Kepler22b-first exoplanet found in hab-zone of sun-like star

[marcus]

Kepler22b--first exoplanet found in hab-zone of sun-like star

http://science.nasa.gov/science-news/science-at-nasa/2011/05dec_firstplanet/

NASA newsletter
==quote==
Kepler Confirms First Planet in Habitable Zone of Sun-like Star
Dec 5, 2011: NASA's Kepler mission has confirmed its first planet in the "habitable zone" of a distant sun-like star.

The newly confirmed planet, Kepler-22b, is about 2.4 times the radius of Earth. Scientists don't yet know if Kepler-22b has a predominantly rocky, gaseous or liquid composition, but its discovery is a step closer to finding Earth-like planets1.

The "habitable zone" of a planetary system refers to the band of orbits where liquid water could exist on a planet’s surface. Kepler has recently discovered more than 1,000 new planet candidates. Ten of these candidates are near-Earth-size and orbit in the habitable zone of their host star. Candidates require follow-up observations to verify they are actual planets.

"This is a major milestone on the road to finding Earth's twin," said Douglas Hudgins, Kepler program scientist at NASA Headquarters in Washington.
Kepler-22b is located 600 light-years away. While the planet is larger than Earth, its orbit of 290 days around a sun-like star resembles that of our world. The planet's host star belongs to the same class as our sun, called G-type, although it is slightly smaller and cooler.

Kepler discovers planets and planet candidates by measuring dips in the brightness of more than 150,000 stars.
==endquote==

 

[Drakkith]

Excellent! Any idea on what the mass of the planet is? I didn't see anything on it.

 

[Chronos]

That is a bit more difficult since planetary masses are typically much smaller than the host star, the difference between orbital period due to mass is virtually negligible under Kepler's Law. The volume of Kepler-b22 is nearly 14 times that of earth, hence, is probably much more massive than Earth even if its density is relatively low.

 

[Drakkith]

That is a bit more difficult since planetary masses are typically much smaller than the host star, the difference between orbital period due to mass is virtually negligible under Kepler's Law. The volume of Kepler-b22 is nearly 14 times that of earth, hence, is probably much more massive than Earth even if its density is relatively low.

I see. I was hoping to be able to caculate the surface gravity!

 

[marcus]

Drakkith, it's worth noting that the Kepler planet search does not use the wobble method.
When planets are detected by the wobble of the host star one can reckon their mass compared with the star's, and one can use long-established means to judge the star mass.

Perhaps a wobble study will be done on this system, but it will take time because the period is over 200 days. Then we will know things like mass, and density, and have a guess as to what material---so be able to infer more about it.

Kepler only finds exoplanets which pass between us and the host star. It measures dips in the lightcurve. The tradeoff is that it can study many stars at once. Detecting a dip in the lightcurve is much less elaborate than recording the very slight wobble by fine doppler measurement.

I sympathise with any feeling of frustrated curiosity. I would like to know more myself. All we know so far is that there is a G-type star that has a planet roughly twice the size of Earth which could be the right temperature for liquid water.

Kepler has found a bunch of candidates so presumably we will be hearing more about this and several others as well.

 

[Drakkith]

That makes sense Marcus. I'm part of planethunters.org myself. Maybe I'll help find a planet or two myself.

 

[marcus]

I'm part of planethunters.org myself. Maybe I'll help find a planet or two myself.

Then you probably could tell me stuff I don't know about the various methods! I'll look up planethunters.org and see what it says the volunteer hunters do. So far it's been missing from my education

 

[DaveC426913]

The volume of Kepler-b22 is nearly 14 times that of earth, hence, is probably much more massive than Earth even if its density is relatively low.

But let us not forget that a planet's surface gravity - even with constant density - does not climb as quickly as its mass.

 

[marcus]

I'm part of planethunters.org myself. Maybe I'll help find a planet or two myself.

Then you probably could tell me stuff I don't know about the various methods! I'll look up planethunters.org and see what it says the volunteer hunters do. So far it's been missing from my education

Wow! it's nicely set up. A beginner immediately gets to try identifying transit events (dips in the lightcurve as something like a planet passes in front.)

So you are working on Kepler data. Bravo for taking that kind of initiative!

(Or Brava as the case may be. :-) )

 

[Drakkith]

Yeah, its pretty interesting. There are some CRAZY light curves there. Most are just kinda random bleh...

 

[D H]

It measures dips in the lightcurve.

It measures the dips so well that it enabled NASA to publish images of it.

