Image of the Week

Celebrity comet spotted among Gaia's stars

   
 

A Gaia image of Comet 67P/Churyumov–Gerasimenko, obtained on 14 September 2015. The image shows the comet's coma and tail. The nucleus and Rosetta, which was some 300 km from the surface at the time, are both hidden in the innermost pixel. A number of background stars are also sprinkled around the image, which measures about 4.5 arc minutes across – about one-seventh of the Moon's diameter.

 
 

A local cosmic celebrity was recently pictured among the multitude of stars and Solar System bodies surveyed by ESA's Gaia satellite: Comet 67P/Churyumov–Gerasimenko, currently accompanied by another ESA spacecraft, Rosetta.

While scanning the sky to map the positions and motions of a billion stars in our Galaxy, Gaia also picks up objects much closer to home, such as asteroids and comets in the Solar System.

With its ability to detect faint and moving objects, Gaia has already identified tens of thousands of asteroids since routine science operations began in July 2014, and these data will be used to determine their orbits to unprecedented accuracy.

Gaia is optimised to detect stars, which appear as point sources in its camera, and measure their properties, but it does not routinely return images of celestial objects. However, a special trick can be used to image a particular object. This is what Gaia astronomers did to ensure that, when the satellite scanned the patch of the sky including Rosetta's comet, the star-mapper camera would capture an image of this iconic object.

Rosetta's comet is currently between the orbits of Earth and Mars. It reached its peak brightness between August and September, having passed the closest point to the Sun on its 6.5 year orbit on 13 August. Rosetta has been at the comet since August 2014, studying the surface and environment as they swing around the Sun, and it will continue these investigations until the end of the mission in September 2016.

Meanwhile, closer to Earth, Gaia surveys the entire sky about every three months, and calculations predicted that it would scan the portion of the sky with Rosetta and its comet on 14 September. For this special occasion, the astronomers made sure that Gaia's star-mapper camera would cover that patch of the sky using a special mode in which a full image is recorded and transmitted to the ground instead of point sources only.

The image shows the comet's coma and tail. The nucleus and Rosetta, which was some 300 km from the surface at the time, are both hidden in the innermost pixel. A number of background stars are also sprinkled around the image, which measures about 4.5 arcminutes across – about one-seventh of the Moon's diameter.

While this image of Rosetta's comet has mainly a symbolic value – an ESA mission, 1.5 million kilometres from Earth, looking at a fellow science mission and its object of study, both located over 260 million kilometres away – scientific data were also collected during this observation.

In fact, besides the special observing mode used to obtain the image, the comet was also caught by the onboard detection software as a 'suspected moving object'. Over the three-second observation, it appeared to move by some 100 km with respect to the background stars, as seen from a distance of 260 million kilometres.

Over its five-year mission, Gaia will observe hundreds of comets and repeatedly measure their positions to unprecedented accuracy. These data will allow scientists to improve the orbit determination of many comets well beyond the precision that can be achieved with ground-based observations alone. They will also use Gaia's observations to investigate their composition and surface properties.

Credits: ESA/Gaia/DPAC

Acknowledgement: F. Mignard & P. Tanga, Observatoire de la Côte d'Azur, France

[Published: 03/11/2015]

This text is also available on the ESA Space Science portal. A blog post, based on the article, is available on the Rosetta blog.

 

