[meteorite-list] When Worlds Collide: Have Astronomers Observed the Aftermath of a Distant Planetary Collision?

From: lebofsky at lpl.arizona.edu <lebofsky_at_meteoritecentral.com>
Date: Thu, 10 Jan 2008 16:50:54 -0700 (MST)
Message-ID: <17247.66.194.95.2.1200009054.squirrel_at_timber.lpl.arizona.edu>

Hi All:

Would a short article in Meteorite magazine on this subject be of interest
to readers?

If so, please let me know and I can contact the authors who I know and are
here at the meeting I am at. There may be issues if this is going to be
published elsewhere, but it can't hurt for me to ask.

Larry

Co-editor, Meteorite magazine

On Thu, January 10, 2008 4:09 pm, Ron Baalke wrote:
>

>
> Public Affairs Office
> Harvard-Smithsonian Center for Astrophysics
> Cambridge, Massachusetts
>
>
> For more information, contact:
>
>
> David A. Aguilar
> Director of Public Affairs
> Harvard-Smithsonian Center for Astrophysics
> 617-495-7462
>
>
> Christine Pulliam
> Public Affairs Specialist
> Harvard-Smithsonian Center for Astrophysics
> 617-495-7463
>
>
> For Release: Wednesday, January 09, 2008 11:00:00 AM EST
>
>
> Release No.: 2008-01
>
>
> When Worlds Collide: Have Astronomers Observed the Aftermath of a Distant
> Planetary Collision?
>
>
> Austin, TX -- Astronomers announced today that a mystery object orbiting
> a star 170 light-years from Earth might have formed from the collision and
> merger of two protoplanets. The object, known as 2M1207B, has puzzled
> astronomers since its discovery because it seems to fall outside the
> spectrum of physical possibility. Its temperature, luminosity, age, and
> location do not match up with any theory.
>
> "This is a strange enough object that it needs a strange explanation,"
> said Eric Mamajek of the Harvard-Smithsonian Center for Astrophysics
> (CfA).
>
>
> The announcement was made in a press conference at the 211th meeting of
> the American Astronomical Society.
>
>
> 2M1207B orbits a 25-Jupiter-mass brown dwarf called 2M1207A seen in the
> direction of the constellation Centaurus. Computer models show that
> 2M1207A
> is very young, only about 8 million years old; therefore its companion
> should also be 8 million years old. At that age, it should have cooled to
> a temperature of less than 1300 degrees Fahrenheit (1000 Kelvin). However,
> observations show that 2M1207B is actually about 2400 degrees F (1600
> K).
> The extra heat might be the result of a protoplanetary collision.
>
>
> "Most, if not all, planets in our solar system were hit early in their
> history. A collision created Earth's moon and knocked Uranus on its side,"
> explained Mamajek. "It's quite likely that major collisions happen in
> other young planetary systems, too."
>
> Given its temperature, astronomers would expect a certain luminosity for
> 2M1207B, but it is 10 times fainter than expected. In 2006, astronomers
> suggested that it is obscured by a dusty, edge-on disk. Mamajek and his
> colleague, Michael Meyer of the University of Arizona, propose an
> alternative explanation: 2M1207B is small, only about the size of Saturn,
> and therefore has a smaller-than-expected surface area radiating energy.
>
>
> They derive a radius of 31,000 miles (50,000 km) for 2M1207B, compared to
> 37,000 miles (60,000 km) for Saturn. Given typical densities for giant
> planets, this would give 2M1207B a mass about 80 times Earth (or
> one-fourth Jupiter). The only plausible way for such a small object to be
> so hot millions of years after it formed is if it suffered a recent,
> titanic collision that heated it.
>
> The planets in our solar system assembled from dust, rock, and gas,
> gradually growing larger over millions of years. But sometimes, two
> planet-sized objects collided catastrophically. For example, the Moon
> formed when an object about half the size of Mars hit the proto-Earth. If
> planet formation works the same way in other star systems, then 2M1207B
> might be the product of a collision between a Saturn-sized gas giant and a
> planet about three times the size of Earth. The two smacked into each
> other and stuck, forming one larger world still boiling from the heat
> generated in the collision.
>
> "The Earth was hit by something one-tenth its mass, and it's likely that
> other planets in our solar system were too, including Venus and Uranus,"
> explained Meyer. "If that one-tenth scale holds in other planetary
> systems, then we could be seeing the aftermath of a collision between a 72
> Earth-mass
> gas giant and an 8 Earth-mass planet, even though such collisions are very
> unlikely."
>
> Mamajek also points out that the collision theory is reasonable from a
> timescale point of view. A 2400-degree, Saturn-sized object would radiate
> its heat away over about 100,000 years. If the system were billions of
> years old, it is unlikely that we would be looking at the right time, but
> since the system is young, the chances are much better that we would catch
> it shortly after the collision while the hot aftermath is still
> observable.
>
> The collision hypothesis makes several predictions that astronomers can
> test. Chief among them is a low surface gravity (which depends on a
> planet's mass and radius). To check this prediction, astronomers will need
> to get a better spectrum of 2M1207B -- a challenge since it is very faint
> and very close to the brown dwarf 2M1207A. Others are checking the dusty
> disk theory by looking for signs of polarization in the light from
> 2M1207B. More answers
> should be forthcoming within a year or two.
>
> Mamajek emphasized that while a planet collision may not be the correct
> explanation for the weirdness of 2M1207B, examples of colliding planets
> are likely to be found by the next generation of ground-based telescopes.
>
> "Hot, post-collision planets might be a whole new class of objects we
> will see with the Giant Magellan Telescope."
>
> "Even if we're wrong, I wouldn't be surprised if someone finds a
> clear-cut case in the next 10 years," Mamajek added.
>
> Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for
> Astrophysics (CfA) is a joint collaboration between the Smithsonian
> Astrophysical Observatory and the Harvard College Observatory. CfA
> scientists, organized into six research divisions, study the origin,
> evolution and ultimate fate of the universe.
>
> [NOTE: An image supporting this release is available at
> http://cfa-www.harvard.edu/press/2008/pr200801_images.html ]
>
>
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Received on Thu 10 Jan 2008 06:50:54 PM PST