Meteor Shower on Mars indicates Cometary Activity far away from the Sun

![published in MNRAS Letters, 437, L71 (2014)]

!!!!!

!!!!!!!!

Aswin Sekhar & David Asher Armagh Observatory & Queen’s University Belfast

United Kingdom !

IAU GA 2015, Hawaii

2

Brief Background !

1. Close encounter of comet C/2013 A1 (Siding Spring) with Mars occurred on 2014 Oct 19 at 1830 h (UT)

!2. Miss Distance between comet-Mars = 0.00093 AU or 132,000 km !3. Minimum Orbit Intersection Distance (MOID) of Siding Spring-Mars = 0.00023 AU or 34,400 km (inside Geo Synchronous Satellite Ring) !4. Extreme Close Encounters with Long Period Comets are Rare for Terrestrial Planets !5. Dynamically New Comets usually contain more volatile material !6. Various space agencies in US, Europe, Japan, India, Russia etc were concerned about threats to Satellites and Space Instruments around/on Mars

3 Credits: Solar System Group, JPL-Caltech

4 Credits: Solar System Group, JPL-Caltech

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Distance Date (TT) Permanent designation! (AU)!! 0.0151 1770 July 1.7 D/1770 L1 (Lexell)! 0.0229 1366 Oct. 26.4 55P/1366 U1 (Tempel-Tuttle)! 0.0312 1983 May 11.5 C/1983 H1 (IRAS-Araki-Alcock)! 0.0334 837 Apr. 10.5 1P/837 F1 (Halley)! 0.0366 1805 Dec. 9.9 3D/1805 V1 (Biela)! 0.0390 1743 Feb. 8.9 C/1743 C1! 0.0394 1927 June 26.8 7P/Pons-Winnecke! 0.0437 1702 Apr. 20.2 C/1702 H1! 0.0601 2011 Aug. 15.34 45P/Honda-Mrkos-Pajdusakova! 0.0617 1930 May 31.7 73P/1930 J1 (Schwassmann-Wachmann)! 0.0628 1983 June 12.8 C/1983 J1 (Sugano-Saigusa-Fujikawa)! 0.0682 1760 Jan. 8.2 C/1760 A1 (Great comet)! 0.0787 2006 May 12.4 73P/Schwassmann-Wachmann! 0.0839 1853 Apr. 29.1 C/1853 G1 (Schweizer)! 0.0879 1797 Aug. 16.5 C/1797 P1 (Bouvard-Herschel)! 0.0884 374 Apr. 1.9 1P/374 E1 (Halley)! 0.0898 607 Apr. 19.2 1P/607 H1 (Halley)! 0.0934 1763 Sept.23.7 C/1763 S1 (Messier)! 0.0964 1864 Aug. 8.4 C/1864 N1 (Tempel)! 0.0982 1862 July 4.6 C/1862 N1 (Schmidt)! 0.1018 1996 Mar. 25.3 C/1996 B2 (Hyakutake)! 0.1019 1961 Nov. 15.2 C/1961 T1 (Seki)

Frequency of Such Events !

!(Credits: IAU-Minor Planet Center)

0.001 AU - Miss Distance between Siding Spring-Mars

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Credits: NASA

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Image from Mars Exploration Rover Opportunity’s

Pancam (Credits: NASA/JPL-Caltech)

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Initial Dynamical Predictions 1. Chances for Meteor Hurricane/Meteor Storm (Vaubaillon, Maquet & Soja

2014/Moorhead, Wiegert & Cooke 2014) !2. In nominal case, dust cone likely to miss Mars (Ye & Hui 2014) !3. No extreme damage to spacecraft/satellites expected (Farnocchia et al. 2014, Kelley et al. 2014, Tricarico et al. 2014) !4. Detailed trajectory analysis of comet nucleus & tail was done (Farnocchia et al. 2014, 2015) !

Famous Wood Cut Engraving of 1833 Leonid meteor storm !!!!(Credits: Seventh Day Adventist)

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Motivation For Our Work 1. Meteor Phenomena Detected on Mars by space instruments !2. Enhanced Ion Rates After Close Encounter Showed Influx of Particles (Gurnett et al. 2015, Restano et al. 2015, Schneider et al. 2015, Benna et al. 2015) from the comet !!

