Spiritual Blogs

Early indications from students who have been processing data from NASA’s Swift satellite, estimate the comet to be around 4.82 km (3 miles) in diameter. They have reached this conclusion by observing the amount of ice and dust emitted from ISON’s surface as it falls through space toward the Sun.

Armada of ground based amateur astronomers and an unprecedented space fleet is tracking and waiting for ISON as it moves through our Solar System to meet the Sun on November 28, 2013. It is however, still to early to make final forecast as to what will happen to it. If ISON survives the Sun, it will deserve to be called "the comet of the century" because in that case it might emerge so bright it will become visible on Earth even in daylight. It is still a big IF, so November 28 is the day when we will know exactly. Check ISON scenarios below and definitely take a look at Alan MacRobert's video: "Comet ISON: The Straight Dope".

Comet ISON flying toward the Sun, ​383 million kilometers away from Earth. ​Dennis Whitmer obtained 40 useful images of ISON on the morning of September 15, 2013. Then Bruce Gary used some of those images to create this GIF animation. Image credit: Dennis Whitmer/Bruce Gary

Comet ISON’s path through the constellations of Gemini, Cancer and Leo up until the end of October when ISON will be well on its way to perihelion due to occur on November 28, 2013. Image credit: NASA’s Goddard Space Flight Center

ISON scenarios

There are three possible scenarios for Comet ISON, scientists say. First one is fizzle, where ISON evaporates under intense tidal forces and solar radiation. Nobody hopes for this, but hey, it's a cruel world out there. The second scenario is break-up. In this scenario, ISON breaks into smaller chunks. This, by the way, might happen any time. The third scenario is what everybody hopes will happen - sizzle - ISON survives the Sun and emerges so bright it becomes visible on Earth in daylight.

Crossing the frost line

At the time of ISON's closest approach to Mars, on October 1, it will be 0.07 AU (10.5 million km) away from it and this flyby comes at a key time in ISON's journey as it will just cross the "frost line", the place outside the orbit of Mars where solar heating is enough to start vaporizing frozen water.

When it crosses the frost line, "the whole comet could erupt in geysers of gas," said Carey Lisse of the Johns Hopkins University Applied Physics Lab.

The amount of outgassing at Mars will give researchers clues to the size of ISON’s nucleus, which is hidden from view deep within the comet’s dusty atmosphere.

If ISON's nucleus is much bigger than 0.5 km, it will probably survive its brush with the Sun and turn into one of the most spectacular comets in many years.

How bright will it be?

In all honesty, none of our astronomers can be sure and say exactly how bright will ISON get simply because all comets, especially ones entering the inner solar system for the first time, like ISON, behave unpredictably and it is therefore impossible to reliably predict what ISON will do.

Comet ISON's approach - 3D model

The team at the Solar System Scope published this amazing 3D model of ISON's approach. This will give you a unique perspective of how ISON's approach looks like. Use your mouse to change viewpoint, zoom, change date, etc.

Comet ISON: The Straight Dope

The most recent observations indicate Comet ISON is on track to hopefully (but not definitely) reach naked-eye visibility in December 2013′s pre-dawn sky. S&T Senior Editor Alan MacRobert explains just why it’s so tricky to predict how bright ISON will be, and previews what you’ll need to know to spot it as it approaches the Sun for its close encounter.

Space fleet tracking ISON

Along with ground observations, an unprecedented space fleet is tracking ISON. When ISON passes Mars on October 1, space missions Curiosity, Opportunity, Mars Reconnaissance Orbiter and Mars Express will all capture and send data back to Earth. This will be the first milestone in observing the comet because ISON will just pass the "frost line" and we'll know more about its size and what to expect as it continues toward the Sun. On November 28, STEREO will play its special part because it's uniquely situated to observe the approach and perihelion passage of comet ISON in November 2013. The STEREO instrument teams — in particular the SECCHI team — are busy putting together observing plans to address a wide range of cometary and heliophysics science objectives. Other missions worth mentioning before the list are BRISSON - sub-orbital balloon due to launch on September 30, and Chandra X-ray Observatory which observes ISON's interactions with the solar wind. All of the missions have/had their important role and below is the list along with the links to their websites.

1. Solar Dynamics Observatory: Observing ISON under extreme-ultraviolet light when the comet is closest to the sun.
2. SOHO: Observing ISON as it passes by the Sun in late November.
3. STEREO: Observing ISON as it passes by on its way to Sun in late November.
4. MESSENGER: Observing ISON as it passes by Mercury on November 19th on its way to the Sun.
5. Venus Express: Observing ISON as it passes by Venus.
6. BRRISON: Sub-orbital balloon that will be launched mid September to study ISON from above nearly all of the Earth's atmosphere.
7. FORTIS: Sounding rocket that will be launched in mid-to-late November to obtain ultra-violet spectra from ISON.
8. Hubble Space Telescope: Observed ISON in April-May and will see it again in October and December (if ISON survives).
9. Spitzer Space Telescope: Observed ISON on 13 June. The comet was 310 million miles away from the sun.
10. Chandra X-ray Observatory: Observing ISON's interactions with the solar wind.
11. International Space Station: Astronauts will be able to observe Comet ISON as it passes by the sun in late November.
12. Lunar Reconnaissance Orbiter: Observing ISON as it passes by the moon in late November.
13. Swift: In January and March, Swift observed ISON when it was 460 million miles away from the sun.
14. Curiosity: Observing ISON as it passes by Mars. Closest approach is 1 October.
15. Opportunity: Also observing ISON as it passes by Mars.
16. Mars Reconnaissance Orbiter: Orbital observations of ISON as it passes by Mars in October.
17. Mars Express: Orbital observations of ISON as it passes by Mars in October.
18. Deep Impact: Imaged ISON for the first time on 17 and 18 January 2013 from 493 million miles away.

Multifaceted observations of Comet ISON covering the electromagnetic spectrum

In the Gamma and X-Ray spectrum are Swift, Chandra and SDO.

The ultraviolet spectrum is covered by STEREO, Hubble and FORTIS.

The visible spectrum will be covered by a wide-ranging fleet of spacecraft ranging from MESSENGER at Mercury to Curiosity at Mars and BRRISON, a balloon that will study the comet from Earth's upper atmosphere. BRRISON uniquely captures H₂O & CO₂ in mid IR.

Spitzer will also observe the comet in the infrared spectrum.

Credit: NASA

Conclusion - dissection of a comet

No matter how Comet ISON will behave in the coming days and months we now have a range of powerful satellites and a new generation of ground-based observatories which will all make this comet a rare and special treat for astronomers and scientific community. The comet will be dissected across the electromagnetic spectrum, from radio to X-rays. “There's a lot of potential in studying ISON,” - Karen Meech of the Institute for Astronomy in Hawaii. “We'll have a huge amount of data to learn from.”

Long live ISON - we are waiting for you on the other side of the Sun.

Resources

Though we will be covering ISON's journey here on The Watchers, below is a list of essential websites for your daily dose of ISON news.

• ISON Campaign - http://www.isoncampaign.org/
• Hubble's ISON blog - http://hubblesite.org/hubble_discoveries/comet_ison
• NASA's Comet ISON toolkit - http://solarsystem.nasa.gov/smallworlds/cometison.cfm