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Astronomers Spot Evidence for Colliding Planet Embryos in Famous Star Cluster

November 14, 2007

Press Release                   November 15, 2007
UCLA / Gemini Observatory

Contacts:

Astronomers have found evidence for the formation of young rocky planets around the star HD 23514 located in the well-known Pleiades (Seven Sisters) star cluster that is easily visible in the current evening sky.

Using an infrared sensitive camera (MICHELLE) on the Gemini North Telescope, Joseph Rhee of UCLA and his collaborators have measured heat from hot dust surrounding a 100 million year old star in the bright star cluster. The star has properties very much like our Sun except that it is 45 times younger and is orbited by hundreds of thousands of times more dust than our Sun. The star is also one of the very few solar-type stars known to be orbited by warm dust particles.

These warm emissions betray catastrophic collisions in an evolving young planetary system around an adolescent-age solar type star. The emission appears to originate from dust located in the terrestrial planet zone between about 1/4 to two astronomical units (AUs) from the parent star HD 23514, a region corresponding to the orbits of Mercury and Mars in our solar system.

Rhee and team members Inseok Song of the Spitzer Science Center and Benjamin Zuckerman of UCLA interpret the presence of so much hot dust as a result of colliding planetary embryos leading to the conclusion that a recent collision occurred between relatively large rocky bodies. According to Zuckerman, this is thought to be similar to the encounter that produced the Earth-Moon system more than four billions ago. "Indeed, the collision that generated the Moon sent a comparable mass of debris into interplanetary orbits as is now observed in HD 23514," said Zuckerman.

The astronomers analyzing the emission from countless microscopic dust particles propose that the most likely explanation is they were pulverized in the violent collision of planets or “planetary embryos.” Song calls the dust particles the “building blocks of planets,” which accumulate into comets and small asteroid-size bodies, and then clump together to form planetary embryos, and finally full-fledged planets. “In the process of creating rocky, terrestrial planets, some objects collide and grow into planets, while others shatter into dust; we are seeing that dust,” Song said.

These new observations indicate that rocky terrestrial planets, perhaps like the Earth, Mars or Venus, appear to be forming or to have recently formed. “This is the first clear evidence for planet formation in the Pleiades, and the results we are presenting strongly suggest that terrestrial planets like those in our solar system are quite common,” said Joseph Rhee, UCLA postdoctoral scholar in astronomy, and lead author of the research.

Astronomers report the findings in an upcoming issue of the Astrophysical Journal, published by the American Astronomical Society.

The Pleiades star cluster, in the constellation of Taurus, is easily visible to the naked eye at this time of the year. The cluster is well-known in many cultures, and is cited in the Bible, noted Rhee: “Can you bind the beautiful Pleiades? Can you loose the cords of Orion?” ( Job 38:31).

Although referred to as the seven sisters, “the cluster actually contains some 1,400 stars,” said Inseok Song, a staff scientist at Caltech’s Spitzer Science Center, former astronomer with the Gemini Observatory, and a co-author of the research. Located about 400 light years away, the Pleiades is one of the closest star clusters to Earth.

Gemini Observatory/Lynette Cook

Figure 1: Artist's rendering of what the environment around HD 23514 might look like as two Earth-sized bodies collide. Artwork by Lynette Cook for Gemini Observatory.

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Credit: Inseok Song/Digital Sky Survey, inset: Gemini Observatory/Lynette Cook

Figure 2: Color composite image of the Pleiades star cluster and surrounding region produced by Inseok Song of the Spitzer Science Center. The image was created by combining B, R and I band images from individual second generation Digital Sky Survey images into blue, green and red image layers, respectively. The location of HD 23514 is shown by the yellow arrow. Inset artwork (lower right) is same as in Figure 1.

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Figure 3: Spectral energy distribution of the dusty 100 million year old solar-type star HD 23514 in the Pleiades star cluster. The unusual mid-infrared excess is most noticeable in the thermal infrared region. There is also a strong silicate feature around 9 microns.

Figure 4: MICHELLE mid-infrared spectrum of HD 23514 obtained on the Gemini North telescope. For comparison, the mid-infrared, (dotted-line) spectrum of another dusty star BD +20 307 is also reproduced. Both reveal the presence of warm dust. HD 23514 has the warmer dust, reflected by its more "blue shifted" bump. For young stars and debris disks, the most prominent spectral feature in the N-band is silicate emission.

Encuentran Evidencia de colisión de los embriones de Planeta en un famoso cúmulo estelar

Press Release
UCLA / Gemini Observatory

Contacts:

La comunidad astronómica ha encontrado evidencia de formación de planetas jóvenes y rocosos alrededor de la estrella HD 23514, ubicada en el conocido cúmulo estelar de las Pleiades (Las Siete Hermanas), el cual es fácilmente visible en el cielo durante el anochecer.

