http://www.esa.int/esl/ESA_in_your_country/Spain/El_derrumbe_de_un_acantilado_desvela_el_interior_del_cometa
El derrumbe de un acantilado desvela el interior del cometa
Collapsing Cliff
21 marzo 2017
Los científicos de Rosetta acaban de establecer el primer vínculo convincente entre una emisión de polvo y gas y el derrumbe de un prominente acantilado, que dejó expuesto el inmaculado interior de 67P/Churyumov–Gerasimenko.
Durante los dos años que Rosetta pasó observando el cometa, se detectaron con cierta frecuencia emisiones breves y repentinas. Aunque se ha debatido mucho sobre sus desencadenantes, estas emisiones parecen deberse al derrumbamiento de superficies débiles y erosionadas, que dejaron expuestos materiales volátiles que se calentarían súbitamente.
En un estudio publicado hoy en Nature Astronomy, los científicos establecen el primer vínculo definitivo entre una emisión y el derrumbe de la pared de un acantilado, ayudándonos a comprender las fuerzas detrás de estos fenómenos.
Comet cliff collapse: before and after
Las primeras imágenes de cerca del cometa, capturadas en septiembre de 2014, mostraban una fractura de 70 m de largo por 1 m de ancho en un prominente acantilado al que después llamarían Asuán, en la región de Seth, en el lóbulo mayor.
A lo largo del año siguiente, a medida que la órbita del cometa lo iba acercando al Sol, fue aumentado la velocidad a la que los hielos subterráneos se evaporaban y expulsaban polvo al espacio. Diversas emisiones de polvo y gas, breves y esporádicas, alteraron la actividad habitual del cometa.
La cámara de navegación de Rosetta pudo capturar una de estas explosiones el 10 de julio de 2015, originada en la superficie del cometa por la región de Seth.
Evolution of a comet cliff collapse
Cinco días más tarde, al observar el acantilado de Asuán, de 134 m de altura, se detectó un borde brillante y escarpado donde previamente se había identificado la fractura, además de numerosas rocas nuevas, de un metro de diámetro, a sus pies.
“La última vez que vimos la fractura intacta fue el 4 de julio y, al no haberse registrado otras emisiones en los diez días siguientes, tenemos la prueba más evidente de que la emisión observada está directamente relacionada con el derrumbe del acantilado”, explica Maurizio Pajola, director del estudio.
Este fenómeno también supuso una oportunidad única para estudiar cómo el hielo de agua pura enterrado a decenas de metros de la superficie del cometa fue cambiando a medida que el material expuesto se evaporó a lo largo de los siguientes meses.
Comet cliff collapse in 3D
De hecho, se calcula que la pared que quedó expuesta tras el derrumbe es al menos seis veces más brillante que la media de la superficie del núcleo del cometa. El día 26 de diciembre de 2015, el brillo se había reducido a la mitad, lo que indica que la mayoría del hielo de agua ya se había evaporado.
Y para el 6 de agosto de 2016, la mayor parte de esa pared del acantilado presentaba el mismo nivel de brillo que la media de la superficie y solo quedaba un bloque, de gran tamaño, más brillante.
Continuar leyendo artículo completo en inglés
Contacto:
Markus Bauer
ESA Science and Robotic Exploration Communication Officer
Tel: +31 71 565 6799
Mob: +31 61 594 3 954
Email: markus.bauer@esa.int
Maurizio Pajola
NASA Ames Research Center, USA
Email: maurizio.pajola@nasa.gov
Matt Taylor
ESA Rosetta project scientist
Email: matt.taylor@esa.int
Markus Bauer
ESA Science and Robotic Exploration Communication Officer
Tel: +31 71 565 6799
Mob: +31 61 594 3 954
Email: markus.bauer@esa.int
Maurizio Pajola
NASA Ames Research Center, USA
Email: maurizio.pajola@nasa.gov
Matt Taylor
ESA Rosetta project scientist
Email: matt.taylor@esa.int
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Collapsing Cliff
21 March 2017
Rosetta scientists have made the first compelling link between an outburst of dust and gas and the collapse of a prominent cliff, which also exposed the pristine, icy interior of the comet.
Sudden and short-lived outbursts were observed frequently during Rosetta’s two-year mission at Comet 67P/Churyumov–Gerasimenko. Although their exact trigger has been much debated, the outbursts seem to point back to the collapse of weak, eroded surfaces, with the sudden exposure and heating of volatile material likely playing a role.
In a study published today in Nature Astronomy, scientists make the first definitive link between an outburst and a crumbling cliff face, which is helping us to understand the driving forces behind such events.
Comet cliff collapse: before and after
The first close images of the comet taken in September 2014 revealed a 70 m-long, 1 m-wide fracture on the prominent cliff-edge subsequently named Aswan, in the Seth region of the comet, on its large lobe.
Over the course of the following year as the comet drew ever closer to the Sun along its orbit, the rate at which its buried ices turned to vapour and dragged dust out into space increased along the way. Sporadic and brief, high-speed releases of dust and gas punctuated this background activity with outbursts.
