Transit Light-Curve Signatures of Artificial Objects

Hot on the trail of Transit Light Curve (TLC*) Mechanics, I’d like to follow up my previous post dealing with transits by featuring this topic: Transit Light-Curve Signatures of Artificial Objects. It's a "Dysonian SETI" paper written by Luc Arnold from way back in 2005 that also mentions possible signals that might be encoded within transit light curves, and hints at the detection of ringed planets as well.

The main idea is that non-spherical objects have different light curve signatures and should be distinguishable from the usual patterns of a transiting planet.

Because hundreds or thousands of people are now looking at light curves via the Planet Hunters project, I thought it’s a good idea to post what the paper says about unusual light-curve patterns that might be caused by the transit of artificial planet-sized objects. Who knows? Perhaps the common folk hunting for planets might end up finding Civilizations as well!

So, dear planet-hunter slash civilization-hunter, start familiarizing yourself with the sample patterns I compiled below (as a quick reference) while you're classifiying light curves at PlanetHunters.org. Good luck with spotting that Kardashev Type II Civilization !!!

* TLC Mechanics/Dynamics, A sub-field of the science of planet-hunting focused on the study and analysis of Transit Light Curves

Bow Shock Transits

Just a quick note to all the Citizen Planet Hunters (CPH) involved in Zooniverse's Planet Hunter project. Based on this paper, Transit Variability in Bow Shock-Hosting Planets, exoplanet bow shocks can affect the light curve during transits. There will be small variations in the light curve caused by the bow shock when the planet’s magnetosphere adjusts in response to "variations in the surrounding ambient medium."

In essence, the variations and irregularities are caused by "shock transits". We should be aware of them when analyzing light curves. I believe that many of the exoplanet candidates in Kepler's data release have bow shocks because most of them lie very close to their respective host stars.

Also, I think that bow shocks are bright, especially when the planet plows through material from a massive coronal mass ejection (CME). Hence some bow shock transits should cause a spike (instead of a dip) in the light curve. This spike, I assume, should occur a short moment before the planet crosses the star, or shortly before the "ingress".

However, there's a disclaimer I'd like to add to this post: The paper says that the effect of the shock transit shows up in the near-UV light curves. But Kepler's light curves are photometric optical light curves, so i am making an inference that effects of bow shocks might show up in Kepler's optical light curves as well. (I will dig more about this topic and post as soon as i get more info).

But For now, take a look at the snapshot below and note the pattern of how the bow shock's transit shows itself in the light curves. And more importantly, a reversed pattern might show up for planets that have "behind shocks". The main principle is that bow shocks can affect light curves.

Good luck! And don't be shocked if you find yourself one of the co-discoverers of a planet with an amazing bow shock!

A Tale for the Transit Method

I’ve always been fascinated when planet-hunters describe the difficulty they face regarding the detection of exoplanets. They often refer to the analogy of trying to find a firefly against the backdrop of a huge bright searchlight. As if that's not hard enough, so I had a crazy “what if” moment, as i imagined other factors that could screw up their data. What if a fly actually walked across the field of view (FOV) of a CCD/telescope? Would it mimic the transit of an exoplanet across the face of a star when doing photometry?

I went on to find out by asking several astronomers about it. The ones i caught were displaying their awesome telescopes at Battery Park during the World Science Festival in New York. [Incidentally, that was also the same night when the James Webb Space Telescope was being showcased--a full-size replica was on display].

So when I asked real astronomers what the effect would be, if a fly (or any insect, for that matter) walked across the mirror of a telescope with a CCD during a photometry session--they all agreed that the fly would actually cause a dip in the captured brightness of the star!

Honestly, I don’t think so. And I am not yet convinced that the “fly effect” would occur when a housefly transits a star by way of strolling across the surface of the telescope mirror. I have no CCD at hand (and no volunteer fly as well), so I have no way to find out for sure. But my gendanken experiment ended up as a short story entitled The Fly and the Planet-hunter.

