Image of the Week

Gaia intersects A Perseid Meteoroid

  Figure 1: Corrective torques applied to recover spacecraft attitude after a meteoroid strike.  

In orbit at the second Sun-Earth/Moon Lagrange point (L2), Gaia is exposed to a flux of high-velocity meteoroids. When a meteoroid strikes Gaia, these particles carry enough momentum to disturb the spacecraft attitude and at the same time cause local heating and deformation of the spacecraft structure. The Gaia measurements of a single meteoroid strike from 2015 are presented here.

To perform its astrometric mission, Gaia is equipped with extremely sensitive sensors for measuring its attitude and movement, and so the deviations due to a meteoroid strike are detected within a few seconds and corrected by use of the fine attitude control cold gas thrusters. Figure 1 shows the torque applied to correct for the above mentioned meteoroid strike. Some information about the direction of origin of the meteoroid can be extracted from the magnitude of the applied corrective torques, but because a meteoroid hit can occur at any point on the spacecraft, it is not possible to know the forces involved because the lever arm length is generally unknown.

Gaia is also equipped with many sensors which are used to continually monitor the spacecraft temperature. If the point of impact is sufficiently close to one of these temperature sensors, then the effects of the impact are detectable as small increases in the temperature which coincide with the attitude disturbances. Figure 2 shows the temperature change as measured on the Gaia sunshield (DSA) due to the same meteoroid strike. These impacts, which are also detected by the temperature sensors, are interesting for study because they provide more information about the nature of the impact. Firstly, because the location of the temperature sensor is known, it is possible to reduce the possible originating direction of the impactor to a 180 degree arc. Secondly, the lever arm length is known to allow calculation of the forces of impact from the torques. Finally, an estimate of the energy of the impact can be calculated from the measured heating of the structure.

Figure 2: Localised temperature increases are occasionally observed to coincide with meteoroid strikes.

The temperature sensors on the DSA are mounted in a thermally isolated box made from 350 g of aluminium with a heat capacity of just under 1 J/gK. To heat this box by the observed 0.25 K requires 84 J of energy which is the lower limit of the kinetic energy of the impactor relative to Gaia as the efficiency of energy transfer is unknown. For comparison, 84 J is about half the energy of a .22 calibre bullet as it leaves the muzzle of a gun.

Meteoroids are known to mostly originate from comets and recently the ESA spacecraft Rosetta has provided spectacular images of dust separating from the comet 67P Churyumov-Gerasimenko. After ejection from the parent body, these dust particles continue to orbit the Sun following approximately the same orbit in a stream.

The example meteoroid impact might be special because it occurred on 18 August 2015 which is within the time period where the Earth, and therefore Gaia, traverses the meteoroid stream that causes the Perseid shooting stars. The Perseid meteoroids have been ejected from comet 109P Swift-Tuttle and are known as Perseids because the shooting stars that they generate appear to originate from the constellation Perseus. Figure 3 shows in blue the outline of the Perseus constellation with the apparent point of origin (radiant) of the Perseids on 18 August 2015 as a red dot. The green line shows the arc of possible origins of the Gaia impactor as determined by the torque and temperature measurements with the green dot representing the central (zero radial component) direction.

Figure 3: All-sky map showing constellation Perseus and arc of possible origins of Gaia impactor.

Although it has not been possible to prove that the meteoroid originated from comet 109P with the current analysis, it is tempting to imagine that it may have done so and to calculate the mass of such a particle. The Perseid meteoroids are known to be travelling at 59 km s-1 relative to the Earth and Gaia, and a particle at this speed needs to have a mass of only 48 μg to carry 84 J of kinetic energy.

These serendipitous measurements from Gaia will allow scientists to study the meteoroid environment for future missions to L2 and beyond, including manned missions to asteroids and Mars. Due to the incredible precision of its instruments, Gaia is able to join Giotto and Rosetta as one of ESA's comet explorers!

Acknowledgement: these figures were prepared by Edmund Serpell, a Gaia Operations Engineer working in the Mission Operations Centre at ESA's European Space Operations Centre in Darmstadt, Germany.

Credits: ESA/Gaia-CC BY-SA 3.0 IGO

[Published: 06/01/2016]


Image of the Week Archive

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
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
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
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
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
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
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
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.