The Disintegration of Comet ISON

Some had hoped comet ISON would be the comet of the century, lighting Earth’s skies during the latter months of 2013. Instead, it was barely visible for ground-based observers, but the Solar and Heliospheric Observatory (SOHO) had a ring-side seat to watch its disintegration.

This image is a montage spanning three days from 28–30 November 2013. The comet enters the image at the lower right, passes round the Sun and exits the frame towards the upper right. The bright star to the lower left is the red supergiant star Antares.

Astronomers had been tracking the comet for more than a year as it edged closer to the Sun, and by late November it had passed into the field of view of SOHO’s LASCO C3 camera. It was to skim the Sun, just 1,165,000 km above the fiery surface.

This is approximately 50 times closer to the Sun than innermost planet Mercury, and the comet was officially termed a ‘sungrazer’. If it survived the encounter it was expected to become extremely bright and be a well-placed object, visible to the naked eye in Earth’s night sky.

Calculations based on its orbit show that ISON began its journey towards the Sun about 3 million years ago, dislodged from its distant orbit by a passing star. Now, its fate would be sealed within days.

On 27 November, the comet brightened dramatically by a factor of about ten. Yet just before it reached closest approach to the Sun, it began to fade. This was a strong indicator that the heart of the comet, the icy nucleus, had broken up. Many expected it would disperse completely but, at first, it looked as if they were wrong.

Comet ISON appeared to survive the close approach, emerging on the other side of the Sun. Some still hoped for a bright display in the night skies. But they were to be disappointed. Quickly, the comet began to disappear. A recent analysis of SOHO data showed that the nucleus had indeed disintegrated just before closest approach to the Sun. Nothing appreciable was left of it, just a lot of dust and vapor.

The disintegration of comet ISON provided scientists with an exceptional chance to see a comet inside and out. Another rare opportunity is being provided by comet 67P/Churyumov-Gerasimenko. ESA’s Rosetta spacecraft caught up with this comet early in August 2014 and deployed the lander Philae to the surface in November. The orbiter will accompany comet 67P/C-G along its orbit and through its closest approach to the Sun, which takes it between the orbits of Mars and Earth. While this comet is unlikely to suffer the same fate as comet ISON, it will provide an unsurpassed insight into the nature of comets.

Image credit: ESA/NASA

Comet C2012 S1 ISON

Analysis of data from the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) instrument on the ESA/NASA Solar and Heliospheric Observatory (SOHO) spacecraft has revealed that comet 2012/S1 (ISON) stopped producing dust and gas shortly before it raced past the Sun and disintegrated.

Shown here is the SUMER image from 18:01 GMT on 28 November 2013. The white line indicates the bisector of the tail. Red dots mark the predicted position of the comet's nucleus at one minute intervals for the previous 10 minutes. The red cross is the position at the time of this image. The tail is offset from the comet trajectory, curved, and pointed with a length of at least 240,000 kilometers. The observations are consistent with models indicating that the comet stopped producing dust and gas hours earlier.

The white arrow indicates the direction of the Sun.

Image credit: MPS

Note: For more information, see Comet ISON's Dramatic Final Hours.

Comet Encke

MESSENGER image of comet 2P/Encke during its closest approach to Mercury. At that time, Encke was approximately 2.3 million miles (3.7 million kilometers) from MESSENGER and 32.7 million miles (52.6 million kilometers) from the Sun. The image is 7° by 4.7° in size and has been slightly smoothed to enhance the faint tail of the comet. The tail was oriented nearly side on to MESSENGER in this image and is seen to stretch several degrees from the comet's bright coma in the direction away from the Sun.

MESSENGER's cameras have been acquiring targeted observations (watch an animation here) of Encke since October 28 and ISON since October 26, although the first faint detections didn't come until early November. During the closest approach of each comet to Mercury, the Mercury Atmospheric and Surface Composition Spectrometer (MASCS) and X-Ray Spectrometer (XRS) instruments also targeted the comets. Observations of ISON conclude on November 26, when the comet passes too close to the Sun, but MESSENGER will continue to monitor Encke with both the imagers and spectrometers through early December. Read this mission news story for more details.

