In the original article it says:
"Since 1997, astronomers have discovered five planets
circling 55 Cancri (including 55 Canrci e in 2004).
All five alien worlds were detected using the so-called
radial velocity -- or Doppler -- method, which looks
for tiny wobbles in a star's movement caused by the
gravitational tugs of orbiting planets."
So, we know it has four other planets. But each planet
has a different orbital period and the frequency of the
"wobble" matches the orbital period of each separate
planet, so we can tell the individual effect of each planet.
55 Cancri e is very close to the star, practically skimming
the surface, and gravity gets stronger in effect as you get
objects closer and closer, by the inverse square of the
distance, half the distance, four times the gravity effect
and so forth.
Even so, these are TINY "wobbles" and the data really
have to massaged to get a result.
Sterling K. Webb
-----------------------------------------------------------------------------
----- Original Message -----
From: "Steve Witt" <[email protected]>
To: "Richard Montgomery" <[email protected]>; "Meteorite List"
<[email protected]>; "Sterling K. Webb"
<[email protected]>
Sent: Monday, May 02, 2011 11:35 PM
Subject: Re: [meteorite-list] A New Nearby Oddball Planet
Sterling and List,
Great answer Sterling, but I have a question. What if there are 10 other
as yet undiscovered planets orbiting this star? Wouldn't that change the
equation considerably. And why would anyone assume that the planet in
question is the only mass making the star wobble?
thanx,
Steve
Steve Witt
IMCA #9020
http://imca.cc/
--- On Mon, 5/2/11, Sterling K. Webb <[email protected]>
wrote:
From: Sterling K. Webb <[email protected]>
Subject: Re: [meteorite-list] A New Nearby Oddball Planet
To: "Richard Montgomery" <[email protected]>, "Meteorite List"
<[email protected]>
Date: Monday, May 2, 2011, 10:54 PM
Richard, List,
Ok, here goes...
The mass of the planet? Well, there's a slight "wobble"
of a star caused by the gravitational pull of the planet.
The extent of this movement can be used to estimate
the planet's mass as a proportion of the stellar mass -
which itself is another estimate based on the star's
spectral characteristics and the star's luminosity once
we know the star's distance from Earth which we know
by parallax and other techniques.
The Hertzsprung-Russell equation (boy, I hope I spelled
that right!) relates the mass of the star to its
luminosity
and color:
http://outreach.atnf.csiro.au/education/senior/astrophysics/stellarevolution_hrintro.html
So, once we have a handle on the star's mass, we can
translate the "wobble" into what planet mass it would
take to make that amount of "wobble."
OK, we got the mass of the planet down.
Now, when the planet crosses the face of the star, it
causes a tiny reduction in the strength of the light
and that tiny reduction is proportional to the size of
the disc of the planet compared to the disc of the star.
If the star dims by 0.0001%, the the area of the planet
is 0.0001% of the area of the star.
And we can measure the angular diameter of the star's
disc. And because we know the distance to the star, we
can can calculate the physical diameter of the star from
the
angular diameter. And from that we can calculate the
diameter of the planet in actual physical terms. And,
once we have the planet's diameter and mass, we can
calculate the density of the planet.
All you need is a ream or two of paper and a jar of
sharp No. 2 Ticonderoga pencils.... Yes, there is some
error introduced, or more correctly, a range of answers,
but that density of 11.0 is very unlikely to actually be
as low as the density of iron (8-ish) and just as likely
to be a higher density than a lower one.
Sterling K. Webb
---------------------------------------------------------------------------
----- Original Message -----
From: "Richard Montgomery" <[email protected]>
To: "Sterling K. Webb" <[email protected]>;
"Meteorite List"
<[email protected]>
Sent: Monday, May 02, 2011 8:12 PM
Subject: Re: [meteorite-list] A New Nearby Oddball Planet
> Neophyte question again, from someone with a sharp
interest and a lack
> of astophysic knowledge:
>
> In short, how can we determine the density of a
planet, other than
> ours and the locals...?? I can do it for
gold-quartz samples
> (fortunately, the other reason for metal-detectors in
the filed
> :>) )...but I need terrestrial gravity to pull it
off.
