gives Poisson S/N ~ 20 if star light can be suppressed gives Poisson S/N ~ 20 if star light can be suppressed entirely by a superb technology.entirely by a superb technology.

No atmospheric absorption

Earth-like clear atmospheric absorption

Projected like we’d observe.

Light curve for Earth

Ocean planet with clear atmosphere;Rayleigh suppressed (long wavelength)

With clouds too

Half-BakedBetter than “not even wrong”…

About costs… Net worth of US households is 50 T$ in 2000. Net worth of US households is 50 T$ in 2000.

The aggregate value of corporate equities directly The aggregate value of corporate equities directly held was 9 T$ in 2000 and was 4 T$ in 2003, so it held was 9 T$ in 2000 and was 4 T$ in 2003, so it declined by ~2 T$ per year for three consecutive declined by ~2 T$ per year for three consecutive years. That's 1 B$ per hour of each and every working years. That's 1 B$ per hour of each and every working day for three years.day for three years.

The median market capitalization of a corporation in The median market capitalization of a corporation in the DJIA is 108 B$ (as of Oct 31, 2006).the DJIA is 108 B$ (as of Oct 31, 2006).

Pfizer, a pharmaceutical company founded in 1849, in Pfizer, a pharmaceutical company founded in 1849, in 2005 had annual revenue of 51 B$ and spent 7 B$ on 2005 had annual revenue of 51 B$ and spent 7 B$ on R&D. NASA by comparison was awarded 16 B$ in 2005 R&D. NASA by comparison was awarded 16 B$ in 2005 by the US Congress.by the US Congress.

Something more immediate than global warming…

Europe, different rendering…

Various thoughts…sustainability Is colonization of the Moon a metaphor for solving Is colonization of the Moon a metaphor for solving Earth's geopolitical problems? A quasi-sustainable Earth's geopolitical problems? A quasi-sustainable presence on the Moon wouldn't use fossil fuels; it presence on the Moon wouldn't use fossil fuels; it would use solar or nuclear with a considerable would use solar or nuclear with a considerable emphasis on conservation. emphasis on conservation.

Making scientific equipment on the moon is desirable Making scientific equipment on the moon is desirable strategically even if its possible to bring it there from strategically even if its possible to bring it there from Earth.Earth.

A flywheel with 2-m radius and 2-m height filled with A flywheel with 2-m radius and 2-m height filled with lunar regolith has a mass of 40 metric tons, and if spun lunar regolith has a mass of 40 metric tons, and if spun to 1000 rpm, has a kinetic energy of 110 kwh, which to 1000 rpm, has a kinetic energy of 110 kwh, which corresponds to 330 Watts for the 300-hour duration of corresponds to 330 Watts for the 300-hour duration of the lunar night. the lunar night.

On the Moon, a need for UPS may exist for these On the Moon, a need for UPS may exist for these reasons: reasons:

to buffer solar power to the nightto buffer solar power to the night

to provide for the variable power demand of to provide for the variable power demand of human habitationhuman habitation

to mitigate riskto mitigate risk

Various thoughts…bandwidth JWST is bandwidth limited from L2.JWST is bandwidth limited from L2.

LSST = 10 Terabyte/night. LSST = 10 Terabyte/night.

That data rate may be impractical to transmit to That data rate may be impractical to transmit to Earth from sensors on Moon or L2, but can be carried Earth from sensors on Moon or L2, but can be carried home on a disk if there’s a regular data delivery home on a disk if there’s a regular data delivery service:service:

One kg equals 1 Terabyte in 2006. By 2020, 14 One kg equals 1 Terabyte in 2006. By 2020, 14 doublings later, that’ll be 8000 Terabytes per kg, so doublings later, that’ll be 8000 Terabytes per kg, so 400 Petabytes will weigh as much as a human. 400 Petabytes will weigh as much as a human.

Alternatively, transmitting from lunar surface to Alternatively, transmitting from lunar surface to lunar orbit for storage and subsequent transport to lunar orbit for storage and subsequent transport to Earth may be desirable.Earth may be desirable.

