Major extrasolar planet discovery announcement on Aug 31st

[ToSeek]

Yeah, the more inclined the orbit, the smaller the noticable effect from Earth. If the planet's orbit is inclined 90 degrees, you can't see any wobble -- the planet is undetectable using the doppler method, and has a lower mass limit of 0.

I think you're better off considering it the other way around: assume that the planet is in an orbit co-planar with the Earth. Then it's possible to calculate the mass that would cause the given wobble. If the planet's orbit is inclined to that plane, the greater its mass has to be to cause the same effect. So without being able to determine the orbital inclination there is no upper limit to the mass (not mathematically, at least), but there's always a lower limit.

[Doodler]

Given the extremely short orbital periods of these planets, couldn't some basic parameters for an upper limit be determined?

As I understand it, the further out a planet is projected to be, the faster and heavier it has to be in order to induce stellar wobble.

Given detection threshholds of Brown dwarves and the threshold of orbital velocity and planetary mass versus star's gravitational pull on a suspected planet being able to keep it in orbit without being thrown free, couldn't an upper range be established?

[Andreas]

As I understand it, the further out a planet is projected to be, the faster and heavier it has to be in order to induce stellar wobble.

The orbital speed does not depend on its mass. Thus the further out, the slower.

[Doodler]

As I understand it, the further out a planet is projected to be, the faster and heavier it has to be in order to induce stellar wobble.

The orbital speed does not depend on its mass. Thus the further out, the slower.

If they are detecting the duration of the orbit before determining the distance and mass of a planet, they have to back into a figure on the velocity.

A planet orbiting at 2.4 million miles completing the circuit in just under three days is not moving as fast as a planet that would be orbiting at 30 million miles and completing the orbit in the same amount of time.

Keep in mind with these radial velocity measurements, the orbital period is a predetermined constant, you have to insert the planet's mass, velocity and distance from the star into the equation as variable to create the envelope of possible solutions.

The further out from a star the planet is, the heavier it has to be to induce a detected amount of wobble, and the faster it must be moving in order to complete an orbit in the detected amount of time. Between those two factors, some level of certainty to an upper threshold should be possible. At some point, you're generating a solution that would have a massive planet that would be distant enough from the star have enough velocity to break out of its orbit.

[Ut]

The orbital period is a function of the length of the semi-major axis of the orbit and the mass of the parent star. If you have a planet at 3 million miles, and another at 30 million miles, they can't both complete an orbit in the same amount of time. If you speed up the more distant planet, it will spiral into a higher orbit, or escape the stellar system all together.

Also, more massive planets have a greater effect the more distant they are from their star. The more distance between the two, the farther the centre of mass of the system is from the centre of the star, and the more the star will wobble. The current observational bias in planet hunting is due to the short time scale in which the stars have been observed. It takes two or three orbits to really nail down a planet, and if a planet has a period of 10 years, that's 20-30 years of observations. The first planets were discovered 9 years ago.

[Stinger]

I missed the live announcement and want to applaud ToSeek for taking the time for disseminating it here. Good work as usual. =D>

[Doodler]

The orbital period is a function of the length of the semi-major axis of the orbit and the mass of the parent star. If you have a planet at 3 million miles, and another at 30 million miles, they can't both complete an orbit in the same amount of time. If you speed up the more distant planet, it will spiral into a higher orbit, or escape the stellar system all together.

Also, more massive planets have a greater effect the more distant they are from their star. The more distance between the two, the farther the centre of mass of the system is from the centre of the star, and the more the star will wobble.

I know this and agree. That's part of what I'm asking, after a certain distance from a star, you're dealing with a planet that simply could not maintain that orbit. The numbers I used were deliberately that disparate to make a point.

In determining a planet's mass from the wobble of a star, you have a range of possibilities starting that come down to how much wobble and at what distance can a planet of a given mass cause. You can take that equation with a given amount of wobble and say that a planet is mass X at distance Y.

Add to that you also have to balance the distance Y against a velocity Z, where Z has to be less than the escape velocity of the star itself. The velocity is bound by the given orbital period. The greater Y becomes against the given orbital period, the greater Z must become.

Now I might be wrong, but I thought the escape velocity of a planet was also a function of its mass. A planet of greater mass would require less velocity at a given distance than a lighter planet to escape because the heavier world would have more momentum. A Jupiter sized planet would have an escape velocity lower than an Earth sized world at the same distance from a star.