Credits: NASA

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Activity of Comet C/2013 A1 (Siding Spring) 1. This Comet was discovered at 7.2 AU from Sun (McNaught et al. 2013);

Original orbit (P < 4 Myr) showed dynamically new comet !2. Recent works (Farnham, Kelley & Bodewits 2014, Kiss et al. 2014) suggests beginning of activity in this comet between 10 AU and 8 AU. !3. Carbon monoxide & Carbon dioxide emission can start from 15 AU and 13 AU respectively (Meech & Svoren 2004, Farnham, Kelley & Bodewits 2014) !4. Meech et al. (2009) presents records of dynamically new comets active between 6 AU and 14 AU !!!

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Our Present Work & Methodology 1. Ejection of particles from comet is done from 15 AU to 1.4 AU !2. Technique is such that velocities form a symmetrical cubic lattice around the comet (at different combinations of ejection distances and radiation pressure) !3. Transformation of this cube to parallelepiped over time for all cases are studied !4. Linearity of the transformation is central to this model and verified

Te

W

W

T

T

S

S

Figure: S - Radial , T - Transverse, W- Normal Direction

Description of Calculations 1. Checking the dimensions & shape of transformed lattice and subsequent intersection with Mars’ trajectory tells us which ejection model (i.e. which combinations of heliocentric ejection distance and ejection velocity components) works !2. Integrations are repeated for different values of radiation pressure (or particle sizes) !3. Calculations show that large particles (100 microns size & higher) ejected from the comet mainly between 13 AU and 7 AU intersect Mars at about 100 min after close approach time

Figure: Trajectory of Mars inside the velocity vector cloud with no radiation pressure (i.e. large particles) ejected at 10 AU from the comet

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Finding Exact Ejection Velocities Favouring Mars IntersectionMeteor shower on Mars indicates cometary activity at large distances 3

diation pressure to gravity (Burns, Lamy & Soter 1979)=0.1, 0.01, 0.001, 0.0.

The final position vectors (in X, Y, Z frame) of the par-ticles and Mars are taken from MERCURY’s output for theperiod from -24hr to 0hr to +24hr from real comet-Marsclose encounter time (which is the zeroth time here). Theseposition vectors are transformed into S, T, W directions.The final X, Y, Z position vectors of Mars are first madecometocentric (before transforming into S, T, W frame) sothat one could plot the cloud remaining stationary (at closeencounter time) along with Mars (which is moving from -24hr to +24hr from close encounter time) in the same plot. Fig-ures 1(a), 1(b), 2(a) and 2(b) are plotted in this way. Marsmovement (top to bottom on the plot as time increases) isshown in these four plots.

Figures 1(a) and (b) show the (S, T) and (S,W) spaceof particles at close encounter time respectively (for parti-cles ejected at r

eject

=10 au with �=0.0; i.e. no radiationpressure). The plot clearly shows that Mars go through thecloud of particles near the close encounter time. A very sim-ilar picture was seen in the simulations with �=0.001 (notshown in the plots here) as well.

Figures 2(a) and (b) show the (S, T) and (S,W) spaceof particles at close encounter time respectively (for parti-cles ejected at r

eject

=10 au with �=0.01). The plots clearlyshow that Mars misses the cloud of particles which is in starkcontrast to the case of �=0.001 and 0.0. Integrations with�=0.1 showed a similar trend (i.e. missing Mars by substan-tial distances) as well. It can be seen that particles (of thesizes of few microns to hundreds of microns) encounteringhigh radiation pressure are swept away from the comet. Ob-viously high radiation pressure is acting for a long time herebecause these are ejected from relatively large heliocentricdistances.

Integrations were repeated for low heliocentric distancesfrom 1.4 au to 3 au (i.e. some tens of days to few hundredsof days before the close encounter time) with high ejectionvelocities in the range of -500 to +500 ms�1 (the gas expan-sion velocity limit is about 1 kms�1) to check for consistency.The results showed Mars missing the cloud by about 0.002au (about twice the comet-Mars minimum close encounterdistance) in the case of �=0.01. For �=0.1 the cloud missesMars by about 0.02 au (about twenty times the comet-Marsminimum close encounter distance).