Various thoughts… Hoyle’s ideas on panspermia could be tested by Hoyle’s ideas on panspermia could be tested by trying to detect life in lunar regolith, suitably nurtured, trying to detect life in lunar regolith, suitably nurtured, much like Viking did on Mars but much more seriously. much like Viking did on Mars but much more seriously. PCR or equivalent technique(s) might permit detection PCR or equivalent technique(s) might permit detection at very trace levels.at very trace levels.

A satellite can be sustained with some propulsion A satellite can be sustained with some propulsion inside L2 so it is in Earth’s shade all the time. Nuclear inside L2 so it is in Earth’s shade all the time. Nuclear power required.power required.

Things too dangerous (or not permitted) on or near Things too dangerous (or not permitted) on or near Earth could perhaps be done on the Moon. One Earth could perhaps be done on the Moon. One example, Clementine. Another example: perturbing a example, Clementine. Another example: perturbing a small asteroid to orbit (or hit) the moon instead of the small asteroid to orbit (or hit) the moon instead of the Earth (in case it misses).Earth (in case it misses).

Nuclear explosions could be used for excavations of Nuclear explosions could be used for excavations of and transmuting elements of the regolith. Also for and transmuting elements of the regolith. Also for pinging the moon for tomography.pinging the moon for tomography.

The pristine fossil water ice in the lunar polar craters The pristine fossil water ice in the lunar polar craters could be burned like fossil fuels are on earth.could be burned like fossil fuels are on earth.

Various thoughts… security and economics

Those examples (I hope) make you think that not all Those examples (I hope) make you think that not all things that are possible are desirable or ethical. things that are possible are desirable or ethical.

The return to the Moon is supposed to enhance our The return to the Moon is supposed to enhance our national security. Bored children tend to fight; busy national security. Bored children tend to fight; busy and intrigued children fight less. Perhaps the same and intrigued children fight less. Perhaps the same could be true for nations and their peoples.could be true for nations and their peoples.

Economic enhancement? Economic enhancement?

When asked how much the US should spend and on When asked how much the US should spend and on which scientific disciplines, someone (I forget who) which scientific disciplines, someone (I forget who) replied, “[exactly as much as it takes to be number replied, “[exactly as much as it takes to be number one in each and every one.]” one in each and every one.]”

Seward’s Folly (buying Alaska) and multi-national Seward’s Folly (buying Alaska) and multi-national Antartica are possible answers to why the US will go to Antartica are possible answers to why the US will go to the Moon.the Moon.

Yankee ingenuity fostered at grad-student level if Yankee ingenuity fostered at grad-student level if few-100 kg payloads are delivered regularly to space. few-100 kg payloads are delivered regularly to space. (If not, the best brains will do biology, computer (If not, the best brains will do biology, computer science, etc.)science, etc.)

Various thoughts… Human+robot surgery will develop tools we can use.Human+robot surgery will develop tools we can use.

Parabola or Sphere?Rotating Liquid Mirrors produce parabolas naturally.

Two surfaces rubbed together produce a sphere naturally. So does a bubble via surface tension.

Arecibo and Hobby Eberly Telescope are both spheres.

Spheres have advantages over Parabolas:

1) multiple focal planes can look at very different directions on the sky using a single sphere.

Parabola looks up.

F

Parabola or Sphere?

F

C

F F

Parabola or Sphere?Rotating Liquid Mirrors produce parabolas naturally.

Two surfaces rubbed together produce a sphere naturally. So does a bubble via surface tension.

Arecibo and Hobby Eberly Telescope are both spheres.

Spheres can have advantages over Parabolas:

1) multiple focal planes can look at very different directions on the sky using a single sphere.

2) segmented optics are identical for a sphere.

3) replica optics fabricated on the moon, subsequently ion polished (or equivalent) and coated in place courtesy of the lunar vacuum, and actively controlled to maintain figure could be an alternative to rotating liquid mirrors.

Summary

1) Transiting planets are great science.

2) Somewhere in space is a good site for a 0.6-m telescope to monitor known transiting systems.

3) The Moon is in space.

4) Polarization may be more practical than spectra for physical characterization of exo-earths.

5) A 10-m diameter telescope with imaging polarization capability and more modest wavefront quality requirements than TPF-C can detect oceans if they exist on terrestrial exoplanets and nearly map continental boundaries.

6) Return to the Moon will inspire creative ways to overcome challenges and tap new opportunities.