Several Extrasolar Planets May Be Optical Illusions

person-0.9a writes "Seems that a few of the extrasolar planets detected via their sun's wobble might be written off according to a CNN article. You can also read it about it in New Scientist."

Comments

clarification of illusion

[beaverfever]

In the article it's described not as an optical illusion - it was a spectral illusion.

I can now go to my grave knowing that at least once in my life I used the term "spectral illusion" in a serious discussion.

What can we learn from this?

[wildcard023]

It seems that if we have discovered 100 'planets' and 95% of them really are planets, we have discovered an interesting occurance which happens to about 5% of the stars that are capable of supporting planets.

Isn't there something we can learn from these stars? They seem to be unstable at best if they have spots that large on them. Maybe we can use this information to learn more about the formation of stable vs unstable stars.

--
Mike

Guesses based on conjectures

[CommieLib]

An astronomy prof described astronomy as that in a frosh astro course. In particular, we were discussing methods of determining stellar distance. For stars fairly close we use an ultra reliable method called paralactic displacement. For methods beyond that, we start using methods that basically say "as long as our theories about how such and such behaves turn out to be true, this method of determining stellar distance should hold true."

This article just goes to show how fragile human knowledge is. But this is a good thing, and part of the natural progression of science.

Anyone who knows more care to elaborate?

[deglr6328]

It seems strange to me that the reason the planets were found not to exist is because the sunspots on the surface of the star somehow masqueraded as doppler shifts, thereby creating the illusion that a doppler spectroscopy observation had found a planet. This is the scenario that both news sources allude to. It seems much more likely that the giant sunspot would fool an astronomer using the so called transit photometry method of planet detection, whereby the transit of a planet in front of the stars disk dimms it slightly, having the same effect that a large sunspot would as it traverses the rotating stars viewable surface. Can anyone who knows more about this story explain what really happened?

Re:Anyone who knows more care to elaborate?

[renard]

Sun spots can masquerade as Doppler shifts by altering the spectrum of the star systematically as the star rotates. You think it's the planet's period, but it's actually the star's rotation (at the latitude of the sunspot). That's why Greg Henry's discovery of photometric variability with the same period as the "planet" is so damning.

Planetary transit searches will be subject to sunspots as a noise source (star's light changing by small amounts, erratically), but are unlikely to be fooled by them. A planetary transit causes the star's light to dim in a distinct flat-bottomed way that a sunspot cannot mimic.

Note also that no one has discovered a planet yet using the transit-search technique. The transiting planet of Henry & Charbonneau was known to exist already thanks to the spectroscopic surveys.

-Renard

Re:Anyone who knows more care to elaborate?

[TMB]

(preface: yes, I Am An Astronomer)

The important thing to realize is that you're measuring the spectrum integrated over the entire surface of the star WEIGHTED BY THE FLUX (read: brightness) AT THAT PART OF THE SURFACE.

The star is rotating, so part of the star is moving away from us and is red-shifted, while part is moving toward us and is blue-shifted. If the surface were all radiating at the same level, then we'd always see part of the spectrum blue-shifted and part red-shifted.

Now stick a big starspot on. The starspot is fainter than the rest of the star. When the starspot is on the approaching side of the star, there is less blue-shifted light and so the net spectrum appears slightly red-shifted. Half a period later, the starspot is on the receding side of the star so there is less red-shifted light, and the net spectrum appears slightly blue-shifted.

The end result is a spectrum that systematically shifts back and forth, very similar to that of a star with an orbiting planet.

[TMB]

Numbers Out Of Hand.

[phriedom]

I love to see the way the story progresses. First, the Scientific American article says ONE found planet, which was suspect all along, has been disproven, and they do not expect this to apply to many other planets because it is a particularly young star.

The CNN article turns the statement from a negative to a positive and says 95% are secure and 5% NEED TO BE CHECKED IN MORE DETAIL

Then it gets posted on slashdot and ONE becomes SEVERAL.

Now Wildcard has concluded that the 5% that are "unsure" do have this wild sunspot activity, and that they constitute 5% of the stars capable of supporting planets.

Oh crap, I just fed a troll, didn't I. Shame.