So, I dedicate that story to all the astronomers in the world (grumpy or not), and to all the flies, bugs and mosquitos who make astronomers’ lives astronomically difficult. No, its not that astronomers are grumpy, nor that planet-hunters are mean old men. Astronomers are actually very nice people, and eager to share their passion for astronomy. Sidewalk astronomers would even let you peer through their telescopes--but just don't touch the eyepiece because that will freak them out.

But the real work of astronomers are really tedious and requires a lot of maddening patience. Reflecting upon that, I had the urge to cheer up these dedicated folks, specially the amateur planet-hunters who go through challenging and dangerous situations (bear, anyone?) just to find exoplanets.

So I hope you'll enjoy the story. Perhaps it's a tale you can tell your grandkids as you show them the stars and how to find exoplanets, oh ye grumpy ol' man! :)


Short Story: The Fly and the Planet-hunter

How To Know an Exoplanet's Orbit

One can never get enough of oddballs. A new exoplanet named WASP-17 b was found orbiting the wrong way relative to the direction of it's star's rotation. It is on a retrograde orbit.
Typically a star's spin, as well as the orbital motion of all it's planets go in the same direction of the swirls of the primeval gas and clouds from which they formed. This is the case with our own solar system--but not so with WASP-17, which is the first star system known with a planet orbiting in an odd way.
The story says that a violent collision with another massive rock sent the WASP-17's planet flying off in the other direction.
But how did the Astronomers find out about the direction of WASP-17b's orbit in the first place? A transit light curve alone does not tell whether an exoplanet passes across it's star from left to right or vise-versa.
It turns out that the WASP Team needed help from the planet hunters at the Geneva Observatory, who specialize in Radial Velocity (RV) measurements.
Here's the low-down on how Radial Velocity was used for WASP-17b which was primarilly a transiting exoplanet, "astronomers can identify the direction of a planet's orbit because of slight discrepancies in the radial velocity data when a planet transits a star. Because a star is rotating, one side of it is moving towards (or away) from Earth faster than the other side. During a transit, the planet covers first one side of the star and then the other, causing a slight but measurable shift in the radial velocity readings. If during the transit the star first appears to be moving relatively slowly towards the Earth, but then faster as the transit progresses, then the planet is orbiting in the same direction as the star's rotation. But if the reverse is the case – as it is for WASP-17 – then the planet is in a retrograde orbit."
That description is actually the The Rossiter–McLaughlin effect, and it was also mentioned to me by the twitter hive mind. I think The Rossiter–McLaughlin effect is the key part in understanding how to find out an exoplanet's direction of orbit. It's a phenomenon that weaves together the elements of the Doppler Shift, the star's wobble and Photometry.
It seemed counter-intuitive for me at first, knowing that the Transit Method used to find WASP-17 b is primarily used for detecting exoplanets from star systems whose orbital plane is edge-on with our view. While Radial Velocity (RV) I thought was used only for non-transiting exoplanets--whose orbital plane is not edge-on with our line of sight.
But now i realized that the planet-hunting methods can be used in tandem as "Planet-hunting Mash-ups" to make novel discoveries, as what happened with WASP-17b.
It's truly great to know that now we can find out the direction of an exoplanet's orbit, no matter how odd it is.

Yay! Kepler Works!

Even though twitter was mostly down for the important announcement of the Kepler Mission, it did not dampen the excitement surrounding the update.
Kepler Works!
To prove it, the Kepler team produced a lightcurve of a previously known exoplanet, HAT-P-7 b, and found that Kepler's findings agree with previous observations of that planet. Oh, but there is so much more!
A cleaner light curve means that Kepler's data has less noise than those gathered by ground-based telescopes, which means more precision, and thus proves that Kepler is truly capable of detecting earth-sized worlds.
Most of all, Kepler's precision allowed the team to detect the atmosphere of a known gas giant planet. Based on the light curve, the trailing small dip corresponds to the occultation of HAT-P-7b--the part where the planet "hides" behind it's star. Taking this in consideration with the actual transit curve (the first major dip), the depth of the occultation and the shape and amplitude of the light curve show the planet has an atmosphere with a day-side temperature of about 4,310 degrees Fahrenheit. The occultation time compared to the main transit time also shows that the planet has a circular orbit.
All these bonus information is simply amazing! Not only does Kepler work, it works beautifully! Therefore, the Kepler Mission Team deserves a great commendation! And I'll drink to that! Yay! Kepler Works!

