Monday, November 17, 2014

First observations of the surface of objects from the Oort cloud

CFHT observations of C/2014 S3 and C/1996 O1 (Hale Bopp)
The cometary coma is very strong on the Hale Bopp image while there is a faint hint of a coma on the image of C/2014 S3. 
Images Credits: K. Meech, O. Hainaut, and J. Bauer

Gemini image of C/2013 P2. 
Very little coma is seen despite the proximity to the Sun. 
Credits: K. Meech.

Astronomers from the University of Hawaii in Manoa, ESO, ASIAA in Taiwan, DLR in Berlin and IAA in Bangalore, India announced the discovery of two unusual objects in comet-like orbits but with almost no activity, giving scientists a first look at their surfaces. These results, presented at the annual meeting of the Division of Planetary Sciences of the American Astronomical Society in Tucson, Arizona, are particularly intriguing because the surfaces are different from what astronomers expected, and they give us clues about the movement of material in the early solar system as the planets were assembled.

The two objects, named C/2013 P2 and C/2014 S3, were discovered using Pan-STARRS survey telescope (PS1) on Haleakala, Maui, Hawaii. Both objects have the orbit of a comet coming from the Oort cloud, a spherical halo of comet nuclei in the outer solar system that extends to about 100,000 times the Earth-sun distance, which is known as 1 astronomical unit, or 1 AU. 

Follow-up observations were done on CFHT for both objects and C/2013 P2 was also followed-up with Gemini. Very little coma is seen despite the fact that they are both on a cometary orbit on its closest approach to the Sun. When they get that close to the Sun, comets erupt and produce tails that have been observed across all of humanity's History. In 1996, a team of astronomers at the University of Hawaii used MegaCam on CFHT to observe the center of comet Hale Bopp (C/1995 O1) where it clearly had a massive coma and tail. 

Furthermore, Gemini observations of C/2013 P2 also shows that this object may be an inactive Oort cloud comet. Such objects were hypothesized by Jan Oort back in 1950 when he inferred the existence of what we now call the Oort cloud. Oort suggested that these bodies might have a layer of "volatile frosting" left over from 4.5 billion years of space radiation that disappears after their first pass through the inner solar system. The activity seen in C/2013 P2 is consistent with ice sublimation models but at a level that is one thousand to a million times less than we typically see for comets coming from the Oort cloud. The CFHT data were critical for these models since they need brightness to be sampled over time. 

On the other hand, CFHT images of C/2014 S3 portrais it as a bluer object whose composition is similar to inner solar system asteroid material. This would make C/2014 S3 a unique asteroid that orbits the Sun like a comet. This discovery may help shed some light on some mysteries related to the formation of the solar system. There are several models that try to explain how the planets grew in the early solar system, and some of these predict that material formed close to the sun could have been thrown outward into the outer Solar System and Oort cloud, where it remains today. Bodies like C/2014 S3 could be evidence of this.

Additional information:  Official press release


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