Water is essential for life as we know it, so it's particularly exciting to hear that astronomers have recently discovered a brown dwarf about 7 light years away that could yield the first direct evidence of water clouds outside of our solar system. The study was led by Jacqueline Faherty of the Carnegie Institution for Science and the paper has been published in The Astrophysical Journal Letters.
Brown dwarfs are essentially failed stars. During their formation, they do not become massive enough for energy-producing nuclear fusion to occur in the core. Without that fuel, they cool down significantly and become less luminous. The discovery of the coolest brown dwarf on record was announced back in April after it had been imaged by NASA’s Wide-field Infrared Survey Explorer (WISE). The brown dwarf, WISE J085510.83–071442.5 (W 0855), has an average temperature of -48 and -13°C (-55 and 8°F) is the fourth nearest star to our own Sun at about 7.3 light-years away.
Directly imaging dim objects like W 0855 can be difficult, as the glare from other stars is typically too bright and washes out most of the detail. Many exoplanets are detected when they transit the star, and data about its composition are extrapolated based on the amount of light it obscures. Fortunately, W 0855 is out far enough on its own that it can be imaged directly without interference from nearby stars.
Faherty’s team made follow-up observations using the Magellan Baade telescope in Chile, which operates with optical and near-infrared wavelengths. The 151 images obtained from the study yielded data that W 0855 appears to have an atmosphere with partial (50%) cloud cover. Computer models indicate that the most likely scenario right now is that the clouds are a mixture of sulfide and water ice.
Water clouds are fairly common within our solar system, though they cannot be directly observed on planets past Mars due to atmospheric conditions on each respective planet. While atmospheric water vapor has been detected outside the solar system, water in clouds has not. W 0855 also opens up the question as to how common it is to have partly cloudy conditions, similar to Earth, or if total cloud cover, like Venus, is the norm.
Unfortunately, it is going to be a while before the composition of W 0855’s clouds can be confirmed. Because it is so dim, the brown dwarf will need to be imaged deeper at near-infrared wavelengths. The upcoming James Webb Space Telescope will be perfectly equipped to do just that, but it is not scheduled to launch until 2018.
Image credit: NASA/Penn State
[Hat tip: Science]