Links: Kepler Press Release

Starspots and Exoplanets

This image is way too cool! It looks like it's from a page of a comic book or graphic novel, but it wasn't drawn by an artist. A supercomputer made this simulation of a sunspot in striking scientific detail.
Here's a little trivia:
Did you know that most sunspots are bigger than Earth? Sunspots can be up to several times larger than the diameter of the Earth. And sunspots are really "cool", cooler than the surrounding region of the Sun's surface.
Now this pretty model of a sunspot may be similar to the spots on the surface of other stars. And so we call them Starspots.
Starspots may be pretty but it's not really appealing to planet-hunters. The reason is that starspots may interfere with the transit method of finding planets. It may even distort the measurement of the exoplanet's true size.
The transit method relies on measuring the slight dimming of starlight as the planet passes across our field of view of the star. But huge starspots of an active star may be mis-interpreted as a planet since it also dims the light as the spots move across the star, often in the same direction as the planets.
That is why planet-hunters hoping to bag a new exoplanet discovery are wary of starspots when trying to interpret their data. They use all sorts of noise-reduction techniques to normalize the figures, and avoid the confusion.
But here's the interesting part: because of starspots, known exoplanets are given a chance to help astronomers study the surface of other stars. Irregular dips, bumps and spikes along the lightcurves may be attributed to starspots (if proven that it was not another planet that caused the bumps). Thus, known exoplanets then allow astronomers to approximate the size of the starspot, it's speed of movement, and it's rotational period around the parent star.
And consequently, the spots tell a lot about it's parent star such as the "solar-like" activity cycle, and the star's speed of rotation.
And there you have it! The unexpected relationship between Starspots and Exoplanets is actually a bitter-sweet engagement that poses a challenge to planet-hunters at first, but eventually brings us greater knowledge of exoplanetary systems in the long run.

An Amateur Astronomer and an Exoplanet Transit

Just before the end of Pi Day, I received an alert saying that an amateur astronomer has observed the exoplanet transit of XO-2b.
The thread can be found via cloudynights which starts with an enthusiastic "I think I saw an exoplanet!" and culminates with a much more proper remark "I saw an exoplanet transit!!!" along with the light curve being posted by the observer after a few rounds of data processing and calibrations.
This is great news for exoplanet enthusiasts who may someday jump into the Amateur Exoplanet Observing bandwagon.
A lot can be learned from this report and one of them is this list from TransitSearch which gives the predicted transit date and time for a large number of transiting exoplanets.
Someone has now reported this particular observation of XO-2b to the Exoplanet Transit Database (ETD) with credits to the observer named Tieman B.
Perhaps it will still be subjected to further verification, perhaps not.
Whichever is the case, I am getting more and more convinced that it is truly possible for amateur astronomers to observe exoplanet transits. And that amateurs will continue to contribute mightily to exoplanet research in the coming years.