The image from NASA all over the internet. No "Artist Rendition" caption. I'm mildly annoyed.

 

[Drakkith]

It measures the dips so well that it enabled NASA to publish images of it.

The image from NASA all over the internet. No "Artist Rendition" caption. I'm mildly annoyed.

Umm, what?

 

[marcus]

But let us not forget that a planet's surface gravity - even with constant density - does not climb as quickly as its mass.

Indeed! Just for fun we could imagine this thing has similar density to Earth and as they say 2.4 times the radius we could suppose 2.4 times the surface gravity and 2.4 times the escape velocity. All just wild guesses.

The higher escape velocity suggest it may have retained more atmosphere and volatile stuff and have a denser atmosphere. Too early to start speculating what that could mean.

Butterflies anyone? Birds? I hope their greenhouse isn't too bad. I don't like really hot days.
======================
@DH
I agree it is annoying when people drop off the "ARTIST CONCEPTION" caveat and spread it around like a real photograph.

 

[D H]

Umm, what?

Just do a google image search for Kepler-22b. My local news presented this image as if it was a photo taken by the Kepler satellite. Lots of news stories are presenting it as the same.

The mission page for the mission presents the image as the first thing you see when you enter the site. There is no mention on this page that the image of Kepler-22b is an artist's conception. They at least do say this in the detail pages.

 

[marcus]

@Dave,
please read what I wrote.
===========

@DH
I googled "Kepler-22b" and the first hit had the picture WITH the caption "Artist rendering".

It was the online NY Daily News and it said it was Associated Press.
So maybe we have a mix of good and bad journalism here. You saw some bad but the top google hit is correctly captioned.

 

[D H]

What? No.

With the proviso that other things being equal (i.e. density) - if its mass doubles, then surface gravity does not double.

g ~ m/r^2 M has doubled - but so has r.

If density remains the same as the Earth's and the radius is twice that of the Earth, the mass is eight times that of the Earth. Gravitational acceleration doubles.

 

[DaveC426913]

@Dave,
please read what I wrote.
===========

Of course I read what you wrote. (I don't now why people say this.)
I've retracted my former claim because I am doubting its veracity.

I could have sworn that (assuming a fixed density) - as a planet's radius increases and its mass increases - its surface gravity does not go up as fast as its mass. This is because the radius is increasing, putting the surface farther from the CoM.

Now I'm not so sure. And it's too late this evening to check.

 

[marcus]

Indeed! Just for fun we could imagine this thing has similar density to Earth and as they say 2.4 times the radius we could suppose 2.4 times the surface gravity and 2.4 times the escape velocity. All just wild guesses.

What? No.

With the proviso that other things being equal (i.e. density) - if its mass doubles, then surface gravity does not double.

No one suggested that mass doubles --> surface gravity doubles. What were you contradicting?
In my post I suggested OTBE that radius doubles --> surface gravity doubles.

Or in this case let the factor be 2.4 instead. I asked you to read my post again so you would realize what I said was right, and did not call for a "What? No." reaction.

 

[JonDE]

Very interesting and very exciting times we live in! Although it does pose some questions.
According to wikipedia (which I'm pretty sure has never been wrong about anything), that when using the transit method, if the planet passes both in front of, and behind the star (relative to earth), we should be able to detect its temperature and elements of its atmosphere, and possibly even if it has clouds! Although no mention of this...
Do we then assume they didn't mention this because it didn't transit behind the star relative to us? Or did they just not bother to mention it because they didn't realize there would be this much excitement? Obviously the latter can't be possible (unless they are really really dense).
Edit: the link to wikipedia:
http://en.wikipedia.org/wiki/Transit_method#Transit_method

 

[Drakkith]

The Kepler satellite is not equipped to do that kind of analysis. It merely looks at light curves.

 

[Gliese123]

Well, the greenhouse gases is quite crucial for the global temperature of course. Does anybody know how its big diameter/gravity/mass affects the atmospheric airpressure? "If the greenhouse effect caused by the atmosphere is Earthlike, this corresponds to approximately 22 °C (72°F) average surface temperature - Wikipedia.

 

[Drakkith]

Well, the greenhouse gases is quite crucial for the global temperature of course. Does anybody know how its big diameter/gravity/mass affects the atmospheric airpressure? "If the greenhouse effect caused by the atmosphere is Earthlike, this corresponds to approximately 22 °C (72°F) average surface temperature - Wikipedia.

The mass has yet to be determined, so we don't know anything about it or it's gravity.

