http://news.bbc.co.uk/1/hi/sci/tech/6611557.stm

is reporting that Corot has found its first planet. I can't find an arxiv paper about this, or even a press release, but there are many here better at squirreling out data releases than me.

1.3Mj, 1.8Rj so it's a very inflated planet, 1.5-day orbit around a 'star quite similar to the Sun' might account for that. In the Monoceros field (Corot is now pointing at the Scutum/Aquila field).

Here's ESA's release.

And according to this New Scientist article COROT could be up to 30 times more sensitive than it's original design specification.

http://space.newscientist.com/article/mg19...ized-prize.html

Emily has a new blog entry. Also, I'm not sure if it's mentioned here or not, but there is a new, related paper in press with Icarus:

Could we identify hot Ocean-Planets with CoRoT, Kepler and Doppler velocimetry?
Icarus, In Press, Accepted Manuscript, Available online 1 May 2007,
F. Selsis, B. Chazelas, P. Bordé, M. Ollivier, F. Brachet, M. Decaudin, F. Bouchy, D. Ehrenreich, J.-M. Grießmeier, H. Lammer, et al.
1.5 Mb PDF preprint

And the CNES release (in French).
http://www.cnes.fr/web/5891-corot-decouvre...exoplanete-.php

I've been wondering, is there any reason to think that the orbital planes of other solar systems [in specific directions] will be aligned in such a way that we'll see more eclipses than total randomness would dictate?

Are there going to be tantalizing glimpses of transits that don't reoccur within reasonable timeframes?

The Corot photometry is wonderfully stable, and looks as if it can pick up eclipses on a single occurrence rather than having to do a phased integral; Jupiter's diameter is 1/10 of the Sun, so a Jupiter transit would be a 1% drop in light, which Corot would pick up very happily, It would last (I think) jupiter_orbital_period * (sun_diameter / 2*pi*jupiter_orbit_diameter) = 4330 days * 1.4e6 km / (6.28 * 778e6km) = 1.25 days.

I don't think there's much that dims a star in a spectrally-uniform way with a flat bottom and that kind of ingress and egress period, so you would really see it in the data. I don't know how long Corot will last, it's working in the optical spectrum so doesn't have cryogens to exhaust, and it doesn't have to do very complicated station-keeping so the fuel should last reasonably, but two Jupiter-years is maybe a little long to expect, and the cadence where it looks at Monocerus for six months and Scutum for six months starts to be troublesome at the longer periods.

I'm looking forward to seeing the low-mass and long-period bits of phase space get populated, and to hearing complaints that there's not enough high-resolution-spectrograph time available to follow up all the transit detections!

Steve: The Kepler guys figure about 1/2 percent of stars with planets will be aligned enough for us to see transits -- assuming random alignment.

http://kepler.nasa.gov/sci/basis/character.html

Wikipedia claims 10%, but in this case I think I know whom to believe.

http://en.wikipedia.org/wiki/Methods_of_de...#Transit_method

I've also wondered whether this will REALLY be random, but I note that so far very few observed planets are transiting -- no surprise given only 200-odd extrasolar planets so far.

So I guess we can say that, if it's not random, it's not hugely skewed either.

I note also that Kepler claims they can detect Jovian-sized transits from a single event; it's only for Earth-sized transits that it needs to see three events to be sure.

--Greg

10% claim should be true in the case of hot Jupiters. For more distantly orbiting planets, the value is of course considerably lower.

"Planets with small orbits" says Wikipedia so it's apparently correct if not clear.

0.5% is for Earth-like orbits around Sun-like stars.

Interesting. Hopefully Kepler prospers for a good many many years then!

Also that 0.5% figure is both plenty high, yet depressing in the regard that 99.5% will still be hidden from this technique. But it's no doubt conservative. I again wonder how many "near misses" will be detectable. Should be great to see.

