The largest variations in brightness ever seen on a cool brown dwarf have turned up on the brown dwarf 2MASS 2139 (known as 2MASS J21392676+0220226 to its friends). The findings, reported at the Extreme Solar Systems II conference in Jackson Hole, Wyoming, show a remarkable 30 percent change in brightness in a period of just under eight hours. The assumption is that brighter and darker patches of atmosphere are periodically moving into view as the brown dwarf rotates.
In fact, Ray Jayawardhana (University of Toronto), co-author of the paper on this work, thinks one possibility is something similar to what we see in our own Solar System. “We might be looking at a gigantic storm raging on this brown dwarf, perhaps a grander version of the Great Red Spot on Jupiter in our own solar system,” says Jayawardhana, “or we may be seeing the hotter, deeper layers of its atmosphere through big holes in the cloud deck.”
Image: Astronomers have observed extreme brightness changes on a nearby brown dwarf that may indicate a storm grander than any seen yet on a planet. This finding could new shed light on the atmospheres and weather on extra-solar planets. Credit: Art by Jon Lomberg.
Whatever the case, this is helpful stuff. Older brown dwarfs have atmospheres not unlike giant planets, so we may be able to use this brown dwarf work to make inferences about exoplanet atmospheres. That will involve studying the brightness variations on 2MASS 2139 over time as we watch weather patterns evolve. The work should allow us to calculate wind speeds in the atmosphere and help us understand how winds are generated in this extreme environment.
Weather is poorly enough understood even on nearby planets, but brown dwarfs simplify the picture. The paper has this to say on the subject:
BDs represent a simpliﬁed case where atmospheric dynamics result primarily as a consequence of rapid rotation and internal heat, without the complication of external forcing due to irradiation from a parent star. In addition, the observation of weather on BDs extends the study of cloud meteorology to a higher gravity regime, never before probed.
L and T-class brown dwarfs offer up temperatures in the range of 2200 to 500 Kelvin, with atmospheres cool enough that we can consider them precursors to the study of giant planet atmospheres. How dust grains of silicates and metals condense to form clouds is an ongoing study:
Our current understanding of ultracool atmospheres, including the formation and sedimentation of condensate clouds has developed based on comparisons of detailed atmosphere models to observations of hundreds of L and T dwarfs identiﬁed in the solar neighborhood… Nonetheless, fundamental questions remain concerning the most basic properties of condensates including their vertical and horizontal distributions, and how these evolve as a function of eﬀective temperature, as well as the role of secondary parameters such as gravity, metallicity, convection, and rotation.
And the authors go on to point out the need for long-term monitoring both photometrically and spectroscopically over a wide range of wavelengths to reveal the true nature of the brown dwarf’s variability. It’s interesting to see that the researchers looked into the possibility that 2MASS 2139 might be an interacting binary (which is exactly what I wondered when I first read this), but they concluded that the scenario was highly implausible. The study is based on data from the 2.5-meter telescope at Las Campanas Observatory in Chile.
The paper is Radigan et al., “High Amplitude, Periodic Variability of a Cool Brown Dwarf: Evidence for Patchy, High-Contrast Cloud Features,” submitted to the Astrophysical Journal and available online.