 

[skydivephil]

As has beein pointed out Kepler uses Photometry and to get mass you need to use a kinematic technique ie radial velocity.
I watched the press conference last night and they said they would be able to do the follow up radial velocity this summer. However not sure they meant start this summer or finish this summer. I can only preusme they mean start this summer, which means it will be some time before the mass of the planet will be known. Wonder how far you have to book Keck and the like in advance?

 

[daveb]

I have a question for all the planet gurus out there. On earth, radioactivity is largely responsible for the majority of the heat from the planet's interior. How much of this heat is responsible for the warmth of the Earth's surface? I ask because it seems it wouldn't be that much if the habitable zone doesn't take into account internal heating. If there was massive tectonic activity on planets, any idea how much larger the habitable zone could be (yes, I'm aware of the massive vulcanism on Io, but I thought that was due to the massive gravity of Jupiter).

 

[DaveC426913]

No one suggested that mass doubles --> surface gravity doubles. What were you contradicting?
In my post I suggested OTBE that radius doubles --> surface gravity doubles.

Or in this case let the factor be 2.4 instead. I asked you to read my post again so you would realize what I said was right, and did not call for a "What? No." reaction.

I thought yours was wrong too. But I spoke too soon. It's been a while since I've played with planetary mass and surface g. I'm rusty and responded hastily.

So: for a given density, surface gravity is directly proportional to r. As you say, for Kepler22a's 2.4 r_e, its surface gravity is 2.4 g_e.

 

[marcus]

As has beein pointed out Kepler uses Photometry and to get mass you need to use a kinematic technique ie radial velocity.
I watched the press conference last night and they said they would be able to do the follow up radial velocity this summer. However not sure they meant start this summer or finish this summer. I can only preusme they mean start this summer, which means it will be some time before the mass of the planet will be known. Wonder how far you have to book Keck and the like in advance?

Phil, I haven't checked news yet today and also am very far from expert about this stuff. I'll just guess that the main time factor in measuring planet mass by how much the star wobbles is likely to be the planet's own orbital period. To do a good job it seems to me you'd have to watch it for a year---or at least a sizeable fraction of one of its years (290 days).

It's a beautiful technique. My information is all out of date, going back to the 1990s, when I heard Geoff Marcy give a slide-talk. If I can still speak from what I heard about it then, they measure slight doppler shifts in the spectral lines of the star's light to detect, as you say, RADIAL (towards and away) motion. So it is the to-and-fro wobble of the star and the the speeds might just be a few meters a second.

This has probably occurred to everyone who's joined this thread or ever been interested but I'll say it anyway---even 30 meters a second (which is faster than the to-and-fro wobble they have to measure) is only a ten-millionth of the speed of light.
So the doppler effect would be to shorten or lengthen the wavelengths by only one ten-millionth of a wavelength.

And you only get the benefit of the full orbital speed if and when the planet is coming directly at you or going directly away---which only happens a couple of times a year.

And the platform you are on is not sitting still either. So the feat of measuring star wobble is a beautiful exquisite accomplishment. I'd appreciate if someone who has kept informed about this and has current information wants to report. I don't even know what telescopes they are using currently or what methods to measure the slight doppler shifts.

 

[ChrisPhy]

Sorry if dumb question, but what is the generally agreed reason given for why there are approx. 40 stars closer to Earth than the closest star with a detected planet ?

1)We looked exhaustively at the first 40 and found no evidence of planets ?
2)Is there some property of these closer stars that make it more difficult to detect planets ?
If answer is 1, then does this mean that we think that only maybe 1 in 40 or 1 in 100 stars has planets ?

Thanks

 

[ChrisPhy]

Sorry if dumb question, but what is the generally agreed reason given for why there are approx. 40 stars closer to Earth than the closest star with a detected planet ?

1)We looked exhaustively at the first 40 and found no evidence of planets ?
2)Is there some property of these closer stars that make it more difficult to detect planets ?
If answer is 1, then does this mean that we think that only maybe 1 in 40 or 1 in 100 stars has planets ?

Thanks

Answered my own question after thinking about it...
We need to SEE the planet transit the star, and most times the planet transit won't be in our 'line of sight', so I guess that's the reason...

 

[marcus]

Sorry if dumb question, but what is the generally agreed reason given for why there are approx. 40 stars closer to Earth than the closest star with a detected planet ?

1)We looked exhaustively at the first 40 and found no evidence of planets ?
2)Is there some property of these closer stars that make it more difficult to detect planets ?
If answer is 1, then does this mean that we think that only maybe 1 in 40 or 1 in 100 stars has planets ?