One such outburst was captured by Rosetta’s navigation camera on 10 July 2015, which could be traced back to a portion of the comet’s surface that encompassed the Seth region.
Evolution of a comet cliff collapse
The next time the Aswan cliff was observed, five days later, a bright and sharp edge was spotted where the previously identified fracture had been, along with many new metre-sized boulders at the foot of the 134 m-high cliff.
“The last time we saw the fracture intact was on 4 July, and in the absence of any other outburst events recorded in the following ten-day period, this is the most compelling evidence that we have that the observed outburst was directly linked to the collapse of the cliff,” says Maurizio Pajola, the study leader.
The event also provided a unique opportunity to study how the pristine water-ice otherwise buried tens of metres inside the comet evolved as the exposed material turned to vapour over the following months.
Comet cliff collapse in 3D
Indeed, after the event, the exposed cliff face was calculated to be at least six times brighter than the overall average surface of the comet nucleus. By 26 December 2015 the brightness had faded by half, suggesting much of the water-ice had already vapourised by that time.
And by 6 August 2016, most of the new cliff face had faded back to the average, with only one large, brighter block remaining.
Fallen cliff debris
In addition, the team had a clear ‘before and after’ look at how the crumbling material settled at the foot of the cliff. By counting the number of new boulders seen after its collapse, the team estimated that 99% of the fallen debris was distributed at the bottom of the cliff, while 1% was lost to space.
This corresponds to around 10,000 tonnes of removed cliff material, with at least 100 tonnes that did not make it to the ground, consistent with estimates made for the volume of dust in the observed plume.
Furthermore, the size range of the new debris, between 3 m and 10 m, is consistent with the distributions observed at the foot of several other cliffs identified on the comet.
“We see a similar trend at the foot of other cliffs that we have not been so fortunate to have before and after images, so this is an important validation of cliff collapse as a producer of these debris fields,” says Maurizio.
But what actually led to the cliff suddenly collapsing at this particular moment?
Cliff collapse and comet activity
An earlier study suggested that both rapid daily changes in heating or longer-term seasonal changes can create thermal stresses that lead to fracturing and subsequent exposure of volatile materials, triggering a rapid outburst that can cause the weakened cliff to collapse.
Even though the Aswan cliff region had been experiencing large temperature changes in the months before the collapse, interestingly, the collapse occurred at local night, ruling out a sudden extreme temperature change as the immediate trigger.
Instead, both daily and seasonal temperature variations may have propagated fractures deeper into the subsurface than previously considered, predisposing it to the subsequent collapse.
“If the fractures permeated volatile-rich layers, heat could have been transferred to these deeper layers, causing a loss of deeper ice,” explains Maurizio. “The gas released by the vapourising material could further widen the fractures, leading to a cumulative effect that eventually led to the cliff collapse.
“Thanks to this particular event at Aswan, we think that the cumulative effect led by strong thermal gradients could be one of the most important weakening factors of the cliff structure.”
“Rosetta’s images already suggested that cliff collapses are important in shaping cometary surfaces, but this particular event has provided the missing ‘before–after’ link between such a collapse, the debris seen at the foot of the cliff, and the associated dust plume, supporting a general mechanism where comet outbursts can indeed be generated by collapsing material,” says Matt Taylor, ESA’s Rosetta project scientist.
Notes for Editors a vuelo
“The pristine interior of comet 67P revealed by the combined Aswan outburst and cliff collapse,” by M. Pajola et al, is published in Nature Astronomy.
Additional details about the Aswan region are available in “Aswan site on comet 67P/Churyumov-Gerasimenko: Morphology, boulder evolution, and spectrophotometry” by M. Pajola et al, published in Astronomy & Astrophysics, August 2016.
Additional details about the size-frequency distribution of boulders on the comet are available in “Size-frequency distribution of boulders ≥7 m on comet 67P/Churyumov-Gerasimenko,” by M. Pajola et al, published in Astronomy & Astrophysics, November 2015.
For further information, please contact:
Markus Bauer
ESA Science and Robotic Exploration Communication Officer
Tel: +31 71 565 6799
Mob: +31 61 594 3 954
Email: markus.bauer@esa.int
ESA Science and Robotic Exploration Communication Officer
Tel: +31 71 565 6799
Mob: +31 61 594 3 954
Email: markus.bauer@esa.int
Maurizio Pajola
NASA Ames Research Center, USA
Email: maurizio.pajola@nasa.gov
NASA Ames Research Center, USA
Email: maurizio.pajola@nasa.gov
Matt Taylor
ESA Rosetta project scientist
Email: matt.taylor@esa.int
ESA Rosetta project scientist
Email: matt.taylor@esa.int
ESA
Guillermo Gonzalo Sánchez Achutegui
ayabaca@gmail.com
ayabaca@hotmail.com
ayabaca@yahoo.com
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