messenger - comet ison observing campaign
TRANSCRIPT
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)
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
Nicely complements View from Earth
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)
0.0
0.5
1.0
1.5
Dis
tanc
e(A
U)
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)
0.0
0.2
0.4
0.6
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
Observa/ons of C/2012 S1 (ISON)
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
Observa/ons of C/2012 S1 (ISON)
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).
Observa/ons of C/2012 S1 (ISON)
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
Observa/ons of C/2012 S1 (ISON)
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
Observa/ons of C/2012 S1 (ISON)
Observing Circumstances for 2P/Encke
Orbit diagram from JPL Horizons Small-‐Body Browser
Closest approach is on UT November 18, 2013 Mercury-‐Encke distance is 0.025 AU Sun-‐Encke distance is 0.349 AU
Observing Circumstances
Orbit diagram from JPL Horizons Small-‐Body Browser
Closest approach is on UT November 18, 2013 Mercury-‐Encke distance is 0.025 AU Sun-‐Encke distance is 0.349 AU