Preliminary exploration

Brazilian researchers perform studies on Pluto system that may contribute to the voyage of NASA’s New Horizons space probe to the planet in 2015.

By Elton Alisson

Agência FAPESP – The New Horizons space probe launched by NASA in 2006 should pass through the Pluto system in 2015 to study the geology and morphology and map the surface of the dwarf planet. Pluto lies in a distant region of the Solar System, difficult to observe and as yet unvisited by a space probe.

In order to contribute to the probe’s mission by collecting a large amount of data needed for the space mission, researchers from the Engineering School of the Universidade Estadual Paulista (Unesp) Guaratinguetá campus have conducted a series of studies on the dwarf planet.

In 2004, Ana Helena Fernandes Guimarães began her Master’s Degree research under the orientation of Professor Silvia Giuliatti Winter with FAPESP funding.

Through a set of numerical simulations and analytical models, the study identified the so-called stable regions around Pluto and its largest moon, Caronte, both of which will be explored by New Horizons.

The results of the work were presented in 2009 at the General Assembly of the  International Astronomical Union (IAU) in Rio de Janeiro, where they called the attention of Deputy Project Scientist for New Horizons, Lesley Young.

The Southwest Research Institute scientist sought Winter out to discuss and create some simulations about the Pluto-Caronte system’s stable regions which could have accumulated objects ranging from micrometers to meters.

 “These regions are important because they can accumulate material and pose a problem in the path of the space probe. Or, in contrast, they can be the focus of exploration trying to locate and identify objects and register their images,” Winter told Agência FAPESP.

Another of Winter’s students, Pryscilla Maria Pires dos Santos, continued the work in her Master’s Degree research in 2008 and two years later with a Doctorate (currently underway), both with FAPESP funding.

At the beginning of 2011, the Unesp group analyzed the stable regions both for small particles (measurable in centimeters) and for satellites (measurable in kilometers) located after Caronte’s orbit, where the satellites Nix and Hydra were discovered in 2005.

Expectations for the possibility of these regions to have satellites and what their maximum size and orbit (trajectory) would be were consolidated with the discovery announced at the end of July by NASA of a fourth moon orbiting around Pluto.

The satellite, identified by the Hubble telescope, lies in the expected region and has the size described in the study published in January 2011 in the Monthly Notices of the Royal Astronomical Society.

“The location and size of the satellite, temporarily named P4, agree with our results. And if others have now discovered it, the fourth satellite, Pluto could possibly have more,” said Winter.

Winter and his team also discovered that the effects of solar radiation pressure are significant even in a region as far away as Pluto’s system. And that if a ring exists around the dwarf planet composed of parts originally from the satellites Nix and Hydra, it would be difficult to observe and much more tenuous than the rings of Jupiter.

“The results of our work were also corroborated by another group of researchers from the University of Maryland in the United States that began making these observations and did not identify any ring system on Pluto,” she said. The study was submitted for publication in Astronomy and Astrophysics.

Unique system

According to Winter, one of the motives for the international astronomical community’s interest in the Pluto-Caronte system is that, aside from never having been visited and explored by a space probe, it is a unique system.

 “Plutão-Caronte is what we call a binary system. In other words, they have nearly equal masses. Because of this, their dynamic model (of movement) is different from a system like Jupiter and its satellites. It’s something unique to this body that has never been seen from up close,” she said.

The articles Gravitational effects of Nix and Hydra in the external region of the Pluto–Charon system (doi:10.1111/j.1365-2966.2010.17437.x) and Exploring S-type orbits in the Pluto–Charon binary system (10.1111/j.1365-2966.2010.16302.x), by Silvia Maria Giuliatti Winter and others can be read by subscribers to the Monthly Notices of the Royal Astronomical Society.