Steve: What is more interesting about the 0.5% number is that it is independent of the distance of the star; at first it would seem that the further away it is, the less likely a planet is to be lined up so as to transit, but it turns out this is not the case. (Play with the geometry a bit and see.)

Of course the further away a star is, the harder it will be to tell that there was a transit; geometry can't fix that!

--Greg

The fundamental purpose of missions like Corot and Keplar (and "Ogle" type searches for lensing events as well as whatever transits they catch) is to establish the statistical patterns of planetary system occurrence.

Star: 1) What mass stars, 2) what metallicity stars 3) what environment stars (disk, halo, globulars.. ) 4) what age stars. (yes. the last 3 are all significantly correlated)

Planet: Mass, Diameter, thus (density and gross composition)

Orbit: Toasty, close, distant, eccentric vs circular.

Before we build EITHER of the Terrestrial Planet Finder mission, we need a good model of how many there will be of what sizes -- around what mass and metallicity stars -- in what orbits -- in the solar neighborhood.

If we design and fly an inadequate TPF and find 3 barely-quasi-terrestrial planets for a budget of 3 billion dollars. Uh.......

If we know a 1.5 billion dollar TPF will find 2 or 3 dozen substantially terrestrialish planets (.8 to 1.5 earth mass, similar stellar insolation), it may fly a lot sooner than that 3 billion doller mission.

And... even though we'll not see a good spectrum or hardly anything from most terrestrial size or so planets Keplar and Corot may find, we'll get fabulous understanding of the population of planets out there and the type of planetary systems they are part of that we only half or quarter get from the doppler surveys.

Are you sure about this? The width of the 'band' of sky that can see a transit is the same width as the diameter of the primary as seen from the planet, hence a planet twice as close as another will be visible as transiting from twice the area of sky. The 0.5% number comes from the fact that a planet in a habitable orbit should have its primary subtend about 0.5 degree -- which actually suggests that its transit should be visible from about 0.44% of the sky. A planet ten times closer would have its primary subtend about 5%, so its transit would be visible over about 4.4% of the sky, and so on.

Bill

Mongo: You're correct, if "distance of the star" means "from the exoplanet," but I meant "from Earth." A star 50 light years away is (all other things being equal) just as likely as one 5 light years away to have a transiting planet. Maybe that's obvious, but it surprised me at first.

--Greg

"...eclipses that can be detected are “shallower and thus the planets detectable are going to be smaller. If the periods are short enough so that we can see enough eclipses for a given planet (a process called epoch-folding) we are going to be so sensitive that we could see one earth-radii planets.”

From a quick update with Malcolm Fridlund at spacEurope.

According to the SpacEUROPE blog COROT's sensitivity may be just enough to detect reflected light from an extrasolar planet's surface in a similar manner Spitzer has done... but instead of infrared, it observes in the visible light.

Anyone know when the COROT guys are going to make their next announcement? Any rumors yet?

Their first was a wonderful tease...

A small update was posted yesterday on the CNES website.
http://smsc.cnes.fr/COROT/GP_actualite.htm#juil2007a

Interesting; thanks for posting this. Spitzer has done both emission and absorption, but reflection?! I guess they must be using IRAC 3.6 microns, as the longer wavelength bands will be swamped by intrinsic emission from the planet. Oh boy, that would be quite an achievement if they can do it. I would hate to be the sucker PI reducing the data for that observation.

Thanks for pointing out the update, Rakhir.

Now, I assume they mean 12,000 light curves from stars that are candidates for hosting exoplanets. 12,000 light curves involving exoplanets in one month would be utterly mind blowing.

Not helping with the anticipation...

Oh, no, not at all! Doesn't sound beyond the pale, though. We really are on the verge of finding out whether planets are more plentiful than stars, if that is indeed the case...the smart money's always been on 'yes'. Mach's Principle may yet prove to be far more powerful than we realize at the local level, although in a quantitative, not qualitative sense...

