messenger - Comet ISON Observing Campaign

A NASA Discovery Mission!

MESSENGER Observa/ons of C/2012 S1 (ISON)

Ronald J. Vervack Jr. The Johns Hopkins University/Applied Physics Laboratory

and The MESSENGER Team

Comet ISON Observer’s Workshop 1 August 2013

Observing Circumstances for C/2012 S1 (ISON)

Orbit diagram from JPL Horizons Small-‐Body Browser

Closest approach is on UT November 19, 2013 Mercury-‐ISON distance is 0.242 AU Sun-‐ISON distance is 0.474 AU

Observing Circumstances for C/2012 S1 (ISON)


Closest approach is on UT November 19, 2013 Mercury-‐ISON distance is 0.242 AU Sun-‐ISON distance is 0.474 AU

Nicely complements View from Earth

MESSENGER Instruments

MESSENGER Instruments

What can we do and when can we do it?

10/19 10/25 10/31 11/06 11/12 11/18 11/24 11/30 12/06 12/12 12/18Date (UT 2013)

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MESSENGER-ISONSun-ISONSun-Mercury

ClosestApproach ISON

Perihelion

NotVisible

Nucleus VisibleWith MASCS

NotVisible

What can we do and when can we do it?

11/12 11/15 11/18 11/21 11/24 11/27Date (UT 2013)

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Distance(AU)

NotVisible

NotVisible

MESSENGER-ISON

Mercury Dual Imaging System (MDIS) •  Wide-‐angle camera (10.5° × 10.5° FOV)

–  ~6500 km/pixel at closest approach to ISON –  Overall emission using clear filter at 700 nm

(600 nm bandwidth) –  Possible C2 band emission using filter at

559.2 nm (4.6 nm bandwidth)

•  Narrow-‐angle camera (1.5° × 1.5° FOV) –  ~900 km/pixel at closest approach to ISON –  One “filter” (750 nm center, 100 nm bandwidth)

•  Pivot allows imaging over large period of eme –  Observaeon figures only show emes for imaging of the nucleus –  Tail may be observed for longer periods of eme

Observa/ons of C/2012 S1 (ISON)

Mercury Atmospheric and Surface Composieon Spectrometer (MASCS) •  Small Cassegrain telescope with an aperture

that simultaneously feeds two channels •  Ultraviolet and Visible Spectrometer (UVVS)

–  Scanning monochromator –  Point spectrometer with two slit sizes

 (0.04° × 1° or 0.04° × 0.05°) –  Three PMTs (two operaeng at same eme)

 FUV (115-‐190 nm at 0.3 nm spectral resolueon)  MUV (160-‐320 nm at 0.7 nm spectral resolueon)  VIS (250-‐600 nm at 0.6 nm spectral resolueon)

–  Some spaeal informaeon can be obtained via pushbroom scanning of FOV


Mercury Atmospheric and Surface Composieon Spectrometer (MASCS)

•  Visible and Infrared Spectrograph (VIRS)

–  Array spectrograph, 0.023° circular FOV –  VIS channel

  300-‐1050 nm at 4.7 nm spectral resolueon –  NIR channel

  850-‐1450 nm at 4.7 nm spectral resolueon   Temperatures at Mercury limit the useful wavelength range to maybe 1200 nm

  Comet observaeons are near apoapse of MESSENGER orbit so they may be less affected than the surface observaeons of Mercury


X-‐Ray Spectrometer (XRS) •  Energy range of 1-‐10 keV

–  Measures low-‐energy lines from Mg, Al, Si, S, Ca, Ti, Fe

•  Relaevely large FOV (12° full-‐angle hexagonal)

•  Separate solar unit measures flux from Sun for calibraeon

•  Regular calibraeons against Cas A

•  X-‐ray emission from ISON should be at levels that are detectable based on previous Chandra observaeons

Energeec Parecle and Plasma Spectrometer (EPPS) •  If ion tail is swept in the appropriate direceon, EPPS can

measure both ions (50 eV to 20 keV, up to 40 M/Q) and electrons (25 keV to 1 MeV).


Current Plans •  Will start observing ISON with the imagers a few weeks before the

closest approach to Mercury –  Start cadence at one set of WAC and NAC images per day and transieon to one set

per orbit as it gets closer (reverse of that as comet moves away) –  During closest approach image more frequently to capture any rotaeonal aspects

we can and obtain images in all WAC filters

•  Both MASCS and XRS spectra will be obtained during the period near closest approach during a number of point-‐and-‐stare observaeons –  Approximately 18 hours of integraeon eme with each instrument will be possible

over four orbits

•  EPPS is always on 24/7 and may be able to sample any ion tail that sweeps across Mercury


Complicaeng Issues •  Closest approach occurs during what we call a “hot season”

–  MESSENGER’s orbit is oriented noon-‐midnight during these periods so it passes close to the subsolar point on each orbit

–  For the health of the spacecral, poreons of each orbit must be spent in a thermally safe amtude – precludes gemng data over the enere orbit

–  Leads to slightly higher backgrounds in the instruments

•  This also happens to be during a low-‐downlink-‐rate period for MESSENGER –  We can’t fill up the SSR on the spacecral so care must be taken –  We also have to keep taking Mercury data which makes that SSR fill up even faster –  Negoeaeng with the DSN to lay in extra 70-‐meter tracks about a week before,

during, and a week aler the closest approach to miegate this issue

•  Comet needs to hold up its end of the bargain, but we’re good to go if it does


But wait – there’s a bonus!

Observing Circumstances for 2P/Encke


Closest approach is on UT November 18, 2013 Mercury-‐Encke distance is 0.025 AU Sun-‐Encke distance is 0.349 AU

Observing Circumstances


Closest approach is on UT November 18, 2013 Mercury-‐Encke distance is 0.025 AU Sun-‐Encke distance is 0.349 AU

Observa/ons of 2P/Encke

10/19 10/25 10/31 11/06 11/12 11/18 11/24 11/30 12/06 12/12 12/18Date (UT 2013)

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Nucleus VisibleWith MASCS

ClosestApproach

NotVisible

Documents

messenger - Comet ISON Observing Campaign