Asteroids@home
About
Asteroids@home is a volunteer distributed computing project that needs your help to derive the shape and spin for a significant part of the asteroid population. The BOINC application employs photometric measurements of asteroids from observed data. The results are asteroid convex shape models with the direction of the spin axis and the rotation period. The models are published in peer-reviewed journals and then made public in the DAMIT database.
With a huge amount of photometric data coming from big all-sky surveys as well as from backyard astronomers, the lightcurve inversion becomes a computationally demanding process. In the future, we can expect even more data from surveys such as (PanSTARRS) and (Gaia, LSST). However, data from surveys are often sparse in time, which means that the rotation period - the basic physical parameter - cannot be estimated from the data easily. Contrary to classical lightcurves where the period is "visible" in the data, a wide interval of all possible periods has to be scanned densely when analyzing sparse data. This fact enormously enlarges the computational time and the only practical way to efficiently handle photometry of hundreds of thousands of asteroids is to use distributed computing. Moreover, the problem is ideal for parallelization - the period interval can be divided into smaller parts that are searched separately and then the results are joined together.[1]
Asteroids@home is based at Astronomical Institute, Charles University in Prague in cooperation with Radim Vančo from CzechNationalTeam. The project is directed by Josef Durech.
Asteroid basics
An asteroid is a small rocky body orbiting the sun. Large numbers of these, ranging in size from nearly 600 miles (1,000 km) across (Ceres) to dust particles, are found (as the asteroid belt ) especially between the orbits of Mars and Jupiter, though some have more eccentric orbits, and a few pass close to the earth or enter the atmosphere as meteors. Asteroids can be described as irregular solid bodies without any atmosphere or coma.
There are almost half a million known asteroids - we know their orbit in the solar system (by measuring their position at different times) and their approximate size (by measuring their brightness and knowing their distance). To learn more about their physical properties, other observing techniques have to be used. One of them is photometry - we measure brightness variations caused by rotation. By this technique, rotation periods were derived for several thousands of asteroids
Asteroid lightcurves
Similarly to planets, asteroids shine by the reflected sunglight. Because the distance of an asteroid to the Sun and the Earth changes as the asteroid and the Earth orbit the Sun, the brightness of the asteroid also changes with time. Apart from this easily predictable change of brightness, asteroids also exhibit brightness variations that are caused by their irregular shape and their rotation.
Asteroids rotate, the cross-section of the visible and illuminated part of their surface varies with time and so varies their brightness. This brightness variation is called a lightcurve. By measuring lightcurves, we can measure asteroid rotation periods. The shape of a lightcurve depends on the mutual geometry of the Sun, the Earth, and the asteroid (which is known because we know the orbit of the asteroid in the solar system), and on asteroid spin axis orientation and shape (which we do not know).
Lightcurve inversion
If there are enough lightcurves from different geometries available, the shape model, the spin axis direction, and the rotation period of an asteroid can be derived. For example, an almost spherical asteroid would be constantly bright, whereas an elongated asteroid would exhibit large brightness variations when viewed edge-on and small variations when viewed pole-on. The process of the shape and spin reconstruction from lightcurves is called lightcurve inversion. From a mathematical point of view, lightcurve inversion is a nice and interesting example of an inverse problem. It can be shown that a unique convex shape model of an asteroid can be derived from its lightcurves. From an astronomical point of view, the lightcurve inversion method enables us to reveal basics physical characteristics of individual asteroids by inverting their lightcurves. So far, models for more than 200 asteroids have been derived this way. They are stored in the Database of Asteroid Models from Inversion Techniques (DAMIT).[2]
Scientific publications
- Durech, J., J. Tonry, N. Erasmus, L. Denneau, A. N. Heinze, H. Flewelling and R. Vanco. Asteroid models reconstructed from ATLAS photometry. (2020). DOI: 10.48550/ARXIV.2010.01820.
- Durech, Josef, Josef Hanus and Radim Vanco. Inversion of asteroid photometry from Gaia DR2 and the Lowell Observatory photometric database. (2019). DOI: 10.48550/ARXIV.1909.09395.
- Durech, Josef, Josef Hanus and Victor Ali-Lagoa. Asteroid models reconstructed from the Lowell Photometric Database and WISE data. (2018). DOI: 10.48550/ARXIV.1807.02083.
- Hanuš, J., J. Ďurech, D. A. Oszkiewicz et al. New and updated convex shape models of asteroids based on optical data from a large collaboration network. Astronomy & Astrophysics (2016). DOI: 10.1051/0004-6361/201527441.
- Durech, J., J. Hanus, D. Oszkiewicz and R. Vanco. Asteroid models from the Lowell Photometric Database. (2016). DOI: 10.48550/ARXIV.1601.02909.
- Cibulková, H., J. Ďurech, D. Vokrouhlický, M. Kaasalainen and D. A. Oszkiewicz. Distribution of spin-axes longitudes and shape elongations of main-belt asteroids. Astronomy & Astrophysics (2016). DOI: 10.1051/0004-6361/201629192.
- Ďurech, J., J. Hanuš and R. Vančo. Asteroids@home—A BOINC distributed computing project for asteroid shape reconstruction Astronomy and Computing (2015). DOI: 10.1016/j.ascom.2015.09.004.
- Durech, J., B. Carry, M. Delbo, M. Kaasalainen and M. Viikinkoski. Asteroid Models from Multiple Data Sources. (2015). DOI: 10.48550/ARXIV.1502.04816.
- Durech, Josef, J. Hanus, R. Vanco, D. Oszkiewicz and E. Bowell. New Asteroid Shape Models Derived from the Lowell Photometric Database. (2013).