Understandable

[guttentag]

I thought Earth was just an illusion when I first passed through this region of space.

Then WHAM!!!

Now I'm stuck here. Anyone know where I can buy secondhand trilithium crystals and a really good radar system? Apparently, mine sucked.

The "Moon": A Ridiculous Liberal Myth

[Anonymous Coward]

It amazes me that so many allegedly "educated" people have fallen so quickly and so hard for a fraudulent fabrication of such laughable proportions. The very idea that a gigantic ball of rock happens to orbit our planet, showing itself in neat, four-week cycles -- with the same side facing us all the time -- is ludicrous. Furthermore, it is an insult to common sense and a damnable affront to intellectual honesty and integrity. That people actually believe it is evidence that the liberals have wrested the last vestiges of control of our public school system from decent, God-fearing Americans (as if any further evidence was needed! Daddy's Roommate? God Almighty!)

Documentaries such as Enemy of the State have accurately portrayed the elaborate, byzantine network of surveillance satellites that the liberals have sent into space to spy on law-abiding Americans. Equipped with technology developed by Handgun Control, Inc., these satellites have the ability to detect firearms from hundreds of kilometers up. That's right, neighbors .. the next time you're out in the backyard exercising your Second Amendment rights, the liberals will see it! These satellites are sensitive enough to tell the difference between a Colt .45 and a .38 Special! And when they detect you with a firearm, their computers cross-reference the address to figure out your name, and then an enormous database housed at Berkeley is updated with information about you.

Of course, this all works fine during the day, but what about at night? Even the liberals can't control the rotation of the Earth to prevent nightfall from setting in (only Joshua was able to ask for that particular favor!) That's where the "moon" comes in. Powered by nuclear reactors, the "moon" is nothing more than an enormous balloon, emitting trillions of candlepower of gun-revealing light. Piloted by key members of the liberal community, the "moon" is strategically moved across the country, pointing out those who dare to make use of their God-given rights at night!

Yes, I know this probably sounds paranoid and preposterous, but consider this. Despite what the revisionist historians tell you, there is no mention of the "moon" anywhere in literature or historical documents -- anywhere -- before 1950. That is when it was initially launched. When President Josef Kennedy, at the State of the Union address, proclaimed "We choose to go to the moon", he may as well have said "We choose to go to the weather balloon." The subsequent faking of a "moon" landing on national TV was the first step in a long history of the erosion of our constitutional rights by leftists in this country. No longer can we hide from our government when the sun goes down.

This solves a problem

[stwrtpj]

From the CNN article:

Henry and his colleagues took a new look at the star identified as HD 192263, which both California and Swiss researchers said in 1999 had large, gaseous Jupiter-like planet swinging around it in a tight orbit.

The fact that this particular planet is not a planet at all actually neatly solves a dilemma that scientists had with this discovery in the first place. If I recall correctly, the fact that this was an apparent gas-giant type planet so close to its star threw a monkey wrench into the standard theory about star system formation. The standard theory calls for only those planets sufficiently distant from the primary to retain their primordial gas envelopes. The planets closer to the star would have theirs blown off by the intense solar wind generated by the star when it first ignites. I believe the technical term for this phenominon is the T-Tauri wind.

Naturally, the idea of gravitational capture after the star was formed is cited as an alternate explanation, but it would take a rather precise vector for the planet to be captured into such a tight orbit without crashing into the star or being flung out into space. This new information solves the problem,

Not quite...

[barawn]

Unfortunately this is only one of many "hot Jupiters" as they're called. The prevalence of these odd planets is primarily due to an observation bias, as our method of detection is only sensitive to large-mass objects close to a star. Thus, when you look, and see a lot of "hot Jupiters", go fig, that's all you could detect.

Giant planets with orbital radii 1 AU are not, however, completely impossible to understand. The current theory is that they form out beyond the ice-condensation point (this is what allows gas giants to balloon to such a huge size/mass), and then some mechanism forces them to slowly migrate inward toward the star. They've managed to do this in simulations, however, it's not a wonderfully good explanation. It doesn't, after all, explain why Jupiter is where it is for us.