Image of the Week

Gaia reveals the composition of Asteroids

 

Figure 1: Gaia reflectance spectra (green circles) of four asteroids with well known ground-based spectra (violet circles). The Gaia BP and RP data, which are calibrated independently, are merged in one single reflectance. The ground based data were obtained from the (Small Asteroid Spectroscopic Survey) SMASS of the MIT in the USA. Error bars due to the photometric uncertainties are of the order of the size of the plot symbols (also for the ground-based data). However, systematic uncertainties are certainly bigger due to the still preliminary calibration of the Gaia BP and RP data used here (see text). (Image credit: ESA/Gaia/DPAC/CU4+CU5/Marco Delbo)

While Gaia is pinpointing the positions of more than one billion stars with unprecedented accuracy, it also catches the light of asteroids along the way. The visible-light spectra of these asteroids is measured using Gaia's Blue and Red photometers (BP and RP for short). Asteroid spectra are very important for planetary scientists: spectra carry information about the composition of the body, allowing to distinguish, for instance, rocky from carbonaceous and/or water-rich asteroids.

As asteroids are the leftovers of the bricks that built the planets 4.5 Gyr ago, their composition gives to scientists clues about the planetary formation processes and the evolution of the Solar System. Even considering the preliminary nature of these data, the agreement with the known spectra shows the potential of Gaia in this kind of analysis.

The measurement of asteroid spectra requires a delicate approach and coordinated team-work: each single Gaia observation is calibrated by the Photometric processing unit (CU5) in Cambridge (UK) taking into account the responses of the BP and RP instruments. The contribution of the solar spectrum is then removed from the several observations that Gaia obtains for each asteroid, in order to derive the reflectance of its surface. This is the fraction of incident solar light that is reflected by the surface. This procedure is part of a fully automated processing of spectra that runs at the CNES Data Processing Centre (also called the DPCC in Toulouse, France) and it is being optimised at the Observatoire de la Côte d'Azur (Nice, France) as part of the “Object processing” unit (CU4). By comparing the reflectance spectrum as a function of wavelength with those of meteorites and different minerals, planetary scientists derive the composition of asteroids.

In the accompanying image we show spectra that Gaia obtained for asteroids whose diverse reflectance spectra were already known from previous ground-based telescopic observations. The spectrum of asteroid (158) Koronis is similar to those of ordinary chondrite meteorites; that of (19) Fortuna is compatible with CM carbonaceous chondrite meteorites; (21) Lutetia with enstatite chondrite meteorites; and (279) Thule with cometary nuclei (ESA’s Rosetta mission showed that cometary nucleus has an organic-rich and dehydrated surface). The scientists of DPAC (the Data Processing and Analysis Consortium) use asteroids with well measured spectra to validate the quality of Gaia measurements. The spectra presented in the figure are based on an early calibration of the Gaia instruments. These "cycle 1” data were not made public and are not intended for scientific use, as the full calibration was not yet complete at the cycle 1 stage. This might explain some discrepancies between the Gaia and the ground based spectra, also shown in this figure.

Even considering the preliminary nature of this data, the agreement with the known spectra is remarkable and shows the high potential of Gaia in this kind of analysis. Thanks to efforts of Gaia scientists, the instrument calibrations are improving and likewise the reliability of asteroid spectra. Eventually, Gaia will provide the largest survey of asteroid spectra ever made. This will allow planetary scientists to build a map of the composition of the Main asteroid Belt and of other populations of asteroids, such as that of the near-Earth and the potentially-hazardous objects.

Several DPAC Coordination Units were involved in the preparation of this story. Laurent Galluccio, Marco Delbo and Francois Mignard from CU4 and Francesca De Angeli from CU5 helped preparing this story. A special acknowledgement and thank you also to Paolo Tanga, Alberto Cellino and Anthony Brown for their supervision.

Credits: ESA/Gaia/DPAC/Galluccio/DeAngeli/Delbo/Mignard

[Published: 24/04/2017]

 

Image of the Week Archive

2017
24/11: Gaia-GOSA service
27/10: German Gaia stamp in the making
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.