Thanks for the update Rakhir.
tacitus,
Here's what I got from Dr. Fridlund (ESA COROT Project Scientist) some days ago, when it was announced the discovery of water by Tinetti and co-workers:
"COROT is progressing according to plan. There will not be any new announcements before we have had time to write a few papers and submit them to the journals so with vacations you are talking about at least 3 months.
We have a lot of exo-candidates that we are beginning to follow up from the ground (I was myself in Tenerife last week and observed one of them). But as I said above it will be some time."

Man...I'm trying to contain irrational exuberance, but boy oh boy oh boy...we might just actually know a thing or two in detail--FINALLY--about how things really are around other stars after all the novels and stories, even sans starships, in a few short years!

Well, the negative side of the COROT survey is that the search is limited to closely orbiting transiting planets so we get a very biased sample. Which is far better than nothing, of course.

A microlensing planet survey equipped even with a relatively small telescope could find Earth-mass or smaller planets in any orbital distance (including free-floating terrestrial planets)! It could detect every planet of the Solar System except Mercury, which is not massive enough and orbits too close the Sun. The obvious downside is of course that the lensing events are unique and no physical properties of the planets can be studied. But it could give a good sample of planets around very different kinds of stars.

I'm wondering...what would be required for such a "gravity lensing" mission? Could COROT not search for such events (change in radiance of microlensing instead of small dips by transit)?

This isn't related to Corot, but it may be of interest to people who are interested in Corot. Venus Express is taking observations of Earth, from Venus, using the Virtis and Spicav spectrometers. The idea is to try and gather a data point regarding what a habitable planet would look like from a distance. Once the technology is available, observations like this may give an idea of what would be best to look for.

Several of these observations have been taken, with more scheduled. It is a low priority thing, and I have no idea when any results may come out of it, but it is an interesting idea and some observation time is being dedicated to it.

All planet lovers

COROT update may be coming next week during the European Planetary Science Conference - August 20-24th.

http://meetings.copernicus.org/epsc2007/annotation.html

COROT abstract
http://www.cosis.net/abstracts/EPSC2007/00...7-J-00316-1.pdf

Craig

http://www.planetary.org/blog/article/00001089/

That's about it - it was more 'CoRoT will be great when we get our ground software finished' than 'Look - Exo-Earth's!'

Doug

Thanks Doug!!

I suspect they are going to keep things pretty close to their chests for a while.... but still an interesring report. And a teaser for what is to come.

Craig

I think they just want to be 100% sure on REALLY interesting things with follow-up ground based obs with spectroscopy before going "WE FOUND AN EARTH"

Doug

Yes, they certainly need to be prudent.

What I am reading sounds very promising as far as what COROT is capable of. Much to look forward to.

Thanks Again Doug.

Yeah...to quote Carl, "Extraordinary claims require extraordinary evidence." Seems that the COROT team is employing this invaluable heuristic, and should be commended for doing so...but, boy howdy, I sure hope that there's something extraordinary just around the corner...

Check my math in trying to characterize the bias.

Given two similar planets orbiting two similar stars, but with one planet N times farther from its star than the other, the ratio of likelihood of detection in a short time frame should be N^2.5. That is, the probability of appropriate geometry for a transit is decreased by N for the farther planet, whereas the probability of a transit taking place at the right time is a function of the orbital period, which introduces another factor of N^1.5.

For example, if Earth were orbiting at 5 AU, it would be precisely 1/5 as likely for its orbit to transit the Sun as seen from afar, and if it did, it would do so about 1/11th as often. So a factor of 5 in distance translates to a factor of 55 in transit observations. A factor of 10 in distance translates to a factor of 300 in transit observations.

The temporal factor is mitigated as the observations continue. Given a mission lasting Y years, we'd get one observation of every transiting planet with a period <=Y, two observations of every transiting planet with a period <=Y/2, and a probability Y/X of one observation of every transiting planet with a period X longer than Y.

