This is part of a collaborative project to search for low-frequency narrowly beamed, highly circular polarized radio emission from "hot Jupiter" extrasolar planets, as part of the HJUDE project. This emission is predicted to be bright enough to be detected by the newly commissioned LWA1 (Long Wavelength Array) radio telescope, and thus the detections (or upper limits) will be used to test planetary magnetospheric physics models. As part of the project, the PIs will train undergraduate and graduate students and a postdoctoral researcher in instrumentation, computational expertise and data reduction and analysis techniques. They will also make the software spectrometer available to other scientists in the community.
All the magnetized planets in our solar system, including Earth, produce intensely bright radio emission at low radio frequencies. In the earth’s case, this radio emission is orders of magnitude brighter than any terrestrial radio emission and is beamed from the magnetic poles in a lighthouse-like fashion sweeping out into space as the planet rotates. It is a powerful means to detect and measure planetary magnetic fields, which may play an important role in defining planetary habitability. The detection of similar radio emission from planets orbiting other stars would provide the first confirmation and measurement of the magnetic field of planets outside our solar system. The first detection will be very challenging, as the emission is very faint and highly variable. The 2-year duration Hot Jupiter Detection Experiment (HJUDE) was the most powerful experiment yet conducted to attempt to detect this radio emission from extrasolar planets. It made use of a new low frequency radio telescope, the Long Wavelength Array (LWA), which is a powerful instrument observing at the lowest radio frequencies available to ground-based astronomy. The HJUDE program was the largest observing program in the first 24 months of operation of the telescope, involving ~1000 beam hours of observations of planetary systems in the solar neighborhood. However, before these observations could commence, a substantial amount of hardware and software development had to take place. First and foremost, the data rate of the telescope is very high, producing 75 MB/sec from each beam during HJUDE observations. This would deliver a huge 270 TB dataset through the course of the project, which is too large to process or store. Therefore, we had to work with the LWA team to deliver a special ‘spectrometer’, written purely in software, that averages the data in real-time to a rate that is manageable for the project. This reduced the data rate to a much more manageable ~1 MB/sec per beam for a total dataset of ~4 TB. To process and store the data, a dedicated server was purchased and placed at the Cahill Center for Astrophysics in Caltech. Data were collected on a sample of planets orbiting nearby stars, with particular focus on giant planets in very tight orbits around their host stars. Due to their close proximity to their host star, these so-called ‘hot jupiters’ are bathed in an intense stellar wind, which is predicted to lead to radio emission that is many orders of magnitude brighter than that detected from the planets in our solar system and potentially detectable with telescopes like the LWA. However, the emission is highly variable due to two effects, i) the beaming of the emission combined with the rotation of the planet and ii) the variable magnetic activity of the star. In order to account for the first effect, the HJUDE program observed planets in carefully planned observations designed to maximally cover the rotation period of each planet. Observations were thus carefully scheduled drawing from our primary target list consisting of 13 of the nearest hot jupiters (< 50 light years away). This management of the observations was carried out by a postdoctoral researcher at Caltech, Jake Hartman, together with the LWA group based at the University of New Mexico. In order to search the data for exoplanet signatures, special software had to be developed. This part of the project was carried out by Jake Hartman, assisted by a Caltech freshman undergraduate student, Lin Cheng, who together developed a data pipeline written in the Python programming language. Lin Cheng participated in the project as part of Caltech's Summer Undergraduate Research Fellowships (SURF), funded by PI Gregg Hallinan, and produced a final report and presentation on her work. This data pipeline allowed the data to be carefully searched in a systematic fashion for planetary radio emission. No detections were made in the 1000 hours of data collected. Although this was the deepest survey yet attempted, it became apparent that continuous monitoring of a large sample of planets would be necessary to maximize the chance of detection, due to the effects of the variable magnetic activity of the host star. Development of a new telescope that can achieve this capability are underway. Results from the HJUDE program have been presented by the HJUDE team at a number of conferences in 2014 and are being prepared for publication. Motivated by the science goals of the HJUDE project, PI Gregg Hallinan jointly organized a Keck Institute for Space Studies (KISS) workshop on the topic of ‘Planetary Magnetic Fields: Planetary Interiors and Habitability’ - www.kiss.caltech.edu/workshops/magnetic2013/index.html, inviting the top scientists from all over the world to discuss how best to detect the magnetic fields of extrasolar planets, particularly with radio telescopes. The final report jointly written by this group will become publicly available in early 2015, including discussion of the HJUDE program.