So back to my original question, if you take two ranges of possible solutions, one showing the range of mass and distance solutions relative to the wobble, and another showing a range of distance and velocity solutions relative to the orbital period, can someone arrive at a reasonable upper limit to the size of the planet?

[The Bad Astronomer]

The period of the wobble is directly measured from the wavelength of th sinusoidal-shape Doppler curve of the starlight. Knowing the mass of the star, that period gives you a distance. The amount (amplitude) of the tug gives you the mass, or, more accurately, mass times the sine of the orbital inclination.

[Ut]

Now I might be wrong, but I thought the escape velocity of a planet was also a function of its mass. A planet of greater mass would require less velocity at a given distance than a lighter planet to escape because the heavier world would have more momentum. A Jupiter sized planet would have an escape velocity lower than an Earth sized world at the same distance from a star.

Ok, I see where you were saying this, but I didn't understand it the first time.

Regardless of the mass, a body must reach escape velocity to escape. It's a constant for each star. Having more momentum simply means the more massive planets will get farther away from its parent star before it begins to fall back. This only helps it escape more easily if it can get far enough out to be affected by another massive body from outside the system.

[Doodler]

The period of the wobble is directly measured from the wavelength of th sinusoidal-shape Doppler curve of the starlight. Knowing the mass of the star, that period gives you a distance. The amount (amplitude) of the tug gives you the mass, or, more accurately, mass times the sine of the orbital inclination.

Nifty, that I wasn't aware of. I was under the impression that the distance of the planet from the star was a variable, too.

[daver]

Regardless of the mass, a body must reach escape velocity to escape. It's a constant for each star. Having more momentum simply means the more massive planets will get farther away from its parent star before it begins to fall back. This only helps it escape more easily if it can get far enough out to be affected by another massive body from outside the system.

Maybe I'm misunderstanding you, but the orbit of a planet is pretty much independent of the mass of the planet (not quite independent--if the mass of the planet is a significant percentage of the mass of the star it's orbiting then things get messier). So if you put swapped out some comet at perihelion and put Jupiter in its place, the difference in the orbits of Comet Jupiter and the original would be insignificant.
[edit--neglecting the influence of the other bodies in the solar system]

[George]

55 Cancri: 5 million year old star (??), about mass of Sun, four planets. Jupiter-mass planet at Jupiter-like distance. Two more Jupiter-mass planets but closer in. New planet orbits in only 2.8 days, 4% of Earth's distance from Sun. Lower mass limit is 14x Earth's, then used HST to determine plane of solar system, yielded about 18x Earth's.

I'll bet a new BA book you meant "upper mass limit".

Wow. I will withdraw the offer since you, forunately for me, did not accept. I thought I'd get a free book.

At 14 times the mass of Earth, the newfound planet -- circling a star similar in size and brightness to our Sun -- is about as heavy as Uranus, a world of gas and ice and the smallest giant planet in our solar system. Theorists say 14 Earth-masses is roughly the upper limit for a planet to possibly remain rocky, however. And because this planet is so close to its host star, it likely had a much different formation history than Uranus.

The limit was not from Doppler determination. Of course, the Doppler discussion is certainly pertinent.

The quote is from a side link from the original article and is found ....
here .

The leading theory of planet formation has the gas giants forming from a rocky core, a process in which the core develops over time, then reaches a tipping point when gravity can rapidly collect a huge envelope of gas.
...
Finally, Boss said, the star mu Arae has a higher metal content than the Sun, and theory says a planet forming close to such a star can be expected to gather more mass. It's all about how much building material is available, he said.

Would this be true in the case where planets form from accretion disks within the stellar disk (as per a Spitzer finding)? If not, this should allow for > 14x Earth's mass, right? #-o

[umop ap!sdn]

I missed the live show #-o but caught the rerun. It was interesting how they discussed the possibility of two new classes of extrasolar planet - "super-Earths" made of rock that formed at Earthlike distances and migrated inward, and "ice giants" that formed at Uranus-like distances. But it seems to me if an "ice giant" formed and then got pulled into one of these really small orbits, wouldn't that make it a steam giant? :-k

[Launch window]

Somewhat of a let down by NASA :x

another nothing to get excited about news-annoucement,
seen as the Euros and Portuguese researchers had already talked about these "super Earths" orbiting a sunlike star

Still, I think the NASA new report had a bit more info. Good read all the same

[Kullat Nunu]

Somewhat of a let down by NASA :x

another nothing to get excited about news-annoucement,
seen as the Euros and Portuguese researchers had already talked about these "super Earths" orbiting a sunlike star

Well, can't blame them because that announcement was already scheduled before the Europeans released their findings. And these planets were discovered earlier.