Utilizando una cámara sensible en el infrarrojo en el Telescopio de Gemini Norte, Joseph Rhee de la UCLA y sus colaboradores, han medido el calor del polvo caliente que rodea una estrella de 100 millones de años de antigüedad en el brillante cúmulo estelar. La estrellas tiene propiedades muy parecidas a las del Sol excepto que es 45 veces más joven y tiene una nube de polvo orbitando alrededor de ella. La estrella es también una de las pocas estrellas del tipo solar conocida por ser orbitada por partículas de polvo tibio.

Estas emisiones tibias revelan colisiones catastróficas en un sistema planetario en evolución alrededor de una estrella en edad adolescente de tipo solar. La emisión parece originarse del polvo ubicado en la zona de planetas terrestres entre aproximadamente 1/4 a dos unidades astronómicas (UAs) de su estrella madre HD 23514, una región que corresponde a las órbitas de Mercurio y Marte en nuestro sistema solar.

Rhees y los miembros del equipo, Inseok Song del Centro de Ciencia Spitzer y Benjamin Zuckerman de la UCLA, interpretan la presencia de tanto polvo caliente como una consecuencia de la colisión de embriones planetarios, lo cual lleva a la conclusión que, recientemente, hubo una colisión entre cuerpos rocosos relativamente grandes.. Según Zuckerman, se cree que esto es similar al encuentro que creó el sistema Tierra-Luna hace más de cuatro mil millones de años atrás. “De hecho, la colisión que generó la Luna, envió una cantidad de desecho similar hacia la órbita interplanetaria, como se puede observar ahora en HD 23514,” señaló Zuckerman.

Los astrónomos que analizaron la emisión de innumerables partículas de polvo microscópicas proponen que la explicación más probable es que fueron pulverizadas en la violenta colisión de planetas o “embriones planetarios.” Song denomina a las partículas de polvo como los “ bloques de construcción de planetas”, los que se acumulan en cometas y asteroides de pequeños tamaños, para luego agruparse y formar embriones planetarios llegando finalmente a planetas completamente desarrollados. “En el proceso de crear planetas rocosos terrestres, algunos objetos chocan y crecen hasta converstirse en planetas, mientras otros se fragmentan en el polvo; ese es el polvo que estamos viendo”, señaló Song.

Estas nuevas observaciones indican que los planetas rocosos terrestres, quizás como la Tierra, Marte y Venus, parecen estarse formando o haberse formado muy recientemente. “ Esta es la primera evidencia clara de formación planetaria en las Pleiades, y los resultados que estamos presentando sugieren firmamente que los planetas terrestres como aquellos en nuestro sistema solar son bastante comunes” dice Joseph Rhee, autor y líder de la investigación.

Los astrónomos informan de este hallazgo en la próxima edición de la revista The Astrophysical Journal publicada por la Sociedad Americana de Astronomia.

El cúmulo estelar de las Pleiades, en la constelación de Tauro es fácilmente observable a ojo desnudo durante esta época del año. El cúmulo es bastamente conocido en muchas culturas, y se cita en la Biblia, señala Rhee: “Puedes enlazar las hermosas Pleiades? Pueden aflojar las cuerdas de Orion?” ( Job 38:31).

Aunque se le conoce como las siete hermanas “el c’umulo en realidad alberga a más de 1,400 estrellas,” dice Inseok Song, científico del Centro Espacial Spitzer de Caltech, ex astrónomo del observatorio Gemini, y co autor de la investigación. Ubicada alrededor de 400 años luz de distancia, las Pleiades es uno de los cúmulos estelares más cercanos a la Tierra.

Gemini Observatory/Lynette Cook

Figure 1: Artist's rendering of what the environment around HD 23514 might look like as two Earth-sized bodies collide. Artwork by Lynette Cook for Gemini Observatory.

Full-Resolution TIFF | 24.10mb
Med-Resolution JPEG | 498kb

Credit: Inseok Song/Digital Sky Survey, inset: Gemini Observatory/Lynette Cook

Figure 2: Color composite image of the Pleiades star cluster and surrounding region produced by Inseok Song of the Spitzer Science Center. The image was created by combining B, R and I band images from individual second generation Digital Sky Survey images into blue, green and red image layers, respectively. The location of HD 23514 is shown by the yellow arrow. Inset artwork (lower right) is same as in Figure 1.

Full-Resolution without arrow/text/insert TIFF | 55.52mb
Med-Resolution without arrow/text/insert JPEG | 6.02mb
Full-Resolution as shown TIFF | 55.55mb
Med-Resolution as shown JPEG | 5.33mb

Figure 3: Spectral energy distribution of the dusty 100 million year old solar-type star HD 23514 in the Pleiades star cluster. The unusual mid-infrared excess is most noticeable in the thermal infrared region. There is also a strong silicate feature around 9 microns.

Figure 4: MICHELLE mid-infrared spectrum of HD 23514 obtained on the Gemini North telescope. For comparison, the mid-infrared, (dotted-line) spectrum of another dusty star BD +20 307 is also reproduced. Both reveal the presence of warm dust. HD 23514 has the warmer dust, reflected by its more "blue shifted" bump. For young stars and debris disks, the most prominent spectral feature in the N-band is silicate emission.