The brown dwarf known as WISE 0855 has captivated scientists ever since it was discovered in 2014. It is the coldest object known outside of our solar system and is just just detectable at infrared wavelengths with the greatest ground-based observatories. It is only 7.2 light-years away from Earth.
Key Points
Now, using the Gemini North telescope in Hawaii, a team led by astronomers at UC Santa Cruz has been successful in acquiring an infrared spectrum of WISE 0855, providing the first information on the object’s composition and chemistry. Strong evidence for the existence of water or water ice clouds—the first of their kind discovered outside of our solar system—is one of the discoveries.
According to Andrew Skemer, an assistant professor of astronomy and astrophysics at the University of California, Santa Cruz, “we would anticipate an object that cold to have water clouds, and this is the best evidence that it does.” Skemer is the first author of a study on the fresh discoveries that is already online and scheduled for publication in Astrophysical Journal Letters.
False star
A brown dwarf is basically a failed star since it developed through the gravitational collapse of a gas and dust cloud in the same manner that stars do, but it did not gather enough mass to trigger the nuclear fusion processes that give stars their luminosity. WISE 0855 is similar to Jupiter in many ways, with a mass that is around five times that of the gas giant planet. It is around 10 degrees Fahrenheit (minus 250 Kelvin) colder than Jupiter, which has a temperature of 130 Kelvin.
Our first chance to investigate an extrasolar planetary-mass object that is almost as cold as our own gas giants is WISE 0855, according to Skemer.
Based on little photometric evidence, earlier observations of the brown dwarf, which were reported in 2014, gave hesitant suggestions of water clouds. The only method to determine an item’s molecular makeup, according to Skemer, a coauthor of the previous research, is to collect a spectrum, which divides the light from an object into its component wavelengths.
However, thermal emission from the deep atmosphere at wavelengths in a small window about 5 microns gave a chance where spectroscopy would be “difficult but not impossible,” he added. WISE 0855 is too weak for conventional spectroscopy at optical or near-infrared wavelengths.
The team observed WISE 0855 over the course of 13 nights, lasting a total of around 14 hours, using the Gemini-North telescope in Hawaii and the Gemini Near Infrared Spectrograph.
According to Skemer, it is five times fainter than any other object that has been found using ground-based spectroscopy at this wavelength. “With a spectrum in hand, we can finally begin to consider what is happening inside this thing. Our analysis of WISE 0855’s spectrum reveals that it is primarily made up of clouds and water vapor, giving it a strikingly similar appearance to Jupiter.”
a cloudy environment
In order to calculate the spectra under various presumptions, such as cloudy and cloud-free models, the researchers developed atmospheric models of the equilibrium chemistry for a brown dwarf at 250 Kelvin. The cloudy model produced the best fit to the features in the spectrum of WISE 0855. The models predicted a spectrum dominated by features resulting from water vapor.
The team discovered that the brown dwarf and Jupiter’s spectra are remarkably similar in terms of water absorption characteristics. The high concentration of phosphine in Jupiter’s atmosphere is one notable difference. The presence of phosphonate in the spectrum indicates turbulent mixing in Jupiter’s atmosphere because it forms in the planet’s hot interior and reacts to form other compounds in the cooler outer atmosphere. The lack of a strong phosphine signal in WISE 0855’s spectrum suggests that its atmosphere is less turbulent.
With this extrasolar world, Skemer said, “the spectrum enables us to investigate dynamical and chemical properties that have long been studied in Jupiter’s atmosphere.”
Graduate student Caroline Morley and astronomy and astrophysics professor Jonathan Fortney from the University of California, Santa Cruz, as well as Katelyn Allers from Bucknell University, Thomas Geballe from the Gemini Observatory, Mark Marley and Roxana Lupu from the NASA Ames Research Center, Jacqueline Faherty from the Carnegie Institution of Washington, and Gordon Bjoraker from the NASA Goddard Space Flight Center are coauthors of the study.
