Comet ISON

Comet of the Century

Or Another Kohoutek?

Matthew Knight 4/26/13

XProbably won’t be the comet of the century,

but it should be very interesting anywayMatthew Knight 4/26/13

What Are Comets?• Dirty Snowballs??• Icy Dirtballs??

“Model” made in class using dry ice (frozen CO2), 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”)

• http://www.isoncampaign.org/History

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 = 0.0046524 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 1.000003965769344  

a -3151.448801895306 AU

q .01249791904782889 AU

i 61.89330313591056 deg

node 295.7315226419997 deg

peri 345.5130824347451 deg

M 359.9982853205539 deg

tp2456625.282733283460

(2013-Nov-28.78273328)JED

periodnana

Dyr

•Perihelion is 28 Nov 2013

•1,100,000 miles from the sun

•6,700,000 miles from Mars on 01 October 2013

•39,000,000 miles from Earth on 26 December 2013

Orbit• http://svs.gsfc.nasa.gov/vis/a010000/a011200/a011222/index.html

• Has some details about the path of ISON, but hidden on the page is a link to

• http://svs.gsfc.nasa.gov/vis/a010000/a011200/a011222/Paper_Model_of_Comet_ISONs_Orbit.pdf

Observing Comet ISON

Observing Comet ISON

These charts are fromhttp://www.mattastro.com/ison/charts.html,

but there are other sites like Stuart Atkinson’shttp://isonatlas.wordpress.com/

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 2011.

17

Comet ISON Potential Observations

• Inbound: Mars - Comet closest approach ~0.08 AU (Oct 4,2013)– Late Sept: Earth - 8-10” 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 M

VE

M

M

VE

M

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/CO2/H2O– 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 PalomarMatthew Knight 4/26/13

Links• www.isoncampaign.org/ • www.cometisonnews.com/ • waitingforison.wordpress.com/

– isonatlas.wordpress.com/ • solarsystem.nasa.gov/smallworlds/cometison.cfm • www.astronomy.com/Events/Year%20Of%20The

%20Comet/Ison.aspx • www.skyandtelescope.com/community/skyblog/

observingblog/Comet-ISON-Updates-193909261.html• svs.gsfc.nasa.gov/vis/a010000/a011200/a011222/