Deep Impact/EPOXI Status and Plans

Transcription

1 Deep Impact/EPOXI Status and Plans SBAG January 14-16, 2013 T. Larson, M. A Hearn, S. Chesley

2 Deep Impact Launch 01/12/2005 9P/Tempel 1 Impact 07/04/ P/Hartley 2 Flyby 11/04/2010 SBAG, January 14-16,

3 Since Hartley 2 Observation campaign of comet Garradd (C/2009 P1) in Spring of 2012 Gravitational microlensing demonstration campaign during Summer of 2012 Data analysis under way (Dave Bennett Notre Dame) Senior review proposal for FY13&14 not approved Faced team shut down and long term hibernation starting Fall 2012 Discovery Program Exec provided funding to delay hibernation and enable initial imaging campaign for comet ISON Visible light images and IR spectra to be collected Jan 17 March 10 Currently operating s/c with 1 full time engineer and scattered part time support Second pre-perihelion opportunity to image ISON in July-August 2013 Funding for this is TBD SBAG, January 14-16,

4 Future Opportunities More ISON imaging opportunities (post-perihelion) in 2014 Deep Impact is uniquely positioned to view comet 67P/Churyumov- Gerasimenko while Rosetta is deep inside the coma near the nucleus Essentially unobservable from earth DIF has 7 month view period in 2015 TCMs performed in 2011 and 2012 put DIF on course for a flyby of PHA 2002 GT in January 2020 Additional bright comet observation opportunities No funding is yet committed for any of these Availability of FY14 funding is TBD C-G and 2002 GT are in future senior review proposal periods SBAG, January 14-16,

5 C/Garradd (C/2009 P1) Intrinsically active, therefore bright & widely observed Dynamically very young (1/a)0= Two windows for DIF (post-perihelion) Feb-Apr 2012, r~2.0 & Δ~1.9 AU - vis & IR data, next slide Jul-Aug 2012, r~3.2 & Δ~2.9 AU - no ops Data-taking severely limited by lack of DSN downlink availability (s/c is far from Earth so bandwidth is low) Spectral results now using latest recalibration of IR spectrometer Similarly no observations of C/PanSTARRS 5

6 Vis Camera Results Coma structure amorphous no jets Rotational light curves from broad-band visible (dust) and from narrow band CN (gas) Amplitude only few% (1% in dust)- enabled by stable environment and 24- hour coverage Only measured period for this comet: P=10.42±0.04 hr Release of CN and OH consistent with ground-based measurements with additional information on rotational variation Bodewits, Farnham, & A Hearn CBET

7 Spectrum of Garradd Q(H2O)/Q(CO2)/Q(CO) = 1.0/0.08/0.6 Optically thick model in red Note detection of what is likely OH Not usually observed in IR but not unexpected CO 2 fraction normal 5% < 8% < 25% Only one measurement no other facility can measure CO 2 Higher CO/H2O than any previous observer of Garradd Q(CO) increases systematically around orbit!! Totally unexpected behavior Don t know which species CO 2 follows 7

8 Variation Along Orbit 8

9 New Insights - Garradd CO in nucleus is not correlated with H2O Certainly not in release from nucleus Spatially separate originally? Or only as a result of selective release? Excess of CO from cosmic ray irradiation of CO2 below sublimation front? Is this typical of dynamically new and/or very young comets? Not like C/Hale-Bopp (dynamical age uncertain) Another example of new cometary behavior (totally unlike best studied previous comet) discovered with DIF 9

10 DIF Windows for ISON Date Range Heliocentric Distance S/C Range App Mag 2013 Jan 5 Mar Jul 7 Sep Mar 7 May Aug 29 Nov Only first window is funded! Observations start 17 Jan! UM still working on spec 10

11 DIF Contributions Pre-Perihelion Window 1: 1 st determination of rotational period critical for understanding breakup (if it happens) CO or CO 2 hyperactivity? Window 2: Abundances of H 2 O & CO 2 & CO? Slope of activity variation needed for perihelion predictions & physical model Post-Perihelion Window 3: Asymmetry around perihelion; needed for evolutionary models near sun Abundances (H 2 O, CO 2, CO) needed for physical models Window 4: Asymmetry & outbound slope needed for physical models Changes in rotational period 11