Walking on Super-Earth CoRoT-Exo-7 b

The suspense is over. Here is the latest Exoplanet Discovery: CoRoT-Exo-7 b. This discovery via transit method is not of an earth-like world just yet. But at least it's a super-earth because it's almost 11 times the mass of earth. And it's a little bit bigger than earth as well, having almost twice the earth's radius.
Now, in contrast to the recently reported exoplanet (HD 80606 b) which has a very eccentric orbit 0.927, CoRoT-Exo-7 b in turn has an almost perfect circular orbit around it's K-type star, having an Orbital Eccentricity equal to zero.
Now, with an orbital period of just 0.85 days or 20 hours, it must be whizzing around it's star so fast and mighty close to it's star. Hence it has a high temperature, between 1000 and 1500°C, still scorchingly hot by my standards.
I'm guessing that it might be tidally locked - meaning only one side faces it's sun. On the other hand, it could be spinning so fast, so my guess could go in both extremes.
Reports say that it is a terrestrial rocky world, and one can walk on it's surface, they say. Although, getting someone to get there and do it is another story, it is quite interesting to think about.
For starters, I would weigh a lot heavier in that exoplanet, and so I will get increasingly tired with each step. Upon which case, my foot would sink deep into it's molten lava surface. And the heat would be quite unbearable. And assuming it spins fast, day and night would alternate so much quicker than what i am accustomed to. However, if it was tidally locked, I would rather be on it's "dark side" because it's probably be much cooler in that region of the planet.
I might skip the stroll on this super-earth and take my chances on the discovery of an earth-like world soon, where it would be like a walk in the park.

CoRoT-Exo-7 b
Radius: between 1.75 and 2 Earth radius
Orbital period: 0.85 around a K star (T= 5300K)
Orbital Eccentricity: 0
Mass: less than 11 M_Earth

Links:
ESA News Release
CoRoT-Exo-7 b on Exoplanet Encyclopedia

Interactive: Four Planet-Hunting Methods

Here's a neat interactive from MSNBC providing an overview of 4 Methods of Exoplanet Detection: Astrometry, Radial Velocity, Transit, and Microlensing. Plus a chart of your local backyard sky showing the locations of some major exoplanet discoveries.
(Hover your mouse on the lower left and click on "Planet Finder").


Source: Other Worlds

No Joke: 10 New Exoplanets for April 1st!

WASP-3b: One of the Extrasolar planets discovered by SuperWASP. WASP-3b is one of hottest exoplanets ever detected. It was discovered in 2007.

No, this is not an April fools day joke: 10 new Exoplanets have just been discovered by the SuperWASP (Wide Area Search for Planets) team. The SuperWASP technique involves two sets of cameras to watch for events known as transits, where a planet passes directly in front of a star and blocks out some of the star's light. From the Earth the star temporarily appears a little fainter.
The SuperWASP cameras work as robots, surveying a large area of the sky at once. Each night astronomers receive data from millions of stars. They can then check for transits and hence planets. The transit technique also allows scientists to deduce the size and mass of each planet.
A total of 46 planets have been found to transit their stars. Since they started operation in 2004, the SuperWASP cameras have found 15 of these. SuperWASP is the most successful transit survey in the world.
After they formally announce their findings at the Royal Astronomical Society's National Astronomy meeting in the U.K. on Wednesday, April 2, I will then add the names of the new extrasolar planets into the Exoplanetology Catalogue on Freebase.
This is wonderful news for the field of Exoplanetology! Way to go SuperWASP!

link: Eurekalert

Google Enters the Field of Exoplanetology

Google joins the the hunt for exoplanets by funding the development of the wide-field digital cameras needed for the Transiting Exoplanet Survey Satellite (TESS). TESS, a satellite-based observatory for hunting Earth-like planets is currently being designed by MIT scientists. TESS would perform its transit method of exoplanet-detection high above the clouds - a big advantage over its ground-based counterparts who use the same technique. Ground-based telescopes are obscured by the earth's atmosphere, hence their resolution is limited in detecting much smaller terrestrial planets like the earth. But a space-based telescope like TESS, being free of interference from atmospheric clouds and dust, will be able to resolve light coming from distant stars in much greater detail, allowing it to detect Earth-like planets, as well as those with larger orbits. Now, more resolution means more data - and this is where Google has shown interest as well - processing huge amounts of data to find useful information. But hold on to your horses though, TESS won't be launched until 2012. So the concept logo for Google Exoplanetology (designed by yours truly) might not be used...yet?