Terrestrial Planet Finder Options

[imran]

To me this is one of the most exciting missions to be launched in the next decade. In April 2004, the Terrestrial Planet Finder (TPF) got the go ahead from NASA as a set of two complementary observatories: a visible-light coronagraph (to launch around 2014) and a mid-infrared formation-flying interferometer (to launch before 2020).

Here's the official web site:
http://planetquest.jpl.nasa.gov/TPF/tpf_index.html

[Guest_Richard Trigaux_*]

Thanks for your approbation, JRehling.

I am much bothered by the very eccentric orbits found, as they go straight against the standard model of accretion disk. In an accretion disk, we can expect that, due to friction, any particule in an eccentric or inclinated orbit will quickly join a circular orbit in grossly the plane of the ring. This does not allow for very eccentric or very inclinated bodies. If such bodies are real, they require special processes to form, or to go on the orbits they are today.

But I join your opinion about, once a heavy body is formed, it forces the formation of the others on resonant orbits, leading to a system which obeys the Titus Bode law. (regularly spaced circular and coplanar orbits).

But with my opinion it is not so simple, and there are very likely different scenarios for the formation of a system, depending on the sequence of events.

The simplest scenario is when an homogenous primordial cloud falls quickly to form an homogenous accretion ring. Some million years later, the primordial cloud is cleared, and this ring starts to form ringlets on resonant orbits, to give a regular planet system like ours.

By the way a perfect accretion cloud would never form planets, as there is no way to decide where will appear the first clump of matter or heavier ringlet. Happily such a ring cannot be perfectly homogenous, and somewhere an heavier clump will sooner or later start to drive the other parts of the ring on and off resonant orbits. This is basically a problem where a tiny disturbance in the beginning will cause drastic differences in the future evolution. In simulations, we are even compelled to artificially introduce such disturbances, otherwise we could obtain a perfect simulation of a water pan on the fire, but which would never have convection movements.

In our solar system, things may have happened this way, except that, obviously, the ring was not homogenous: many matter accumulated at the distance of Jupiter, depleting the level of Mars and Asteroids. Why it was such? There can be several reasons:
-this structure appeared at the time the matter was still falling on the ring, producing an accumulation at a random distance from the Sun;
-A process into the ring, for instance fast spiraling inwards due to a larger accumulation of matter somewhere (similar to the chained collapses of the floors in the World Trade Center). This process could form the "hot Jupiters" fast enough to protect them from fractionned distillation. In our system, a first fall would have depleted Mars and asteroids orbits, and a second was still falling when it formed Jupiter, stopping the fall.
-A process of fractionated distillation due to the heat of the Sun. In this case we could find a statistical corellation between the distance of Jupiter-like planets and the size of the star. From this the interest to have a statistics of many solar systems, which could give us clues about their formation, in the same way the Herzprung Russel statistics of stars enlightened us about their evolution.



But it is clear that besides this "standard" process, some anomalous process could play in various ways:
- the fall of matter from the primordial cloud is not finished when the formation of the planets begins, and this could mask the effect of fractionned distillation.
- heavy clumps of matter could exist into the primordial cloud, before falling on the disk. Eventually these clumps would already contain a planet or brown dwarf. When they fall into the accretion disk, the later is too light weight to efficiently circularise their orbit. Such clumps could then quickly form large planets of their own, eventually in eccentric/inclinated orbits. I think we can explain most of the "freaks" that way. And they left very few place for other stable orbits.
- Planets would migrate from constant accretion of matter with a different momentum, from nearby orbits. This was proposed to explain the "hot Jupiters" in a way which avoids them to undergo fractionned distillation. But seemingly this did not happened in our solar system, as it would require a complex and corellated set of migrations to explain the Titus Bode law.
-Planets on close orbits would interact at the time of a close encounter, to give very eccentric orbits. But if this happened somewhere, we could see the two orbits having a common point, like the Neptune-Pluton system.

[ljk4-1]

Paper: astro-ph/0601028

Date: Mon, 2 Jan 2006 16:17:47 GMT (84kb)

Title: Linear and Bayesian Planet Detection Algorithms for the Terrestrial
Planet Finder

Authors: N. Jeremy Kasdin, Isabelle Braems
\\
Current plans call for the first Terrestrial Planet Finder mission, TPF-C, to
be a monolithic space telescope with a coronagraph for achieving high contrast.
The coronagraph removes the diffracted starlight allowing the nearby planet to
be detected. In this paper, we present a model of the planet measurement and
noise statistics. We utilize this model to develop two planet detection
algorithms, one based on matched filtering of the PSF and one using Bayesian
techniques. These models are used to formulate integration time estimates for a
planet detection with desired small probabilities of false alarms and missed
detections.

