Comet C/2012 S1 (ISON): A pristine visitor from the Oort Cloud, sungrazing comet ISON was the subject of the most coordinated observing campaign in history. Over the course of a year, more than a dozen spacecraft and numerous ground-based observers collected what is believed to be the largest single cometary dataset in history.
NASA Begins Search For What Is Left Of Comet ISON
Dr. Carey Lisse
Just prior to its closest approach to the sun on November 28, Comet ISON went through a major heating event, and likely suffered a major disruption. At this time, scientists are not sure how much of the comet survived intact. We may be seeing emission from rubble and debris in the comet's trail, along its orbit, or we may be seeing the resumption of cometary activity from a sizable nucleus-sized chunk of ISON.
Most agree that ISON was destroyed (with greater than 90% probability of this having occurred), leaving behind small (< 10 m radius) pieces of rubble, but perhaps, with maybe 10% probability of occurring, also leaving behind some important fragments 100m radius or larger, big enough to study. If previous sungrazing comets are any guides, there may be a sizeable piece of comet nucleus left. At this point, though, scientists are waiting for a variety of telescopes to make observations before the status of Comet ISON can be confirmed.
What remains of Comet ISON appears to brighten and spread out, then fade. The disappearance of a strong central brightness condensation after perihelion is telling, the comet is clearly fainter and more diffuse going out than going in, but it continues to shine. The spread out light is likely due to dust emitted in the few hours before perihelion going around the sun.
An unprecedented space fleet tracked ISON:
- Solar Dynamics Observatory: Searched for ISON under extreme-ultraviolet light when the comet is closest to the sun.
- SOHO: Observed ISON as it plunged into the solar atmosphere.
- STEREO: Observed ISON as it plunged into the solar atmosphere.
- MESSENGER: Observed ISON as it passed by Mercury.
- Venus Express: Observed ISON as it passed by Venus.
- BRRISON: Payload anomaly, Unable to collect data.
- FORTIS: This sounding rocket obtained ultra-violet spectra from ISON.
- SOFIA: Observed ISON in late-October and obtained images with its FORCAST camera at wavelengths of 11.1, 19.7, and 31.5 microns.
- Hubble Space Telescope: Observed ISON several times.
- Spitzer Space Telescope: Observed ISON on 13 June. The comet was 310 million miles away from the sun.
- Chandra X-ray Observatory: Chandra observed ISON with its X-ray instruments.
- International Space Station: Astronauts observed Comet ISON's approach to the sun.
- Lunar Reconnaissance Orbiter: Lunar Reconnaissance Orbiter was not able to observe ISON.
- Mars Reconnaissance Orbiter imaged comet ISON over three days in late September and early October. The comet's brightness was on the low end of expectations.
- Curiosity: Used its MastCAM to look for ISON, but the comet was too faint to detect.
- Opportunity: Rover also did not detect ISON, consistent with the faintness of the Mars Reconnaissance Orbiter observations.
- Mars Express: Used its camera to search for ISON, but it was too faint to detect.
- Swift: Swift observed ISON when it was 460 million miles away from the sun.
- Deep Impact: Imaged ISON on 17 and 18 January 2013 from 493 million miles.
- Amateur Astronomers: Many amateur astronomers took spectacular images of ISON as it approached the sun.
- Research Telescopes: NASA Infrared Telescope Facility, Keck Observatory and many more observed ISON's solar plunge.
Papers and Presentations