>
> Always ready for a lesson,
> Richard Montgomery
>
> ----- Original Message -----
> From: "Sterling K. Webb" <[email protected]>
> To: "Meteorite List" <[email protected]>
> Sent: Monday, May 02, 2011 3:44 PM
> Subject: [meteorite-list] A New Nearby Oddball Planet
>
>
>> Back in January, there was a List discussion of a
planet
>> of the Kepler 10 (unnamed) star which has a
density of
>> 8.8, as heavy as iron and an argument about
whether
>> an entirely iron planet could exist and how.
>>
>> Now we have a (roughly) terrestial planet with a
density
>> of 11.0, or about the density of a solid lead
ball... Iron
>> ain't gonna do it.
>>
>> http://www.space.com/11544-densest-alien-planet-55cancrie.html
>>
>> Nearby Alien Planet Nearly Dense as Lead
>>
>> Astronomers have pinned down some details of an
>> exotic nearby alien planet that's almost as
>> dense as lead.
>>
>> The exoplanet, called 55 Cancri e, is 60 percent
>> larger in diameter than Earth but eight times
>> as massive, researchers revealed Friday (April
29).
>> That makes the alien world the densest solid
planet
>> known -- twice as dense as Earth. [2 x 5.5 =
11.0]
>>
>> Astronomers previously thought 55 Cancri e took
>> about 2.8 days to orbit its parent star. But the
>> new study reveals that the exoplanet is so close
>> to its host star that it completes a stellar lap
>> in less than 18 hours.
>>
>> "You could set dates on this world by your
wristwatch,
>> not a calendar," study co-author Jaymie Matthews,
>> of the University of British Columbia, said in a
statement.
>>
>> Updating views of 55 Cancri e:
>>
>> The super-dense alien world is part of a
multiplanet
>> solar system about 40 light-years from Earth, in
the
>> constellation Cancer (The Crab). Its sunlike
parent
>> star, 55 Cancri, is bright enough to be seen from
>> Earth by the unaided eye, researchers said.
>>
>> This wide-angle photograph of the night sky shows
>> the location of 55 Cancri, a star where
astronomers
>> have found five planets, including a hot, dense
>> super-Earth.
>>
>> This wide-angle photograph of the night sky shows
>> the location of 55 Cancri, a star where
astronomers
>> have found five planets, including a hot, dense
>> super-Earth.
>>
>> Since 1997, astronomers have discovered five
planets
>> circling 55 Cancri (including 55 Canrci e in
2004).
>> All five alien worlds were detected using the
so-called
>> radial velocity -- or Doppler -- method, which
looks
>> for tiny wobbles in a star's movement caused by
the
>> gravitational tugs of orbiting planets.
>>
>> Initially, astronomers thought 55 Cancri e had an
>> orbital period of about 2.8 days. But last year,
>> two researchers -- Harvard grad student Rebekah
>> Dawson and Daniel Fabrycky of the University of
>> California, Santa Cruz -- re-analyzed the data.
>> They suggested that the alien planet might
actually
>> zip around its host star much faster than that.
>>
>> So Dawson and Fabrycky joined up with a few
others
>> to observe 55 Cancri e more closely. The team
trained
>> Canada's MOST (Microvariability & Oscillations
of STars)
>> space telescope on the planet's star, then
watched
>> for the tiny brightness dips caused when 55 Cancri
e
>> passed in front of -- or transited -- it from the
>> telescope's perspective.
>>
>> This is the same technique used by NASA's
prolific
>> Kepler space observatory, which has found 1,235
>> alien planet candidates since its March 2009
launch.
>>
>> The team found that these transits occur like
clockwork
>> every 17 hours and 41 minutes, just as Dawson and
>> Fabrycky had predicted. The starlight is dimmed
by
>> only 0.02 percent during each transit, telling
the
>> astronomers that the planet's diameter is about
>> 13,049 miles (21,000 kilometers) -- only 60
percent
>> or so larger than Earth.
>>
>> Using this information, the researchers were able
to
>> calculate 55 Cancri e's density.
>>
>> "It's wonderful to be able to point to a
naked-eye
>> star and know the mass and radius of one of its
planets,
>> especially a distinctive one like this," said
study
>> lead author Josh Winn of MIT.
>>
>> The research was released online Friday at the
website
>> arXiv.org, and it has been submitted for
publication
>> in The Astrophysical Journal Letters.
