1. Future Didymos Observing Strategy
Cristina Thomas (Northern Arizona University)
Andy Rivkin (JHU-APL)
& the Observing Working Group

2. DART Working Group 2: Observations
Refine the properties of the Didymos binary system, including pole position, sizes, orbits, rotation rates, densities, orbital phase, and photometric properties.
Constrain the composition and spectral properties of the Didymos system.
Level 1
WG Objective
WG Task 3
Determine Didymos system properties
2019 , observations
PDS release of telescope data after apparitions
Report back results to other working groups
Measure change in orbital period
Didymos system observations during impact apparition
Didymos system observation results and determination of period change
PDS release of telescope data after end of impact observing period 4B
Observe dynamical evolution of ejecta from telescopic observations
We are also responsible for coordination this goes into the reference model!

3. DART Working Group 2: Observations
In addition to what the mission needs, we should consider what we want for our own science. Publications? Presentations?
Level 1
WG Objective
WG Task 3
Determine Didymos system properties
2019 , observations
PDS release of telescope data after apparitions
Report back results to other working groups
Measure change in orbital period
Didymos system observations during impact apparition
Didymos system observation results and determination of period change
PDS release of telescope data after end of impact observing period 4B
Observe dynamical evolution of ejecta from telescopic observations
2023 will likely be when we have a lot of things to present at ACM, PDC.

4. 2017 Campaign Strategy
Applied for NASA Solar System Observations Funding for & 2019 apparitions. Not funded.
Started the 2017 Campaign with 4 key goals:
Confirm the pole of the Didymos system orbit
Gather data for determination of BYORP
Establish if the secondary is in synchronous rotation
Constrain the inclination of the satellite orbit
Learned many lessons. Confirmed pole (#1), gathered data for #2, need more observations for #3 & #4
Update from P. Pravec before April IT meeting

5. 2019 and Beyond Strategy
As we heard yesterday, we do not need as many observations as we once thought for the upcoming pre-impact apparitions.
We do need high quality observations from large telescopes.
Did not submit a NASA Solar System Observations proposal for 2019 &
We should be thoughtful about requirements, timing, and communication as we plan the 2019 & campaigns.

6. 2019 Observing Circumstances
5 Jan – 15 Apr 2019
Peak 2019 brightness
V = 19.79, 12 – 13 Mar 2019
Moon 25-35% illuminated, 122°-109° distant
Full Moon on 21 Jan, 20 Feb, 21 Mar 2019
Date
RA & Dec
5 Jan 2019
12 Mar 2019
15 Apr 2019
Peak brightness in 2017: V~20.25
V <20.25, 17 Feb – 26 Mar 2019

7. Possible 2019, 2020 HST Observations
DART!
Likely goal to observe half Didymoon’s orbit (5.96 hr)
Robust solution for period of Didymoon’s orbit
Improved constraints on the orbit pole
Epoch for constraining Didymoon’s orbital drift caused by BYORP
Bright
Observations possible
Can we use HST to extend the observing window for the next apparitions?
Faint
Slide modified from M. Knight’s IT meeting presentation

8. HST Timing Considerations
Didymos is brighter and available in 2019, 2020, 2021
Expect there to be a mid-cycle call in September 2018 and normal call in March 2019
Mid-cycle logistics
Time harder to get
Stronger proposal once DART moves to Phase C
Can only request up to 10 orbits
Are there any mission-critical observations will need to be done quickly?
Director’s Discretionary Time proposals are an option
Slide modified from M. Knight’s IT meeting presentation

9. 2020-2021 Observing Circumstances
5 Jul 2020 – 16 Mar 2021
Peak 2021 brightness
V = 18.91, 16 – 19 Feb 2021
Moon 17-43% illuminated, ~30-60° distant
Full Moon on 30 Dec 2020, 28 Jan, 27 Feb, 28 Mar 2021
16 Feb Moon:
In Degrees: RA: DEC:
19 Feb Moon
RA: DEC:
Didymos
RA: DEC:
RA: DEC:
63 deg, 31
Date
RA & Dec
5 Jul 2020
17 Feb 2021
16 Mar 2021

10. Spectral Type and Composition
de León et al. (2010)
Observations by Binzel et al. (2004) and de León et al. (2010)
Pretty clearly S type
Not exotic, new type
Context for Eros/Itokawa
Most common NEO type
Dunn et al. (2013): L/LL chondrite best analog, very common meteorite type
Originally from Flora family?
LL chondrite parent family?
Chelyabinsk link?
Gaspra link?

11. Do we need more spectroscopy?
always
Reasonably secure in terms of spectral type
Reasonably secure in terms of meteorite analog
Albedo somewhat low for S class? 0.15 ± 0.04
Measure thermal inertia?
Possible to separate Didymos A and B spectra during mutual events?
Probably not
Didymos B contributes ~4% of light
Not likely that we could tell anything unless Didymos B radically different from Didymos A?

12. Possible JWST Observations
JWST launch “approximately May 2020”
Cycle 1 starts ~6 months later, January 2021?
Observable 1-20 Jan, V ~ 19.5, phase angle ~30°
Observable 27 March – 30 May, V ~
In January window:
T ~ K
~8 mJy at 8 µm, ~17.5 mJy at 15 µm.
NIRSpec prism
30 groups, 4 integrations, 30 minutes
MIRI Low Resolution Spectroscopy
500 groups, 8 integrations, 10 minutes

13. 2022 Observing: Ground-based
Closest Approach: 4 October 2022 
04:52: :55:14.0
Δ=0.07 AU
V=14.7 
Impact: 5 October 2022
Brightest: 26 September 2022
V=14.5
V < 18 July 20 - January 29
V < 17 August 4 - January 16
V < 16 August 20 - November 3
V < 15 September 9 - October 10
UT 4 Oct 2022
A lot of people will be observing this event and the post-impact changes

14. 2022 Observing: Space-based
JWST elongation angle=85-135°, < 30 mas/sec= 108”/hr Window 1: Apr ”/hr Δ=1.68 AU July ”/hr Δ=0.51 AU Window 2: Sep ”/hr Δ=0.09 AU On closest approach: Oct ”/hr Δ=0.07 AU Under rate limit: Nov ”/hr Δ=0.12 AU Dec ”/hr Δ=0.19 AU If we could double the allowable rate, Oct 25 Δ=0.09 AU
Hubble
Possibly available until 2025
Didymos is in elongation range

15. 2022 Observing: Space-based
JWST elongation angle=85-135°, < 30 mas/sec= 108”/hr Window 1: Apr ”/hr Δ=1.68 AU July ”/hr Δ=0.51 AU Window 2: Sep ”/hr Δ=0.09 AU On closest approach: Oct ”/hr Δ=0.07 AU Under rate limit: Nov ”/hr Δ=0.12 AU Dec ”/hr Δ=0.19 AU If we could double the allowable rate, Oct 25 Δ=0.09 AU
Hubble
Possibly available until 2025
Didymos is in elongation range

16. We have a lot of work to do, how are we going to do this well?
Coordination Platform. Website?
List of observing proposal deadlines, PIs of proposal, when observations happened, status of data
Deadlines. We need to act quickly!
This enables us to make new plans if things fail and know the quality of data while Didymos can still be observed.
Observing guide to guarantee consistency in datasets?
Sidereal vs. non-sidereal, exposure time, filters, etc.
We need to communicate effectively with each other and with the other DART Working Groups!
Do we want to observe 2001 CB21?
Data archiving is being negotiated right now. How are we going to manage this? If DART pays, it gets archived, but there are plenty of other datasets.