Opportunities in the Study of Extrasolar Planets : Opportunities in the Study of Extrasolar Planets Peter R. McCullough, STScI
Astrophysics Enabled by the Return to the Moon
Nov 30, 2006
Outline (also the summary) : Outline (also the summary)
Transiting planets are great science.
Somewhere in space is a good site for a 0.6-m telescope to monitor known transiting systems.
The Moon is in space.
Polarization may be more practical than spectra for physical characterization of exo-earths.
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.
Return to the Moon will inspire creative ways to overcome challenges and tap new opportunities.
Historical Precedent : Historical Precedent
Captain Cook’s International Expedition : Captain Cook’s International Expedition Transit of Venus, 1769 in Tahiti
Hoped to measure the physical scale of the solar system.
How much did it cost? Endeavor
Site Infrastructure lasts for Generations : Site Infrastructure lasts for Generations
XO’s Site #1 is Haleakala’s Site #1, the SAO BakerNunn Building. : 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: : XO-1 telescope parade:
Exoplanets are relevant to these Satellites: : Exoplanets are relevant to these Satellites: Hubble
Spitzer
MOST
COROT
Kepler
JWST
TPF * *Flight Opportunity for TPF is TBD.
HD 209458 with HST/STIS Spectrophotometry : HD 209458 with HST/STIS Spectrophotometry Brown et al 2001
XO targets Bright Stars that allow … : Absorption Spectra of Planetary Atmosphere
Precise photometry and timing of transits
Oblateness (rotation rate) of planet
Rings, Satellites of planet
Perturbations from TP: d(TOA) ~ many seconds
Limb darkening and star spots
Secondary Eclipse
Temperature, df/f ~ ( Tp/Ts ) ( Rp/Rs )2 ~ 0.4% in IR
Eccentricity better than RV method
Albedo, df/f ~ 0.02% x optical albedo XO targets Bright Stars that allow …
An Extrasolar Planetary Atmosphere : An Extrasolar Planetary Atmosphere Spectrophotometric observations of four planetary transits taken in sodium doublet at 589.3nm. Charbonneau et. al. 2002, ApJ, 568, 377 DI (sodium/cont.):
2.32 ± (0.57) x 10-4
Habitable worlds : Satellites of warm Jupiters
Could be more prevalent habitable exoworlds than exoplanets (!?)
Detectable by its gravitational influence on its host planet: transits arrive early and late.
At some wavelengths, planet is much darker than its satellite(s).
There are ~10 transiting Jupiters of stars V<12 and periods ~1 year; they will be found before lunar sorties. Habitable worlds 70 Vir, available from Extrasolar Visions Inc.
Lunar Deployable Telescope : Lunar Deployable Telescope Drake Deming (PI), Peter McCullough, and David Charbonneau
LDT’s terrestrial radius mass diagram : LDT’s terrestrial radius mass diagram Drake Deming (PI), Peter McCullough, and David Charbonneau
LDT’s terrestrial planet transit : LDT’s terrestrial planet transit Drake Deming (PI), Peter McCullough, and David Charbonneau
LDT as concept : LDT as concept Drake Deming (PI), Peter McCullough, and David Charbonneau
Slide17 : 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 Bigger Light Buckets… : Much Bigger Light Buckets…
Transiting Planet Spectroscopy (1 of 2) : 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) : 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 : Imaging Stars with Transits
Does this help? : Does this help? Size of error bar ~ 1/(A Dn t)1/2
Water… needs more than a bucket : Water… needs more than a bucket
Slide24 : McCullough (2006 astroph 2007 ApJ)
A few others independently working on this concept also: Ford, Hough, Williams, Stam, Schmid
Unpolarized Light : Unpolarized Light Satellite images Simulations
Polarized Light : Polarized Light S-pol P-pol
10-m or 20-m precision-surface (but not TPF-C) steerable telescope required. : 10-m or 20-m precision-surface (but not TPF-C) steerable telescope required. Total flux 2x flux difference
What’s great about this? : What’s great about this? Speckle pattern (think JWST-like PSF) can be designed to be nearly identical in the two polarizations, so the glare of the star can be suppressed not only by coronagraphy but also by subtracting one polarized image from the other. The unpolarized star cancels out; the polarized planet doesn’t.
Spectra imply dividing light into 100+ bins; linear polarization implies two bins.
Rayleigh scattering is very blue; glint from oceans is achromatic. (so four bins: 2 polarization; 2 wavelengths)
Glint is very localized (~15 degrees of “longitude”).
The glint’s flux difference in the two polarizations is 0.15 photons per second for a 10-m telescope observing Earth-Sun system at 10 pc. Long integrations (days) can pick out the polarized light from an oceanic planet in the glare of the star. One hour integration gives Poisson S/N ~ 20 if star light can be suppressed entirely by a superb technology.
