So now, so now. The mission's page says it is ahead of schedule. Like most of the past few missions I have mentioned SIM is an interferometry mission, but this one's goal is not to detect the light of other worlds directly. SIM is an astrometry mission, it will be measuring the positions of nearby stars and seeking the wobble induced by planetary companionship. Among some of its nearer targets SIM might detect worlds as small as twice Earth's mass.

This observatory goes into Earth-trailing orbit, drifting out over the course of several years (5.5) to its placement position 95 million km away. And, surprise surprise! SIM will operate in visual light. Its apertures (for all three scopes) will be only 0.3m, mounted on a 9m baseline.

HAHAHAHAHA! Now I get to toss aside this instrumentation and move to more interesting matters. Also to transform this into a presentation with illustrations and effects and all. 2 hours.

Ehdithe: SIM is supposed to launch sometime before 2016.

Their list of what it could find (minimum size constrained by distance) -

• Earth mass around 6 stars
• Twice Earth mass aruond 30 stars
• 3.2 Earth mass planets around 120 stars
• Neptune massed planets around 2,000 stars (Wikipedia says Neptune is 17 times as massive as Oit)
  

Filter: crazy

It is a planet-finding scope being built by the ESA (that'd be the European Space Agency [trying to err on the side of too much info rather than too little, at least when I feel like providing it]), that's what. Intended to launch in 2015 this one will consist of a flotilla of three craft/scopes (oh, plus one other for communications). Like TPF-I, Darwin will operate in the infrared and each of its telescopes will be at three metres in diameter. This scope is going to be placed in orbit at L₂, 1.5 million kilometres from Earth. Will likely excise starlight as a nulling interferometer.

Well, what else is there to be said? I feel that, having not slept last night, I must be missing important things but could not say what. I recommend checking out the ESA's site for Darwin, very clear and informative.

Ugh! I had been tappin' away at a post on NASA's TPF (that's Terrestrial Planet Finder, for - can you guess?) and now a careless delete tab has et it. So, hum, let's do a quick reiteration instead, top o' my head.

So indeed, we have the Terrestrial Planet Finder, a mission in development by NASA as part of its Origins program. The goal is to find and to study earth-like planets within 60 light years (18.4 parsecs). Will be looking at F, G and K type stars in particular.

Originally being considered were four projects within the scope of the TPF, since reduced to two. Those two being what they call the moderate sized coronagraph (TPF-C, 4 by 6 metres, compare with the 2.4m Hubble scope) and a formation-flying interferometer (TPF-I, as opposed to one with its compnents held in place by struts).

Talking about TPF-I first. It is intended to consist of a number of component telescopes - at no point have I seen any information describing exactly how many - three to four metres in diameter (again compare with the 2.4 metre Hubble, though perhaps there is another, better comparison to make. If there is I do not know it) and, as mentioned, free flying, so they will need to correct any drift in relative position with little rocket engines. And they will have to. An interferometer works by combining light picked up by two (or more) components to create a single overall image. I do believe the components need to be kept in place to within half a wavelength in order for the whole dealie to work. In this case, because TPF-I will operate in the mid infrared, these telescopes need to be positioned to within 5 micrometres. I wonder if that was any part of the reason for TPF-I being an IR mission and TPF-C going visible. Not sure what else there is to say except, being that it operates in the infrared TPF-I needs a cooling system to prevent heat glow from the intruments themselves spoiling the image, apparently. And though I have not seen it stated outright I have the impression it is to be placed somewhere far enough away that Earth won't get in the way as it does for Hubble. Oh, and that the thing is expected to solve the contrast problem by being a nulling interferometer, which, far as I can understand it right now, I think means that signals direct from the star are canceled out by being combined destructively when the overall image is put together, while the planet(s?) gets to shine through constructively. Ah, this is what I get for being three years past optics and failing EM twice - better luck next semester!

Past time for a new paragraph, don't you think, dear reader? Well, this mission is in early stages yet, not even testing of components. Aimed to launch sometime before 2020, but probably after 2016 as that is when TPF-C is meant to launch and TPF-C is meant to go first.

And what of TPF-C? I'm afraid all I can find right now is the mirror size, hoped ofr launch year and visible lightness of it. And that a coronagraph is basically a screen for blotting out starlight to see dimmer objects which would be otherwise obscured.