Date acquired: 22:56 UTC on November 17, 2013
Instrument: Wide Angle Camera (WAC) of the Mercury Dual Imaging System (MDIS)

Photo credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington/Southwest Research Institute

Note: For more information, see PIA17693: MESSENGER's First Images of Comets Encke and ISON and Two Comets to Fly By Mercury.

Comet Ison

The remains of comet ISON at 07:18 UT on 29 November, as seen in SOHO's LASCO C3 field of view after its close encounter with the Sun the previous evening.

Photo credit: SOHO (ESA & NASA)

Note: This is the most recent image showing up in the Minister's feed of the comet after its perihelion with the Sun. The Minister will continue to update with more photos and links as they become available. In the meantime, the following links may be of interest:
* What Happened to Comet ISON?
* When Ice Meets Fire
* ISON at 13:37, 29 November
* ISON at 00:18, 29 November
* ISON at 21:24, 28 November
* ISON at 15:42, 28 November
* ISON at 15:37, 28 November
* Comet ISON approaches the Sun (12:42, 27 November)
* PIA17740: A Tale of Two Comets: ISON (An image of the comet taken by MESSENGER, which is in orbit around Mercury.)
* Three Questions About Comet ISON
* Comet ISON vs. the Solar Storm
* Two Comets to Fly By Mercury
* Comet ISON: What's Next?
* Comet ISON to fly by Mars (23 August 2013)


Video credit: NASA, ESA, SOHO (HT: APOD)

Comet C2012 S1 ISON as of 10 April 2013

This NASA Hubble Space Telescope image of Comet (C/2012 S1) ISON was photographed on April 10, when the comet was slightly closer than Jupiter’s orbit at a distance of 386 million miles from the Sun (394 million miles from Earth).

Even at that great distance the comet is already active as sunlight warms the surface and causes frozen volatiles to sublimate. A detailed analysis of the dust coma surrounding the solid, icy nucleus reveals a strong, jet blasting dust particles off the sunward-facing side of the comet’s nucleus.

Preliminary measurements from the Hubble images suggest that the nucleus of ISON is no larger than three or four miles across. This is remarkably small considering the high level of activity observed in the comet so far, said researchers. Astronomers are using these images to measure the activity level of this comet and constrain the size of the nucleus, in order to predict the comet’s activity when it skims 700,000 miles above the sun's roiling surface on November 28.

The comet’s dusty coma, or head of the comet, is approximately 3,100 miles across, or 1.2 times the width of Australia. A dust tail extends more than 57,000 miles, far beyond Hubble’s field of view.

More careful analysis is currently underway to improve these measurements and to predict the possible outcome of the sungrazing perihelion passage of this comet.

This image was taken in visible light. The blue false color was added to bring out details in the comet structure.

ISON stands for International Scientific Optical Network, a group of observatories in ten countries who have organized to detect, monitor, and track objects in space. ISON is managed by the Keldysh Institute of Applied Mathematics, part of the Russian Academy of Sciences.

Image credit: NASA, ESA, J.-Y. Li (Planetary Science Institute), and the Hubble Comet ISON Imaging Science Team

Note: For more information, see Hubble Sees Comet ISON and Comet ISON Meteor Shower.

Comet C/2012 S1 (ISON)

This series of images of comet C/2012 S1 (ISON) was taken by the Medium-Resolution Imager of NASA's Deep Impact spacecraft over a 36-hour period on January 17 and 18, 2013. At the time, the spacecraft was 493 million miles (793 million kilometers) from the comet.

Video credit: NASA/JPL-Caltech/UMD; text credit: NASA/JPL-Caltech

Note: For more information, see NASA's Deep Impact Spacecraft Eyes Comet ISON.