A ST ER OIDS @HOM E
Josef Ďurech1, Josef Hanuš1, Radim Vančo2
1 – Astronomical Institute, Charles University in Prague, Czech Republic, 2 – Czech National Team, Czech Republic
email: durech@sirrah.troja.mff.cuni.cz

Abstract
Asteroids@home (http://asteroidsathome.net) is a volunteer­computing project that uses an open­source BOINC (Berkeley OpenInfrastructure for Network Computing) software to distribute tasks to volunteers, who provide their computing resources. The project wascreated at the Astronomical Institute, Charles University in Prague, in cooperation with the Czech National Team. The scientific aim of theproject is to solve a time­consuming inverse problem of shape reconstruction of asteroids from sparse­in­time photometry. The time­
demanding nature of the problem comes from the fact that with sparse­in­time photometry the rotation period of an asteroid is not apriori
known and a huge parameter space must be densely scanned for the best solution. The nature of the problem makes it an ideal task to besolved by distributed computing – the period parameter space can be divided into small bins that can be scanned separately and thenjoined together to give the globally best solution. In the framework of the the project, we process asteroid photometric data from surveys
together with asteroid lightcurves and we derive asteroid shapes and spin states. The algorithm is based on the lightcurve inversion
method developed by Kaasalainen et al. (2001, Icarus 153, 37). The enormous potential of distributed computing will enable us toeffectively process also the data from future surveys (Large Synoptic Survey Telescope, Gaia mission). We also plan to process data of asynthetic asteroid population to reveal biases of the method.

Why distributed computing?
With huge amount of photometric data coming from big all­sky surveys as well as from backyard astronomers, the lightcurve inversion
becomes a computationaly demanding process. In the future, we can expect even more data from surveys that are either alreadyoperating (Pan­STARRS) or under construction (Gaia, LSST). Moreover, data from surveys are often sparse in time, which means that therotation period – the basic physical parameter – cannot be estimated from the data easily. Contrary to classical lightcurves where theperiod is "visible" in the data, a wide interval of all possible periods has to be scanned densely when analysing sparse data. This fact
enormously enlarges the computational time and the only practical way to efficiently handle photometry of hundreds of thousands ofasteroids is to use distributed computing. Moreover, the problem is ideal for parallelization – the period interval can be divided intosmaller parts that are searched separately and then the results are joined together.

BOINC Manager

Users
Users install the BOINC client and set up thepreferences. The tasks are then automaticallydownloaded, computed, and the results areuploaded to the server. Each user scans a smallpart of the parameter space. The whole periodinterval 2–100 hours is divided into typicallyseveral hundreds of workunits that are distributed
to users. The typical time needed for computing
one workunit is of order of hours.

Project status

log inServer software version: 26042 / 4 Oc t 2012 | 12:56:31 UT C

ServerServer status

Computing status

HostStatus
The results
sent
by users are validated byprojec t
Runningcomparing
theRunningsame tasks computed by two
upload/download
server projec t
sc heduler
projec t users.Runningdifferent
If the results are different, thefeeder
projec t
workunit
is sentRunningto other users until an agreementtransitioner
projec t
Running
is reached.
TheRunning
results are stored in the database
file_deleter
projec t
and areaccesible
via a web interface.
period_searc h_validator
project
Running
Programdata-driven web pages

sample_assimilator

projec t

Computing status (Oct 4, 2012)Users#T asks ready to send

16,483

with rec ent c redit

169

T asks in progress

Work3,205#with c redit

194

Workunits waiting for validation

0

registered in past 24 hours 4Workunits waiting for assimilation 0Computers#Workunits waiting for file deletion 0with rec ent c redit386

T asks waiting for file deletion

0with c redit

477

T ransitioner bac klog (hours)

0registered in past 24 hours 11

Runningc urrent GigaFLOPs

543

Running: Program is operating normally
Not Running: Program failed or the projec t is down
Disabled: Program is disabled

Tasks by application
application
Period Searc h Applic ation

unsent16,476in progress
3,202

av g runtime of last 100 results in h (min-max)
4.43 (1.64 - 13.38)users in last 24h70

Server statistics

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Copyright © 2012 Asteroids@homeResults
The aim of the project is to derive shapes andspins for a significant part of the asteroid
population. As input data, we use any asteroid
photometry that is available. The results areasteroid convex shape models with the direction ofthe spin axis and the rotation period. New models
will be published in peer­reviewed journals andthen made public in the Database of Asteroid
Models form Inversion Techniques (DAMIT).
http://astro.troja.mff.cuni.cz/projects/asteroids3DHome | Project
Asteroids@home| DAMIT
database| Basics about asteroids
Firstasteroid models
basedon Asteroids@home
results| Scientific results

Scientific results
Asteroid models derived so far:Asteroidλ[deg]
150 Nuwa
0175
359
272 Antonia

β[deg]
P[h]shape20
8.13456
fig
19
fig
-90
3.85479
fig

computed byBobCat13,koll
Qubity,zombie67 [MM]Here λ and β are ecliptic longitude and latitude of the spin axis direction and P is the rotation period.
Usually, there are two possible pole directions and corresponding shape models for one asteroid - thelightcurve inversion cannot solve this ambiguity for asteroids orbiting close to the ecliptic plane. Eachfigure shows the corresponding shape model from its equator (the first two views, 90 degrees apart)and pole-on (the third view). The 'computed by' column lists all users that provided valid results that
contained the solution listed in the table.

Shape model of asteroid (150) Nuwa

Shape model of asteroid (272) Antonia© 2012 Asteroids@home