Okay, one final thing of this mission. According to the project's newsletter their funding for the 2007 to 2011 fiscal years is zero. And according to other sources what we have to thank for that is Bush's declaration of intent to return humans to the Moon and  beyond along with the providing of very little extra money to actually accomplish the deed, forcing the cutting or sidelining of other programs. Well, any regular reader of Bad Astronomy will be familiar with this.

Kay, next! (Questions, though welcome as always, I 'spect will come too late for the answering to do anything for my marks. Still helpful and still fun hough)

Filter: busy

Okay. This had better be the last time I go over this particular subtopic. I want to move on!

Now, prime difficulty once you have a scope large enough to resolve the seperated components is the matter of contrast. What you want to do is damp out the overbright starlight (A rhyme! I should be a songwriter) but leave the little ember glow of that darling planet still bright as it can be just an infinitesimal distance to one side. And without building a miror the size of the moon, please. I am not going to be able to process an entire unit's worth of information on optics or electromagnetism in a few days (that is for next semester) so... I leave it to be taken as given for the moment that the telescope size needed at visual wavelengths is about five to ten metres. We already have telescopes this size but not in space. In infrared we would need a scope 20m + in size [what? 100 - 300m is larger than 20] (wavelength is longer therefore we need a larger detector to achieve comparable detector, gain required is lower too but as I do not understand EM well enough to talk about gain I will leave it aside as much as I can).

One thing we can do is use a mask to, um, back up actually. Even though most telescopes do not have sufficient resolution to show stars as anything but a point of light we still have to deal with what is called the Airy disc, the star actually appears as a small fuzzy circle of light. It is surrounded by concentric rings of light of diminishing intensity, fringes produced by diffraction. What we don't want is for the planet to be obscured by the Airy disc, nor to find itself in the midst of a fringe. With the use of an annular pupil mask the first dark ring can be broadened and deepened. Looking at 10 micrometres (that's in the infrared) we would need then a telescope diamater 'only' 20 metres across. If we want to go further we would need to use an interferometer.

Okay, enough. Not as finished as I hoped to be. Tired now, need sleep - up early omorrow and work hard. Good night/day all.

Filter: sleepy

I am very not interested in observation and detection methods. At least not compared to the stuff they let us see. So I am trying to burn through this as quickly as I can while still at least giving the appearance of thoroughness.

Okay, (I am trying not to be so repetitive) the main things needed to be overcome to image extrasolar planets are:

• Contrast between nearby stellar brightness and far dimmer target


• Zodiacal light in the target system


• Zodiacal light in our system


• Skyglow (when observing from Earth [Honestly, who would?])

Alrighty then. Last time I left off at... saying a 0.4 metre aperture is insufficient for directly detecting extrasolar planets (exoplanets? that term is much more convenient to type and to say so why not use it instead?), even though it is sufficient to resolve the components. One problem: Magnitude 27 is very very dim. 6 is generally considered the cut-off for what can be seen with the unaided human eye (though many people's eyes are better or worse and light pollution can signifcantly reduce what is visible), so while the star is visible to the unaided eye the planet is more than ten thousand times dimmer. So we need to make sure our telescope is gathering sufficient light to even detect the planet.

*runs over to text-bearing bookcase*

Yes, this is basic stuff, and yes, I did have to look some up. In fact I was rather getting off on the wrong foot. Y'see, although a larger aperture helps to gather more light at once, dimmer objects can still be seen with a smaller scope if the integration time is increased. Doesn't work if one is observing with their own eyes - not being able to adjust exposure time and all. Actually, oh dear, I am rather afraid I might be spouting nonesense now. But I will correct my own errors as soon as I may, and sooner if they are pointed out to me. This is the kind of thing that will get one embarrassed looking back at the bloggings of their youth in years to come (well, actually actually what will really be embarrassing are the side musings I have not posted this past week on behalf of the illusion of focused discipline but that will just have to wait). Let us just go instead to the matter of contrast.