>>
>> A scorching-hot world
>>
>> Because 55 Cancri e is so close to its parent
star,
>> it wouldn't be a very pleasant place to live.
>> Temperatures on its surface could be as high as
>> 4,892 degrees Fahrenheit (2,700 degrees Celsius),
>> researchers said.
>>
>> "Because of the infernal heat, it's unlikely that
>> 55 Cancri e has an atmosphere," Winn said. "So
this
>> is not the type of place where exobiologists
would
>> look for life."
>>
>> If you could somehow survive the heat, however,
>> the view from the planet's surface would be
>> exotic and spectacular.
>>
>> "On this world -- the densest solid planet found
>> anywhere so far, in the solar system or beyond --
>> you would weigh three times heavier than you do
>> on Earth," Matthews said. "By day, the sun would
>> look 60 times bigger and shine 3,600 times
brighter
>> in the sky."
>>
>> But the appeal of 55 Cancri e is not limited to
>> such gee-whiz factoids. Because it's so close to
>> Earth, the planet and its solar system should
>> inspire all sorts of future work, researchers
said.
>>
>> "The brightness of the host star makes many types
of
>> sensitive measurements possible, so 55 Cancri e
is
>> the perfect laboratory to test theories of planet
>> formation, evolution and survival," Winn said.
>>
>>
------------------------------------------------------------------------
>>
>> With a surface temperature of nearly 5000F (or
~2700K),
>> this can't be a lead world -- it would have boiled
away by
>> now. A solid iron planet would just barely survive
-- iron
>> boils at 3134K.
>>
>> A planet of 75% iron with a 25% crust of Tungsten
would
>> have a density of 11, and I suppose that if
everything less
>> refractory than tungsten had boiled away, you
could get
>> such a planet...
>>
>> Here's everything heavier than iron and its
density.
>>
>> I got tired of entering boiling points but you can
see
>> that the dense elements have high boiling
points...
>>
>> Boiling points alone do not tell the story; vapor
>> pressures are high above the melting point and
>> such elements could slowly escape.
>>
>> Tungsten is the best bet. MP 3680K, BP 5828K.
>> and moderately abundant in the universe, about
>> like uranium.
>>
>> 76 Os Osmium 22.61 BP 5285K
>> 77 Ir Iridium 22.56 BP
4701K
>> 78 Pt Platinum 21.46 BP
5869K
>> 75 Re Rhenium 21.02 BP 5869
>> 93 Np Neptunium 20.45 BP
4273K
>> 94 Pu Plutonium 19.84 BP
3501K
>> 79 Au Gold 19.282 BP 3129K
>> 74 W Tungsten 19.25 BP
5828K
>> 92 U Uranium 18.95 BP 4404K
>> 104 Rf Rutherfordium 18.1
>> 73 Ta Tantalum 16.654 BP 5731K
>> 91 Pa Protactinium 15.37
>> 98 Cf Californium 15.1
>> 97 Bk Berkelium 14.79
>> 95 Am Americium 13.69
>> 80 Hg Mercury 13.5336
>> 96 Cm Curium 13.51
>> 99 Es Einsteinium 13.5
>> 72 Hf Hafnium 13.31
>> 45 Rh Rhodium 12.41
>> 44 Ru Ruthenium 12.37
>> 46 Pd Palladium 12.02
>> 81 Tl Thallium 11.85
>> 90 Th Thorium 11.72
>> 43 Tc Technetium 11.5
>> 82 Pb Lead 11.342
>> 47 Ag Silver 10.501
>> 42 Mo Molybdenum 10.22
>> 89 Ac Actinium 10.07
>> 71 Lu Lutetium 9.84
>> 83 Bi Bismuth 9.807
>> 69 Tm Thulium 9.321
>> 84 Po Polonium 9.32
>> 68 Er Erbium 9.066
>> 29 Cu Copper 8.96
>> 28 Ni Nickel 8.912
>> 27 Co Cobalt 8.86
>> 67 Ho Holmium 8.795
>> 48 Cd Cadmium 8.69
>> 41 Nb Niobium 8.57
>> 66 Dy Dysprosium 8.55
>> 65 Tb Terbium 8.229
>> 64 Gd Gadolinium 7.895
>> 26 Fe Iron 7.874
>>
>> You put together a planet from the list...
>>
>>
>> Sterling
>>
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