The diameter of the planet is also a minor factor. Jupiter might graze the Sun's disk whereas a Pluto in the same location would just miss. As the planets get much smaller than the star, this factor almost vanishes.

COROT will survey a few different areas, none for more than 150 days or so, so repeat detections will be strictly limited to planets in close-in orbits. Single detections of planets farther out will (presumably!) take place, and could help us get an idea of the distribution of planets in different-sized orbits. But at some point out there, the data will be too sparse to make predictions significant.

So overall, I think it's going to be pretty sparing in telling us about the raw numbers of Venuses, Earths, and Neptunes. But a few data points would be a lot nicer than none.

I get the same result, JR.

A good question would be "how many transits do they need to see to confirm a discovery?" On the Kepler site, they say they'll only need one for Jovian planets (although obviously you need two to get the orbital period), but that for Earth-sized planets, they want to see three transits.

If COROT switches targets every few months, that'd mean it really wouldn't spot any Terrestrial planets with periods longer than a few weeks. That'd still be very interesting, but makes it seem unlikly they'll find anything that could fairly be described as "another Earth."

--Greg

Just out of curiosity, would the habitable zone of a fairly anemic red dwarf be close-in enough for a period of a few days to be possible for "another Earth?"

Wouldn't something that close be tidally locked?

Tidal locking time is an interesting problem.

http://en.wikipedia.org/wiki/Tidal_locking

Considering the warning that these figures can be off by a factor of 10, I get the following for putting an Earth with a 12-hour day to start with around some familiar stars:

Sol: 365.25 day period, 5.4 billion years to tidally lock. (Ignoring the effect of the moon).
Alpha Centauri A: 524-day year, 16 billion years (Earth years) to lock.
Tau Ceti: 221-day year, 1.7 billion years
Alpha Centauri B: 207-day year, 800 million years
Epsilon Eridani: 134-day year, 170 million years
Gliese 581: 7.8-day year, 120,000 years.
Proxima Centauri: 3.9-hour year, 350 days.

The difference between Tau Ceti and Epsilon Eridani surprises me; I hadn't realized there was almost a factor of two luminosity difference, even though the latter is actually slightly more massive.

Anyway, even with all the caveats, it seems to be a cinch that any earthlike planet with a period under 100 days will be tidally-locked.

(Anyone want to check the math?)

--Greg

So what if it is tidally locked?

http://www.liebertonline.com/doi/abs/10.1089/ast.2006.0124

http://www.astrobio.net/news/article1694.html

Craig

Iiiiinteresting. I wonder what the climate models predict for temperature maps on the sun-facing side?

I also find it interesting that the earth would be tidally locked in a mere 5 billion years sans luna.

Remember that there's enough fudge in these numbers that it might really be 50 billion, not 5 billion. Thing is, the effect of radius (a SIXTH power!) is so strong and the ages of these systems is so great (billions of years, typically) that it doesn't really matter. Anything with an estimate under ten million years was almost certainly tidally locked long, long ago -- even those with estimates under 100 million.

It's interesting to note that Luna makes the moment of inertia of the system over 100 times larger, so that'd probably push that number up to 500 billion years, although that wouldn't rule out Earth being tidally locked to the moon well before that happened.

--Greg (The other major caveat is that this equation came from Wikipedia -- I didn't derive it myself.) :-)

"Simulations of the Atmospheres of Synchronously Rotating Terrestrial
Planets Orbiting M Dwarfs: Conditions for Atmospheric Collapse and
the Implications for Habitability"
http://www.seismo.unr.edu/ftp/pub/gillett/joshi.pdf

Also, ANY terrestrial planet around any star will probably lose the internal heat needed to keep plate techtonics going after 10 billion years or so. When that ends, the cycles that reprocess the geochemical needs of a biosphere will grind to a halt.