Oh, okay. (At least) One more diversion first. I find it interesting that an Earth-equivalent planet has an absolute magnitude only a little less than a Jupiter-equivalent (28.1[Woolf & Angel 1998] vs. 27 [Marcy & Butler 1998]). Being closer to the host star will make it still harder, though. Aaaanyway-

We already have telescopes capable of detecting such faint objects (e.g.), the difficulty is preventing the image from being washed out by the overwhelmingly brighter nuclear furnace sight right next door. Repeating myself enough yet? It is a sign of lack of thorough knowledge and clarity of thought. But if I work hard and study much that may improve.

What we need to do is find a way to suppress unwanted illumination so that what we are after is not obscured. Lessee, quote:

The criterion for resolving and detecting objects of enormously different intensity needs some discussion. The planet does not have to be brighter than the local halo of scattered starlight, but its detection does require that, at a minimum, the random fluctuations in the halo due to photon noise be smaller than the planet signal.

Filter: awake

    Talking mostly about giant planets here, one reason they are so difficult to detect directly is the matter of contrast. The host star (parasitic connotations!) is expected to be roughly 10⁹ times brighter than the planet. That's (because this kind of explicating is easier and more fun than contributing new trickier information) a difference of one thousand million or (in US-now-standard use) a whole billion. This is in visible light. In infrared (well, wavelengths from 20 - 100 micrometres) the difference is ~10⁴. or about ten thousand times. This is because main sequence stars tend to have their peak luminosity in the visible part of the electromagnetic spectrum and decline fairly rapidly in the infrared whereas giant planets are expected to be brightest (they radiate in infrared from gravitational collapse, at least until they are done [Jupiter still does])

The paper I am looking at right now (Detection of Extrasolar Giant Planets by Marcy & Butler, 1998) uses the example of a solar type star with a Jupiter-equivalent planetary companion, seen from a distance of 10 parsecs. The star would have a visual magnitude of 5 (that would be an approximation, Sol's absolute magnitude is actually 4.8) while 'Jupiter' would have a magnitude of 27*. In this hypothetical system 'Jupiter' would have an angular separation from the star of half an arcsecond. If diffraction were the only limiting factor all we would need to resolve it is a scope with at least a 0.4 metre aperture**. Obviously since there are plans to build rather expensive scopes (especially interferometers) in space something more is required. And since it looks like I may be running out of time tonight I think I will stop here for now.

*For those who don't know, in the magnitude system astronomers us the lower the number the brighter the object, extending into negative numbers if necessary. Each five steps of magnitude represent a change in brightness of 100 times, so a magnitude 1 object is 100 times as bright as a magnitude 6 one. Or, each step is brighter/dimmer by the fifth root of one hundred (~2.512 - the scale is logarithmic, see?)

**D > 0.4 (lambda/1mu)(d/10pc)(5AU/r), with lambda being the wavelength observations happen at, d the distance to the star and r is their orbital seperation.

Filter: sad

(What do you mean I could just edit the previous entry? I'm sure I would have heard of such a feature)

While I was in Borders the other day I picked up a copy of Astronomy magazine, not available in most places yet (Borders got it in through air freight, or so says the sticker, which would explain why it was so expensive), which may be the mag my lecturer recommended we check out.  It is a special feature on extrasolar planets with a fold-out poster and everything Interesting contrast in progress and expectations from some of the older papers I have been looking at - three years ago we knew of only half as many planets and none were so small as the ones with all the buzz in this issue. Future missions had not been pushed back so far and some that will not go up for years were expected to have launched by now, or in the near future.

According to this magazine there has been at least one planet discovered so far from lensing (though I am still not entirely clear on circumstances for detection [for shame!]) and possibly one directly detected orbiting a brown dwarf (hm, sounds a little like Hephzibah).

But now, to the pointmobile!

Filter: busy

Questions, please. Anything I can clarify will help me to learn and help me to present. These notes are based mostly on the paper Astronomical Searches for Earth-Like Planets And Signs Of Life by Neville Woolf and J. Roger Angel. It dates back to 1998 so much may be out of date by now.

Lensing -
    Off-the-cuff summary (Cuffs off! Yucky formal boy clothes!): Like all things light is affected by gravity. The presence of mass bends its path and if the situation is right a massive object can act as a lens, focusing light from an object in the background in our direction. What we are specifically interested in is when a star in the foreground passes in front of a star in the background and the lensing effect temporarily brightens the background star.And sometimes, just sometimes, if the background star has a planet we will see a secondary brightening from that too.