12 Why Does it Matter? DI is only platform able to measure CO 2, a key volatile that drives the activity in some comets. Must understand volatiles at larger distances to understand transitions in behavior at small r DI has demonstrated (C/Garradd) ability to determine rotational periods from very small amplitude activity in coma. Period needed early for interpreting any breakup phenomena at perihelion C/ISON not observable from Earth in window 2 turn on point for water sublimation 12

13 Deep Impact Flyby of 2002 GT Deep Impact is now on course for Jan flyby of a sub-km NEA Targeting completed in Oct. 2012, leaving >7 m/s for cruise and flyby targeting Flyby target is (2002 GT), a PHA ~800 m in diameter Orbit and absolute magnitude are both well-constrained, but little else is known about the body (or bodies) Excellent observing circumstances in mid-2013, providing the best opportunity for pre-flyby characterization SMD is supporting characterization effort, but flyby mission is not yet funded Absolute Mag Diameter Est. ~780m ( m) * Peri- & Aphelion 0.89 x 1.79 AU Eccentricity 0.33 Inclination 7.0 Earth MOID Taxonomic type Spin state AU Unknown Unknown * Assumes albedo range from SBAG, January 14-16,

14 2002 GT Characterization Campaign Variety of observing techniques Light curves Radar UV, Vis. & IR spectra Vis. & IR flux Astrometry Derived asteroid properties Albedo Diameter Shape & spin state Taxonomy/Mineralogy Multiplicity Numerous Observatories Involved Worldwide SBAG, January 14-16, 2013 Santana/GMARS 0.35m Palmer Divide 0.5m Table Mountain 0.6m Ondrejov 0.6m Palomar 1.5m La Silla 1.5m Lulin 1.0m UH 2.2m Magdalena Ridge 2.4m Yunnan 2.4m IRTF 3.0m Kitt Peak 4.0m Palomar 5.1m MMT 6.5m Gemini N 8.1m GranTeCan 10.4m Arecibo 305m 14

15 2002 GT Flyby Scenario The encounter circumstances are listed at right. The phase angle is unfavorable for inbound imaging, and so the team has developed a novel flyby technique whereby the spacecraft will slew to an outbound imaging attitude after the terminal guidance imaging and maneuver activities are complete, approximately 2 minutes prior to encounter. Both Deep Impact cameras, the MRI (10 mrad FOV) and the HRI (2 mrad FOV), will take images continuously until the target is captured in the field post-flyby. After acquisition, autonav will track the nucleus through duration of flyby imaging sequence. The first image will be at a range of km, yielding HRI resolutions of 4-10 cm/pixel. Flyby Details Encounter Date 4 January 2020 Flyby Velocity 7.1 km/s App./Dep. Phase Angle 138/41 deg. Flyby Distance 1-2 km Best Resolution 4-10 cm MRI Full-frame dist. ~78 km Full frame res. ~0.8 m Full frame imaging with MRI and HRI. Flyby distance of 1-2 km Asteroid MRI & HRI res. in cm Autonav commands slew to follow asteroid as soon as asteroid appears in images. B R m Target Asteroid B T m Spacecraft targeting ellipse SBAG, January 14-16,

16 2002 GT Flyby Science Drivers The geology of asteroids is still poorly understood, especially for sub-km asteroids that are more susceptible to YORP-induced spin up and possible binary formation through fission. The high-resolution flyby imagery will reveal the crater and boulder distribution across the surface and will aid understanding of the distribution and nature of fines on the surface, including size sorting through seismic shaking or electrostatic dust levitation. The existence of features at the scale of the body can indicate the relative importance of cohesive forces. The surface slopes will indicate the extent to which the body s surface is relaxed and provide an indication of the mechanical properties of the surface material. The overall shape, taken together with size and rotation state, can allow inferences as to the fundamental nature of the body, whether it be monolithic, fractured or a rubble pile. If the object is a binary (~16% probability), the science returns would significantly increase, revealing the mass and density of the bodies and providing the first highresolution imagery of a binary asteroid system. NEAR-Shoemaker Hayabusa Chang E 2 SBAG, January 14-16,