Image of the Week Archive

2017
19/10: Hertzsprung-russell diagram using Gaia DR1
05/10: Updated prediction to the Triton occultation campaign
31/08: Close stellar encounters from the first Gaia data release
16/08: Preliminary view of the Gaia sky in colour
07/07: Chariklo stellar occultation follow-up
24/04: Gaia reveals the composition of asteroids
20/04: Extra-galactic observations with Gaia
10/04: How faint are the faintest Gaia stars?
24/03: Pulsating stars to study Galactic structures
09/02: Known exoplanetary transits in Gaia data
31/01: Successful second DPAC Consortium Meeting
2016
23/12: Interactive and statistical visualisation of Gaia DR1 with vaex
16/12: Standard uncertainties for the photometric data (in GDR1)
25/11: Signature of the rotation of the galactic bar uncovered
15/11: Successful first DR1 Workshop
27/10: Microlensing Follow-Up
21/10: Asteroid Occultation
16/09: First DR1 results
14/09: Pluto Stellar Occultation
15/06: Happy Birthday, DPAC!
10/06: 1000th run of the Initial Data Treatment system
04/05: Complementing Gaia observations of the densest sky regions
22/04: A window to Gaia - the focal plane
05/04: Hipparcos interactive data access tool
24/03: Gaia spots a sunspot
29/02: Gaia sees exploding stars next door
11/02: A new heart for the Gaia Object Generator
04/02: Searching for solar siblings with Gaia
28/01: Globular cluster colour-magnitude diagrams
21/01: Gaia resolving power estimated with Pluto and Charon
12/01: 100th First-Look Weekly Report
06/01: Gaia intersects a Perseid meteoroid
2015
18/12: Tales of two clusters retold by Gaia
11/11: Lunar transit temperature plots
06/11: Gaia's sensors scan a lunar transit
03/11: Celebrity comet spotted among Gaia's stars
09/10: The SB2 stars as seen by Gaia's RVS
02/10: The colour of Gaia's eyes
24/09: Estimating distances from parallaxes
18/09: Gaia orbit reconstruction
31/07: Asteroids all around
17/07: Gaia satellite and amateur astronomers spot one in a billion star
03/07: Counting stars with Gaia
01/07: Avionics Model test bench arrives at ESOC
28/05: Short period/faint magnitude Cepheids in the Large Magellanic Cloud
19/05: Visualising Gaia Photometric Science Alerts
09/04: Gaia honours Einstein by observing his cross
02/04: 1 April - First Look Scientists play practical joke
05/03: RR Lyrae stars in the Large Magellanic Cloud as seen by Gaia
26/02: First Gaia BP/RP deblended spectra
19/02: 13 months of GBOT Gaia observations
12/02: Added Value Interface Portal for Gaia
04/02: Gaia's potential for the discovery of circumbinary planets
26/01: DIBs in three hot stars as seen by Gaia's RVS
15/01: The Tycho-Gaia Astrometric Solution
06/01: Close encounters of the stellar kind
2014
12/12: Gaia detects microlensing event
05/12: Cat's Eye Nebula as seen by Gaia
01/12: BFOSC observation of Gaia at L2
24/11: Gaia spectra of six stars
13/11: Omega Centauri as seen by Gaia
02/10: RVS Data Processing
12/09: Gaia discovers first supernova
04/08: Gaia flag arrives at ESAC
29/07: Gaia handover
15/07: Eclipsing binaries
03/07: Asteroids at the "photo finish"
19/06: Calibration image III - Messier 51
05/06: First Gaia BP/RP and RVS spectra
02/06: Sky coverage of Gaia during commissioning
03/04: Gaia source detection
21/02: Sky-background false detections in the sky mapper
14/02: Gaia calibration images II
06/02: Gaia calibration image I
28/01: Gaia telescope light path
17/01: First star shines for Gaia
14/01: Radiation Campaign #4
06/01: Asteroid detection by Gaia
2013
17/12: Gaia in the gantry
12/12: The sky in G magnitude
05/12: Pre-launch release of spectrophotometric standard stars
28/11: From one to one billion pixels
21/11: The Hipparcos all-sky map
15/10: Gaia Sunshield Deployment Test
08/10: Initial Gaia Source List
17/09: CU1 Operations Workshop
11/09: Apsis
26/08: Gaia arrival in French Guiana
20/08: Gaia cartoons
11/07: Model Soyuz Fregat video
01/07: Acoustic Testing
21/06: SOVT
03/06: CU4 meeting #15
04/04: DPCC (CNES) 
26/03: Gaia artist impression 
11/02: Gaia payload testing  
04/01: Space flyby with Gaia-like data
2012
10/12: DPAC OR#2. Testing with Planck
05/11: Galaxy detection with Gaia
09/10: Plot of part of the GUMS-10 catalogue
23/07: "Gaia" meets at Gaia
29/06: The Sky as seen by Gaia
31/05: Panorama of BAM clean room
29/03: GREAT school results
12/03: Scanning-law movie
21/02: Astrometric microlensing and Gaia
03/02: BAM with PMTS
12/01: FPA with all the CCDs and WFSs
2011
14/12: Deployable sunshield
10/11: Earth Trojan search
21/10: First Soyuz liftoff from the French Guiana
20/09: Fast 2D image reconstruction algorithm
05/09: RVS OMA
10/08: 3D distribution of the Gaia catalogue
13/07: Dynamical Attitude Model
22/06: Gaia's view of open clusters
27/05: Accuracy of the stellar transverse velocity
13/05: Vibration test of BAM mirrors
18/04: L. Lindegren, Dr. Honoris Causa of the Observatory of Paris
19/01: Detectability of stars close to Jupiter
05/01: Delivery of the WFS flight models
2010
21/12: The 100th member of CU3
17/11: Nano-JASMINE and AGIS
27/10: Eclipsing binary light curves fitted with DPAC code
13/10: Gaia broad band photometry
28/09: Measuring stellar parameters and interstellar extinction
14/09: M1 mirror
 
Please note: Entries from the period 2003-2010 are available in this PDF document.