\\ ( http://arXiv.org/abs/astro-ph/0601028 , 84kb)

[ljk4-1]

Paper: astro-ph/0601469

Date: Fri, 20 Jan 2006 02:37:42 GMT (462kb)

Title: Comparative Planetology and the Search for Life Beyond the Solar System

Authors: Charles A. Beichman, Malcolm Fridlund, Wesley A. Traub, Karl R.
Stapelfeldt, Andreas Quirrenbach, Sara Seager

Comments: To Appear in Protosars and Planets V
\\
The study of planets beyond the solar system and the search for other
habitable planets and life is just beginning. Ground-based (radial velocity and
transits) and space-based surveys (transits and astrometry) will identify
planets spanning a wide range of size and orbital location, from Earth-sized
objects within 1 AU to giant planets beyond 5 AU, orbiting stars as near as a
few parsec and as far as a kiloparsec. After this initial reconnaissance, the
next generation of space observatories will directly detect photons from
planets in the habitable zones of nearby stars. The synergistic combination of
measurements of mass from astrometry and radial velocity, of radius and
composition from transits, and the wealth of information from the direct
detection of visible and mid-IR photons will create a rich field of comparative
planetology. Information on proto-planetary and debris disks will complete our
understanding of the evolution of habitable environments from the earliest
stages of planet-formation through to the transport into the inner solar system
of the volatiles necessary for life.

The suite of missions necessary to carry out the search for nearby, habitable
planets and life requires a ``Great Observatories'' program for planet finding
(SIM PlanetQuest, Terrestrial Planet Finder-Coronagraph, and Terrestrial Planet
Finder-Interferometer/Darwin), analogous to the highly successful ``Great
Observatories Program'' for astrophysics. With these new Great Observatories,
plus the James Webb Space Telescope, we will extend planetology far beyond the
solar system, and possibly even begin the new field of comparative evolutionary
biology with the discovery of life itself in different astronomical settings.

\\ ( http://arXiv.org/abs/astro-ph/0601469 , 462kb)

[ljk4-1]

"Cancellation of the long-sought Terrestrial Planet Finder, a mission also supported in the original Vision for Space Exploration, to discover Earth-like planets and possible abodes for life around other stars."

http://www.planetary.org/about/press/relea...ty_Charges.html

[ljk4-1]

Canceling NASA's Terrestrial Planet Finder: The White House's Increasingly
Nearsighted "Vision" For Space Exploration

http://www.spaceref.com/news/viewnews.html?id=1092

To quote:

According to President Bush, as he unveiled his Vision for Space Exploration: "We do not know where this journey will end, yet we know this: human beings are headed into the cosmos."

If there was one singular mission that embodied humanity casting its collective "vision" outward "into the cosmos" so as to look for places to "head" toward, it was the Terrestrial Planet Finder.

This is a bad decision. A really bad one. In making it, one has to question whether this White House really meant what it said 2 years ago when it raised everyone's expectations, invoking an expansion "into the cosmos" in so doing.

With every passing year this "vision" is becoming increasing nearsighted.


-- Planetary Society Charges Administration with Blurring its Vision for Space
Exploration

http://www.spaceref.com/news/viewpr.html?pid=18944

"The NASA Budget released today shortchanges space science in order to fund 17
projected space shuttle flights. Despite recent spectacular results from NASA's science programs, this budget puts the brakes on their growth within the agency.

"It seriously damages the hugely productive and successful robotic exploration of our solar system and beyond."

[antoniseb]

This is a bad decision. A really bad one. In making it, one has to question whether this White House really meant what it said 2 years ago when it raised everyone's expectations, invoking an expansion "into the cosmos" in so doing.

Sometimes I wonder whether this is part of a strategy to postpone as long as possible the discovery of life on other planets, so as to not face certain quetions that some categories of fundementalist religious people don't want to have answered.

Independent of that, there's a lot that we could be doing, but aren't. It'll be interesting to see how the priorities shift around 2010 when our obligations to the shuttle and ISS wind down. Will roboic missions start making a comeback?