Fortunately they didn't announce an already-known planet like in the case of the ancient pulsar planet in M4. #-o

Still, I think the NASA new report had a bit more info. Good read all the same

Yeah, those planets are really interesting. Last place I expected they to discover a new planet around 55 Cancri was inside the planet b's orbit.

[George]

It made "Good Morning America" this morning along with some graphics. =D>

[TimberWolf]

Hello,

I saw the announcement of the " super-Earth " planet orbiting mu Arae. Interesting. A gargantuan world. At 14x Earth mass, what heavy of g would such a world possess?

Cordially,

TimberWolf

[mikeh9741]

Assuming the planet has the same density as Earth, I figure that its g would be about 24 m/(s^2).

[TimberWolf]

Hello,

Unfortunately, I don't understand the answer given, though I wish I did. What would the answer be in g?

Cordially,

TimberWolf

[mikeh9741]

TimberWolf,

Earth's g is 9.8 meters per seconds squared (9.8 m/(s^2)) so at about 24 m/(s^2), this planet's g (acceleration due to gravity) would be about two and a half times that of Earth's. It would be pretty hard to walk around!

Mike

[TimberWolf]

Hello,

Cool. So, gravity is measured by the rate that local gravity would accelerate an object? Does that mean that objects falling on Earth accelerate at a rate of 9.8 meters a second? Thanks for the explanation.

Cordially,

TimberWolf

[mikeh9741]

Does that mean that objects falling on Earth accelerate at a rate of 9.8 meters a second?TimberWolf

Well, it's 9.8 meters per second per second. So after falling with an initial velocity of 0, the object's speed would be 9.8 m/s, after 2 seconds it would be 19.6 m/s, after 3 seconds it would be 29.4 m/s, etc.

In reality, falling objects will reach terminal velocity due to air resistance and stop accelerating.

[ToSeek]

Somewhat of a let down by NASA :x

another nothing to get excited about news-annoucement,
seen as the Euros and Portuguese researchers had already talked about these "super Earths" orbiting a sunlike star

Still, I think the NASA new report had a bit more info. Good read all the same

The press conference noted that the NASA findings had been peer-reviewed, while the European findings had not.

[ToSeek]

NASA's latest planetary discovery rings a literary bell

NASA is not known for making literary recommendations. But its discovery of a new class of planet came with a plug for the science-fiction classic Ringworld.

At a briefing this month on the planet found orbiting a red-dwarf star, reporters pressed NASA astronomy and physics chief Anne Kinney for a celestial counterpart in science fiction.

Her answer: Ringworld, the 1970 novel by Larry Niven that won the 1971 Hugo Award for science-fiction achievement and spawned four sequels.

[ToSeek]

The Planet Hunter

Despite what 'Rolling Stone' magazine says, the folks at UCSC are doing more than toking hooners in the redwoods. Meet Steven Vogt, UCSC professor and leader in the race to find other worlds.

[Manchurian Taikonaut]

a bit of news on the topic

February 2005
animation shows the number of stars in our local stellar neighbourhood that have been identified to have planets orbiting them.


In 2004, it was announced that the NASA/ESA Hubble Space Telescope had been used to detect an additional 100 planets

http://www.esa.int/esaSC/SEM2DOW4QWD_index_0.html


First direct sighting of an extrasolar planet
http://www.newscientist.com/article.ns?id=dn6864


Extrasolar Planets Conference Marks 10th Anniversary
http://www.spaceref.com/news/viewpr.html?pid=15948

[Kullat Nunu]

In 2004, it was announced that the NASA/ESA Hubble Space Telescope had been used to detect an additional 100 planets.

I wonder how real that detection is or is it just hype. For example, OGLE survey has found well over hundred planetary-like transits, but most of them are caused by red dwarfs, grazing transits by Sun-like stars and other non-planetary phenomena. So far, five of them have been proved to be real extrasolar planets.