• I am referred to the papers Peale 1997 & Paczynski 1996 for more information
• Looking in the direction of the galactic centre the rate of microlensing events observed is 1 per day. It is suggested that 1 in 30 will show the presence of a giant planet
• To find an Earth-like planet would require very high time resolution and telescopes dedicated to the search
• Finding large numbers of giant planets would indicate there should be terrestrial planets too, as they are believed to be easier to form. The authors are careful to note, though, that 'should' =/= 'is'

Filter: sleepy

But if I don't do this now I will just fall farther behind. Please please please ask questions. I am trying to improve my ability to explain this clearly and concisely. So. Methods for detection of extrasolar planets.

• Radial Velocity measurements (includes pulsar timing)
• Astrometry
• Transits
• Direct Detection
• Gravitational Lensing

Filter: tired

Tentative outline for my project:

Chapter 1 - Methods for detection of extrasolar planets.

Chapter 2 - Taxonomy of planets detected so far

Chapter 3 - Formation of planetary systems

I have two weeks to prepare my presentation and another two weeks to finalise my eight to ten thousand words if necessary, so be prepared for annoying postery as I work things outout.

Other Goals:

Short Term -

• Find new, better job
• Pass driving test
• Pass this unit
• Get back to posting stories
• Write 100 words a day

• Find more time to be me
• Read in a bookstore or cafe dressed
• Increase writing to 400 words/day minimum
• Sparkle/Project RT
• Finish degree

• HRT (and beyond?)
  
• Publication
• Be with my love
• Be someone I can be proud to be
• Live happily ever after

Filter: busy

This was the base of a presentation I gave two years ago for astrobiology. Since it was focused on the same topic I am studying for this semester's project I thought it might help to refresh me by retyping it here. Too bad so much of the information in this is out of date, incomplete or even wrong. Click on childish abstract for for reading 'fun'.

Filter: loved

That presentation is delayed from Mondee to Thorsdee and so I have a little more time to work on it. Nonetheless I have fallen much behind, however, so... learning awaaaay!

Filter: cynical

I have a use for this site.

Filter: busy

One of the resources I am using for my report is this site: http://planetquest.jpl.nasa.gov/index.cfm

First thing to look at: The SIM PlanetQuest mission. I think last time I checked on this it was only called the SIM for Space Interferometry Mission (so that mission I threw in there was probably a case of RAS).

Firster things first. SIM is an optical interferometry mission. This means it combines the input from several instruments to form a higher resolution image. It saves us the trouble of trying to build a ten metre mirror in space (or building one down here and lifting it into space). The description is poor in this place because I need to reacquaint myself with the stuff.

Filter: working

Bodenheimer et al. 2000 (planet formation)
Fischer & Valenti 2005 (relationship between stellar metallicity and prevalence of planets - I remind the reader that in astronomer talk a metal is any element with Z > 2)
Butler et al. 2004 and Bonfils et al. 2005 (deficit of M_J planets orbiting M dwarfs) Note: Especially the latter of the two.
Chabrier & Braffe 2000 (size/mass relation in substellar bodies) Relevant as an object detected with ~jovian radius by the transit method may turn out to be a brown dwarf by mass under the radial velocity method. That is, although Jupiter is not the most massive of planets, it is just about the largest.
Bouchy et al. 2005b (unclear referenece in paper, curious to follow up)
Laughlin et al. 2005 (planetary structure and measurement)
Charbonneau et al. 2002; Deming et al. 2005a; Narita et al. 2005; Charbonneau et al. 2005; Deming et al. 2005b (detection of planetary atmospheric composition in absorption/emission features)

Filter: cheerfully productive

Decided not to visit the bible study group after all, as I could think of no way to do so without being either sneaky or disruptive. My heart was just not in it today. So here I am, being slightly more productive by studying in the library. I have in front of me a copy of The Astronomical Journal for July this year and I am reading the paper SURVEY FOR TRANSITING EXTRASOLAR PLANETS IN STELLAR SYSTEMS. III. A LIMIT ON THE FRACTION OF STARS WITH PLANETS IN THE OPEN CLUSTER NGC 1245.

