Scientists investigate change in activity of comet 17P/Holmes

January 11, 2016 by Tomasz Nowakowski report
Time series of selected images of 17P/Holmes taken with an RC filter. All images have the standard orientation, that is, north is up and east to the left. At the bottom right in each image, solid vectors denote the orientation of the negative velocity of the comet, and dashed vectors show radial vectors outward from the solar direction. Credit: Yuna Grace Kwon et al., 2014.

(—Periodic comet 17P/Holmes is usually a very faint object. However, during its historic outburst in October 2007, when the comet's coma expanded to a diameter greater than that of the sun, it became visible to the naked eye and was temporarily the largest object in our solar system. This event has drawn the attention of astronomers worldwide trying to investigate the comet's uncertain and changing nature. 17P/Holmes has been intensively monitored during its perihelion passage in 2014 and the results of these observations were detailed in a paper published Dec. 29, 2014 on the arXiv pre-print server.

17P/Holmes is a Jupiter-family comet discovered by Edwin Holmes in 1892. Although the comet's massive outburst event in 2007 was well-observed, very little is known about the long-term evolution in the activity of 17P/Holmes. The perihelion passage seven years later was expected to be a great occasion to study the comet in detail. Unfortunately, in March 2014, it passed its perihelion so far that there have been no published reports about the physical state of the comet during this passage.

Now, a research team led by Yuna Grace Kwon of the Seoul National University in South Korea, reports its photometric monitoring observations of the comet over a period of nearly two years from May 2013 to March 2015, including the 2014 perihelion passage. To monitor the comet's activity, six ground-based telescopes were employed at five observatories: the Ishigakijima Astronomical Observatory (IAO), the Okayama Astrophysical Observatory (OAO), the Nishi-Harima Astronomical Observatory (NHAO), the Siding Spring Observatory (SSO), and the Bohyunsan Optical Astronomy Observatory (BOAO).

Thanks to these observations, the researchers were able to detect the comet's circumnuclear coma and its feeble dust tail. They found out that the dust mass loss rate of 17P/Holmes' inner dust coma has been declining with increasing heliocentric distance. They also noticed that the dust production rate became equivalent to the level before the 2007 outburst.

"The dust production rates around the 2014 perihelion passage were about five orders of magnitudes lower than the maximum value during the 2007 outburst, while they were comparable to that of the pre-outburst data," the researchers wrote in the paper.

According to research team, this similarity suggests that the comet's activity was restored to its former state, although it has shown lingering activity for years when it was around its aphelion.

They noted that the mass loss process yields valuable information for monitoring the activity of the 17P/Holmes.

Besides determining dust production rates, the scientists also calculated the diurnal skin depth and growth timescale of the comet's dust mantle, inferring that it is now nearly five to seven centimeters thick and has been developing apace over the last seven years.

"17P/Holmes spends more than half a revolution period beyond the heliocentric distance of three astronomical units. Taking into account the persistent activities of the around its aphelion it should have had favorable conditions in developing the dust mantle with continuously outward sublimating volatiles over quite large portions of its orbit," the paper reads.

The researchers assume that the activity of 17P/Holmes is highly controlled by the formation and evolution of dust mantle. By monitoring the evolution of the fractional active area over the cometary surface, they concluded that the overall activity of 17P/Holmes has been significantly restrained during the 2014–2015 outbound orbits. The new results might also indicate that inactive or dormant comets are aided by the development of their dust mantles acquired over their evolutionary histories in the inner part of our solar system.

Explore further: Mini-Comets within a comet lit up 17P/Holmes during megaoutburst

More information: Monitoring Observations of the Jupiter-Family Comet 17P/Holmes during 2014 Perihelion Passage, arXiv:1512.08797 [astro-ph.EP]

We performed a monitoring observation of a Jupiter-Family comet, 17P/Holmes, during its 2014 perihelion passage to investigate its secular change in activity. The comet has drawn the attention of astronomers since its historic outburst in 2007, and this occasion was its first perihelion passage since then. We analyzed the obtained data using aperture photometry package and derived the Afrho parameter, a proxy for the dust production rate. We found that Afrho showed asymmetric properties with respect to the perihelion passage: it increased moderately from 100 cm at the heliocentric distance r_h=2.6-3.1 AU to a maximal value of 185 cm at r_h = 2.2 AU (near the perihelion) during the inbound orbit, while dropping rapidly to 35 cm at r_h = 3.2 AU during the outbound orbit. We applied a model for characterizing dust production rates as a function of r_h and found that the fractional active area of the cometary nucleus had dropped from 20%-40% in 2008-2011 (around the aphelion) to 0.1%-0.3% in 2014-2015 (around the perihelion). This result suggests that a dust mantle would have developed rapidly in only one orbital revolution around the sun. Although a minor eruption was observed on UT 2015 January 26 at r_h = 3.0 AU, the areas excavated by the 2007 outburst would be covered with a layer of dust (<~ 10 cm depth) which would be enough to insulate the subsurface ice and to keep the nucleus in a state of low activity.

Related Stories

Image: Rosetta comet observed with Very Large Telescope

September 8, 2014

( —Since early August 2014, Rosetta has been enjoying a close-up view of comet 67P/Churyumov–Gerasimenko. Meanwhile, astronomers on Earth have been busy following the comet with ground-based telescopes. As Rosetta ...

Image: NASA's NEOWISE captures Comet C/2014 Q2 (Lovejoy)

January 19, 2015

Comet C/2014 Q2 (Lovejoy) is one of more than 32 comets imaged by NASA's NEOWISE mission from December 2013 to December 2014. This image of comet Lovejoy combines a series of observations made in November 2013, when comet ...

Image: Increasingly active Comet 67P

July 1, 2015

On 13 August 2015, Comet 67P/Churyumov–Gerasimenko will reach its closest point to the Sun along its 6.5-year long orbit. It will be around 185 million km from the Sun at 'perihelion', between the orbits of Earth and Mars.

Recommended for you

Pulsar discovered in an ultraluminous X-ray source

September 26, 2016

(—A team of European astronomers has discovered a new pulsar in a variable ultraluminous X-ray source (ULX) known as NGC 7793 P13. The newly found object is the third ultraluminous X-ray pulsar detected so far, ...

Mercury found to be tectonically active

September 26, 2016

Images acquired by NASA's MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft show geologic features that indicate Mercury is likely still contracting today, joining Earth as a tectonically ...

New low-mass objects could help refine planetary evolution

September 26, 2016

When a star is young, it is often still surrounded by a primordial rotating disk of gas and dust, from which planets can form. Astronomers like to find such disks because they might be able to catch the star partway through ...

Rosetta: The end of a space odyssey

September 26, 2016

Europe's trailblazing deep-space comet exploration for clues to the origins of the Solar System ends Friday with the Rosetta orbiter joining robot lab Philae on the iceball's dusty surface for eternity.

Sounding rocket solves one cosmic mystery, reveals another

September 26, 2016

In the last century, humans realized that space is filled with types of light we can't see – from infrared signals released by hot stars and galaxies, to the cosmic microwave background that comes from every corner of the ...

1 comment

Adjust slider to filter visible comments by rank

Display comments: newest first

3 / 5 (2) Jan 12, 2016
I love that comet. Those were some great times watching it for months, particularly when it crossed the Milky Way around Perseus. I've taken over 10,000 astrophotos and I'd rate some of those as my all time favorites.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.