Centauri Dreams readers will want to know about Systemic, a research collaboration led by astronomer Gregory Laughlin (University of California, Santa Cruz). Scheduled for launch in 2006, the Systemic Collaboration is a simulation that will study a catalog of 100,000 stars, some of which are surrounded by planetary systems created by the team. The idea is to observe these stars by running their radial velocity information through the Systemic Console, a java applet that has just been released in beta form for early use and debugging.
Radial velocity measurements have been a key tool in the hunt for extrasolar planets, using slight perturbations in a star’s motion as evidence for distant planetary systems. A radial velocity measurement, according to Laughlin, is …”the component of the velocity of the star along the line of sight from the Earth to the star.” We can get measurements of motion along this line of sight down to 1 meter per second, telling us how stars are moving in relation to the Sun, and also allowing us to detect the slight wobble in motion that may be introduced by orbiting planets.
To check out the method first-hand, try the first of three Systemic tutorials, this one based on data from HD 4208, a Sun-like star some 110 light years from Earth. The tutorial explains how to use the Systemic Console to examine this star’s radial velocity and manipulate the data to explore possible planetary configurations. The exciting thing about this work is that everyone from professional researchers to educators and the interested public can have a hand in refining our tools for extrasolar planet detection.
Be aware, too, that the Systemic site contains an ongoing weblog laced not only with gorgeous photography but Laughlin’s insightful posts, the most recent of which discusses, in addition to the Lagrangian points associated with Jupiter and the Sun, the question of whether a stable orbit exists on the opposite side of the Sun from the Earth and in the Sun’s habitable zone — a twin of Earth, in other words. The intriguing result is that such an orbit is nonlinearly stable. Laughlin describes the scenario this way:
As one planet tries to pass the other one up, it receives a forward gravitational pull. This forward pull gives the planet energy, which causes it to move to a larger-radius orbit, which causes its orbital period to increase, which causes it to begin to lag behind. Likewise, the planet which is about to be passed up receives a backward gravitational pull. This backward pull drains energy from the orbit, causes the semi-major axis to decrease, and causes the period to get shorter. The two planets are thus able to toss a bit of their joint orbital energy back and forth like a hot potato, and orbit in a perfectly stable variety of a 1:1 orbital resonance, known as a horseshoe configuration. The horseshoe orbit is an example of the negative heat capacity of self-gravitating systems, which is one of the most important concepts in astrophysics: If you try to drain heat away from a self gravitating object, it gets hotter.
Have we observed any planetary systems with planets in this configuration? It seems unlikely, but the idea can’t be ruled out. Laughlin again: “It is dynamically possible that 51 Peg b (or any of the other extrasolar planets that do not transit within the predicted window) is actually two planets participating in a stable 1:1 orbital resonance…”
Laughlin is a major player in the extrasolar planet game and the Systemic Collaboration is a form of distributed science at its best. Those interested in rolling their sleeves up and getting into the hard data — in the process making a contribution toward fine-tuning our exoplanet hunting techniques — should bookmark the Systemic site not only for work with the console, but for provocative posts on a wide variety of astronomical subjects.