Thanks

Answered my own question after thinking about it...
We need to SEE the planet *transit* the star, and most times the planet transit won't be in our 'line of sight', so I guess that's the reason...

Well it is a good general question. Someone who knows more than I do about the exoplanet search would have to give a more thorough answer. I can give you some idea though:
http://arxiv.org/abs/1109.2497

A lot of stars are less than half as massive as Sol and much less bright. From what reports I have looked at, the planet searchers have tended to investigate SUN-LIKE stars, the spectral types F, G, and K. I also think a lot of stars are in binary or triple systems and they may have tended to skip those.

The Mayor et al paper (1109.2497) talks about a sample of sun-like stars they looked at over 8 years.
It says that going on that basis they think conservatively over 50% of all sunlike stars have at least one planet.

So when you see statistics it seems as if they are not looking at the stars that are much more massive than Sol and burn very hot and are shorter lived, and they are not looking at the ones that are small and puny (as a lot of the nearby ones are) or at least not giving these colder ones as much attention in the reports. (the specral "type M").
I could be wrong but that's what it looks like to me. These medium size sunlike stars (types F G and K) have nice wide habitable zones where temperature is right for liquid water.

The smaller colder ones have only a narrow zone close into the star that has the right temperature. A planet close in would probably not rotate, always one face to the star. For whatever reason it is just not as interesting to look for wobble in type M stars.

About *transit*, searches like this one do not require transit. They measure the slight wobble of the star to and fro, caused by the planet going around. The orbit plane can be tilted, it does not have to be exactly lined up with us so that we see it edge-on

EDIT: changed uppercase TRANSIT to *transit* to avoid it being mistaken for some unfamiliar acronym. I just want to stress the word.

 

[Drakkith]

About TRANSIT, searches like this one do not require transit. They measure the slight wobble of the star to and fro, caused by the planet going around. The orbit plane can be tilted, it does not have to be exactly lined up with us so that we see it edge-on

Which searches are you referring to?

 

[marcus]

Which searches are you referring to?

As I understand it I'm referring to the typical method sometimes called "doppler". It does not require that we see the system edge on. The planet does not have to pass "in front" of the star.
What I'm talking about is the method used for example by Geoff Marcy and Paul Butler in the exoplanet discoveries of the 1990s and subsequently by them and co-workers.

Sometimes also called "radial velocity" method. I'm puzzled by your question since you are involved in exoplanet search---although your search involves the other main technique (the dip in the lightcurve when the planet passes in front.)

Maybe I've said something unclearly and miscommunicated. Let me know if it's still unclear what I'm talking about.

I looked back and thought maybe it was confusing to use uppercase to emphasize the word TRANSIT. So I changed it to *transit* in red. I want to show that my comment refers to where ChrisPhy used that word in his post.
It is important to make clear that at least until recently most of the exoplanet discoveries did NOT use the detection of a transit by dip in the lightcurve. The predominant method was picking up the star's wobble by doppler spectroscopy.

 

[Drakkith]

Sometimes also called "radial velocity" method. I'm puzzled by your question since you are involved in exoplanet search---although your search involves the other main technique (the dip in the lightcurve when the planet passes in front.)

Maybe I've said something unclearly and miscommunicated. Let me know if it's still unclear what I'm talking about.

Yeah, I was confused by this:

About *transit*, searches like this one do not require transit.

The sentences after this didn't seem to add up to what you just said. IE they aren't about transit.

 

[marcus]

Sorry about the confusion. Well do you understand now? What I should have said to ChrisPhy was probably something like "About your using the word *transit* in your post, about detecting exoplanets in the 40 nearest stars, it shows you have a mistaken idea about the technique used. I'll try to correct that. Until recently at least most exoplanets were not found by observing a transit..."

Anyway,...:-(

But did you look at the 2011 paper by Mayor et al?
http://arxiv.org/abs/1109.2497
It uses doppler wobble, and it's great.
Though not an expert, and not folowing exoplanets closely, I't say it represents the first real statistics on the prevalence of the mediumsized planets. the super-earth and neptune class.

It's remarkable they came up with a 50% figure for sunlike stars (ie FGK and single).

 

[Drakkith]

Lol, no big deal Marcus.

I agree that the results look pretty amazing.

 

[bobsmith76]

Is it possible to find out if kepler is solid or gaseous or is that something that our instruments cannot now detect.