Why note this in my journal? It is a convenient way of making information and notes available to myself at home, plus it is possible someone out there may actually be interested. If I could not flatter myself into thinking I had an audience I probably would not be taking notes at all.

If anyone wants an image of the cluster in question, there is a photo and some background on it available here. I see from the abstract some new nomenclature has come into use since I last studied this field: Very Hot Jupiter has been added as a class of planet. There is a helpful bit of definition in the abstract too. A Hot Jupiter has a period of 3.0 to 9.0 days while a Very Hot Jupiter has a period from 1.0 to 3.0 days. I suppose this means no planet has yet been found with a shorter period, or perhaps even that their existence has been determined impossible. Something else to check up on.

Back to the paper. The authors performed a search for transits over 19 nights and found no planets. The essence of their paper is the use of this result to constrain the number of planets likely to be found orbiting stars in this cluster.

I stop here for now. May or may not edit this entry after finishing reading.

Update: Referred to Perryman 2000 for detection methods, http://obspm.fr/encycl/catalog.html for catalogue of planets. At the time of writing the number was 168.

Update 2: The observations described took place October/November 2001. Ah, the speed of science.

Filter: working

The new, improved version.

An extrasolar planet is any planet which does not orbit the Sun. Methods with which they can be detected include direct detection, astrometry, pulsar timing, transits and the doppler method. Although the doppler method has had most success so far transits are more promising in the long run, especially if the goal is to detect terrestrial planets. Properties of planets detected tend to these categories: Hot Jupiters (giant planets in extremely close orbits about their parent stars with low eccentricities), Eccentric Giants (giant gaseous planets in more distant orbits with high eccentricities). Pulsar Planets (any planet found orbiting a pulsar), and more familiar giants resembling the ones found in the solar system. Although no earthlike planets have been detected so far projects such as SIM, Kepler and Darwin offer hope that this will change in the future.

Filter: loved

    I have the task of presenting a 100/150ish word abstract on Monday to summarise the assigment that makes up the astronomy unit I am taking this semester. This is my draft version of the general form needed:Extrasolar planets are planets which do not orbit the Sun. Methods with which they can be detected are X, Y and Z. Although Z has had most success so far Y is more promising in the long run. Properties of planets detected tend to these categories. Although no earthlike planets have been detected so far projects A, B and C offer hope that this will change in the future.
    But it needs to be filled in and expanded before I can submit it. X can be pulsar timing. To maintain the order I gave, Z should be the doppler method and Y the transit method. I also need to add in at least another, direct detection. We can pretend it was originally designated W. For the future projects I can use Kepler and the Terrestrial Planet Finder (or whatever those things have become since I last looked into this area) and any others there may be. Hopefully there is at least one. This does not, of course, have to be the same as the abstract I present at the front of the final essay but it does need to show I am putting effort and thought towards this unit.
    Categorising the planets found so far is a little trickier at least in part because I don't quite remember their names. The hot jupiters is an easy one; those giant planets found in extremely close near-circular orbits about their parent star. There is a group of planets recognised as having (somewhat) more distant, more eccentric orbits as well as another called the familiar giants. And the pulsar planets.

But I grow tired now, so verifying what I wrote here and filling out the text can wait until tomorrow.

Filter: working

    Can I remember what I have been up to and give a full report? Time to find out. We start with Monday, in which I went back to study for the first time in most of a year. It is a very small class of two students and all I have to do is produce a report on extrasolar planets over the course of this semester. For next Monday all I need to have done is a hundred or so words of an abstract for my project.
    The big scope was working for a short time while I was gone but now it is busted for a different reason, so once again I am not going to get to use it. However we did for once get to use a few of the smaller scopes - can you believe, dear reader, that I have almost finished my degree and only just had a lesson on setting up a telescope for observing? At least I got to see some wonders: I saw Jupiter for the first time, with Io, Europa and Ganymede in line (and that order), the Jewel Box ( well named) and Omega Centauri (like a cloud of stars).
    On occasion as we were out there a train would pass, looking like a luminescent serpent behind its screen of trees. Also, at night it is cold.

Filter: optimistic