3 FINDING THE EXACT EJECTIONVELOCITIES FAVOURING INTERSECTIONWITH MARS

Although the technique employed in the previous sectionhelps to distinguish clearly the cases of intersections ormisses of Mars with the cloud, it doesn’t directly tell usthe exact combinations of ejection velocities involved whichare conducive for Mars intersection at a particular time. Inan ideal and abstract ejection model, any direction and mag-nitude is equally probable. But in the real scenario, this isindeed not the case and hence the knowledge of each di-rectional component and their limits is vital for practicalpurposes.

For this we employ a simple matrix technique to findout the exact combinations of ejection velocities (in terms ofX, Y, Z components) required for a particle to become Mars

intersecting at -24hr to 0hr to +24hr for di↵erent ejectiondistances. The matrix formulation is:

CV = M

where M is a 3⇥3 matrix,

V =

0

BBB@

dv

x

dv

y

dv

z

1

CCCAM =

0

BBB@

x

y

z

1

CCCA

V is the initial ejection velocity components of the parti-cle and C is the cometocentric final position vector of theparticle at a given time. Using the numerical integrator onecould find the output C corresponding to input V

x

, Vy

, Vz

(in ms�1) where

V

x

=

0

BBB@

1

0

0

1

CCCAV

y

=

0

BBB@

0

1

0

1

CCCAV

z

=

0

BBB@

0

0

1

1

CCCA

and M

xx

, M

xy

, M

xz

corresponds to Vx

; M

yx

, M

yy

, M

yz

corresponds to Vy

;Mzx

,Mzy

,Mzz

corresponds to Vz

. Theseare approximations of partial derivatives.

C =

0

BBB@

M

xx

M

yx

M

zx

M

xy

M

yy

M

zy

M

xz

M

yz

M

zz

1

CCCA

Then one could find the exact required ejection velocitycomponents V which make the particle Mars intersecting byinversion operation:

V = C

�1M (1)

where M is the cometocentric position of Mars at the giventime (which can be taken from integrator).

Then the dv

x

, dv

y

, dv

z

are transformed to dv

s

, dv

t

,dv

w

and plotted (along with the magnitude of the veloc-ity |dv|) for di↵erent times (steps of 10 min) from -24hrto 0hr to +24hr. Figures 3(a), 3(b) and 3(c) shows the re-quired ejection velocity components profile vs di↵erent timesof particle-Mars intersection for ejections (with �=0.001) at13 au, 10 au and 7 au respectively. The ejection profile isalmost similar for particles with �=0.0 (i.e. no radiationpressure) as well.

| dv |=p

(dv2s

+ dv

2t

+ dv

2w

) (2)

This whole formulation works on the assumption of lin-earity. Extensive checks were made to verify that linearity ispreserved in all the calculations in this work. Figures 1(a),1(b), 2(a) and 2(b) show that the ejected particles show alinear geometry in the limits and ranges discussed here. Asimilar approach of matrices confirming linearity is discussedin section 5 of Farnocchia et al. (2014).

In all the three figures 3(a), 3(b) and 3(c) one could seethat -S (i.e. ejection in solar direction from any point on thesunward hemisphere) is the favoured ejection direction forintersections after close encounter time (0hr). One could findthat required velocities in S direction reduces substantiallyas ejections occur at large heliocentric distances. This is one

c� 0000 RAS, MNRAS 000, 000–000

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Solid green line (radial direction), red dotted line (transverse direction), dashed blue line (normal direction) & solid black line (absolute velocity magnitude) are shown.

Fig: Ejection velocities (in individual radial, transverse & normal directions plus collective magnitude) required for particles to intersect Mars for ejection at 13 AU for particle sizes of 1 mm approx.

Time of Intersection of Particles with Mars (hr)

Summary 1. Extreme Close Approaches from Long Period Comets are rare !2. Direct indication of Meteor phenomena on Mars from the comet !3. Our calculations show that the Meteor activity was mainly

produced by particles ejected between 13 AU - 7 AU. !4. Range of Ejection velocities, Ejection distances and Timing of

Meteoroid intersections give a consistent peaking time of the shower

!5. Observed Meteor phenomena & this theoretical approach shows

indirectly the confirmation of Cometary activity at distances as large as 13-15 AU which are rarely observed directly by Telescopes

!6. Close Approaches of similar distances from Dynamically new Comets with Earth requires attention & modelling is important

Acknowledgements: Authors wish to thank Prof Mark Bailey for interesting thoughts and discussions related to this research project.

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