Comet ISON Comet of the Century Or Another Kohoutek?

Matthew Knight 4/26/13 X Probably won’t be the comet of the century, but it should be very interesting anyway Matthew Knight 4/26/13

What Are Comets? Dirty Snowballs?? Icy Dirtballs?? “ Model ” made in class using dry ice (frozen CO 2 ), water, dirt, Windex (ammonia), chocolate syrup (CHx). White areas are frost that forms because of the cold dry- ice freezing out the humidity in the air.

Matthew Knight 4/26/13 Why study comets? Comets are remnants of the formation of the solar system Stored in the outer solar system –Largely unchanged since formation Contain ice, dust, and organics –Building blocks of the planets –Ingredients for life Hazardous to life on Earth Images from Google image search

Comets

Comets are Highly Diverse And Very Unpredictable!

Some Great Comets of the Past

C/2012 S1 (ISON) Historical discovered on September 21, 2012 Artyom Novichonok and Vitali Nevski International Scientific Optical Network (“ISON”)

Why ISON? Likely its first passage through the inner solar system –Discovered at a large enough distance to study in more detail than most “dynamically new” comets On a “sungrazing” orbit that will bring it very close to the Sun –Discovered much earlier than any previous sungrazer –Perihelion Nov 28, 2013 at a distance of 2.7 solar radii Projected to get very bright near perihelion Favorable viewing geometry for observing from Earth post-perihelion Dec 25, 2013 Image credit: NASA GSFC Scientific Visualization Studio Matthew Knight 4/26/13

Different temperature and stress regime than typical comets –Reveals least volatile components of solar system –Fragmentation is common High phase angles that can’t be seen elsewhere in the solar system –Yields unique information about dust properties “Solar probes” that can inform studies of the solar wind, magnetic field, corona, etc. Why are sungrazers special? C/2011 W3 Lovejoy Image credit: helioviewer.org Matthew Knight 4/26/13

Sungrazing comet basics Perihelion distance less than a few solar radii –1 solar radius = AU ≈ 700,000 km A handful of historically bright comets in history –Most are dynamically related to each other as members of the Kreutz group Coronagraphic observations over last ~30 years have revealed a steady stream of small fragments –Most do not survive perihelion –Typical observations span hours to days –Includes several new groups of “sunskirting” comets Top: Ikeya-Seki in 1965, Bottom: Great Comet of 1680 from Google Image Search Matthew Knight 4/26/13

Orbit e a AU q AU i deg node deg peri deg M deg tp (2013-Nov ) JED period na D yr Perihelion is 28 Nov ,100,000 miles from the sun 6,700,000 miles from Mars on 01 October ,000,000 miles from Earth on 26 December 2013

Orbit Has some details about the path of ISON, but hidden on the page is a link to omet_ISONs_Orbit.pdfhttp://svs.gsfc.nasa.gov/vis/a010000/a011200/a011222/Paper_Model_of_C omet_ISONs_Orbit.pdf

Observing Comet ISON

These charts are from but there are other sites like Stuart Atkinson’s

What can we expect to see? Potential to be visible during daytime/twilight Visible from northern hemisphere Lovejoy is a good analog although it was probably ~2-5x smaller Matthew Knight 4/26/13

Missions Asked to Observe Comet ISON (to date) Deep Impact – no joy during planned summer observing window Stereo SDO Juno LRO ISS MSL/Curiosity MRO BRRISON MESSENGER SOHO Hubble Chandra SWIFT Rosetta Ground-based Observatories: Keck, NASA/IRTF, Kitt Peak, Sac Peak, Big Bear Amateur astronomy clubs Comet Lovejoy as seen from the International Space Station in late

Comet ISON Potential Observations Inbound: Mars - Comet closest approach ~0.08 AU (Oct 4,2013) –Late Sept: Earth ” telescopes will be able to observe –Late Oct-Nov: Earth – Naked Eye Brightness Perihelion: Sun – Comet closest approach Nov 28, 2013, ~0.008 AU! Outbound: Earth - Comet closest approach ~0.44 AU (Jan 2, 2014) Comet-Mars Earth-Comet MVEMMVEM MVEMMVEM Inbound Outbound

Other NASA assets BRRISON balloon experiment (October) –120,000 ft altitude allows some UV/IR not possible from ground Deep Impact Flyby spacecraft (ongoing) –Unique ability to measure CO/CO 2 /H 2 O –Continuous monitoring over many days possible - potentially yields lightcurve and rotation period –Observes ISON when not possible from ground Various Mars missions (October ~2) –Close approach (0.07 AU) so high spatial resolution MESSENGER at Mercury (November ~19) –More favorable viewing geometry than Earth at the same time Matthew Knight 4/26/13 

Space telescopes Hubble –Already observed in April, additional observations planned in May, October, post-perihelion –Key science: nucleus size estimate, composition, fragment search Spitzer –Solar elongation constraints: May-June 2013, Jan-Feb 2014 –Key science: dust properties, constrain nucleus size Swift –Already observed in Jan/Feb, monitoring throughout apparition –Key science: production rates Herschel –Already observed in March –Key science: composition, nucleus size X-ray telescopes (Chandra, XMM, Suzaku, etc.) –Minimal pointing constraints –Key science: Solar wind diagnostics, possible comet/corona interaction Matthew Knight 4/26/13

Will ISON live up to expectations? There is always a chance it will underperform (e.g. Kohoutek in 1973) or disintegrate completely (e.g. Elenin in 2011) Even if it massively underperforms it should still be very impressive in SOHO/STEREO images Recovered by amateurs ~12 Aug… still difficult to observe since it is in the morning twilight… not quite as bright as one would hope…? Kohoutek 1/12/74 at Palomar Matthew Knight 4/26/13

Links waitingforison.wordpress.com/ –isonatlas.wordpress.com/isonatlas.wordpress.com/ solarsystem.nasa.gov/smallworlds/cometison.cfm met/Ison.aspxwww.astronomy.com/Events/Year%20Of%20The%20Co met/Ison.aspx gblog/Comet-ISON-Updates htmlwww.skyandtelescope.com/community/skyblog/observin gblog/Comet-ISON-Updates html svs.gsfc.nasa.gov/vis/a010000/a011200/a011222/