A lot of interesting studies going on ........................ what COROT and KEPLER may give us is a stat on
how prevalent the above fates are.

Craig

So it seems that any true red dwarf exoEarths should blink rapidly enough for detection using mass sampling...sounds like a seed for a mission proposal, here, if the observable (key point; they're so damn faint that they'd have to be fairly nearby) number of dwarves is large enough to make it worthwhile.

It seems that at least four factors help here: As you say, there are more red dwarves in the first place and more transits per unit of time. As JR pointed out above, there's a greater chance of having transits in the first place. There should also be a greater difference in brightness transiting a smaller star than a larger one.

One would predict that if Corot finds any "Earth-like" planets, they'll be around red dwarves, but if they find any, they'll find lots of them.

--Greg

Seems to me that possibility means two "habitable zones". One for the substellar point and one for the dark side.

That would depend on the amount of uranium present to begin with. Also geochemical cycling would not stop completely even in the absence of tectonics. For example glacial erosion can be very powerful and impact cratering would have some effect too. I would expect that some kind of low-nutrient, low-energy biosphere would persist rather like what we have in Australia (where there has been practically no tectonics over most of the continent for hundreds of million years).

While I understand that there are two target regions between which COROT will alternate every six months, I hadn't realized they were planning to observe new locations within those region each time the spacecraft came back to them. I can imagine that at some point (maybe in an extended mission) they might decide to return to a spot previously observed in an attempt to observe repeat events caused by planets with longer orbits.

I guess it all depends on what sort of data they observe in the first few observational runs. If they find a number of great Earth-sized candidates in one region, I should have thought they would be tempted to return to it the next year.

In which parts of the Electromagnetic spectrum are COROT's detectors active ( Visible and radio for the astroseismology ? )

Not necessarily. A thick atmosphere could do a really good job of distributing heat. Both Venus and Titan (OK Venus isn't technically tidally locked - but you get the idea) have pretty much the same temperature on the nightside and dayside.

[And the "habitable zone" is really only a product of our surface prejudice for stable liquid surface water].

[And OK - Titan and Venus don't fit the description for fitting a "habitable zone" at the surface.]

IIRC, the paper belleraphon1 referenced took into account various greenhouse atmospheres expanding considerably our ideas of the "habitable zones" around M-class dwarfs. Atmosphere dynamics really matter, it's not just a bunch of hot air (sorry, couldn't resist).




As well as hot-spot volcanism. Without active plate tectonics to exchange heat the interior, I would imagine hotspots would develop to make up the exchange. Long-lasting calderas or hydrothermal systems might exist well into the "geochemical twilight".

Case in point: Io doesn't have plate tectonics but it does a pretty good job of staying active.

There may be local long-lasting habitation zones rather than a large overall habitable area. (Might make interesting isolated "biosphere islands" as well with lotsa cool possibilities for evolutionary divergence.)

I wouldn't discount any planets COROT finds as not being potential biospheres. (But I'd probably look more carefully at the cooler ones).

-Mike

I'd guess its 350nm-750nm range and it doesn't cover radio, basically the Europeans want to do highly sensitive measurements of a star from space that can't be done on the ground, hopefully NASA will be doing it soon with Kepler. Space is more stable, there is no heat/noise and the viewing time is uninterrupted. This is why a small telescope in the visible spectrum can outperform giant ground-based scopes. Corot will look at stars with an accuracy, stability, precision, and a duration off uninterrupted periods that are impossible to reach from our ground based telescopes.
I quote from the esa site
http://sci.esa.int/science-e/www/object/in...fobjectid=31706
"The detectors are 4 CCD's 2048 x 2048 wide, (EEV, 13.5-μm thinned, back illuminated), working in the visible in the MPP mode. They are installed in the focal box, which is at a temperature of -40 °C with a variation that is less than 0.05 °C per hour.
For the seismology mission, the image spot for a star is spread out on about 400 pixels, with an exposure time of 1 second."