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Weighing planets and asteroids using pulsars

A team of scientists from the ‘International Pulsar Timing Array’ consortium, led by researchers from the Max Planck Institute for Radio Astronomy in Bonn, Germany, with contributions by researchers from ASTRON, has used pulsar timing data to measure the masses of the dwarf-planet Ceres and other asteroids. The team has also measured the masses of the major planets of the solar system with much improved precision than a past study and demonstrated how pulsar-timing data can be used to explore unknown massive objects orbiting the Sun. The results are presented online as refereed publication in the “Monthly Notices of the Royal Astronomical Society”.

Published by the editorial team, 26 October 2018

Fig. 1: Size comparison of Earth, Moon and dwarf planet Ceres. The analysis from pulsar timing observations results in 4.7×10-10 times the solar mass, or 1.3% of the mass of the moon for the mass of Ceres. This measurement agrees with the current best numbers from spacecraft operated by NASA. Credit: Gregory H. Revera, NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

Solar system bodies can be weighed based on data from pulsars. The technique called pulsar timing relies on the precise measurements of signals from multiple pulsars and the technique was first applied in 2010 for the measurement of planet masses. Astronomers observe the periodical lighthouse-like signals from pulsars with extreme accuracy using the largest radio telescopes around the world.

“Using sophisticated models of their rotation we can predict the arrival time of the pulses of millisecond-pulsars to within a couple hundreds of nanoseconds over decades. This allows us to use them as accurate celestial clocks”, says Nicolas Caballero, the leading author of the publication.

Astronomers use the centre of mass of the entire solar system as a reference point for their highly accurate pulsar observations. The work therefore needs a complete description for the solar system and the movement of all the bodies in it. This description is called a solar-system ephemeris and is created by planetary astronomers using several sources of data, including spacecraft flybys of the planets and moons.

If the ephemeris uses an incorrect mass this would result in an offset in the location of the centre of mass and, in turn, periodic changes in the expected arrival time of pulses from pulsars.

“Our current data set is about two decades long, and is built from observations taken with telescopes around the globe, including the Westerbork Synthesis Radio telescope”, says Gemma Janssen, staff member in the Astronomy group at ASTRON.

Using the latest published data by the ‘International Pulsar Timing Array’ (IPTA), this work gives an independent measurement of the masses of planets and asteroids in the solar system. For example, the mass of dwarf planet Ceres, was determined to be only 1.3% of the mass of the Moon.


Although spacecraft flybys provide 3-100000 times more precise measurements for the different objects in our solar system, the results from pulsar timing will improve when longer data sets are available. This method gives a completely independent way of measuring the masses of objects in our solar system. Moreover, the data can be used to place upper limits on any unknown body in orbit around the Sun, like Planet Nine or even dark matter in the solar neighbourhood.

Fig. 2: Telescopes used for the observations within the International Pulsar Timing Array (IPTA). Clockwise from upper left: Effelsberg/Germany, Nancay/France, Arecibo/Puerto Rico, Parkes/Australia, Lovell Telescope/UK, Westerbork/The Netherlands, and GBT/UnitedStates.

Credit: MPIfR, Nancay, Arecibo, Parkes, Jodrell Bank, ASTRON, Green Bank (radio telescope images)

The authors of the paper are R. N. Caballero, Y. J. Guo, K. J. Lee, P. Lazarus, D. J. Champion, G.Desvignes, M. Kramer, K. Plant, Z. Arzoumanian, M. Bailes, C. G. Bassa, N. D.R. Bhat, A. Brazier, M. Burgay, S. Burke-Spolaor, S. J. Chamberlin, S.Chatterjee, I. Cognard, J. M. Cordes, S. Dai, P. Demorest, T. Dolch, R. D.Ferdman, E. Fonseca, J. R. Gair, N. Garver-Daniels, P. Gentile, M. E. Gonzalez, E. Graikou, L. Guillemot, G. Hobbs, G. H. Janssen, R. Karuppusamy, M. J. Keith,M. Kerr, M. T. Lam, P. D. Lasky, T. J. W. Lazio, L. Levin, K. Liu, A. N.Lommen, D. R. Lorimer, R. S. Lynch, D. R. Madison, R. N. Manchester, J.W.McKee, M. A. McLaughlin, S. T. McWilliams, C. M. F. Mingarelli, D. J. Nice, S.Oslowski, N. T. Palliyaguru, T. T. Pennucci, B. B. P. Perera, D. Perrodin, A.Possenti, S. M. Ransom, D. J. Reardon, S. A. Sanidas, A. Sesana, G. Shaifullah,R. M. Shannon, X. Siemens, J. Simon, R. Spiewak, I. Stairs, B. Stappers, D. R.Stinebring, K. Stovall, J. K. Swiggum, S. R. Taylor, G. Theureau, C. Tiburzi,L. Toomey, R. van Haasteren, W. van Straten, J. P. W. Verbiest, J. B. Wang, X.J. Zhu and W. W. Zhu.

ASTRON authors of this paper include Cees Bassa, Gemma Janssen and Golam Shaifullah

Original Paper:

R. N. Caballero et al: Studying the solar system with the International Pulsar Timing Array, 2018, Monthly Notices of the Royal Astronomical Society (DOI: 10.1093/mnras/sty2632)



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