No atmospheric absorption : No atmospheric absorption
Earth-like clear atmospheric absorption : Earth-like clear atmospheric absorption
Projected like we’d observe. : Projected like we’d observe.
Light curve for Earth : Light curve for Earth
Ocean planet with clear atmosphere; Rayleigh suppressed (long wavelength) : Ocean planet with clear atmosphere; Rayleigh suppressed (long wavelength)
With clouds too : With clouds too
Half-Baked Better than “not even wrong”… : Half-Baked Better than “not even wrong”…
About costs… : About costs… Net worth of US households is 50 T$ in 2000.
The aggregate value of corporate equities directly held was 9 T$ in 2000 and was 4 T$ in 2003, so it declined by ~2 T$ per year for three consecutive years. That's 1 B$ per hour of each and every working day for three years.
The median market capitalization of a corporation in the DJIA is 108 B$ (as of Oct 31, 2006).
Pfizer, a pharmaceutical company founded in 1849, in 2005 had annual revenue of 51 B$ and spent 7 B$ on R&D. NASA by comparison was awarded 16 B$ in 2005 by the US Congress.
Something more immediate than global warming… : Something more immediate than global warming…
Europe, different rendering… : Europe, different rendering…
Various thoughts…sustainability : Various thoughts…sustainability Is colonization of the Moon a metaphor for solving Earth's geopolitical problems? A quasi-sustainable presence on the Moon wouldn't use fossil fuels; it would use solar or nuclear with a considerable emphasis on conservation.
Making scientific equipment on the moon is desirable strategically even if its possible to bring it there from Earth.
A flywheel with 2-m radius and 2-m height filled with lunar regolith has a mass of 40 metric tons, and if spun to 1000 rpm, has a kinetic energy of 110 kwh, which corresponds to 330 Watts for the 300-hour duration of the lunar night.
On the Moon, a need for UPS may exist for these reasons:
to buffer solar power to the night
to provide for the variable power demand of human habitation
to mitigate risk
Various thoughts…bandwidth : Various thoughts…bandwidth JWST is bandwidth limited from L2.
LSST = 10 Terabyte/night.
That data rate may be impractical to transmit to Earth from sensors on Moon or L2, but can be carried home on a disk if there’s a regular data delivery service:
One kg equals 1 Terabyte in 2006. By 2020, 14 doublings later, that’ll be 8000 Terabytes per kg, so 400 Petabytes will weigh as much as a human.
Alternatively, transmitting from lunar surface to lunar orbit for storage and subsequent transport to Earth may be desirable.
Various thoughts… : Various thoughts… Hoyle’s ideas on panspermia could be tested by trying to detect life in lunar regolith, suitably nurtured, much like Viking did on Mars but much more seriously. PCR or equivalent technique(s) might permit detection at very trace levels.
A satellite can be sustained with some propulsion inside L2 so it is in Earth’s shade all the time. Nuclear power required.
Things too dangerous (or not permitted) on or near Earth could perhaps be done on the Moon. One example, Clementine. Another example: perturbing a small asteroid to orbit (or hit) the moon instead of the Earth (in case it misses).
Nuclear explosions could be used for excavations of and transmuting elements of the regolith. Also for pinging the moon for tomography.
The pristine fossil water ice in the lunar polar craters could be burned like fossil fuels are on earth.
Various thoughts… security and economics : Various thoughts… security and economics Those examples (I hope) make you think that not all things that are possible are desirable or ethical.
The return to the Moon is supposed to enhance our national security. Bored children tend to fight; busy and intrigued children fight less. Perhaps the same could be true for nations and their peoples.
Economic enhancement?
When asked how much the US should spend and on which scientific disciplines, someone (I forget who) replied, “[exactly as much as it takes to be number one in each and every one.]”
Seward’s Folly (buying Alaska) and multi-national Antartica are possible answers to why the US will go to the Moon.
Yankee ingenuity fostered at grad-student level if few-100 kg payloads are delivered regularly to space. (If not, the best brains will do biology, computer science, etc.)
Various thoughts… : Various thoughts… Human+robot surgery will develop tools we can use.
Parabola or Sphere? : 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:
multiple focal planes can look at very different directions on the sky using a single sphere.
Parabola looks up. : Parabola looks up. F
Parabola or Sphere? : Parabola or Sphere? F C F F
Parabola or Sphere? : 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:
multiple focal planes can look at very different directions on the sky using a single sphere.
segmented optics are identical for a sphere.
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 : Summary
Transiting planets are great science.
Somewhere in space is a good site for a 0.6-m telescope to monitor known transiting systems.
The Moon is in space.
Polarization may be more practical than spectra for physical characterization of exo-earths.
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.
Return to the Moon will inspire creative ways to overcome challenges and tap new opportunities.