[meteorite-list] A New Nearby Oddball Planet

Mon May 2 18:44:23 EDT 2011

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.

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