Using the Rosetta Navigation Camera and Star Trackers to study comet outbursts and dust properties Bernhard Geiger SSW#9 – Akersloot – 7-9 November 2016

Content Comet outbursts imaged by the NAVCAM. Continuous measurements by the Star Trackers. Characterisation of the properties of dust particles. Radiometric calibration of the NAVCAM.

1. Comet outbursts imaged by the NAVCAM Regular images were acquired with the NAVCAM for navigation purposes. In addition, context images for science instruments were scheduled. A number of outbursts were caught by the NAVCAM which were not seen by the OSIRIS camera. Some individual cases were looked at in detail by the Rosetta community. A systematic analysis of available images has not yet been done. -> ESA-SCI funded project, NAVCAM work by the University of Stuttgart

Comet outburst examples ~150km, ~250km 2015-07-10 2015-08-06

2. Continuous star tracker measurements Star Trackers continuously measure the background signal in up to 9 sub-windows centred on tracked stars. Information is reported via AOCS housekeeping telemetry. A rough radiometric calibration has been applied. The Star Tracker information was used as an additional source of information for studying individual outburst events, complementing the measurements of the scientific instruments.

Outburst on 19 February 2016: OSIRIS 35km. Grün et al. (MNRAS, 2016)

Outburst on 19 February 2016: Star Tracker Grün et al. (MNRAS, 2016)

Outburst on 3 July 2016: OSIRIS+STR 10km Agarwal et al. (in prep.)

Signal evolution over the mission Note: The graph shows un-cleaned data with artefacts.

Signal evolution over the mission Note: The graph shows un-cleaned data with artefacts.

3. Characterisation of dust particles Characterisation of Dust Grains from Rosetta Navigation Camera Images Florencia Calandra, Esteban García Migani, Mariela Huamán, Cecilia Lopez Sisterna, Ximena Ramos, Macarena Zinardi, Bernhard Geiger Results obtained during the COSPAR Capacity Building Workshop on Planetary Data Analysis, Guaratinguetá, Brazil, 26 October - 6 November 2015

Resolved dust particles in the images number of particles 2 4 6 8 10 instrumental magnitude There are two orders of magnitude more objects detected than stars expected. -> dust particles 150-160km 2015-07-06T10:41:02

Out of focus images of dust particles number of particles 10m 60m distance size of image circles -> distance of particles flux -> size of particles ~0.1mm to 0.5mm 2015-07-07T21:11:30

Histogram of particle distances dark number of particles bright 200m 1000m distance

4. Radiometric Calibration of the NAVCAM Difficulties: Instrument was developed ~15-20 years ago. Relevant information and laboratory data not available. Broad spectral sensitivity band. Methods: Manufacturer calibration: “Instrumental magnitudes” for point sources. Calibration studies based on stellar images. Cross-calibration with OSIRIS images of the comet nucleus. (Extended source.)

NAVCAM Stellar Calibration

NAVCAM Cross-Calibration with OSIRIS NAVCAM 1 August 2014 OSIRIS spectral radiance relative frequency -> determination of the calibration factor to convert NAVCAM digital number counts to average spectral radiance Statella and Geiger (in preparation)

Summary NAVCAM: Un-calibrated images (Level2) are all available in the PSA. Calibrated image datasets (Level 3) will be available in 2017. (to be documented in detail in Geiger et al., in preparation) Images have been used for scientific purposes by the Rosetta community. Project for systematic analysis on-going. Star Tracker: Data have been used scientifically in individual cases. More potential. Archiving of the data pending.

NAVCAM Spectral Sensitivity Curve